WO2017168126A1 - Electrodes - Google Patents

Abstract

The application relates to an electrode comprising a support and metal oxide catalyst, wherein the metal oxide catalyst comprises a nanoforest structure. Also provided is a composition comprising a support and hydrated metal oxide catalyst precursor, wherein the metal oxide catalyst precursor comprises a nanoforest structure. Also provided is a method of making an electrode and of making a composition that is useful as an electrode precursor. Also provided is a fuel cell comprising a said electrode. Use in a fuel cell of an electrode of the invention is also provided.

Description

Electrodes

[0001] This invention relates to electrodes. More specifically, the invention relates to C03O4 electrodes. The invention also relates to methods of synthesising C03O4 electrodes. Electrodes of the invention may be used in direct ethanol fuel cells.

BACKGROUND

[0002] A fuel cell is a device that converts the chemical energy from a fuel into electricity through a controlled chemical reaction of the fuel with an oxidant. Exemplary fuels that are commonly used in a fuel cell include hydrogen, an alcohol such as methanol or ethanol, or a hydrocarbon. The oxidant is typically oxygen.

[0003] Fuel cells represent a promising means for converting chemical energy into electrical energy with a number of applications. One application of particular interest is the use of fuel cells to power electric vehicles, because fuel cells can provide high power densities at low cost with zero emissions. (Stambouli, A. B., Renew. Sustain. Energy Rev., 2011 , 15, 4507-4520). Direct ethanol fuel cells have several advantages over other types of fuel cell because they have a high power density, have high efficiency, and are considered relatively eco-friendly.

[0004] Tailored nano-object design and surface morphologies may provide electrode catalysts with improved electroactive site accessibility. This can lead to preferential surface coverage of ethanol molecules, shorter ion/electron diffusion pathways, better mass transfer of reactants through the nanoscale structure, and faster or reversible kinetics in the ethanol electrooxidation reaction. However, the effects of catalyst morphology, in terms of anisotropy, density of exposed active sites, and density of multi-diffusive voids in the direction of the longitudinal axis, on the ethanol electrooxidation reaction remains unknown.

[0005] Current methods of forming electrodes results in the formation of structures with randomly oriented morphologies. Furthermore, typical methods involve small-scale, multi-step processes owing to the cost of current electrode materials such as platinum. The drawbacks of current industrial catalyst-based electrodes include the high cost of materials such as platinum and the finite cycling lifetime of the electrodes. Furthermore, the platinum catalyst can readily bind with carbon monoxide, thus "poisoning" the ethanol oxidation-reduction reactions. There is therefore a need to provide improved electrodes, for example electrodes for use in direct ethanol fuel cells. SUMMARY OF THE INVENTION

[0006] The present invention provides an electrode architecture which benefits from low- and high-index single and interface planes with multi-diffusive mesocage cavities and windows. The present disclosure provides a simple, one-pot, hydrothermal method of synthesizing various electrode architectures along the longitudinal axis by using multi-component carbon/Co304/substrate layers. The methods of the invention provide versatile control over the production of a variety of anisotropic morphological C03O4 architectures with low- and high-index single and interface planes with multi-diffusive mesocage cavities and windows.

[0007] This invention provides significant advantages of cost over current electrode systems as it utilises low cost materials including porous nickel substrates and C03O4 mesocrystals. Furthermore, the invention provides electrodes having improved electron transport and diffusion compared with electrodes in the art. The metal oxide catalysts of the invention, such as C03O4 have low-cost fabrication and in embodiments have unique features such as hierarchical morphologies (for example nanoforest structures as disclosed herein), high surface area coverage and single crystals with high-index exposure active-site plane surfaces. These parameters provide high-efficiency performance of electrochemical catalysis of oxygen-reduction reactions (ORR) or alcohol-oxidation reactions (AOR).

[0008] The electrodes of the invention provide a number of advantages. The electrodes have improved catalytic efficiency for ethanol electrooxidation compared with a conventional platinum/carbon (Pt/C) electrode.

[0009] It is an aim of the present invention to provide low-cost electrodes with high catalytic efficiency. It is therefore a further aim to provide a method of fabricating said electrodes. The applicant considers that these aims have been achieved by embodiments of the invention.

[0010] In an aspect the invention provides an electrode comprising a support and metal oxide catalyst, wherein the metal oxide catalyst comprises a nanoforest structure.

[0011] In an embodiment the metal oxide catalyst is a transition metal oxide. In an embodiment the transition metal oxide catalyst is a cobalt oxide (e.g. C03O4 and/or CoO), a nickel oxide (e.g. NiO), a manganese oxide (e.g. Mn02), or a cadmium oxide. In an embodiment the metal oxide catalyst is a cobalt oxide. In an embodiment the cobalt oxide comprises C03O4, CoO, or a mixture of C03O4 and CoO. In an embodiment the cobalt oxide comprises C03O4. In an embodiment the cobalt oxide is C03O4. The cobalt oxide typically comprises a mixture of cobalt atoms in the Co²⁺ and Co³⁺ forms. Without wishing to be bound by any theory, it is believed that this provides enhanced catalytic activity, particularly in combination with the nanoforest structures in embodiments of the invention.

[0012] In an embodiment the nanoforest structure is oriented in a vertical direction relative to the surface of the support. In an embodiment the nanoforest structure comprises a mesocrystal architecture. In an embodiment the nanoforest structure comprises a morphological architecture selected from corn tubercle pellets (CPs), banana clusters (BCs), lamina sheets (LSs) and multiple cantilever sheets (MCSs), or a combination thereof. In an embodiment the nanoforest structure comprises a morphological architecture comprising corn tubercle pellets (CPs), optionally wherein the CPs are vertically oriented away from the longitudinal plane of the surface of the support in nanorod (NR) domains. In an embodiment the nanoforest structure comprises a morphological architecture comprising banana clusters (BCs), optionally wherein the BCs are vertically oriented away from the longitudinal plane of the surface of the support in nanorod (NR) domains. In an embodiment the nanoforest structure comprises a morphological architecture comprising lamina sheets (LSs). In an embodiment the nanoforest structure comprises a morphological architecture comprising multiple cantilever sheets (MCSs). In an embodiment the CPs, and/or BCs, and/or LSs, and/or MCSs are oriented in a vertical direction relative to the surface of the support. In an embodiment the CPs, are oriented in a vertical direction relative to the surface of the support. In an embodiment the BCs are oriented in a vertical direction relative to the surface of the support. In an embodiment the LSs are oriented in a vertical direction relative to the surface of the support. In an embodiment the MCSs are oriented in a vertical direction relative to the surface of the support.

[0013] In an embodiment the metal oxide catalyst comprises crystals with an interface having Miller indices {11 1}/{1 12} and/or {112}/{11 1} and/or {110}/{001} and/or {001}/{1 10} and/or {112}. In an embodiment the metal oxide catalyst comprises crystals with an interface having a Miller indices {1 1 1}/{112} and /or {1 12}/{ 11 1}. In an embodiment the metal oxide catalyst comprises crystals with an interface having Miller indices {110}/{001} and/or {001}/{1 10}. In an embodiment the metal oxide catalyst comprises crystals with a facet having a Miller index of {112}. In an embodiment the nanoforest structure comprises the crystals. Without wishing to be bound by any theory, it is believed that the provision of interfaces, e.g. {11 1}/{1 12} or {110}/{001} provide advantages over materials that only have high-index single crystal facets. For example, it is believed that the interface facets produce more favourable adsorption, binding and surface energies for typical reactions on the catalyst compared to similar materials that only have high-index single crystal facets.

[0014] In an embodiment the support comprises a substrate comprising carbon. In an embodiment the carbon comprises graphite, graphene sheets (g-C), or carbon nanotubes (C-NTs). In an embodiment the carbon comprises g-C or C-NTs. In an embodiment the carbon comprises g-C. In an embodiment the carbon comprises C-NTs. In an embodiment the C-NTs are multi walled carbon nanotubes (MWCNT). In an embodiment the metal oxide catalyst is deposited on the substrate.

[0015] In an embodiment the support comprises a base comprising a metal foam, glassy carbon (GC), or a ceramic membrane (e.g. an alumina or titania membrane). In an embodiment the support comprises a base comprising a metal foam or glassy carbon (GC). In an embodiment the support comprises a base comprising glassy carbon (GC). In an embodiment the support comprises a base comprising a metal foam. In an embodiment the metal foam comprises or consists of a nickel foam or an aluminium foam. In an embodiment the metal foam comprises nickel foam. In an embodiment the nickel foam is 3D porous nickel foam (3D PNi).

[0016] In an embodiment the support comprises the substrate as defined herein deposited on the base as defined herein.

[0017] In an embodiment the nanoforest structure is on an exposed surface of the electrode.

[0018] In an embodiment the electrode has a surface area of > 50 m²/g. In an embodiment the electrode has a surface area of > 75 m²/g, e.g. a surface area of > 100 m²/g.

[0019] In an aspect the invention provides a composition comprising a support and metal oxide catalyst precursor, wherein the metal oxide catalyst precursor comprises a nanoforest structure. The composition may be a composition for use as an electrode precursor. For example, after the metal oxide catalyst precursor is converted to a catalyst, the converted composition may be for use an electrode.

[0020] In an embodiment the metal oxide catalyst precursor is or comprises a hydrated metal oxide precursor. In an embodiment the metal oxide catalyst precursor is a hydrated transition metal oxide catalyst precursor. In an embodiment the hydrated transition metal oxide precursor is a cobalt oxide (e.g. C03O4 and/or CoO), a nickel oxide (e.g. NiO), a manganese oxide (e.g. Mn02), or a cadmium oxide. In an embodiment the metal oxide catalyst precursor is a hydrated cobalt oxide. In an embodiment the metal oxide catalyst precursor has the formula CoO(OH)x(C03)o.5.0.11 H20, wherein x is selected from 1 , 2 or 3, or a mixture thereof.

[0021] In an embodiment the nanoforest structure is oriented in a vertical direction relative to the surface of the support. In an embodiment the nanoforest structure comprises a mesocrystal architecture. In an embodiment the nanoforest structure comprises a morphological architecture selected from corn tubercle pellets (CPs), banana clusters (BCs), lamina sheets (LSs) and multiple cantilever sheets (MCSs), or a combination thereof. In an embodiment the nanoforest structure comprises a morphological architecture comprising corn tubercle pellets (CPs), optionally wherein the CPs are vertically oriented away from the longitudinal plane of the surface of the support in nanorod (NR) domains. In an embodiment the nanoforest structure comprises a morphological architecture comprising banana clusters (BCs), optionally wherein the BCs are vertically oriented away from the longitudinal plane of the surface of the support in nanorod (NR) domains. In an embodiment the nanoforest structure comprises a morphological architecture comprising corn tubercle pellets (CPs). In an embodiment the nanoforest structure comprises a morphological architecture comprising multiple cantilever sheets (MCSs). In an embodiment the CPs, and/or BCs, and/or LSs, and/or MCSs are oriented in a vertical direction relative to the surface of the support. In an embodiment the CPs, are oriented in a vertical direction relative to the surface of the support. In an embodiment the BCs are oriented in a vertical direction relative to the surface of the support. In an embodiment the LSs are oriented in a vertical direction relative to the surface of the support. In an embodiment the MCSs are oriented in a vertical direction relative to the surface of the support.

[0022] In an embodiment the support comprises a substrate comprising carbon. In an embodiment the carbon comprises graphene sheets (g-C), carbon nanotubes (C- NTs), graphite, carbon fibre, mesoporous carbon, or carbon nitrides. In an embodiment the carbon comprises graphene sheets (g-C), carbon nanotubes (C- NTs), graphite, carbon fibre, or mesoporous carbon. In an embodiment the carbon comprises graphene sheets (g-C), carbon nanotubes (C-NTs), graphite, or carbon fibre. In an embodiment the carbon comprises graphite, graphene sheets (g-C), or carbon nanotubes (C-NTs). In an embodiment the carbon comprises g-C or C- NTs. In an embodiment the carbon comprises g-C. In an embodiment the carbon comprises C-NTs. In an embodiment the C-NTs are multi walled carbon nanotubes (MWCNT). In an embodiment the metal oxide catalyst is deposited on the substrate.

[0023] In an embodiment the support comprises a base comprising a metal foam, glassy carbon (GC), or a ceramic membrane (e.g. an alumina or titania membrane). In an embodiment the support comprises a base comprising a metal foam or glassy carbon (GC). In an embodiment the support comprises a base comprising glassy carbon (GC). In an embodiment the support comprises a base comprising a metal foam. In an embodiment the metal foam comprises or consists of a nickel foam or an aluminium foam. In an embodiment the metal foam comprises nickel foam. In an embodiment the nickel foam is 3D porous nickel foam (3D PNi).

[0024] In an embodiment the support comprises the substrate as defined herein deposited on the base as defined herein.

[0025] In an embodiment the nanoforest structure is on an exposed surface of the electrode.

[0026] In an embodiment the composition has a surface area of > 50 m²/g. In an embodiment the electrode has a surface area of > 75 m²/g, e.g. a surface area of > 100 m²/g.

[0027] In one aspect the invention provides a method of making an electrode. The method comprises forming an aqueous solution comprising cobalt (II) cations, a urea or a cyclic amide and carbon in the presence of an electrode base; activating the solution; allowing a reaction to proceed such that a composition comprising cobalt and carbon deposited on the electrode base is formed; isolating the composition from the solution; and calcining the composition to form an electrode comprising a cobalt oxide catalyst.

[0028] In an embodiment the cobalt (II) cations are provide by a salt. In an embodiment the salt comprises cobalt chloride, cobalt nitrate, or a combination thereof. In an embodiment the salt comprises cobalt chloride. In an embodiment the salt comprises cobalt nitrate.

[0029] In an embodiment the urea or cyclic amide is urea. In an embodiment the urea or cyclic amide is a cyclic amide. In an embodiment the cyclic amide is hexamethylenetetramine (HMT).

[0030] In an embodiment the carbon comprises graphene sheets (g-C), carbon nanotubes (C-NTs), graphite, carbon fibre, mesoporous carbon, or carbon nitrides. In an embodiment the carbon comprises graphene sheets (g-C), carbon nanotubes (C- NTs), graphite, carbon fibre, or mesoporous carbon.. In an embodiment the carbon comprises graphite, graphene sheets (g-C), or carbon nanotubes (C-NTs). In an embodiment the carbon comprises g-C, or carbon nanotubes C-NTs. In an embodiment the carbon comprises g-C. In an embodiment the carbon comprises carbon nanotubes C-NTs. The C-NTs may be multi walled carbon nanotubes (MWCNT).

[0031] In an embodiment the electrode base is or comprises a metal foam, glassy carbon (GC), or a ceramic membrane (e.g. an alumina or titania membrane). In an embodiment the electrode base is or comprises a metal foam or glassy carbon (GC). In an embodiment the base is or comprises glassy carbon (GC). In an embodiment the support is or comprises a metal foam. In an embodiment the metal foam comprises or consists of a nickel foam or an aluminium foam. In an embodiment the metal foam comprises or consists of nickel foam. In an embodiment the nickel foam is 3D porous nickel foam (3D PNi).

[0032] In an embodiment the carbon provides a substrate for deposition of the cobalt (II) cations during the step of allowing the reaction to proceed. In an embodiment the substrate deposits on the electrode base during the step of allowing the reaction to proceed.

[0033] In an embodiment the allowing the reaction to proceed comprises the step of activating the solution.

[0034] In an embodiment the activating the solution and allowing the reaction to proceed are performed in a pressure vessel. In an embodiment the activating the solution and allowing the reaction to proceed are performed at a pressure of greater than 1 atmosphere (e.g. at a pressure of at least 2, 5, or 10 atmosphere).

[0035] In an embodiment activating the solution comprises heating, irradiating with electromagnetic radiation (e.g. UV, infrared, or microwave radiation), or sonicating the solution. In an embodiment activating the solution comprises heating the solution to a temperature selected from at least 80°C, at least 100°C, at least 120°C and at least 140°C. In an embodiment activating the solution comprises heating the solution to a temperature in the range of 100 - 200°C. In an embodiment activating the solution comprises heating the solution to a temperature in the range of 120 - 180°C. In an embodiment activating the solution comprises heating the solution to a temperature in the range of 130 - 170°C. In an embodiment activating the solution comprises heating the solution to a temperature in the range of 140 - 160°C. In an embodiment activating the solution comprises heating the solution to a temperature of about 150°C (e.g. 145 - 155°C). [0036] In an embodiment allowing the reaction to proceed comprises a time period of at least 1 hour. In an embodiment allowing the reaction to proceed comprises a time period of at least 4 hours. In an embodiment allowing the reaction to proceed comprises a time period of at least 8 hours. In an embodiment allowing the reaction to proceed comprises a time period of 1 hour - 48 hours. In an embodiment allowing the reaction to proceed comprises a time period of 4 hours - 36 hours. In an embodiment allowing the reaction to proceed comprises a time period of 8 hours - 24 hours.

[0037] In an embodiment the composition comprises a hydrated cobalt oxide. In an embodiment the hydrated cobalt oxide has the formula Co(OH)_x(C03)o.5.0.11 H20, wherein x is selected from 1 , 2 or 3, or a mixture thereof.

[0038] In an embodiment the hydrated cobalt oxide comprises a nanoforest structure. In an embodiment the nanoforest structure is oriented in a vertical direction relative to the surface of the support. In an embodiment the nanoforest structure comprises a mesocrystal architecture. In an embodiment the nanoforest structure comprises a morphological architecture selected from corn tubercle pellets (CPs), banana clusters (BCs), lamina sheets (LSs) and multiple cantilever sheets (MCSs), or a combination thereof. In an embodiment the nanoforest structure comprises a morphological architecture comprising corn tubercle pellets (CPs), optionally wherein the CPs are vertically oriented away from the longitudinal plane of the surface of the electrode base in nanorod (NR) domains. In an embodiment the nanoforest structure comprises a morphological architecture comprising banana clusters (BCs), optionally wherein the BCs are vertically oriented away from the longitudinal plane of the surface of the electrode base in nanorod (NR) domains. In an embodiment the nanoforest structure comprises a morphological architecture comprising corn tubercle pellets (CPs). In an embodiment the nanoforest structure comprises a morphological architecture comprising multiple cantilever sheets (MCSs). In an embodiment the CPs, and/or BCs, and/or LSs, and/or MCSs are oriented in a vertical direction relative to the surface of the electrode base. In an embodiment the CPs are oriented in a vertical direction relative to the surface of the electrode base. In an embodiment the BCs are oriented in a vertical direction relative to the surface of the electrode base. In an embodiment the LSs are oriented in a vertical direction relative to the surface of the electrode base. In an embodiment the MCSs are oriented in a vertical direction relative to the surface of the electrode base. [0039] In an embodiment the composition is washed with at least one solvent between the isolating and the calcining. In an embodiment the washing comprises washing sequentially with at least two solvents. In an embodiment the solvent or solvents (e.g. 2, 3 or 4 solvents) are selected from water and water miscible solvents. In an embodiment the water miscible solvents comprise water and a water miscible organic solvent. In an embodiment the water miscible solvent comprises less than 5% water, e.g. less than 2% water. In an embodiment the water miscible solvents are selected from methanol, ethanol and isopropanol, or mixtures thereof. In an embodiment the water miscible solvent is ethanol (e.g. absolute ethanol).

[0040] In an embodiment the isolated composition is dried prior to the calcining.

[0041] In an embodiment the calcining comprises heating the composition to at least 200°C. In an embodiment the calcining comprises heating the composition to at least 300°C. In an embodiment the calcining comprises heating the composition to at least 350°C. In an embodiment the calcining comprises heating the composition to a temperature of not more than 500°C. In an embodiment the calcining comprises heating the composition to a temperature of 200 - 500°C. In an embodiment the calcining comprises heating the composition to a temperature of 300 - 500°C (e.g. to a temperature of 350 - 450°C).

[0042] Another aspect of the invention provides a method of making an electrode precursor. The method comprises forming an aqueous solution comprising cobalt (II) cations, a urea or a cyclic amide and carbon in the presence of an electrode base; activating the solution; and allowing a reaction to proceed such that a composition comprising cobalt and carbon deposited on the electrode base is formed. The method may also comprise optionally isolating the composition from the solution.

[0043] In an embodiment the cobalt (II) cations are provide by a salt. In an embodiment the salt comprises cobalt chloride, cobalt nitrate, or a combination thereof. In an embodiment the salt comprises cobalt chloride. In an embodiment the salt comprises cobalt nitrate.

[0044] In an embodiment the urea or cyclic amide is urea. In an embodiment the urea or cyclic amide is a cyclic amide. In an embodiment the cyclic amide is hexamethylenetetramine (HMT).

[0045] In an embodiment the carbon comprises graphene sheets (g-C), carbon nanotubes (C-NTs), graphite, carbon fibre, mesoporous carbon, or carbon nitrides. In an embodiment the carbon comprises graphite, graphene sheets (g-C), or carbon nanotubes (C-NTs). In an embodiment the carbon comprises g-C, or carbon nanotubes C-NTs. In an embodiment the carbon comprises g-C. In an embodiment the carbon comprises carbon nanotubes C-NTs. The C-NTs may be multi walled carbon nanotubes (MWCNT).

[0046] In an embodiment the electrode base is or comprises a metal foam, glassy carbon (GC), or a ceramic membrane (e.g. an alumina or titania membrane). In an embodiment the electrode base is or comprises a metal foam or glassy carbon (GC). In an embodiment the base is or comprises glassy carbon (GC). In an embodiment the support is or comprises a metal foam. In an embodiment the metal foam comprises or consists of a nickel foam or an aluminium foam. In an embodiment the metal foam comprises or consists of nickel foam. In an embodiment the nickel foam is 3D porous nickel foam (3D PNi).

[0047] In an embodiment the carbon provides a substrate for deposition of the cobalt (II) cations during the step of allowing the reaction to proceed. In an embodiment the substrate deposits on the electrode base during the step of allowing the reaction to proceed.

[0048] In an embodiment the allowing the reaction to proceed comprises the step of activating the solution.

[0049] In an embodiment the activating the solution and allowing the reaction to proceed are performed in a pressure vessel. In an embodiment the activating the solution and allowing the reaction to proceed are performed at a pressure of greater than 1 atmosphere (e.g. at a pressure of at least 2, 5, or 10 atmosphere).

[0050] In an embodiment activating the solution comprises heating, irradiating with electromagnetic radiation (e.g. UV, infrared, or microwave radiation), or sonicating the solution. In an embodiment activating the solution comprises heating the solution to a temperature selected from at least 80°C, at least 100°C, at least 120°C and at least 140°C. In an embodiment activating the solution comprises heating the solution to a temperature in the range of 100 - 200°C. In an embodiment activating the solution comprises heating the solution to a temperature in the range of 120 - 180°C. In an embodiment activating the solution comprises heating the solution to a temperature in the range of 130 - 170°C. In an embodiment activating the solution comprises heating the solution to a temperature in the range of 140 - 160°C. In an embodiment activating the solution comprises heating the solution to a temperature of about 150°C (e.g. 145 - 155C). [0051] In an embodiment allowing the reaction to proceed comprises a time period of at least 1 hour. In an embodiment allowing the reaction to proceed comprises a time period of at least 4 hours. In an embodiment allowing the reaction to proceed comprises a time period of at least 8 hours. In an embodiment allowing the reaction to proceed comprises a time period of 1 hour - 48 hours. In an embodiment allowing the reaction to proceed comprises a time period of 4 hours - 36 hours. In an embodiment allowing the reaction to proceed comprises a time period of 8 hours - 24 hours.

[0052] In an embodiment the composition comprises a hydrated cobalt oxide. In an embodiment the hydrated cobalt oxide has the formula Co(OH)_x(C03)o.5.0.11 H20, wherein x is selected from 1 , 2 or 3, or a mixture thereof.

[0053] In an embodiment the hydrated cobalt oxide comprises a nanoforest structure. In an embodiment the nanoforest structure is oriented in a vertical direction relative to the surface of the support. In an embodiment the nanoforest structure comprises a mesocrystal architecture. In an embodiment the nanoforest structure comprises a morphological architecture selected from corn tubercle pellets (CPs), banana clusters (BCs), lamina sheets (LSs) and multiple cantilever sheets (MCSs), or a combination thereof. In an embodiment the nanoforest structure comprises a morphological architecture comprising corn tubercle pellets (CPs), optionally wherein the CPs are vertically oriented away from the longitudinal plane of the surface of the electrode base in nanorod (NR) domains. In an embodiment the nanoforest structure comprises a morphological architecture comprising banana clusters (BCs), optionally wherein the BCs are vertically oriented away from the longitudinal plane of the surface of the electrode base in nanorod (NR) domains. In an embodiment the nanoforest structure comprises a morphological architecture comprising corn tubercle pellets (CPs). In an embodiment the nanoforest structure comprises a morphological architecture comprising multiple cantilever sheets (MCSs). In an embodiment the CPs, and/or BCs, and/or LSs, and/or MCSs are oriented in a vertical direction relative to the surface of the electrode base. In an embodiment the CPs, are oriented in a vertical direction relative to the surface of the electrode base. In an embodiment the BCs are oriented in a vertical direction relative to the surface of the electrode base. In an embodiment the LSs are oriented in a vertical direction relative to the surface of the electrode base. In an embodiment the MCSs are oriented in a vertical direction relative to the surface of the electrode base. [0054] In an embodiment the composition is washed with at least one solvent between the isolating and the calcining. In an embodiment the washing comprises washing sequentially with at least two solvents. In an embodiment the solvent or solvents (e.g. 2, 3 or 4 solvents) are selected from water and water miscible solvents. In an embodiment the water miscible solvents comprise water and a water miscible organic solvent. In an embodiment the water miscible solvent comprises less than 5% water, e.g. less than 2% water. In an embodiment the water miscible solvents are selected from methanol, ethanol and isopropanol, or mixtures thereof. In an embodiment the water miscible solvent is ethanol (e.g. absolute ethanol).

[0055] An aspect of the invention provides an electrode precursor obtainable by a method of the invention. Another aspect of the invention provides an electrode precursor obtained by a method of the invention.

[0056] An aspect of the invention provides an electrode obtainable by a method of the invention. Another aspect of the invention provides an electrode obtained by a method of the invention.

[0057] An aspect of the invention provides a fuel cell comprising an electrode of the invention. In an embodiment, an anode of the fuel cell comprises the electrode of the invention.

[0058] Another aspect of the invention provides a vehicle comprising a fuel cell or electrode of the invention.

[0059] An aspect of the invention provides the use of an electrode of the invention in a fuel cell. In an embodiment, the use comprises use of the electrode as an anodic electrode. In an embodiment, the use comprises use of the electrode as an anodic electrode in an ethanol electrooxidation reaction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Embodiments of the invention are further described hereinafter with reference to the accompanying figures, in which:

[0061] Figure 1 provides a schematic flow chart illustrating the formation of corn tubercle pellets or banana clusters. Carbon nanotubes (300) undergo surface activation (301) to become functionalised CNTs (302) with hydroxyl functional groups on the surface. Further reaction with C0CI2.6H2O and urea (303) results in H.T. longitudinal-axis growth of crystals (304). Reaction of (304) with high concentration of urea (305) or low concentration of urea (306) gives C/C03O4 nanorods (307). Heating of (307) obtained through route (305) to 400 °C (308) gives corn tubercle pellets (310). Heating of (307) obtained through route (306) to 400 °C (309) gives banana clusters (311).

[0062] Figure 2 provides a more detailed flow chart of the procedure, with the right side of the figure including micrographs showing (from top to bottom) CPs, BCs, LLs and MCS.

[0063] Figure 3 (A-G) illustrates Low- and high-magnification top-view SEM images of the hierarchically controlled pristine C03O4 nanostructures aligned vertically onto 3D PNi foam along the longitudinal axis. (A-C) SEM images of C03O4 CPs showing the interior structure of dense particle unit blocks of C03O4 mesocrystals forming the CP nanorod architecture. D, E) SEM micrographs of the C03O4 BCs resembling giant bamboo trees throughout the NR columns; the inset indicates the construction of sharp-edges NR architecture along the longitudinal scales. (F, D) SEM images of the C03O4 MCSs illustrating the multiple periphery sheet aggregation of the MCSs preferentially arranged axially to the PNi substrate.

[0064] Figure 4 (A-H) shows a dense aggregation of particle unit blocks of C03O4 or CoO mesocrystals and constituent attachment to the functional core of the c-axis along the longitudinal direction. This aggregation generates a unique molecular carbon/Co304 or CoO structure of CPs synthesized in a vertical fashion with respect to the underlying 3D PNi substrate. (A-E) SEM images of C-NT or g- C/C03O4 CPS/3D PNi illustrate the cylindrical roller sizes of the constructed NRs with core diameters decreased slightly from root section of the upper part along the C-axial arching. (F-l) SEM image of C-NT/CoO CPs/3D PNi showing the concrete arrangements of continuously ribbed and vertically oriented protruded pellets, creating a hierarchical assembly in the NR structure. Significantly, addition of the C-NT and g-C counterpart supports did not affect the stable molecular level morphology of C03O4 or CoO, but decreased the thickened of the NR and NS sized.

[0065] Figure 5 (A-a-A-c, B-a-B-c, C-a, D-a-D-b) provides top view low- and high- magnification FE-SEM micrographs of the hierarchical C-NT or g-C/Co304/3D PNi electrodes fabricated along the longitudinal axis via the one-pot hydrothermal approach. The images illustrate the scalability of the synthesis route. (A-a-A-c) Low and high scanning electron microscopy (SEM) magnifications of the C- NT/C03O4 BCs/3D PNi electrode showing a dense formation of nano-forests with multiple bamboo trees arranged vertically with respect to the 3D PNi substrate. The low-magnification FE-SEM images (A-c) clearly show the formation of a sharp- edged convex at the tip of the BC-NRs. (B-a-B-c) SEM images of the integration of the C-NT/C03O4 into the NR structure by the attachment of the C03O4 NPs along the longitudinal axis. (C-a) Low-magnification FE-SEM images of the g-C/CosCU LS/3D PNi and C-NT/Co₃0₄ MCs/3D PNi, respectively. The images display the efficient surface control of the sheet structure along the longitudinal axis. (C-a) Low-magnification FE-SEM images reveal lamina sheets with double-concave directions in its curvature at each edge. (D-a, D-b) MCSs induce double-helix flattened bands in opposite directions. The micrographic patterns show the controlled architectural morphologies along the longitudinal axes of the NRs and multiple cantilevered and lamina sheets dispersed in vertical orientation to the 3D PNi substrates.

[0066] Figure 6 (A-C, D-a-D-b, and E-a-E-b) illustrates evolution of the geometric features of the hierarchical C/C03O4 MCSs arranged axially around the axial stacking centre at the discrete point of surface direction along the longitudinal axis of C-NTs synthesized via a one-pot hydrothermal approach. (A-D) SEM images of C- NT/C03O4 MCSs/3D PNi electrode showing the structural integration of sheets into complex MCS architectures with inverse opal multilayers in the longitudinal scales vertically oriented to the 3D PNi substrate.

[0067] Figure 7 (A-E) illustrates the N2-absorption/desorption isotherms of the calcined samples showing the textural properties including the specific surface area and pore size distribution measured at 77K. (A) C-NT/Co₃0₄ CPs, (B) C-NT/Co₃0₄ MCSs, (C) g-C/Co₃0₄ LSs, (D) C-NT/Co₃0₄ BCs (E) C-NT/CoO CPs, and (F) pristine C03O4 CPS. The specific surface area (S. BET) of the samples was collected of the liner part of the related absorption loops. The inserts (a-f) represent the corresponding pore size distribution analysed by using NLDFT theory from the N2- adsorption/desorption hysteresis.

[0068] Figure 8A - 8C provides data that illustrates the vertical alignment of the CP-NR, BC-NR, Ls or MCS mesocrystal architectures.

[0069] Figure 9 (A-a-A-d, B-b-B-d, C-a-C-d) illustrates the FIB setup showing the specimen preparation by FIB investigation before characterization by HAADF- STEM. (A-a-A-d) Low-magnification cross-sectional FESEM images indication the stages of sample operation by the FIB system at different electron beams. (B-a-B- d, C-a-C-d) SEM and the corresponding schematic illustration of the microtomed g- C/C03O4 Ls and C-NT/C03O4 BCs, respectively, by etching the specimen parallel direction of longitudinal axis. The lower images are the related HAADF-STEM (bright/dark) images of the microtomed CosC g-C Ls and C-NT/C03O4 BCs specimens.

[0070] Figure 10 provides scanning/transmission electron micrographs and corresponding energy dispersive X-ray spectroscopy mapping of CPs, LSs, MCSs and BCs.

[0071] Figure 11 illustrates (A-D) Low-and high-resolution HAADF-STEM micrographs of hierarchical C-NT/C03O4 BCs/3D PNi substrates observed along the {001} plane illustrating the corresponding electron diffraction. (A,B) Low-resolution HAADF- STEM micrographs at different locations, showing the geometry of the NRs and their surface structures; the insets (B-a, B-b) represent the high magnification at the tip of the engineered NRs. (C-E) HR-HAADF STEM along {001}, showing anisotropic protrusions with a multi-step-terrace topography and many ridges and cavities on the surface edges.

[0072] Figure 12 illustrates results that were obtained for electrodes of the disclosure with C-NT or g-C/Co304 or CoO/3D PNi or glassy carbon architectures used as the anodic electrode in an ethanol electrooxidation reaction.

[0073] Figure 13 (A, B) provides CVs of exemplary electrodes recorded in 0.5 M NaOH at the scan rate of 50 mV s^_1 at room temperature. (A) CV responses of the bare 3D PNi electrodes in the absence and presence of ethanol. (B) CV profiles of the C03O4/3D PNi electrodes in the absence of ethanol.

[0074] Figure 14 (A-C) illustrates the effect of scan rate on the behaviour of exemplary C- NT/C03O4 CPs/3 D PNi electrode. (A) CV responses of C-NT/Co₃0₄ CPs/3D PNi electrode recorded in 0.5 M NaOH at different scan rates from 20-200 mV s^"1 at room temperature. (B, C) Plots of peak currents vs. the applied scan rate (B) at 20- 50 mV s^"1 and (C) at 70-200 mV s^"1.

[0075] Figure 15 (A-D) illustrates an electrochemical evaluation of exemplary carbon/Co304 or CoO/GC electrodes in 0.5 M NaOH and N2-saturated electrolyte in the absence or presence of ethanol at a scan rate of 50 mV s^"1. CV profiles recorded in the absence (A) and presence (B) of 0.5 M ethanol. (C) Current-time relationships of the carbon/Co304 or CoO / GC electrodes in 0.5 M ethanol for 18,000 s. (D) Relative currents of g-C or C/Co₃0₄ or CoO/GC electrodes as a function of the initial current at the start of the CA test. Note that a, b, c, d, e and f represent C-NT/Co₃0₄ CPs/GC, g-C/Co₃0₄ LSs/GC, C-NT/Co₃0₄ MCSs/GC, commercial Pt/C electrode, C-NT/Co₃0₄ BCs/GC, and C-NT/CoO CPs/GC electrodes, respectively. [0076] Figure 16 (A-D) shows CV curves for exemplary C-NT/Co₃0₄ CPs/GC and C- NT/Co30₄ CPs/3D PNi electrodes recorded in 0.5 M NaOH at room temperature. (A) CVs of C-NT/Co₃0 CPs/GC and 3D PNi electrodes in the absence of ethanol of 50 mV s^"1 scan rate. (B) Magnified CV spectra of C-NT/Co₃0 CPs/GC in the absence of ethanol at 50 mV s^"1 scan rate. (C) CVs of C-NT/Co₃0 CPs/GC and 3D PNi electrodes in the presence of 0.5 M C2H5OH at 50 mV s^"1 scan rate. (D) High-resolution CV spectra of C-NT/Co30₄ CPs/GC electrode in the presence of

[0077] Figure 17 (A-E) illustrates CVs of exemplary C-NT/Co₃0₄ CPs/GC modified electrodes recorded in 0.5 M NaOH at room temperature. (A) CVs of C-NT/Co30₄ CPs and bare Co30₄ CPs/GC-based electrodes collected in 0.5 M NaOH solution after 100 sweeps at a scan rate of 50 mV s^"1. (B) CV plots of C-NT/Co₃0₄ CPs/GC electrode recorded in 0.5 M NaOH at various scan rates. (C) Effect of ethanol concentration on CV responses of the C-NT/Co30₄ CPs/GC electrode at 50 mV s^_1 scan rate. (D) CV behaviours at different scan rates measured in 0.5 M NaOH.

[0078] Figure 18 illustrates the CVs of an exemplary C-NT/Co₃0 CPs/3D PNi electrode recorded in 0.5 M NaOH at room temperature. (A) CVs recorded at various concentrations of ethanol (0.05-0.5 M) and a scan rate of 50 mV s^"1. (B) Relationship between ethanol concentration and the corresponding current density measured at the end of the anodic scan. (C) CV responses of the C-NT/Co30₄ CPs/3D PNi electrode at different scan rates from 10-200 mV s^"1 obtained in 0.5 M NaOH containing 0.5 M ethanol. (D) Plot of the catalytic currents (la, lc measured at the end of forward scan and at the cathodic peaks) vs. the square root of the applied scan rate. (E) Plot of la/lc vs. the applied scan rate (F) CV curves of C- NT/Co₃0₄ CPs/3 D PNi electrode collected in 0.5 M NaOH and 0.5 M ethanol after continuous potential cycling at a sweep rate of 50 mV s^"1.

[0079] Figure 19 (A-D) provides CA analyses of an exemplary C-NT/Co₃0 CPs/3D PNi electrode evaluated in 0.5 M NaOH solution, (A) current-time spectra of C- NT/Co30₄ CPs/3D PNi electrode collected in absence of ethanol with a constant applied potential of 0.67 V vs Hg/HgO for 1800 s (B) the relation between the (I_C/IL) and the square roots of time applies measured from the CA date (Figure 3C-a), (C) the dependency of the catalytic current (lc current in presence of ethanol) on the inverse of the square roots of time investigated measured from the CA date (Figure 3C-a), (D) the dependency of the limiting current (k current in absence of ethanol) on the inverse of the square roots of time investigated measured from the CA data (A). [0080] Figure 20 (A-D) illustrates the dependence of the catalytic current (Ic) of exemplary applied electrodes on the inverse of the square roots of time measured from the CA data (Figure 10C, curves b-e) (A) g-C/Co₃0₄ LSs, (B) C-NT/Co₃0₄ MCSs, (C) C- NT/Co₃0₄ BCs, and (D) C-NT/Co₃0₄ CPs/3D PNi electrodes.

[0081] Figure 21 (A-H) illustrates HAADF-STEM images of C-NT/Co₃0₄ BCs/3D PNi and

C-NT/Co₃0₄ CPs/3D PNi electrodes after multiple reuse cycles. The images show that the engineered morphologies of both self-supported electrodes are well preserved. (A-C) HAADF-STEM micrographs of C-NT/Co₃0₄ BCs/3D PNi measured along the {001} plane display the engineered structure after stability testing for 18000 s. (A, B) STEM micrographs illustrate the surface morphology of the NRs at different locations. (C) HR-HAADF-STEM image shows that atomic structure down {001}. (D-G) HAADF-STEM of a single NR of the C-NT/Co₃0₄ CPs/3D PNi electrode (D) obtained at the middle portion and (E) at the top portion after long-term stability testing for 5000 cycles. (F, G) HR-HAADF-STEM obtained after stability testing along {1 12} (F), {112}, and at the {1 11}/ {1 12} interface plane (G). The inset (D) depicts a single poorly oriented polyhedron with low-and high index planes of the C-NT/Co₃0₄ CPs/3D PNi electrode. These single-crystal polyhedral CPs mainly contained different orientation types of low-index (i.e., 8 hexagon {11 1}, and 6 and 12 octagon {100}, and {1 10} planes) and high-index single (i.e., 24 quadrangles) crystals and interface {1 11}/ {112} planes.

[0082] Figure 22 illustrates simulations relating to hierarchical nanoforest catalyst architectures of the disclosure.

[0083] Figure 23 illustrates additional simulation data relating to catalyst architectures of the disclosure.

[0084] Figure 24 (A-F) provides a schematic representation of C-NT/Co₃0₄ CP crystal face. (A) Simulation model of the C-Co₃0₄ CPs. (B-E) Parallel projections along the {1 11}(B), {1 10} (C), {1 12} (D), {1 12} (E), and {001} (F) crystal planes.

[0085] Figure 25 provides TG-DTA curves measured for the Co(OH)_x(CO₃)₀.5 0.11 H₂O CP hierarchical structure revealing the thermal events that occurred. These curves indicate the total weight loss of the target sample during heat treatment.

[0086] Figure 26 (A, B) provide WA-XRD of the as-synthesized and calcines samples assigned according to the databases of the International Center for Diffraction Data provided by Bruker. (A) XRD patterns of Co(OH)_x(CO₃)₀.5 0.1 1 H₂O/ carbon orthorhombic cobalt basic carbonate phase of the engineered surface structures of CPs (a), BCs (b), MCSs (c), and LSs (d). (e) Orthorhombic cobalt basic carbonate phase of the bare Co(OH)_x(C0₃)o.5 0.11 H₂O CPs. (B) XRD spectra of the face- centred-cubic phase of the final product Fd3m C-NT or g-C-Co30₄ and Fm3m C- NT/CoO of the morphological architectures of CPs (a), BCs (b), MCSs (c), and LSs (d). Spectra of bare Co₃0₄ CPs (e) and C-NT/CoO CPs (f).

[0087] Figure 27 (A-E) provides chemical compositions and constituent states of the investigated samples measured by XPS and Raman analyses. (A) Complete survey of the XPS spectrum of C-NT/Co30₄ CPs showing the existence of 01s, C1s, and Co2p distinctive peaks. (B) High resolution of the Co2p peak deconvoluted into two characteristic peaks, with an energy difference of 15.0 eV. (C) High resolution C1s scan deconvoluted into three influential peaks. (D) High resolution 01s peak deconvoluted into three peaks. (E) Raman spectroscopy investigation of the samples measured at a laser beam of 633 nm.

DETAILED DESCRIPTION

[0088] The applicant has made efforts in developing single-crystal cobalt(ll,lll) oxide Co30₄ architectures with unique nanoscale shapes (e.g., sheets, cubes, rods, and belts) and predominantly exposed surfaces in the {11 1}, {100}, {1 10}, and {1 12} planes. For example, the cubic, closely packed structure of spinel Co30₄ mesocrystals, which is composed of Co³⁺ and Co²⁺ ions occupying octahedral and tetrahedral coordination sites, plays a significant role in the material's high catalytic performance. In particular, the exposed {1 10} plane of Co30₄ NCs is more catalytically active for carbon monoxide oxidation than are the {100} and {1 11} planes because of the abundance of rich Co³⁺ active sites in the {1 10} plane. The exposed surfaces of Co30₄ NCs have oxygen reduction activities in the order {111} > {100} » {110}, which is consistent with the density of highly exposed Co²⁺ active sites in each plane. Furthermore, the high-surface-energy {1 12} facets of Co30₄ NCs have been shown to perform better during methane combustion than the {001} and {011} planes.

[0089] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. [0090] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0091] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

DEFINITIONS

[0092] The term "C-NTs" as used herein refers to carbon nanotubes. The carbon nanotubes may be single walled carbon nanotubes or multi walled carbon nanotubes (MWCNT), e.g. MWCNT. The C-NTs may be oxidised, e.g. the C-NTs may be oxidised MWCNT. C-NTs represent a suitable substrate material for the support material of the electrodes of the present disclosure.

[0093] The term "exposed surface" as used herein refers to a surface of a solid or similar material that is available to interact with gas or solution. For example, in an electrode of the disclosure, the exposed surface represents the portion of the electrode with a surface that can interact with the reactants of any redox reaction, including. This may include reactant accessible pores.

[0094] The terms "g-C" as used herein refers to graphene sheets. The graphene sheets may be in the form of graphene oxide. g-C represent a suitable substrate material for the support material of the electrodes of the present disclosure.

[0095] The term "HMT" as used herein refers to the compound hexamethylenetetramine.

[0096] The following terms are used herein in relation to electron microscopy: "high angular annular dark-field - scanning/transmission electron microscope system" (HAADF-STEM), "STEM-energy dispersive X-ray spectroscopy" (STEM-EDS) mapping analysis system. [0097] The term "Miller indices" as used herein refers to a standard system of notation used to define the planes in a crystal lattice. The Miller indices of the equivalent faces of a crystal form are denoted by {hkl} plane. Exemplary Miller indices include {110}, {001}, {11 1} and {112} planes. Where a crystal comprises a surface feature that comprises an interface or boundary between faces having different Miller indices {hiki } plane and {ΠΣ Σ} plane, this interface plane may be denoted using a forward slash 7" in the following manner, {hiki }/{h2k2l2}. Exemplary interface planes (also described as interfaces) include {11 1}/{1 12}, {112}/{11 1}, {1 10}/{001} and {001}/{100}.

[0098] The term "PNi" as used herein refers to porous nickel foam. PNi is typically

provided as a 3 dimensional material, 3D-PNL PNi (and 3D-PNi) represents a suitable base material for the support material of the electrodes of the present disclosure.

[0099] The terms corn tubercle pellets (CP or CPs), banana clusters (BC or BCs), lamina sheets (LS or LSs) and multiple cantilevered sheets (MCS or MCSs) as used herein refer to the surface morphologies or morphological architecture of the metal oxide catalyst. The CPs may be oriented in nanorod (NR) domains, termed CP- NR. The BCs may be oriented in NR domains, termed BC-NR. The surface morphologies or morphological architecture may have surface morphologies oriented vertically away from the support or underlying substrate. The CP (e.g. CP- NR), BC (e.g. BC-NR), LS or MCS surface morphologies may be mesocrystal morphologies.

[00100] The term "mesocrystal" refers to a nanostructured material with a defined long- range order on the atomic scale. This can be inferred, for example, from the existence of an essentially sharp wide angle diffraction pattern (with sharp Bragg peaks) together with clear evidence (e.g. from electron microscopy) that the material consists of individual nanoparticle building blocks. Mesocrystals may have high porosity, providing a high surface area. Mesocrystals may represent more stable analogues of similar nanoparticulate materials. This high surface area and / or better stability may provide advantageous catalytic properties where

mesocrystals or a mesocrystal architecture are used to form a catalytic part of an electrode, e.g. for an electrode used in a fuel cell. For example, high surface area of a mesocrystal architecture may provide a relatively large reactive area with higher current and / or lower resistance. For example, better stability provided by a mesocrystal architecture may lead to a longer electrode life.

CATALYTIC MESOCRYSTAL ARCHITECTURES AND ELECTRODES [00101] Electrodes of the invention may comprise C03O4 mesocrystals.

[00102] Assessing the surface-dependent characteristics of C03O4 mesocrystals in terms of high-energy surfaces and density of exposed facets associated with low- and high-index single and interface planes is important when considering their use in ethanol electrooxidation. The scalable, low-cost, direct growth of homogeneous nanostructures comprising multi-component composites along the longitudinal axis of conductive substrates may provide favourable synergetic properties and competitive advantages over currently used electrodes in terms of enhanced conductivity, better structural stability and flexibility, superior electron-collection efficiency, and richness of electroactive sites.

[00103] An embodiment of the invention provides a method of making electrodes of the invention.

[00104] It is an object of the present invention to provide C03O4 mesocrystals with the following architectural features: (1) a dense aggregation and constituent attachment of C03O4 CP-NRs and BC-NRs along the longitudinal axis with an axial band of CP-NRs or BC-NRs closely packed around a central focal point, leading to the formation of nanoforests comprising structures that resembled giant bamboo trees; (2) the size of the CP-NRs and BC-NRs in the bamboo trees decreased with increasing distance from the central focal point and arched along the c-axis, forming a sharp-edged, convex, needle-like NR architecture with a nanoscale window running internally along the c-axis. This dominant needle-shaped end top surface enabled rapid electron transport by maximizing the diffusion of trigger pulse electrons during the catalytic reactions.

[00105] Figures 1 and 2 illustrate the applicant's simple, one-pot, hydrothermal method for synthesizing self-supported electrodes with novel morphological architectures. The overall structure of the electrodes was [carbon support/Co304 or cobalt(ll) oxide (CoO)/substrate], where the carbon support was either functionalized multi- walled carbon nanotubes (C-NTs) or graphene sheets (g-C), and the substrate was 3D porous Ni foam (3D PNi). The technical advantages of the proposed method are its simplicity, scalability, and low-cost operation. Furthermore, the proposed method allows the synthesis of C03O4 or CoO mesocrystal architectures along the longitudinal plane with surface morphologies oriented vertically away from the substrate in the form of corn tubercle pellets (CPs) or banana clusters (BCs) oriented in nanorod (NR) domains, lamina sheets (LSs), or multiple cantilevered sheets (MCSs) (Figures 3 - 6). [00106] C03O4 mesocrystals with morphologies of CP-NR, BC-NR, LS, or MCS were well dispersed interiorly and oriented vertically away from the 3D PNi support. Monodispersed particles were attached to the functional core of the c-axis, on which the novel, smart CP, BC, LS, and MCS mesocrystal morphologies were formed. Field emission scanning electron microscopy revealed that the disclosed methods afforded mesocrystal morphologies with the following key architectural features, as illustrated in Figures 3 - 6):

(1) Dense aggregation and constituent attachment of C03O4 CP-NRs and BC-NRs along the longitudinal axis with an axial band of CP-NRs or BC-NRs closely packed around a central focal point, leading to the formation of nanoforests comprising structures that resembled giant bamboo trees.

(2) The size of the CP-NRs and BC-NRs in the "bamboo trees" decreased with increasing distance from the central focal point and arched along the c-axis, forming a sharp-edged, convex, needle-like NR architecture with a nanoscale window running internally along the c-axis. This dominant needle-shaped end top surface enabled rapid electron transport by maximizing the diffusion of trigger pulse electrons during the catalytic reactions.

(3) Addition of the surfactant hexamethylenetetramine during catalyst synthesis promoted the formation of dense, vertical lamina aggregates of LSs and MCSs that had distal, non-stacked layers bordered by spacer micro-, meso-, and macro- globule pores, as shown by N2 isothermal profiling (see Figure 7). Therefore, the growth along the vertical axis of the LSs and MCSs originated from the directional growth along the longitudinal axis.

(4) Use of g-C as the carbon support caused the LSs to be discretely stacked with regular spacing (100 nm) or to not stack at all. This multilayered LS structure along the longitudinal axis may be responsible for the efficient catalytic activity observed compared with that of complex MCS architectures with inverse opal multilayers.

(5) The use of C-NTs, cobalt(ll) chloride (C0CI2), and hexamethylenetetramine resulted in the preferential axial arrangement of flattened double-helix bands running in opposite directions and production of multiple-cantilevered sheets along the longitudinal axis of the C-NT domains. Each individual flattened sheet exhibited dynamic flexibility in its curvature in the double-concave direction along each edge (Figures 5 and 6).

[00107] The vertical alignment of the CP-NR, BC-NR, LS or MCS mesocrystal architectures along the longitudinal plane remains a topic of interest with regard to ethanol oxidation reactions. To investigate the internal concentric arrangement and orientation of the constituent units inside these structural morphologies, etching experiments were conducted using a focused-ion beam milling setup to etch specimens parallel to the longitudinal axis to a thickness of 100 nm (Figure 8A-8B). A focused-ion beam system for fabricating thin specimens was integrated into a high angular annular dark-field (HAADF)-scanning/transmission electron microscope system (STEM) (Figure 8 and Figure 9) and STEM-energy dispersive X-ray spectroscopy (EDS) mapping analysis system (Figure 8C).

[00108] Figure 8B-a-8B-d shows the interior structure of the C03O4 CP morphology at a depth of 100 nm and at different locations along the longitudinal axis of the NRs. The concrete arrangements of the protruding pellets on these corn tubercle surfaces and surface inhomogeneity readily sit on the apex of C-NTs covered by numerous oriented tiny tubercles. The internal atomic arrangement of the nanoforests was also well dispersed longitudinally (STEM-EDS mapping, Figure 8C). The CPs in the C03O4 NR skin were ribbed and vertically configured to the longitudinal axis grooves (aligned parallel to the main direction of NR mesocrystal projection), which created canals and window spaces for electron diffusion and transport (i.e., upward and downward movements; Figure 8 and Figure 9).

[00109] HAADF-STEM microscopy revealed the morphologies along the longitudinal axes of the NRs (i.e., C/Co₃0₄ CPs and C/Co₃0₄ BCs) and nanosheets (i.e., C/Co₃0₄ MCSs and g-C/Co304 LSs) (Figure 3A). Individual CP domains exhibited a marked side-to-side anisotropic geometry with well-distributed atomic surface active sites (Figure 10A-a). High-resolution HAADF-STEM microscopy of 50-nm particles (Figure 10A-a, inset) revealed the proposed mesocrystal model of 50-facet polyhedrons. The 50-facet C03O4 CPs, as well as other non-well-defined polyhedral mesocrystals, grew mainly along the low-index {100} and {11 1} planes together with some high-index {112} planes and other poorly developed facets. Twenty-four exposed high-index {1 12} planes had grown axially around each {100} and {11 1} planes of the 50-facet polyhedrons. Increasing the number of high-index planes with a high surface energy and the number of polyhedron CPs oriented longitudinally within the NR morphology are key to improving the performance of the electrodes for ethanol oxidation

[00110] Side-view HAADF-STEM microscopy of the C03O4 MCSs revealed lamina sheets that had been flattened during reassembly and had rough surfaces containing pores aligned perpendicular to the longitudinal axis (Figure 10A-b, c). Top-view HAADF-STEM microscopy of the C03O4 LSs revealed a series of non-stacked, well-oriented, vertical lamina sheets. Nanoscale (40-60 nm) edges of the lamina sheets were located laterally along the longitudinal axis (Figure 10A-d, e). HAADF- STEM microscopy of the C03O4 BCs revealed that they represent the visual architecture of an actual banana cluster with structures built upon one-dimensional NRs and control boundary-layer skin as tunnel-line nanopatterns, dense particles, and smooth surfaces (Figure 10A-f, g).

[00111] High-resolution HAADF-STEM micrographs (Figure 10B) and the corresponding EDS patterns (Figure 10B, insets) taken along {11 1}/{112} (Figures 10B-a, b) and the dominant {112} (Figure 10B- c), {1 1 1} (Figure 10B-a, d), {1 12} (Figure 10B-e), {110}/{001} (Figure 10B-f), and {001} (Figure 10B- f, g) planes further revealed the structures of single-crystals of the C03O4 CPs, LSs, MCSs, and BCs, respectively. Mesocrystal growth in as-prepared samples of Co(OH)x(C03)o.5 0.11 H₂0 with CP-NR, BC-NR, LS, or MCS morphologies primarily produced longitudinally aligned facets exposed along the {001} plane. High- temperature treatment of the CP-NRs, BC-NRs, MCSs, and LSs may strongly influence the atomic configuration and renucleation within the architectures, which would enable sustained relaxation of the atoms around the dominant {001} facet to produce the high surface energy {1 12} and {11 1}/{112} planes of the CPs, MCSs, and LSs (Figure 10B-a-e), and the {1 10}/{001} plane (Figures 10B-f, g) of the BCs.

[00112] The axial orientation change of the crystal planes along the {001} direction under treatment led to the remarkable formation of {1 11}/{112} interface planes between the {112} and {11 1} planes of the C03O4 CPs. A multi-step-terrace topography over the ridges of the nanosheets also caused {11 1 }/{ 112} interface planes to form on the C03O4 LSs and MCSs. In turn, a dense construction of BCs was produced on the smooth, flattened lamina surfaces with tightly joined and closely packed basal edges (i.e., flanked border lines) (Figure 11). A protruding surface with a multi-step- terrace topography forming hedge-saw islands with many ridges and cavities along its edges at a depth of 10 nm was also observed (Figure 10B-f, g). Such an interfacial topography may create an open surface for the diffusion of Co³⁺ atoms into vacancies in the crystal surface. Consequently, the Co³⁺ enriched {1 11}/{112} and {110}/{001} interface planes associated with the main topographic facet islands aligned along the {11 1}, {1 12}, and {001} planes may form (Figure 11). A

continuous electron flow may then be produced parallel to the longitudinal axes of the nanoforests.

[00113] Using a catalytic electrochemical assay as described herein, the applicant

investigated the effects of the following parameters on ethanol electrooxidation: (i) arrangement and orientation of heterogeneous Co²7Co³⁺ site atomic, (ii) type of nanoforest morphology (CP-NR, BC-NR, LS, or MCS), (iii) mesocrystal orientation with exposed high-index {112} planes, (iv) degree of exposure of interior atomic- scale {11 1}/{1 12} interface planes blocks, (v) growth along the longitudinal axis to attain high surface energy and dense Co³⁺ site surfaces, (vi) presence of multi- diffusive pore phases, and (vii) electrode nano-pattern design resulting from the combination of conductive support (C-NT or g-C) and substrate (4D PNi or glass carbon, GC) (Figures 12 - 20).

[00114] Electrodes with C-NT or g-C/Co304 or CoO/3D PNi or glassy carbon architectures were used as the anodic electrode in an ethanol electrooxidation reaction (Figure 12). In a non-alcoholic assay, all of the electrodes revealed two sets of redox couples produced from the reversible reactions between C03O4 and cobalt oxide hydroxide (CoOOH) (peaks I and IV) and between CoOOH and C0O2 (peaks III and/ll) (Figure 12A).

[00115] In the ethanol electrochemical assays, no anodic peaks were observed with any of the electrodes, indicating that oxygen evolution overlapped with the ethanol oxidation and that oxygen was evolved at highly positive potentials from 0.6 to 0.9 V (Figure 12B). In the reverse scan, cathodic peaks from 0.3 to 0.5 V were observed, which were associated mainly with the removal of carbonaceous species (such as carbon monoxide, carbon dioxide, methanoic acid, hydroxymethylene, and methyl methanoate) that were not completely oxidized in the reverse scan and the chemisorption of unknown species onto the electrode (Figure 12B).

[00116] Each of the electrodes used in the assay is proposed to form an electroactive mediator CoOOH layer that facilitated ethanol molecule absorption and electron transport, forming the highly active species Co(IV). As shown in Figure 12B the increase in the current density at 0.9 V follow this order C-NT/C03O4 CPs > g- C/C03O4 LSs > C-NT/C03O4 MCSs > C-NT/C03O4 BCs > C-NT/CoO CPs. Current density markedly increased with the addition of ethanol, indicating that the electrodes catalyzed ethanol electrooxidation (Figure 12A, B and Figure 15 A, B). Moreover, C03O4 mesocrystals, which had catalytically active tetrahedral Co²⁺ and octahedral Co³⁺ sites in exposed high- and low-index planes, showed higher catalytic ethanol electrooxidation activity than did CoO mesocrystals, which had only catalytically active Co²⁺ sites. Without wishing to be bound by any theory, it is therefore believed that surfaces containing both Co²⁺ and Co³⁺ sites have higher catalytic activities than do those with only Co²⁺ sites.

[00117] To further illustrate the superior electrochemical activity conferred by directly growing C-NT or g- C/C03O4 catalysts along the longitudinal axis on 3D PNi, ethanol electrooxidation reactions were performed using a C-NT or g-C/Co304/GC electrode and a commercial Pt/C electrode for comparison (Figure 15C, D). Compared with the performance of commercial Pt/C electrode and the C-NT or g-C C03O4/GC electrode with CP morphology, the performance of C-NT or g-C/ C03O4/3D PNi or GC electrodes with any morphology was comparable to or perhaps even better than commercial Pt/C electrode in terms of current density and electrode stability (Figure 12C, D and Figure 15C, D).

[00118] To determine the current density and stability of the developed electrodes, current-time relationships were determined by means of chronoamperometric testing in 0.5 M ethanol for 18,000 s with carbon/Co₃0₄ or CoO/3D PNi and Pt/C electrodes (Figure 12C). Slight decays in the currents of the C-NT or g-C/ Co₃0₄/3D PNi electrodes indicated superior current stability and resistance to poisoning compared with the C-NT/CoO/3D PNi and Pt/C electrodes (Figure 4C, D and Figure 15C, D). The relative current % at the end of the assessment period (i.e., at t = 18,000 s) decreased in the order C-NT/ Co₃0₄ CP > g-C/ Co₃0₄ LS > C- NT/ Co₃0₄ MCS > C-NT/ Co₃0₄ BC > C-NT /CoO CP > Pt/C, which is consistent with the change in reaction rate (catalytic rate constant) and diffusion coefficient of the electrodes (Table 1). The superior catalytic activity of the C-NT or g- C/Co₃0₄ electrodes over the C-NT or g-C/CoO and Pt/C electrodes suggested that manipulation of anisotropic C-NT or g-C/Co₃0₄ morphologies along the longitudinal c-axis may have enabled the creation of improved catalytic structural features. Compared with the other electrodes examined, it is believed that the high-index exposed surfaces and interfaces of C-NT or g-C/ Co₃0₄ may produce more efficient electron movement over the oxygenated, grooved electrode surface and into Co³⁺ sites via upstream swirls and multi-diffusivity windows.

[00119] Table 1 Measured energies of the exposed facets and interface surfaces

obtained by DFT modelling.

Single

Mean plane Co Adsorption Stabilization Surface Surface

diffusion

Morphology and density energy (E_ads) energy (E_B) area energy

Coefficient listeria on top kJ/fflo! (eV) (A)² (J/m^J)

(D) (cm² s^"1) ees

{ 1 12 } 3 -24.886 -107. 155 201 . 1 9 -8.533

C-NT/C03O4 { 1 11 } 1 -25.845 -104.291 65.80 -23.9387

4.59 * 10^"'5 CPs { l l l }/{

4 -28.472 -114.735 298.62 -6.156

1 12}

{ 1 12} 3 -24.886 -107.155 201.19 -8.533 g-C /C03O4 { 1 1 1 } 1 -25.845 -104.291 65.80 -23.9387

3 x l0^"5

LSs { ! ! ! }/{

4 -28.472 -114.735 298.62 -6.156

112}

(001 } -26.028 -107.875 85.71 -20.1652

[00120] Optimizing the long-term stability, efficiency, and recyclability of electrodes used in direct ethanol fuel cells remains a challenge. To further assess the durability of the developed electrodes, a set of experimental ethanol electrooxidation reactions was conducted with a C-NT/C03O4 CP electrode under continuous potential cycling for 5000 cycles (Figure 12E). The electrode retained approximately 68.7% of its original current density after multiple reuse cycles at 0.9 V (≥5000 cycles), which is superior to other electrodes reported recently (Table 2). Notably, after ≥5000 cycles, the reused electrode of the present disclosure had retained its highly reactive surfaces (Figure 21), demonstrating retention of 71.9% of its current density (Figure 18) in the fresh electrolyte of the electrochemical assay. This result suggests that electrodes of the present disclosure electrodes had markedly improved dead-end workability and recyclability compared with other electrodes (see Table 2).

[00121] Table 2 Retained oxidation currents as percentages of their original values

after long-term stability assessment of the different electrode materials relative to the C-NT/C03O4 CPs/3 D PNi electrode.

Retention percentage of

i ficCis e i o_*

Active material the original value after Target fuel reference of cycles

losig term stability

NiCo₂0 89% 500 methanol 36

90% and 88% for NCO-

N1C02O4 1000 methanol 37

NS and NCO-NC

Go- N1C02O4 79.3% 500 methanol 38

NiCo₂0 72% with SDS and 1000 methanol 39

(75%) without SDS

NiCo₂0₄ 85% 500 methanol 40

71.9% 5000 ethanol this study

PNi substrate [00122] 36. Li, G., Lei, CL, Ying, L, Yanyan, W., Jing, L, Hongyan, Y., & Dan, X.

Microwave-assisted synthesis of nanosphere-like N1C02O4 consisting of porous nanosheets and its application in electro-catalytic oxidation of methanol. Journal of Power Sources 261 , 317-323(2014).

37. Wei, W. et al. Nickel foam supported mesoporous N1C02O4 arrays with excellent methanol electro- oxidation performance. New J. Chem. (2015).

38. Ashok, K., D., Rama, K. L, Nam, H. K., Daeseung, J., & Joong, H. L.

Reduced graphene oxide (RGO)-supported N1C02O4 nanoparticles: an electrocatalyst for methanol oxidation. Nanoscale 6, 10657-10665 (2014).

39. Rui, D., Li, Q., Mingjun, J., & Hongyu, W. Sodium dodecyl sulfate-assisted hydrothermal synthesis of mesoporous nickel cobaltite nanoparticles with enhanced catalytic activity for methanol electrooxidation. Journal of Power Sources 251 , 287-295 (2014).

40. Xin, Y. Y. et al. Facile synthesis of urchin-like N1C02O4 hollow

microspheres with enhanced electrochemical properties in energy and environmentally related applications. ACS Appl. Mater. Interfaces 6, 3689-3695 (2014).

[00123] Included herein is a quantitative investigation of the effects of anisotropic morphology and number of surfaces enriched with Co³⁺ sites on charge transfer (i.e., electrical conductivity) within the developed electrodes. Electrodes with architectures of C-NT/ Co₃0₄ CP, C-NT/ Co₃0₄ BC, C-NT/ Co₃0₄ MCS, g-C/Co₃0₄ LS, and C-NT/CoO CP were assessed by means of electrochemical impedance spectroscopy using an open circuit potential with a 5 mV amplitude at frequencies from 100 kHz to 0.01 Hz in 0.5 M sodium hydroxide containing 0.5 M ethanol (Figure 12F-a-e). The impedance Nyquist plots for all of the electrodes had a semicircular shape at high frequencies, which represents the Ret of the electrode design. In addition, they had a straight line at low frequencies, which represents the solution resistance (Rs), charge-transfer resistance (Ret) and the redox capacitive behaviour (C) of CoO or Co₃04 (Figure 12F-insert). The diameters of the semicircles in the plots increased in the order C-NT/Co₃04 CP < g-C/Co₃04 LS < C- NT/Co₃0₄ MCS < C-NT/Co₃0₄ BC < C-NT/CoO CP.

[00124] Importantly, the hierarchical nanoforest architectures are believed to create multi- diffusive phases of molecular and electron transport along the catalyst morphology through longitudinal monowindow- and mesocylinder-open-pore architectures (CPs and BCs) (Figure 22A), vertical inter-layered spaces and interfaces (LSs and MCSs) (Figure 22C), and catalytically active surfaces and exposure sites (Figure 22B). In such multi-diffusivity phases, "surface-blocking" by the accumulation of intermediate species can "poison" an electrode surface. In addition, the vertical grooves across the longitudinal axis caused the electron flow to perpetually realign in response to changes in internal and external architectures (Figure 22A). Thus, the longitudinally oriented surfaces with catalytically exposed sites may play a critical role in improving the kinetics and diffusion of electrons (Figure 22B). The proposed model (Figure 22B) takes account of electrode surfaces composed of Co²⁺, Co³⁺, and O^2" atoms stacked alternately along the c-axis that become dense at the upper area of the coverage surfaces of the {1 11} and {1 11}/{1 12} planes. Interface-generated plane surfaces (i.e., {11 1 }/{ 112}) provide more

thermodynamically stable and chemically active binding sites and therefore can adsorb ethanol molecules onto its abundant O^2" atoms better than a high-index {112} plane can (Figure 23 and Table 1). Furthermore, a discontinuous jump in electron transfer is expected at the curvature of the stacking point of the MCS double-helix layers (Figure 22C). The electron movement at the intricately connected MCS curvature may provide angular movement transfer (i.e., instant torque blocks) that constrains the degrees of freedom of electron transport with respect to axial movement into the outer surface of vertically oriented, continuous or non-stacked LS structures, as was evident from the diffusion coefficient value and current density of the LS- and MCS-based electrodes (Figure 24C).

[00125] The catalytic efficiency of the developed electrodes for ethanol electrooxidation, in terms of current density, stability, surface electron movement, and molecular diffusivity, was substantially influenced by the structural characteristics of the electrode catalyst. Factors that had marked effects included a morphological architecture oriented along the longitudinal axis, the presence of multi-diffusive pores with fractal connectivity windows, and the presence of facet-dependent surface sites (i.e., high-energy exposed facets, high electron density along the nano-scale architectures, and interface planes). The effect of high-index interface planes tightly joined and closely arranged across entire mesocrystals was evident in the catalytic activities of the electrodes with CP, BC, LS, and MCS morphologies. Models of the atomic configurations and active sites of the predominant {1 11}, {112}, {001}, and {110} planes and their interface planes were simulated by using density functional theory (Figure 24).

[00126] The density of catalytically active Co³⁺ sites arranged normal to the

mesocrystal planes and the top-on-plane the catalyst surfaces are key parameters of surface reactivity that markedly influenced the catalytic performance of the developed electrodes. Co³⁺ density in the catalyst planes decreased in the order {112}/{1 11} > {1 10} ≥ {001} > {1 10}/{001} ≥ {112} > {11 1}. The exposed surfaces of the {1 12}/{11 1} interface plane had more unsaturated bonds (dangling bonds) and higher surface-stabilization energies than did the other facets and interface facets. This finding is consistent with the order of catalytic reactivity of the examined morphologies (i.e., CP > LS > MCS > BC). Ethanol molecules were adsorbed onto the surfaces perpendicularly to O^2- atoms close to active Co³⁺ sites. Similarly, adsorption energy increased in the same order as the increase in Co³⁺ density of the crystal plane surfaces.

[00127] The high-index {112}/{11 1} interface planes in the 50-facet polyhedral catalysts had numerous exposed C/C03O4 CP surfaces enriched with Co³⁺ active sites, which were important for effective adsorption, molecular excretion, and electron transport (Table 1 ). Reactive facets containing a large number of Co³⁺ sites (i.e., the {1 12} side of the {1 12}/{11 1} plane) formed stronger bonds with ethanol molecules at smaller bond distances. Hence, ethanol adsorption was dependent on the active sites in the active adsorption plane (Figure 24) in the exposed interface surfaces of the {1 12}/{1 11} and {110}/{001} planes (interface- site-dependent adsorption energy). The negative adsorption energy indicates that ethanol adsorption onto the high- and low-index crystal surface planes is an exothermic and energetically preferential behaviour in an effective ethanol oxidation reaction. The change in the adsorption energy may be due to the change in atomic charges of the active adsorption surface sites of the crystal {110}, {001}, {11 1}, and {1 12} planes and their interfaces (Table 1).

[00128] Electrostatic potential maps were examined using density functional theory, which showed the gradients in the surfaces in terms of the charge density of Co²⁺, Co³⁺, and O^2- atoms on the isosurface and the unsaturated coordination bonds (i.e., dangling bonds) at the Co³⁺ sites of the exposed {110}, {001}, {11 1}, and {1 12} planes and interfaces (Figure 2 3 ). The change in electrostatic potential distribution on the low- and high-index planes was used to highlight the active sites; the largest deviations in electrostatic potential were found at the interfacial active centres because of the generation of oxygen vacancies in that location. Electrostatic potential mapping of the exposed plane surfaces strongly suggested that the surface oxygen atoms near O^2- vacancy sites had greater negative charges (an electron-rich surface) than those further from the O^2- vacancy sites. [00129] The electrostatic potential map of Co³⁺ atoms showed a more pronounced charge density compared with that of the Co²⁺ atoms, indicating that Co³⁺ atoms, particularly the Co³⁺ atoms of the outer surface near the O^2- vacancy sites, are the most electroactive sites (Figure 23). Therefore, more electron-rich O^2- vacancy sites were generated at the interface facets. As a result, interfacial active centres exhibit high electron density and large-scale electron motion across the surface atoms. The hierarchy in the surface configurations of the C/C03O4 CP electrode oriented longitudinally could feasibly create a markedly complex {11 1}/{1 12} plane with many Co³⁺ atoms and more electron- rich O^2- vacancy sites in both the main- and top-layer crystal surfaces. A high adsorption energy and surface-stabilization energy, as well as an abundance of unsaturated bonds, may be achieved in the reaction, thereby producing more efficient, elastic electron transport and molecule-to-surface diffusion along these interface planes.

REFERENCES

[00130] Also included within the disclosure are the following references, the contents of which are incorporated herein in their entirety:

1. William, C. C, Yong, H., WooChul, J., & Sossina, M. H. High electrochemical activity of the oxide phase in model ceria-Pt and ceria-Ni composite anodes. Nature Materials 11 , 155-

161 (2012).

2. Gewirth, A. A. & Thorum, M. S. Electroreduction of dioxygen for fuel-cell applications: Materials and challenges. Inorg. Chem. 49, 3557-3566 (2010).

3. Lewis, N. S. & Nocera, D. G. Powering the planet: Chemical challenges in solar energy utilization. Proc. Natl Acad. Sci. 103, 15729-15735 (2006).

4. Stambouli, A. B. Fuel cells: The expectations for an environmental-friendly and sustainable source of energy. Renew. Sustain. Energy Rev. 15, 4507-4520 (2011).

5. Bashyam, R. & Zelenay, P. A class of non-precious metal composite catalysts for fuel cells./Vafore 443, 63-66 (2006).

6. Antonino, S. A., Peter, B., Bruno, S., Jean, M. T., & Walter, V. S.

Nanostructured materials for advanced energy conversion and storage devices. Nature Materials 4, 366 - 377 (2005).

7. Huajie, H., Shubin, Y., Robert, V., Xin, W. & Pulickel, M. A., Pt-decorated 3D architectures built from graphene and graphitic carbon nitride nanosheets as efficient methanol oxidation catalysts. Adv. Mater. 26, 5160-5165 (2014).

8. Meher, S. K. & Rao, G. R. Morphology-controlled promoting activity of nanostructured Μηθ2 for methanol and ethanol electrooxidation on Pt/C. J. Phys. Chem. C 117, 4888-4900 (2013).

Wei, H., Jin, W. & Erkang, W. Facile synthesis of highly active PdAu nanowire networks as self-supported electrocatalyst for ethanol electrooxidation. ACS Appl. Mater. Interfaces 6, 9481 -9487 (2014).

Chen, M., Wu, B., Yang, J. & Zheng, N. Small-adsorbate assisted shape control of Pd and Pt nanocrystals. Adv. Mater. 24, 862-879 (2012).

Xu, J. et al. Preparation and electrochemical capacitance of cobalt oxide (C03O4) nanotubes as supercapacitor material. Electrochim. Acta 56, 732-736 (2010).

Liang, Y. Y. et al. Co₃0₄ nanocrystals on graphene as a synergistic catalyst for oxygen reduction reaction. Nat. Mater 10, 780-786 (201 1).

Dawei, S., Shixue, D. & Guoxiu, W. Single crystalline Co₃0₄ nanocrystals exposed with different crystal planes for L1-O2 Batteries. Sci. Rep. 4, 5767 (2014).

Tang, X., Li, J. & Hao, J. Synthesis and characterization of spinel Co₃0₄ octahedra enclosed by the {1 1 1} facets. Materials Research Bulletin 43, 2912- 2918 (2008).

Xiao, J. et al. Surface structure dependent electrocatalytic activity of Co₃0₄ anchored on graphene sheets toward oxygen reduction reaction. Sci. Rep. 3,

2300 (2013).

Ji, F. & Zeng, H. C. Size-controlled growth of Co₃0₄ nanocubes. Chem. Mater. 15, 2829-2835 (2003).

Xie, X. W., Li, Y., Liu, Z. Q., Haruta, M. & Shen, W. J. Low-temperature oxidation of CO catalysed by Co₃0₄ nanorods. Nature 458, 746-749 (2009).

Yang, J., Liu, H., Martens, W. N. & Frost, R. L. Synthesis and characterization of cobalt hydroxide, cobalt oxyhydroxide, and cobalt oxide nanodiscs. J. Phys. Chem. C 114, 1 11-119 (2010).

Linhua H., Qing, P. & Yadong, L. Selective synthesis of Co₃0₄ nanocrystal with different shape and crystal plane effect on catalytic property for methane combustion. J Am Chem Soc

130, 16136-16137 (2008).

Xinhui, X. et al. High-quality metal oxide core/shell nanowire arrays on conductive substrates for electrochemical energy storage. ACS Nano 6, 5531- 5538 (2012).

Xinhui X. et al. A new type of porous graphite foams and their integrated composites with oxide/polymer core/shell nanowires for supercapacitors: structural design, fabrication, and full supercapacitor demonstrations. Nano Lett. 14, 1651 -1658 (2014).

22. Jiang, J. et al. General synthesis of large-scale arrays of one-dimensional nanostructured Co₃0₄ directly on heterogeneous substrates. Cryst. Growth Des., 10, 70-75 (2010).

23. Yanguang, L, Bing, T., & Yiying, W. Freestanding mesoporous quasi-single- crystalline C03O4 nanowire arrays. J. Am. Chem. Soc. 128, 14258-14259 (2006).

24. Laifa, S., Qian, C, Hongsen, L, & Xiaogang, Z. Mesoporous NiCo204 nanowire arrays grown on carbon textiles as binder-free flexible electrodes for energy storage. Adv. Funct. Mater. 24, 2630-2637 (2014).

25. Casella, I. G., & Gatta, M. Study of the electrochemical deposition and properties of cobalt oxide species in citrate alkaline solutions. J. Electroanal. Chem. 534, 31 -38 (2002).

26. Jianhui, Z. et al. CNT-network modified Ni nanostructured arrays for high performance non- enzymatic glucose sensors. RSC Adv. 1 , 1020-1025 (201 1).

27. Junchao, H., Zhaolin, L, Chaobin, H., & Leong, M. G. Synthesis of PtRu nanoparticles from the hydrosilylation reaction and application as catalyst for direct methanol fuel cell. J. Phys. Chem. B 109 16644-16649 (2005).

28. Shukla, A.K., Christensen, P.A., Hamnett, A., & Hogarth, M.P. Vapour-feed direct-methanol fuel cell with proton-exchange membrane electrolyte. J. Power

Sources 55 87-91 , (1995).

29. Petitto, S. C, Marsh, E. M., Carson, G. A. & Langell, M. A. Cobalt oxide surface chemistry: the interaction of CoO (100), Co₃0₄ (110) and Co₃0₄ (11 1) with oxygen and water. J. Mol. Catal. A 281 , 49-58 (2008).

30. Omata, K., Takada, T., Kasahara, S. & Yamada, M. Active site of substituted cobalt spinel oxide for selective oxidation of CO/H2. Part II. Appl. Catal. A 146, 255-267 (1996).

31. Jing, Z., Meng, C, Chuanfu, Z., & Chen, Wang. Synthesis of mesoporous N1C02O4 fibersand their electrocatalytic activity on direct oxidation of ethanol in alkaline media, Electrochimica Acta 154 70-76 (2015).

32. Jafarian, M. et al. A study of the electro-catalytic oxidation of methanol on a cobalt hydroxide modified glassy carbon electrode. Electrochim. Acta 48, 3423-3429 (2003).

33. Qian, L, Gu, L, Yang, L, Yuan, H. Y., & Xiao, D. Direct growth of NiCo204 nanostructures on conductive substrates with enhanced electrocatalytic activity and stability for methanol oxidation. Nanoscale 5, 7388-7396 (2013). 34. Leung, L.W. H., & Weaver M.J. Real-time FTIR spectroscopy as a quantitative kinetic probe of competing electrooxidation pathways for small organic- molecules. Journal of Physical Chemistry B 92, 4019-4022, (1988). EXAMPLES

Materials

[00131] All investigated chemicals and materials were of analytical grade and used without further purification. Cobalt chloride hexahydrate (C0CI2.6H2O, 99%), graphite powder (98%), urea (CO(NH₂)₂, 99%), HMT (C₆Hi₂N₄), and sodium hydroxide (NaOH, 98%) were supplied by Wako Co., Ltd., Osaka, Japan. Cobalt nitrate hexahydrate (Co(N0₃)2.6H₂0, 98%), ammonium nitrate (NH₄N0₃, 99%), absolute ethanol (C2H5OH, 99.5%), nitric acid (HN0₃, 61 %), sulfuric acid (H₂S0₄, 95%), hydrochloric acid (HCI, 36%), and hydrogen peroxide (H2O2, 30%) were purchased from Nacalai Tesque Co., Japan. The MWCNTs (98%) were obtained from Sigma-Aldrich Company Ltd., USA, whereas the potassium permanganate

(KMn0₄, 99.5%) was purchased from Tokyo Chemical Industry Company (TCI), Ltd., Japan. The 3D porous Ni foam (3D PNi) (1 cm ^χ 1 cm) was produced by TCI as a conductive scaffold on which the nanocomposites were grown. Prior to synthesis, the 3D PNi substrates were repeatedly rinsed by sonication in concentrated HCI solution, ethanol, and Milli-Q water in succession and then dried for 12 h at 60 °C.

[00132]

Example 1

Purification and functionalisation of multi-walled carbon nanotubes (MWCNTs)

[00133] The raw MWCNTs were initially mixed with HN0₃/H₂S0 solutions at a 1 :3 ratio.

The mixture was then ultrasonicated at 50 °C for 5 h and then refluxed at 110 °C for 3 h. Afterward, the resulting mixture was diluted at pH 7 using deionized water. The solid (i.e., oxidized MWCNTs) was collected by centrifugation and dried at 65 °C overnight for later use.

Preparation of graphene oxide

[00134] Graphene oxide was synthesized from graphite powder in accordance with the slightly modified Hummers method. Typically, 2 g of graphite powder (-40 μηι) was reacted with a strong oxidizing solution of concentrated H2S0₄ and HNO3 (100 mL, 1 : 1 v/v) by vigorous stirring for 1 h at 25 °C. Afterward, the solution was placed in an ice-water bath, and 7 g of KMn0₄ was slowly added to the solution under stirring for 2 h. The mixture was then ultrasonicated for 6 h at 40 °C to avoid obtaining a homogeneous reaction solution. Deionized water (350 ml_) was then mixed with the formed gel, and the whole mixture was stirred at 80 °C for 1 h. Subsequently, 120 ml_ of 30% H2O2 and 50 ml_ of 15% HCI solutions were added to the mixture and then stirred for 10 min. The gel mixture was allowed to stand until brownish precipitation. The solid materials were washed repeatedly with double-distilled water and dried overnight at 60 °C prior to the next investigation.

Preparation of C-NT/CoO CPs/3D PNi nanostructures

[00135] A simple, one-pot method for the synthesis of C-NT/CoO CPs/3D PNi electrode was achieved through a microwave-assisted technique. In this method, 0.1 M cobalt nitrate hexahydrate and 0.35 M HMT were mixed with 37 ml_ of deionized water while stirring for 10 min. Then, 80 mg of oxidized C-NTs were immersed into the above solution and vigorously stirred for 3 h. The mixture was subsequently transferred into a Teflon-lined autoclave containing a 3D PNi sheet (Scheme 1) and then subjected to microwave irradiation (600 W) at 160 °C for 1 h. The collected sample was carefully washed with ethanol and deionized water, dried at 60 °C overnight, and finally calcined at 400 °C for 4 h in air.

Fabrication of C-NT or q-C/CosCU or CoO/GC

[00136] To investigate the effect of the carrier substrate on EOR efficiency using a longitudinal electrode design, several electrochemical experiments were conducted using C-NT or g-C/Co304 or CoO/GC electrodes at electrochemical conditions similar to those applied to the C-NT or g-C/Co304 or CoO/3D PNi electrode assays. The thin-film-layered C-NT or g-C/Co30₄ or CoO/GC electrode was fabricated by dispersing the active catalyst powder onto a GC substrate through a heterogeneous-assisted ink-deposition method at 25 °C. The homogeneous catalyst ink was prepared by mixing 5 mg of active catalyst to 50 μΙ_ of 5 wt% Nafion solution employed as a binder in 2 ml_ of Milli-Q water under ultrasonication for at least 30 min. The catalyst ink (4 μΙ_) was then loaded onto the 3 active area of a GC (Φ = 3 mm) at -0.143 mg/cm². The catalyst ink-loaded GC electrode was dried in a sealed oven at 50 °C to allow the formation of uniform catalyst layers over the GC substrate area.

Example 2

Characterisation [00137] The morphologies of the annealed samples were investigated by FE-SEM (JEOL Model 6500) at 15 kV. The C-NT or g-C/Co₃0₄ or CoO/3D PNi electrodes were fixed onto the FE-SEM stage using carbon tape before insertion into the FE-SEM chamber. The ion sputter (Hitachi E-1030) was used to deposit thin-layered Pt films on electrodes at 25 °C. A focused ion beam (FIB) system (JEM-9320FIB) operated at accelerating voltages from 5-30 kV with variable steps of 5 kV and magnification ranging from 150* to 300000*. The orientation axis (X and Y) of the powder samples containing C-NT or g-C/Co30₄ or CoO catalysts can be changed within ±1.2 mm through a tilt angle of ± 60°. The samples were inserted inside the FIB machine using a bulk-sample holder (8 * 8 mm²) after deposition by a carbon protection layer. Before FIB investigation, the powder samples of the C-NT or g- C/Co30₄ or CoO catalysts were mixed with small amounts of epoxy (Gatan, Inc.) onto a small silicon wafer using a fine eyelash probe to form very thin films on the silicon substrate (Figures 2 and S7). Each thin film was baked on a hot plate at 130 °C for 10 min and subsequently coated with a uniformly thin carbon layer of about 30 nm. The samples were inserted into the FIB microscope operated at 30 kV and then roughly milled on both sides until a final thickness of 2 μηι using -1.5° and +1.5° tilts. Afterward, the C-NT or g-C/Co30₄ or CoO sample was cut and removed from the FIB system for subsequent HAADF-STEM microscopy.

[00138] HAADF-STEM was employed to perform (i) TEM and (ii) STEM, (iii) EDS for elemental mapping, and (iv) electron diffraction (ED). The HAADF-STEM micrographs were recorded using a JEMARM200F-G instrument supplied with aberration correctors at the illumination and imaging lens systems to observe TEM/STEM images at high resolution. The HAADF-STEM microscope was also equipped with a monochromated electron gun and supported by electron energy- loss spectroscopy at a high-energy resolution. Specifically, the cross-section specimens for HAADF- STEM was prepared by FIB system milling. The fine trapped probes typically sharpened the sample in the parallel direction of the longitudinal c-axis. The well-prepared FIB samples were attached to a silver grid by epoxy materials using a pick-up system. The C-NT or g-C/Co30₄ or CoO attached to the silver grid was inserted again into the FIB system to produce a 100 nm-thick layer. The sample was thinned from both sides by using alternate beams with variable intensity until the final thickness 4 of 100 nm. The 100 nm sample was viewed under the HAADF-STEM microscope to record the cross-sectional images.

[00139] The surface properties of the material involving the pore structure distribution and surface area were estimated by N2 adsorption-desorption isotherms at 77 K using a BELSORP36 analyzer (JP. BEL Co., Ltd.). The samples were thermally treated at 200 °C for at least 6 h under N2 atmosphere. The specific surface area (SBET) was calculated using the Brunauer-Emmett-Teller (BET) method with multipoint adsorption data from the linear section of the N2 adsorption isotherm. The pore size distribution was determined using nonlocal DFT (NLDFT). The structural geometry of the catalysts was further examined by WA-XRD. The WA-XRD patterns were recorded using a 18 kW diffractometer (Bruker D8 Advance) at scan rate of 10 min with monochromated CuKa-X-radiation (λ = 1.54178 A). The DIFRAC plus Evaluation Package (EVA) software with the PDF-2 Release 2009 databases provided by Bruker AXS was used to analyze the diffraction and structure analysis diffraction data. The TOPAS package program was applied to integrate various types of X-ray diffraction (XRD) analyses. XPS analysis was conducted on a PHI Quantera SXM (ULVAC-PHI) instrument (Perkin-Elmer Co., USA) equipped with Al Ka as an X-ray source for excitation (1.5 mm ^χ 0.1 mm, 15 kV, 50 W) under a pressure of 4 ^χ 10-8 Pa. A thin film of the sample was deposited on a Si slide before the start of analysis.

[00140] Raman spectroscopy (HR Micro Raman spectrometer, Horiba, Jobin Yvon) was conducted using an Ar ion laser at 633 nm. A CCD (charge coupled device) camera detection system and the LabSpec- 3.01 C software package were used for data acquisition and analysis, respectively. To ensure the accuracy and precision of the Raman spectra, 10 scans of 5 s from 300 cm^-1 to 1 ,600 cm^-1 were recorded. TG and DTA were achieved using a simultaneous DTA-TG Apparatus TG-60 (Shimadzu, Japan).

Example 3

Electrochemical measurements

[00141] Electrochemical measurements were obtained in a home-made electrochemical cell using mercury/mercury oxide (Hg/HgO, 1 M NaOH) and platinum wire (Φ = 0.1 mm) as the reference and counter electrodes, respectively. The active catalyst C- NT or g-C/Co30₄ or CoO grown on 3D PNi with surface structures of CPs, LSs, MCSs, and BCs and with active loading of 1.5 mg served as the working electrodes for electrochemical investigation. The data were recorded using a Zennium/ZAHNER electrochemical work station (Elektrik GmbH & Co. KG) controlled by the Thales Z 2.0 software. Initially, all of the working electrodes were cycled at least 10 times at a scan rate of 50 mV s^~1 until the signals were stabilized. Then, the CV data were collected. Current density 5 refers to the geometrical surface area of the investigated working electrodes (1 cm²). The measured potentials were reported with respect to the Hg/HgO reference electrode. The freshly prepared electrolyte (0.5 M NaOH) was de-aerated by bubbling a slow stream of purified N2 above the electrolyte in the electrochemical glass cell. The N2 flow was maintained during the electrochemical measurements to ensure an IM2- saturated electrolyte. To guarantee the reproducibility of the recorded results, freshly prepared electrolyte solutions were used for every electrochemical measurement. Chronoamperometry tests (CA) were conducted to evaluate electrode stability during the ethanol electrooxidation reaction. CA measurements were obtained by applying a constant potential of 0.7 V versus Hg/HgO in the presence of 0.5 M ethanol. EIS measurements were performed at a frequency range of 100 kHz-0.01 Hz with a 5 mV amplitude and an open circuit potential.

Example 4

Fabrication of C-NT/C03O4CP or BC/3DPNi electrodes

[00142] BC electrodes were produced from a solution of 1.5 g C0CI2 6H2O, 0.5 g urea (CO(NH2)2), and 60 ml_ H2O. CP electrodes were produced from a solution of 1.43 g C0CI2 6H2O, 3.6 g urea, and 60 ml_ H₂0. C-NTs (80 mg) were added to the solutions, which were stirred for 3 h and then deposited onto 1-cm² 3D PNi in a 100 ml_ Teflon-lined stainless-steel autoclave. The mixture was thermally treated for 12 h at 150 °C and then allowed to cool naturally to 25 °C. The product that had grown on the 3D PNi, C/Co(OH)x(C03)o.s .11 H20, was washed sequentially with absolute ethanol and deionized water and then dried overnight at 60 °C. The as-prepared C/Co(OH)x(C0₃)o.5 .11 H2O/CP or BC electrodes were then calcined at 400 °C with a ramp rate of 5 °C/min for 4 h under a N2 gas flow.

Example 5

Fabrication of C-NT/C03O4MCS/3D PNi and q-C/CosCULS/SD PNi electrodes

[00143] The addition of C-NTs or g-C conductive substrates to the composition was essential for achieving the MCS and LS architectures. A mixture of 1.43 g C0CI2 6H2O, 2.94 g hexamethylenetetramine (C6H12N4), and 60 ml_ H2O was stirred for 10 min. Afterward, 80 mg of C-NTs or g-C was added to the solution, and the mixture was stirred for 3 h and then deposited onto 1-cm2 3D PNi or in a 100 ml_ Teflon-lined stainless-steel autoclave. The mixture was thermally treated for 12 h at 150 °C and then allowed to cool naturally to 25 °C. The product that had grown on the 3D PNi, C-NT or g-C/Co(OH)x(C03)o.5 .1 1 H₂0, was washed sequentially with absolute ethanol and deionized water and dried overnight at 60 °C. The as- prepared C/Co(OH)x(C0₃)o.5 .11 H₂0/MCS and g-C/Co(OH)x(C0₃)o.5.0.1 1 H₂0/LS electrodes were then calcined at 400 °C with a ramp rate of 5 °C/min for 4 h under a N2 gas flow.

Example 6

Mathematical modelling

[00144] DFT is a promising approach to effectively illustrate the electronic correlation effects. In this study, all calculations investigated by DFT were performed in accordance with the DMol3 of BIOVIA Dassault systems2,3. The exchange- correlation energy function was represented by the Perdew-Burke-Ernzerhof (PBE) formalism4. The Kohn-Sham equation was expanded in a double numeric quality basis set (DNP) with polarization functions. To consider the relativistic effect, the DFT Semi- core Pseudo-potentials5 were used for the treatment of the core electrons of the doped clusters. The orbital cutoff range and Fermi smearing were selected as 5.0 A and 0.001 Ha, respectively. The self- consistent-field (SCF) procedures were performed to obtain well-converged geometrical and electronic structures at a convergence criterion of 10^~6 a.u.. The energy, maximum force, and maximum displacement convergence were set to 10^~6 Ha, 0.002 Ha/A, and 0.005 A, respectively. Meanwhile, the electrostatic site potential is a measure of the Coulomb interaction per unit charge experienced by an ion at a given position in space. DFT was also used to calculate the electrostatic potential (EP) distribution. Modelling was performed to show a physical quantitative survey at each point on the isosurfaces using a feature of the surface-charging map. Typically, the isosurfaces of the electron densities were coloured on the basis of EP intensities (EPI) using a lattice representation in which the charges are mapped on the cubic lattice in the so called contour where the EP is calculated. The slab model was constructed with nine atomic layers of each catalyst (Figure 23). To compare the active centre within the structure, oxygen atoms at the surface and subsurface layers were involved in the stoichiometric mode. EP was investigated over the range of -0.06 eV to +0.6 eV as shown in the optimized model.

Example 7

Hvdrothermal-assisted formation of hierarchical C03O4 nanocomposites

[00145] Figure 2 shows an outline of the morphological evolution of exemplary electrodes.

The C-NT or g-C/CosCU nanohybrid structures derived from the hierarchical metal framework grown directly on the 3D PNi substrate with robust mechanical adhesion were obtained after adequate pyrolysis of the as-synthesized C-NT or g- C/ Co(OH)x(C0₃)o.5 .1 1 H₂0/3D PNi electrodes at 400 °C for 4 h (additional details are found in the Experimental section). Scalable and flexible methods were adopted to fabricate morphology-controlled nanohybrids along the longitudinal direction vertically oriented toward the 3D PNi skeleton. In these processes, the surface morphologies of the CPs and BCs in the NR architecture and MCSs and LSs in nanosheet dominates were engineered. GO sheets (g-C) or functionalized multi-walled carbon nanotube (C-NT) counterparts acted as carbon supports.

Basically, the unique structures of the fabricated electrodes were contributed by the directing basic salt (urea and HMT) and cobalt precursor.

[00146] Under hydrothermal treatment conditions described herein, fabrication of self- supported (i.e., C-NT or g-C/Co304 or CoO/substrate) electrodes, Co30₄ or CoO and C-NT or g-C/Co30₄ or CoO hybrids could be hierarchically controlled to yield morphological features similar to those of BC-NR, CP-NR, LS, and MCS structures with uniformly spaced inner pores of micro- and mesoscale sizes (0.5-65.8 nm), as evidenced from field emission scanning electron microscopy (FE-SEM)

micrographs (Figures 3 - 6), thermogravimetry (TG)-differential thermal analysis (DTA), wide-angle powder X-ray diffraction (WA-XRD), and N2 isotherms; see Figures 7, 25 and 26). To investigate the atomic core-level organization of the geometrical C/Co30₄ mesocrystals hybrids in terms of chemical bonding, structural environment, and elemental state, X-ray photoelectron spectroscopy (XPS) analysis and Raman spectroscopy of the C/Co30₄ CPs (Figure 27) was conducted.

[00147] The FE-SEM and HAADF-STEM micrographs (Figures 1 - 6, 8, 9 and 11)

indicate that the reaction time as well as the growth temperature are quite sufficient for the immobilization and nucleation of the free standing nanostructures. In addition, the metal particles were bonded to the surface group of the counterparts by electrostatic interactions during the hydrothermal treatment (Figures 2A-a, B-a, and B-b). These oxygen functional groups provide thorough dispersion of the counterparts into the reaction solution and offer reliable mediators for the successful growth of Co30₄ mesocrystals on the counterpart scaffolds. The porosity of the formed nanostructure was greatly enhanced after decomposition at relatively high temperatures from the release of gases, adsorbed water, and organic molecules. This result indicates enhanced utilization of the active material. Hence, remarkable improvement in their electrochemical performance was expected. Moreover, such a unique structure provides well-defined pathways for the electrolyte solution to pass through the graphene layer and along the carbon tubes, leading to fast electron transport. Interestingly the controlled longitudinal growth of the C-NT or g-C/Co30₄ or CoO/3D PNi electrodes generates more favourably exposed surfaces and interfaces containing an extensive domain of Co³⁺ active sites. This effect enhances the kinetics of the EOR, as evidenced by the HR-HAAF- STEM micrographs (Figures 11)

Claims

I . An electrode comprising a support and metal oxide catalyst, wherein the metal oxide catalyst comprises a nanoforest structure.

2. The electrode of claim 1 , wherein the metal oxide catalyst is a transition metal oxide, optionally wherein the transition metal oxide comprises a cobalt oxide, a nickel oxide, a manganese oxide, or a cadmium oxide.

3. The electrode of claim 1 or claim 2, wherein the metal oxide catalyst is a cobalt oxide, optionally, wherein the cobalt oxide comprises C03O4, CoO, or a mixture of C03O4 and CoO.

4. The electrode of any proceeding claim, wherein the nanoforest structure is oriented in a vertical direction relative to the surface of the support; and / or wherein the nanoforest structure comprises a mesocrystal architecture.

5. The electrode of any preceding claim, wherein the nanoforest structure comprises a morphological architecture selected from corn tubercle pellets (CPs), banana clusters

(BCs), lamina sheets (LSs) and multiple cantilever sheets (MCSs), or a combination thereof.

6. The electrode of any preceding claim, wherein the nanoforest structure comprises a morphological architecture comprising corn tubercle pellets (CPs), optionally wherein the CPs are vertically oriented away from the longitudinal plane of the surface of the support in nanorod (NR) domains.

7. The electrode of any preceding claim, wherein the nanoforest structure comprises a morphological architecture comprising banana clusters (BCs), optionally wherein the BCs are vertically oriented away from the longitudinal plane of the surface of the support in nanorod (NR) domains.

8. The electrode of any preceding claim, wherein the nanoforest structure comprises a morphological architecture comprising lamina sheets (LSs).

9. The electrode of any preceding claim, wherein the nanoforest structure comprises a morphological architecture comprising multiple cantilever sheets (MCSs).

10. The electrode of any of claims 5 to 9, wherein the CPs, and/or BCs, and/or LSs, and/or MCSs are oriented in a vertical direction relative to the surface of the support.

I I . The electrode of any preceding claim, wherein the metal oxide catalyst comprises crystals with an interface having: Miller indices {1 11}/{1 12} and /or {1 12}/{1 11}; or

Miller indices {1 10}/{001} and/or {001}/{110}; or

a Miller index of {112}.

12. The electrode of any proceeding claim, wherein the support comprises a substrate comprising carbon, optionally wherein the metal oxide catalyst is deposited on the substrate.

13. The electrode of claim 12, wherein the carbon comprises graphene sheets (g-C), carbon nanotubes (C-NTs), graphite, carbon fibre, mesoporous carbon, or carbon nitrides; optionally wherein the carbon comprises graphite, graphene sheets (g-C), or carbon nanotubes (C-NTs).

14. The electrode of any preceding claim, wherein the support comprises a base comprising a metal foam, glassy carbon (GC), or a ceramic membrane; optionally wherein the support comprises a base comprising a metal foam or a glassy carbon (GC).

15. The electrode of claim 14, wherein the metal foam comprises or consists of a nickel foam or an aluminium foam.

16. The electrode of claim 14 or claim 15, wherein the metal foam comprises nickel foam, optionally wherein the nickel foam is 3D porous nickel foam (3D PNi).

17. The electrode of any of claims 14 to 16, wherein the support comprises the substrate as defined in claims 12 or 13 deposited on the base.

18. The electrode of any preceding claim, wherein the nanoforest structure is on an exposed surface of the electrode.

19. A composition comprising a support and metal oxide catalyst precursor, wherein the metal oxide catalyst precursor comprises a nanoforest structure.

20. The composition of claim 19, wherein the metal oxide catalyst precursor is or comprises a hydrated metal oxide precursor.

21. The composition of claim 19 or 20, wherein the metal oxide catalyst precursor is a hydrated cobalt oxide, optionally wherein the metal oxide catalyst precursor has the formula Co(OH)_x(C03)o.5.0.11 H20, wherein x is selected from 1 , 2 or 3, or a mixture thereof.

22. The composition of any of claims 19 to 21 , wherein the nanoforest structure comprises the features of any of claims 4 to 11 ; and/or

wherein the support comprises the features of any of claims 5 to 18.

23. A method of making an electrode comprising:

forming an aqueous solution comprising cobalt (II) cations, a urea or a cyclic amide and carbon in the presence of an electrode base;

activating the solution;

allowing a reaction to proceed such that a composition comprising cobalt and carbon deposited on the electrode base is formed;

isolating the composition from the solution; and

calcining the composition to form an electrode comprising a cobalt oxide catalyst.

24. The method of claim 23, wherein the cobalt (II) cations are provide by a salt; optionally wherein the salt comprises cobalt chloride, cobalt nitrate, or a combination thereof, optionally wherein the salt comprises cobalt chloride.

25. The method of claim 23 or claim 24, wherein the carbon comprises graphene sheets (g-C), carbon nanotubes (C-NTs), graphite, carbon fibre, mesoporous carbon, or carbon nitrides; optionally wherein the carbon comprises graphite, graphene sheets (g-C), or carbon nanotubes (C-NTs).

26. The method of any of claims 23 to 25, wherein the electrode base comprises a metal foam, glassy carbon (GC), or a ceramic membrane (e.g. an alumina or titania membrane); optionally wherein the electrode base is a metal foam or glassy carbon (GC).

27. The method of claim 26, wherein the metal foam comprises or consists of a nickel foam or an aluminium foam.

28. The method of claim 26 or claim 27, wherein the metal foam comprises nickel foam, optionally wherein the nickel foam is 3D porous nickel foam (3D PNi).

29. The method of any of claims 23 to 29, wherein the carbon provides a substrate for deposition of the cobalt (II) cations during the step of allowing the reaction to proceed. 30. The method of claim 29, wherein the substrate deposits on the electrode base during the step of allowing the reaction to proceed.

31. The method of any of claims 23 to 30, wherein the allowing the reaction to proceed comprises the step of activating the solution.

32. The method of claim 31 , wherein the activating the solution and allowing the reaction to proceed are performed in a pressure vessel, optionally wherein activating the solution and allowing the reaction to proceed are performed at a pressure of greater than 1 atmosphere.

33. The method of claim 31 or 32, wherein activating the solution comprises heating, irradiating with electromagnetic radiation or sonicating the solution.

34. The method of claim 33, wherein activating the solution comprises heating the solution to a temperature in the range of 100 - 200°C, optionally to a temperature in the range of 120 - 180°C, further optionally to a temperature in the range of 130 - 170°C.

35. The method of any of claims 23 to 34, wherein the allowing the reaction to proceed comprises a time period of at least 1 hour, optionally a time period of at least 4 hours, further optionally a time period of at least 8 hours.

36. The method of any of claims 23 to 35, wherein the composition comprises a hydrated cobalt oxide, optionally wherein the hydrated cobalt oxide has the formula Co(OH)x(C03)o.5.0.1 I H2O, wherein x is selected from 1 , 2 or 3, or a mixture thereof.

37. The method of claim 36, wherein the hydrated cobalt oxide comprises a nanoforest structure, optionally wherein the nanoforest structure comprises the features of any of claims 4 to 1 1.

38. The method of any of claims 23 to 37, wherein between the isolating and the calcining, the composition is washed with at least one solvent.

39. The method of claim 38, wherein the washing comprises washing sequentially with at least two solvents.

40. The method of claim 38 or claim 39, wherein the solvent or solvents are selected from water and water miscible solvents;

optionally wherein the water miscible solvents are selected from methanol, ethanol and isopropanol, further optionally wherein the water miscible solvent is ethanol.

41. The method of any of claims 23 to 40, wherein the isolated composition is dried prior to the calcining.

42. The method of any of claims 23 to 41 , wherein the calcining comprises heating the composition to a temperature of 200 - 500°C, optionally to a temperature of 300 - 500°C. 43. A method of making an electrode precursor comprising:

forming an aqueous solution comprising cobalt (II) cations, a urea or a cyclic amide and carbon in the presence of an electrode base;

activating the solution;

allowing a reaction to proceed such that a composition comprising cobalt and carbon deposited on the electrode base is formed; and

optionally isolating the composition from the solution.

44. The method of claim 43, further comprising a feature as further defined in any of claims 23 to 40.

45. An electrode precursor obtainable by the method of claim 43 or claim 44.

46. An electrode precursor obtained by the method of claim 43 or claim 44.

47. An electrode obtainable by the method of any of claims 23 to 42.

48. An electrode obtained by the method of any of claims 23 to 42.

49. A fuel cell comprising an electrode of any of claims 1 to 18, or of claim 47 or claim 48.

50. The fuel cell of claim 49, wherein an anode of the fuel cell comprises said electrode.

51. Use in a fuel cell of an electrode of any of claims 1 to 18, or of claim 47 or claim 48. 52. The use of claim 51 , wherein the use comprises use of the electrode as an anodic electrode.

53. The use of claim 51 or claim 52, wherein the use comprises use of the electrode as an anodic electrode in an ethanol electrooxidation reaction.