US20120031753A1

US20120031753A1 - Electrode configuration of electrolysers to protect catalyst from oxidation

Info

Publication number: US20120031753A1
Application number: US13/272,400
Authority: US
Inventors: Amitava Roy
Original assignee: Individual
Current assignee: RE HYDROGEN Ltd
Priority date: 2009-04-06
Filing date: 2011-10-13
Publication date: 2012-02-09
Also published as: GB2469265B8; HK1148792A1; GB0905808D0; GB2469265A; GB2469265B

Abstract

The invention relates to an electrode configuration of electrolysers using oxygen storage material to prevent oxidation of anodic active catalyst layer where oxygen storage material will be preferentially oxidised prior to anodic active catalyst. The inventions also relates to the use of hydrogen storage material with cathodic active catalyst to supply hydrogen to react with oxygen supplied from anodes when a reduction load is connected between the anode and cathode. One configuration utilises of individual layers containing oxygen and hydrogen storage materials, active catalyst layers, perforated current collectors, monopolar plates and a porous separator. A reduction load is used during operation of the electrolyser to convert metal oxides into pure metal by consuming oxygen from the electrolyser cell during stand by mode, shut down mode and intermittent operation, which will increase the durability of electrodes.

Description

FIELD OF INVENTION

The present invention relates to an electrolyser and, in particular, to a renewable energy powered electrolyser for hydrogen production.

BACKGROUND TO THE INVENTION

Electrolysers powered by renewable energy sources produce hydrogen gas which can be used as transport fuel or backup electricity generation by fuel cells.
However, the current electrolyser technology is not matured for dynamic and intermittent operation, which suffers from early failures compared to a desirable long life in smooth, steady state operation.
Conventional alkaline electrolysers have a limited on-off switching cycle, for example only 2,500 cycles in conventional electrolysers for intermittent operation which are primarily used for steady state smooth operation in industrial applications.
During stand-by mode and shut-down mode oxygen remains trapped inside the porous anodic catalyst layer and other parts of the electrolyser cell which then creates a high open circuit voltage in contact with the conductive potassium hydroxide electrolyte against the reference platinum electrode.
At high open circuit voltage during stand-by mode and shut-down mode the anodic active catalyst is gradually oxidised and thus the catalytic activity of the anode is decreased, leading to greater electrochemical losses and increased cell voltage which then increases the energy consumption of the electrolyser per unit volume of hydrogen production. This in turn increases the energy consumption of electrolysers by more than 10% within a year.
The guaranteed quota of 2,500 cycles in conventional electrolysers is generally consumed in less than a year for on-off switching cycle of seven times per day which is unsuitable for renewable energy powered intermittent operation, because the electrolyser needs to be capable of an unlimited on-off switching cycle within its lifetime for renewable energy powered intermittent operation.
Some electrolysers available in the market apply a small current across the cell, called a protective current to prevent corrosion or oxidation of the catalyst. The protective current is a very small direct current passing through the stack during the stand-by mode in order to maintain the flow of current in one direction. However, this approach is not feasible due to the limited operating range from 20-100% of alkaline electrolysers. A separate power supply, for example a battery, is required to apply protective current.
Another major concern of protective current is hydrogen and oxygen gas permeate through the membrane and create a potentially explosive mixture over a period of time as the produced gas is not taken out of the cell or consumed. This then requires frequent purging of the cell, followed by nitrogen purging at start up of the electrolyser. All these issues make protective current practically unfeasible or difficult to apply.
As a result current electrolysers are less compatible for renewable energy powered operation and as an example, the electrolyser used in a demonstration project of hydrogen and renewable integration at West Beacon Farm, Loughborough, Leicestershire, UK has been replaced due to stack failure within 2,000 on-off switching cycles and the replaced second stack has also suffered a similar degradation.
Therefore a solution is desirable which prevents oxidation of the catalyst in stand-by and shut-down mode and due to on-off switching.

SUMMARY OF THE INVENTION

In view of the above, the present invention provides an electrolyser comprising an anode and a cathode and having an electrode configuration with oxygen storage material deposited on the positive anode of the electrolyser in contact with anodic active catalyst material to prevent oxidation of the anodic active catalyst material by means of preferential oxidation of the oxygen storage material.
The electrolyser may comprise a unidirectional, resistive reduction load across the anode and cathode to break the oxides from the anode to supply oxygen to react with hydrogen stored at the cathode.
The oxygen storage material and the anodic active catalyst material of the anode may be deposited in adjacent layers in direct contact or in a mixture.
The anodic active catalyst material of the anode may be deposited by a technique selected from the group comprising spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating and painting.
The oxygen storage material and the anodic active catalyst material may be provided in at least one layer having a thickness. The thickness of the layer may be in the range of 0.1 microns to 10 millimetres, more particularly 1 micron to 1 millimetre.
The oxygen storage material may comprise a material selected from the group comprising ceria, zirconium and other similar materials which are preferentially oxidised relative to the anodic active catalyst.
The anodic active catalyst may comprise a material selected from the group comprising silver, nickel, alloys of silver and nickel, titanium, platinum, iridium, ruthenium, gold and other suitable catalyst materials for oxygen evolution reactions.
The surface area of the active catalyst material and oxygen storage material may be in the range of 0.1 m²/g to 1000 m²/g.
The reduction load may be configured for use during stand-by mode, shut down mode, at the start up stage and at open circuit voltage of the electrolyser.
The unidirectional reduction load may comprise a diode and a resistor or another type of electronic circuit to ensure the direction of flow of electrons from the cathode which produces hydrogen to the anode which produces oxygen.
In embodiments of the invention, the open circuit voltage of the cathode against a platinum reference electrode is lowered to substantially zero volts by means of the reduction load by consuming oxygen from the metallic oxide from the anode to react with hydrogen from the cathode under the reducing voltage.
The reduction load is configured to be applied in constant current mode or constant power mode.
The electrolyser may comprise hydrogen storage material deposited on the negative cathode in contact with cathodic active catalyst material to supply hydrogen under the reduction load to react with oxygen from the anode.
The hydrogen storage material and the cathodic active catalyst material of the cathode may be deposited in adjacent layers in direct contact or as a mixture.
The hydrogen storage material and the cathodic active catalyst material of the cathode may be deposited by a technique selected from the group comprising spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating and painting.
The hydrogen storage material and the cathodic active catalyst may be mixed together and deposited onto a cathodic perforated current collector.
The electrolyser may comprise an anodic perforated current collector and a cathodic perforated current collector having porosity and open area from 10% to 90%.
The electrolyser may be of a type selected from the group comprising alkaline, proton exchange membrane, solid oxide, other electrochemical cells, including fuel cells and batteries including alkaline, acidic, proton exchange membrane and solid oxide batteries.
The electrolyser may be configured to apply the reduction load manually or automatically for switchover from normal operation to intermittent operation, stand-by mode and the start up stage of the electrolyser.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings, in which FIGS. 1 to 6 show examples of the sequence of layers in electrode configurations for an electrolyser in accordance with embodiments of the invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Embodiments of the invention relate to an electrode configuration to protect an active catalyst from oxidation in electrolysers by using oxygen storage materials in contact with an anodic active catalyst as a preventive measure, as shown in FIG. 1, where the oxygen storage material will be preferentially oxidised prior to the active catalyst.
The electrode configurations as shown in FIG. 1 to FIG. 6 describe some examples of the sequence of each layer from which several others combinations can be made under this innovation.
During stand-by mode at open circuit voltage the oxygen storage material will preferentially be oxidised than the anodic active catalyst due to close physical contact between the catalyst and oxygen storage materials.
The close contact between the anodic active catalyst and oxygen storage material is ensured by different manufacturing techniques. For example the oxygen storage material is deposited first onto the anodic perforated current collector as shown in FIG. 1 by various methods for example, spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc, followed by depositing the anodic active catalyst on top of the oxygen storage material layer by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc.
The thickness of each layer of anodic active catalyst layer, oxygen storage layer or the combined layer of anodic active catalyst and oxygen storage material is in the range of less than one micron to a few millimetres with nominal thickness of 25-500 microns. The surface area of the anodic active catalyst and oxygen storage material can vary from less than 1 m²/g to 1000 m²/g.
The current collector is normally perforated or highly porous with open area in the range from 20% to 80%.
Embodiments of the invention further relate to reduction of oxides in situ from electrodes during stand-by and shut down mode of electrolysers using a diode assisted unidirectional reduction load to bring the electrode potentials to zero with respect to the platinum reference electrode.
During operation over a period of time if any part of the active catalyst is oxidised, then catalyst-oxides are removed by means of the reduction load. The reduction load is a small resistor connected across the positively charged anode and negatively charged cathode, whose value can vary from less than 1 milli-Ohm to several mega-Ohms depending on the capacity of the stack.
During electrolyser operation some hydrogen is stored in cathodes in the form of metal hydride and oxygen is stored in anodes in the form of oxides and oxygen ions in the active catalyst and oxygen storage materials.
The presence of oxygen in anodes creates a high open circuit voltage which is 1V measured against a platinum reference electrode.
The reduction load connected across the anode and cathode of the electrolyser consumes hydrogen and oxygen in a fuel cell mode to produce a current density from less than 1 mA/cm²to 20 mA/cm², through the reduction load. The reduction load can be applied in constant current mode or in constant power mode.
The half cell voltage of the oxygen electrode will drop rapidly from its open circuit voltage and therefore the anodic metal oxide converts into pure metal by breaking the oxides under reducing voltage to supply oxygen to the fuel cell reaction through the reduction load.
The configuration of the reduction load can have a sophisticated electronic circuit using diodes, capacitors and other electronic components to ensure the direction of electron flow through the reduction load from the hydrogen producing/consuming electrode which is the cathode in the electrolyser mode to the oxygen producing/consuming electrode which is the anode in the electrolyser mode.
Embodiments of the invention also relate to the use of hydrogen storage material in cathodes as shown in FIG. 4 to supply adequate hydrogen to consume all the oxygen when the reduction load is applied. The presence of hydrogen will create a reducing condition and thus it will protect cathodes from oxidation during intermittent operation, shut down and stand by mode.
The above features allow electrolysers to undertake increased on-off switching cycle over a long period of time by repeated reduction of the oxides which makes them suitable for renewable energy powered dynamic and intermittent operation.
To prevent limited on-off switching cycle in conventional electrolysers the present invention uses oxygen storage materials deposited on positively charged anodes of electrolysers in contact with anodic active catalyst materials to prevent oxidation of the anodic active catalyst materials by means of preferential oxidation of oxygen storage materials to allow unlimited on-off switching without corrosion of electrodes during stand-by mode, shut down mode, intermittent operation and normal operation of electrolyser powered by renewable energy and other power sources.
The oxygen storage materials and the anodic active catalyst materials of positively charged anodes become partially oxidised over a period of time, which is then reduced to pure metal by connecting a unidirectional, resistive reduction load across the anode and cathode of electrolysers to break the oxides from anodes to supply oxygen to react with hydrogen stored in cathodes.
The use of oxygen storage material and the use of the reduction load to convert the oxides into pure metal by reduction eliminates the use of protective current in stand by mode as in conventional electrolysers and as a result nitrogen purging during stand by mode and start up phase of electrolyser becomes unnecessary.
The oxygen storage materials and the anodic active catalyst materials of anodes is deposited in adjacent layers with direct contact or as a mixture by various techniques such as spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting and other similar techniques.
The thickness of oxygen storage layer and anodic active catalyst layers or the combination of both materials in one layer of the active catalyst and oxygen storage material vary from less than one micron to few millimetres and it is uniformly distributed all over the electrode area.
Oxygen storage materials such as ceria, zirconium and other similar types are used which is preferentially oxidised than various anodic active catalyst such as silver, nickel, alloys of silver and nickel, titanium, platinum, iridium, ruthenium, gold and other suitable catalyst materials for oxygen evolution reactions. The oxygen storage materials used in anodes can be doped with other materials or combined with other materials suitable for oxygen storage.
The surface area of the active catalyst and oxygen storage material vary from less than 1 m²/g to 1000 m²/g.
The reduction load is used during stand-by mode, shut down mode, at the start up stage and at open circuit voltage of electrolysers.
The unidirectional reduction load has at least a diode and a resistor and any other type of electronic circuit or components for the same purpose of diode as described to ensure the direction of flow of electron from cathodes which produces hydrogen to anodes which produces oxygen.
The open circuit voltage of cathodes against the platinum reference electrodes is lowered to zero volts or close to zero volts by means of the reduction load by consuming oxygen from the metallic oxides from anodes to react with hydrogen from cathodes under the reducing voltage. The reduction load can be applied in constant current mode or in constant power mode.
Hydrogen storage materials are deposited in some configurations as shown in example specification 4 to example specification 6 on the negatively charged cathodes in contact with cathodic active catalyst materials to supply hydrogen under the reduction load to react with oxygen from anodes.
The hydrogen storage material and reduction load create reducing conditions to prevent oxidation and to convert oxides into metal during stand-by mode, shut down mode, intermittent operation and normal operation of electrolyser powered by renewable energy and other power sources.
Hydrogen storage materials and the cathodic active catalyst materials of the cathodes are deposited in adjacent layers with direct contact or as a mixture by various techniques such as spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting and other similar techniques.
The hydrogen storage material and cathodic active catalyst can be mixed together and then deposited onto a cathodic perforated current collector.
The hydrogen storage materials used in cathodes can be doped with other materials or combined with other materials suitable for hydrogen storage.
The thickness of individual layers for porous separator, anodic active catalyst, oxygen storage material, anodic perforated current collector, hydrogen storage material, cathodic active catalyst, cathodic perforated current collector, anode monopolar plate and cathode monopolar plate can vary in the range of less than one micron to few millimetres with nominal thickness of 25-500 micron.
The anodic perforated current collector and cathodic perforated current collector have porosity and open area from 10% to 90%.
The invention primarily relates to electrolysers of any type for example alkaline, proton exchange membrane, solid oxide etc and the invention is also extended to other electrochemical cells for example fuel cells and battery of any type for example alkaline, acidic, proton exchange membrane, solid oxide etc.
The application of reduction load is carried out manually or automatically for switchover from normal operation to intermittent operation, stand-by mode and start up stage of electrolysers.

Example 1

FIG. 1 shows the first example of one of the various electrode configurations according to an embodiment of the invention.
As shown in FIG. 1, oxygen storage material 3 is deposited onto an anodic perforated current collector 4 by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. The anodic active catalyst 2 is then deposited on top of the oxygen storage material 3 by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. The complete anode structure is then placed on one side of a porous separator 1.
An anode monopolar plate 5 is compressed to the back of the anodic perforated current collector 4 for supplying electricity and taking oxygen gas out of the cell. A cathodic active catalyst 6 is deposited onto a cathodic perforated current collector 7, by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. A cathode monopolar plate 8 is compressed to the back of the cathodic perforated current collector 7 for supplying electricity and taking hydrogen gas out of the cell.
This combined configuration with one anode comprising an anode monopolar plate 5, anodic perforated current collector 4, oxygen storage material 3 and anodic active catalyst 2 is placed one side of the porous separator 1. On the opposite side of the porous separator 1 one cathode comprising the cathode monopolar plate 8, cathodic perforated current collector 7 and cathodic active catalyst 6 is placed to construct a complete electrolyser cell.

Example 2

FIG. 2 shows the second example of one of the various electrode configurations according to an embodiment of the invention.
As shown in FIG. 2, an anodic active catalyst 2 is deposited onto an anodic perforated current collector 4 by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. Oxygen storage material 3 is then deposited on top of the anodic active catalyst 2 by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. The complete anode structure is then placed on one side of a porous separator 1.
An anode monopolar plate 5 is compressed to the back of the anodic perforated current collector 4 for supplying electricity and taking oxygen gas out of the cell.
A cathodic active catalyst 6 is deposited onto cathodic perforated current collector 7 by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. A cathode monopolar plate 8 is compressed to the back of the cathodic perforated current collector 7 for supplying electricity and taking hydrogen gas out of the cell. This combined configuration with one anode comprising an anode monopolar plate 5, anodic perforated current collector 4, oxygen storage material 3 and anodic active catalyst 2 is placed on one side of the porous separator 1. On the opposite side of the porous separator 1 one cathode comprising a cathode monopolar plate 8, cathodic perforated current collector 7 and cathodic active catalyst 6 is placed to construct a complete electrolyser cell.

Example 3

FIG. 3 shows the third example of one of the various electrode configurations described in accordance with an embodiment of the invention.
As shown in FIG. 3, an anodic active catalyst and oxygen storage material mixture 2 is deposited onto anodic perforated current collector 3 by various methods, for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. An anode monopolar plate 4 is compressed to the back of anodic perforated current collector 4 for supplying electricity and taking oxygen gas out of the cell.
A cathodic active catalyst 5 is deposited onto a cathodic perforated current collector 6 by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. A cathode monopolar plate 7 is compressed to the back of the cathodic perforated current collector 6 for supplying electricity and taking hydrogen gas out of the cell.
This combined configuration with one anode comprising an anode monopolar plate 4, anodic perforated current collector 3, anodic active catalyst and oxygen storage material mixture 2 is placed one side of the porous separator 1. On the opposite side of the porous separator 1 one cathode comprising a cathode monopolar plate 7, cathodic perforated current collector 6 and cathodic active catalyst 5 is placed to construct a complete electrolyser cell.

Example 4

FIG. 4 shows the fourth example of one of the various electrode configurations described in accordance with an embodiment of the invention.
As shown in FIG. 4, oxygen storage material 3 is deposited onto anodic perforated current collector 4 by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. An anodic active catalyst 2 is then deposited on top of oxygen storage material 3 by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. The complete anode structure is then placed on one side of a porous separator 1. An anode monopolar plate 5 is compressed to the back of the anodic perforated current collector 4 for supplying electricity and taking oxygen gas out of the cell.
Hydrogen storage material 7 is deposited onto a cathodic perforated current collector 8 by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. A cathodic active catalyst 6 is then deposited on top of hydrogen storage material 7 by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. The complete cathode structure is then placed on one side of the porous separator 1.
A cathode monopolar plate 9 is compressed to the back of the cathodic perforated current collector 8 for supplying electricity and taking hydrogen gas out of the cell.
This combined configuration with one anode comprising an anode monopolar plate 5, anodic perforated current collector 4, oxygen storage material 3 and anodic active catalyst 2 is placed one side of the porous separator 1. On the opposite side of the porous separator 1 one cathode comprising a cathode monopolar plate 9, cathodic perforated current collector 8, hydrogen storage material 7 and cathodic active catalyst 6 is placed to construct a complete electrolyser cell.

Example 5

FIG. 5 shows the fifth example of one of the various electrode configurations described in accordance with an embodiment of the invention.
As shown on FIG. 5, oxygen storage material 3 is deposited onto an anodic perforated current collector 4 by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. An anodic active catalyst 2 is then deposited on top of oxygen storage material 3 by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. The complete anode structure is then placed on one side of a porous separator 1. An anode monopolar plate 5 is compressed to the back of the anodic perforated current collector 4 for supplying electricity and taking oxygen gas out of the cell.
A cathodic active catalyst 6 is deposited onto an cathodic perforated current collector 8 by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. Hydrogen storage material 7 is then deposited on top of the cathodic active catalyst 6 by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. The complete cathode structure is then placed on one side of the porous separator 1.
A cathode monopolar plate 9 is compressed to the back of the cathodic perforated current collector 8 for supplying electricity and taking hydrogen gas out of the cell. This combined configuration with one anode comprising an anode monopolar plate 5, anodic perforated current collector 4, oxygen storage material 3 and anodic active catalyst 2 is placed one side of the porous separator 1. On the opposite side of the porous separator 1 one cathode comprising an cathode monopolar plate 9, cathodic perforated current collector 8, cathodic active catalyst 6 and hydrogen storage material 7 is placed to construct a complete electrolyser cell.

Example 6

FIG. 6 shows the sixth example of one of the various electrode configurations according to an embodiment of the invention.
As shown in FIG. 6, an anodic active catalyst 2 is deposited onto an anodic perforated current collector 3 by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. The complete anode structure is then placed on one side of a porous separator 1. An anode monopolar plate 4 is compressed to the back of the anodic perforated current collector 3 for supplying electricity and taking oxygen gas out of the cell.
A cathodic active catalyst 6 is deposited onto a cathodic perforated current collector 7 by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. Hydrogen storage material 5 is then deposited on top of the cathodic active catalyst 6 by various methods for example spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating, painting etc. The complete cathode structure is then placed on one side of the porous separator 1. A cathode monopolar plate 8 is compressed to the back of cathodic perforated current collector 7 for supplying electricity and taking hydrogen gas out of the cell.
This combined configuration with one anode comprising an anode monopolar plate 4, anodic perforated current collector 3 and anodic active catalyst 2 is placed one side of the porous separator 1. On the opposite side of the porous separator 1 one cathode comprising a cathode monopolar plate 8, cathodic perforated current collector 7, cathodic active catalyst 6 and hydrogen storage material 5 is placed to construct a complete electrolyser cell.
The thickness of individual layers in examples 1 to 6, for porous separator, anodic active catalyst, oxygen storage material, anodic perforated current collector, hydrogen storage material, cathodic active catalyst, cathodic perforated current collector, anode monopolar plate and cathode monopolar plate can vary for each layer in the range of less than one micron to a few millimetres with nominal thickness of 25-500 micron.
The surface area of the anodic active catalyst, oxygen storage material, cathodic active catalyst and hydrogen storage material can vary from less than 1 m²/g to 1000 m²/g.
The anodic perforated current collector and cathodic perforated current collector have porosity and open area from 10% to 90%.
In summary, the invention relates to an electrode configuration of electrolysers using oxygen storage material to prevent oxidation of anodic active catalyst layer where oxygen storage material will be preferentially oxidised prior to anodic active catalyst. The inventions also relates to the use of hydrogen storage material with cathodic active catalyst to supply hydrogen to react with oxygen supplied from anodes when a reduction load is connected between the anode and cathode. One configuration utilises of individual layers containing oxygen and hydrogen storage materials, active catalyst layers, perforated current collectors, monopolar plates and a porous separator. A reduction load is used during operation of the electrolyser to convert metal oxides into pure metal by consuming oxygen from the electrolyser cell during stand by mode, shut down mode and intermittent operation, which will increase the durability of electrodes.
In general terms, this invention describes an electrode configuration of electrolysers which increases the on-off switching cycle without degradation over a long period of time. Firstly, oxygen storage material causes preferential oxidation as a preventive measure. Secondly, the application of reduction load converts metal oxides back to pure metal catalyst by consuming oxygen from anodes in a fuel cell reaction which is done by connecting the anode and cathode together using a resistive load. Electricity will be produced when the anodes and cathodes of an electrolyser are directly connected via a resistive reduction load soon after its operation due to recombination of hydrogen and oxygen present in electrodes. The invention relates to the use of hydrogen and oxygen storage materials which would facilitate to break metal oxides into pure active metal catalyst in order to supply oxygen for the fuel cell reaction. The invention provides various configurations of electrode layers as a protective measure to prevent oxidation of anodic and cathodic active catalyst layer. Oxygen storage material is used in anodes to be preferentially oxidised than the anodic active catalyst due to close physical contact between the catalyst and oxygen storage materials during normal operation, stand-by mode, shut down mode, at open circuit voltage and intermittent operation due to on-off switching cycle. Hydrogen storage material is deposited on cathodes in contact with cathodic active catalyst materials to is supply hydrogen under the reduction load to react with oxygen supplied from anodes. A diode-assisted unidirectional, resistive reduction load is connected between the anode and cathode during standby mode and shut down mode to consume oxygen from the electrolyser cell by reacting hydrogen from cathodes and oxygen from anodes and metal oxides. Hydrogen storage material and the reduction load create reducing conditions and lower the cell voltage than the open circuit voltage to prevent oxidation and to convert oxides into pure metal during stand-by mode, shut down mode, intermittent operation and normal operation of electrolyser powered by renewable energy and other power sources.
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.
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.

Claims

1. An electrolyser comprising an anode and a cathode and having an electrode configuration with oxygen storage material deposited on the positive anode of the electrolyser in contact with anodic active catalyst material to prevent oxidation of the anodic active catalyst material by means of preferential oxidation of the oxygen storage material.

2. The electrolyser of claim 1, comprising a unidirectional, resistive reduction load across the anode and cathode to break the oxides from the anode to supply oxygen to react with hydrogen stored at the cathode.

3. The electrolyser of claim 1, wherein the oxygen storage material and the anodic active catalyst material of the anode is deposited in one of adjacent layers in direct contact and a mixture.

4. The electrolyser of claim 3, wherein the oxygen storage material and the anodic active catalyst material of the anode is deposited by a technique selected from the group comprising spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating and painting.

5. The electrolyser of any claim 1, wherein the oxygen storage material and the anodic active catalyst material are provided in at least one layer having a thickness and the thickness of the layer is in the range of 0.1 microns to 10 millimetres.

6. The electrolyser of claim 1, wherein the oxygen storage material comprises a material selected from the group comprising ceria, zirconium and other similar materials which are preferentially oxidised relative to the anodic active catalyst.

7. The electrolyser of claim 1, wherein the anodic active catalyst comprises a material selected from the group comprising silver, nickel, alloys of silver and nickel, titanium, platinum, iridium, ruthenium, gold and other suitable catalyst materials for oxygen evolution reactions.

8. The electrolyser of claim 1, wherein the surface area of the active catalyst material and oxygen storage material is in the range of 0.1 m²/g to 1000 m²/g.

9. The electrolyser of claim 2, wherein the reduction load is configured for use during stand-by mode, shut down mode, at the start up stage and at open circuit voltage of the electrolyser.

10. The electrolyser of claim 2, wherein the unidirectional reduction load comprises at least one of a diode and a resistor and another type of electronic circuit to ensure the direction of flow of electrons from the cathode which produces hydrogen to the anode which produces oxygen.

11. The electrolyser of claim 2, wherein, in use, the open circuit voltage of the cathode against a platinum reference electrode is lowered to substantially zero volts by means of the reduction load by consuming oxygen from the metallic oxide from the anode to react with hydrogen from the cathode under the reducing voltage.

12. The electrolyser of claim 2, wherein the reduction load is configured to be applied in one of constant current mode and constant power mode.

13. The electrolyser of claim 2, comprising hydrogen storage material deposited on the negative cathode in contact with cathodic active catalyst material to supply hydrogen under the reduction load to react with oxygen from the anode.

14. The electrolyser of claim 13, wherein the hydrogen storage material and the cathodic active catalyst material of the cathode is deposited in one of adjacent layers in direct contact and a mixture.

15. The electrolyser of claim 14, wherein the hydrogen storage material and the cathodic active catalyst material of the cathode is deposited by a technique selected from the group comprising spraying, screen printing, hot pressing, sintering, thermal spraying, electroplating, electroforming, co-deposition by electroplating, electroless plating, dip coating and painting.

16. The electrolyser of claim 13, wherein the hydrogen storage material and the cathodic active catalyst are mixed together and deposited onto a cathodic perforated current collector.

17. The electrolyser of claim 1, comprising an anodic perforated current collector and a cathodic perforated current collector having porosity and open area from 10% to 90%.

18. The electrolyser of claim 1, wherein the electrolyser is of a type selected from the group comprising alkaline, proton exchange membrane, solid oxide, other electrochemical cells, including fuel cells and batteries including alkaline, acidic, proton exchange membrane and solid oxide batteries.

19. The electrolyser of claim 2, wherein the electrolyser is configured to apply the reduction load manually or automatically for switchover from normal operation to intermittent operation, stand-by mode and the start up stage of the electrolyser.