TW202511539A - Electrocatalytic hydrogen carrier compositions - Google Patents

Abstract

The present disclosure provides hydrogen carrier fluid (HCF) compositions, comprising a leanliquid organic hydrogen carrier (lean-LOHC) component comprising at least one cyclohexyl-based compound having at least one unsaturated bond, optionally in combination with one or more C _{4 - 12}alkyl alcohol, or a rich-liquid organic hydrogen carrier (rich-LOHC) component comprising at least one cyclohexyl-based compound, optionally in combination with a C _4-7ketone, a C _4-6lactone or a mixture thereof; and an electrolyte component. Also provided is the use of these HCF compositions for storage and release of hydrogen, in an electrochemical reactor system.

Description

Electrocatalytic hydrogen support composition

The present disclosure relates to hydrogen storage via liquid organic hydrogen carriers, and electrochemical cells, battery packs, and fuel cells using hydrogen fuels. More specifically, the present invention relates to liquid organic hydrogen carrier compositions for processing via electrochemical methods.

Hydrogen is a net-zero fuel that is being widely adopted as an alternative to traditional fossil fuels due to its production pathways that are generally from renewable resources, its cleanliness, high energy density, and its nature as a sustainable and transportable energy source. Hydrogen can be used to generate electricity, power, or heat in many applications by powering fuel cell electric vehicles or stationary energy systems. Hydrogen storage is a key enabling technology for the deployment of hydrogen and fuel cell technologies around the world and for accelerating the adoption of clean energy. Hydrogen has the highest energy per unit mass of all fuels. However, due to its low bulk density, the storage of hydrogen is one of the main barriers to its widespread use in portable and stationary applications.

The realization of high-density hydrogen storage is a major challenge for portable and stationary applications as well as long-distance transportation applications. Currently available technologies are usually based on the storage of gaseous hydrogen, which requires large-capacity systems, leading to critical issues for portable applications. In the past decade, extensive investments in hydrogen storage research and commercial development have created commercial solutions in which hydrogen is chemically bonded to molecules of solid/liquid materials, such as metal hydrides and liquid organic hydrogen carriers (LOHCs).

Hydrogen storage in LOHCs is a promising technology that allows for safe storage of hydrogen for long periods of time without extremely high pressures and/or temperatures, and at a volumetric hydrogen storage density comparable to cryogenic liquefied hydrogen. The similar properties of LOHCs and crude oil derivatives under ambient conditions allow for the use of existing gasoline and diesel fueling infrastructure to transport hydrogen in LOHCs at high storage densities, thereby reducing operating costs compared to compressed or liquid hydrogen.

Liquid organic hydrogen carriers (LOHC) refer to compounds that can absorb and release hydrogen via chemical reactions. These compounds include at least part of the unsaturated hydrocarbons (also called poor LOHC), which undergo hydrogenation, for example, under a _H2 -source site, in order to provide a storable and transportable fluid in the form of corresponding (more) saturated hydrocarbons (also called rich LOHC). The saturated hydrocarbons can be dehydrogenated at the use site to release hydrogen and form a hydrogen-depleted fluid comprising at least part of the unsaturated hydrocarbons, which is transferred to the hydrogen source site and converted into the saturated form by a hydrogenation process. Typical carrier fluids are "molecular pairs" in hydrogenated and dehydrogenated forms, such as cyclohexane/benzene, methylcyclohexane/toluene, cyclohexanol/phenol; decahydronaphthalene/naphthalene, butanol/butanone, cyclohexanol/cyclohexenol, cyclohexanol/cyclohexenone, etc.

The storage and release of hydrogen in LOHC is based on a two-step cycle of hydrogenation and dehydrogenation by thermocatalytic or electrocatalytic reactions. Unlike thermocatalytic hydrogenation and dehydrogenation of LOHC, which require relatively high pressures and temperatures, electrocatalytic reactions can be performed under ambient conditions by simpler and potentially more efficient processes. This makes electrocatalytic LOHC systems powered by electrical energy suitable rechargeable storage systems for off-grid and decentralized hydrogen applications.

In a typical LOHC system, poor LOHC reacts with hydrogen to form rich LOHC during hydrogenation, while the opposite occurs during dehydrogenation. In an electrochemical system, this can be further described by the following half reactions occurring at the anode and cathode, where X is defined by the number of hydrogen moieties added/removed from the LOHC during hydrogenation/dehydrogenation, respectively. Hydrogenation: Negative LOHC + _XH2 → Rich LOHC Half-reaction: Oxidation: _XH2 → - 2XH+ + 2Xe- Reduction: 2XH+ 2Xe- + Negative LOHC → Rich LOHC Dehydrogenation : Rich LOHC → Negative LOHC + _XH2 Half-reaction: Oxidation: Rich LOHC → 2XH+ + 2Xe- Reduction: 2XH+ + 2Xe- → _XH2

Electrochemical reactors are deployed in the production of hydrogen gas by electrolysis and in industrial processes such as water treatment. These electrochemical storage systems provide stable, low-energy storage of hydrogen, but are limited in application due to the relatively low density of the stored hydrogen.

The application of electrochemical conversion to hydrogen transport in solution is much less explored. In recent reports from Yokohama National University, toluene hydrogenation via a polymer electrolyte membrane (PEM) electrochemical reactor was explored (Fukazawa et al., Bull. Chem. Soc. Jpn., 2018, 91 (6) pp. 897-899, Takano et al., Bull. Chem. Soc . Jpn. 89 pp. 1178-1183, 2016). These early reports were limited in scope in demonstrating full LOHC conversion and/or stable performance.

Therefore, there is a need for improved hydrogen storage and release systems, and hydrogen carriers designed for use in electrochemical reactors that can overcome one or more of the limitations of the prior art.

This background information is provided for the purpose of making known information that the applicant believes may be relevant to the present invention. It is neither intended nor should it be considered that any of the foregoing information constitutes prior art with respect to the present invention.

An object of the present invention is to provide hydrogen carrier fluid compositions designed for hydrogen storage and release in systems and methods using electrochemical reactors.

According to an aspect of the present invention, a hydrogen carrier fluid (HCF) composition is provided, which comprises a) a poor liquid organic hydrogen carrier (poor LOHC) component, which comprises at least one cyclohexyl-based compound having at least one unsaturated bond and, optionally, one or more _C4-12 alkyl alcohols, or a rich liquid organic hydrogen carrier (rich LOHC) component, which comprises at least one cyclohexyl-based compound and, optionally, a _C4-7 ketone, a _C4-6 lactone or a mixture thereof; and b) an electrolyte component.

According to another aspect of the present invention, there is provided a use of the HCF composition described herein for storing and releasing hydrogen in an electrochemical reactor system.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Unless the context requires otherwise, throughout this specification and claims, the words "including", "comprising", etc. should be interpreted in an open and inclusive sense.

The article "a" is used herein to refer to one or more than one (ie, at least one) of the grammatical object of the article. For example, "an element" means one element or more than one element.

As used herein, the term "about" refers to approximately +/- 10% variation of a given value. It should be understood that such variation is always included in any given value provided herein, whether or not it is specifically mentioned.

The present invention provides a hydrogen carrier fluid (HCF) composition for use with an electrocatalytic reactor system to achieve hydrogenation/dehydrogenation reactions in a method/system for hydrogen storage and release.

In one aspect, the present invention provides a hydrogen carrier fluid (HCF) composition, which comprises a poor liquid organic hydrogen carrier (poor LOHC) component and, optionally, one or more C _4-12 alkyl alcohols, or a rich liquid organic hydrogen carrier (rich LOHC) component and, optionally, a C _4-7 ketone, a C _4-6 lactone or a mixture thereof; and an electrolyte component.

The poor liquid organic hydrogen carrier (poor LOHC) component comprises at least one cyclohexyl-based compound having at least one unsaturated bond.

The liquid organic hydrogen carrier rich (LOHC rich) component comprises at least one cyclohexyl based compound.

As used herein, the term "cyclohexyl-based compound" refers to a monocyclic compound or a condensed-ring compound, either of which may be substituted with one or more OH and/or alkyl groups as appropriate.

The fused ring-based cyclohexyl compound may have at least two fused cyclohexyl rings, or one cycloalkyl ring and one 5- or 6-membered heterocyclic ring having at least one heteroatom such as N, O or S, wherein the cyclohexyl ring may be optionally substituted with one or more OH and C1-C6 alkyl groups.

The substituents of the cyclohexyl ring may be further substituted with cyclohexyl or 5- or 6-membered N-heterocyclic groups as appropriate.

Non-limiting examples of cyclohexyl-based compounds suitable for use in the LOHC-rich component include cyclohexane, methylcyclohexane, decahydronaphthalene, cyclohexanol, decahydro-N-alkylcarbazole, alkyl-perhydroindole, and the like.

Non-limiting examples of cyclohexyl-based compounds suitable for use in the poor LOHC component having at least one unsaturated bond include cyclohexene, cyclohexanol, benzene, toluene, naphthalene, phenol, benzyltoluene, dibenzyltoluene, biphenyl, N-alkylcarbazole, alkylindole, and the like.

In some embodiments, the LOHC-rich component comprises cyclohexane, methylcyclohexane, cyclohexanol, or a mixture thereof. In some embodiments, the LOHC-rich component comprises cyclohexanol or methylcyclohexane.

In some embodiments, the negative LOHC component comprises cyclohexene, methylcyclohexene, cyclohexanol, cyclohexanone, phenol or a mixture thereof. In some embodiments, the negative LOHC component comprises phenol.

In some embodiments, the poor LOHC component comprises methylcyclohexene, toluene or a mixture thereof. In some embodiments, the poor LOHC component comprises phenol.

Suitable alcohols for use in the anhydrous LOHC component may be C _4-12 monohydroxy alkyl alcohols, C _4-12 polyhydroxy alkyl alcohols, or mixtures thereof.

In some embodiments, the alcohol is n-butanol, 2-butanol, n-pentanediol, 2-pentanol, 3-pentanol, or a mixture thereof. In some embodiments, the alcohol is n-butanol.

In some embodiments, suitable ketones for use in the LOHC-rich component are butanone, pentanone, pentanedione, or mixtures thereof.

In some embodiments, the ketone is butanone, pentanedione or a mixture thereof. In some embodiments, the lactone is γ-butyrolactone, δ-valerolactone or a mixture thereof. In some embodiments, the lactone is δ-valerolactone.

The electrolyte component suitable for use in the HCF composition may include an alkali metal salt, an alkali earth metal salt, an ammonium salt, a C _6-14 alkyl-C _6-10 aryl sulfonic acid, or a mixture thereof.

In some embodiments, the electrolyte component comprises an alkali metal salt, an alkaline earth metal salt, an ammonium salt, or a mixture thereof.

In some embodiments, the alkaline metal is lithium, sodium or potassium.

The ammonium component of the ammonium salt may be defined as NR ₄ ⁺ , wherein R is independently selected from H or one or more C _1-4 alkyl groups.

Non-limiting examples of counter ions of the alkali metal salt, alkaline earth metal salt, or ammonium salt are hydroxide anion, perchlorate anion, borate anion, carbonate anion, or acetate anion.

In some embodiments, the electrolyte component is an alkali metal or alkaline earth metal perchlorate. In some embodiments, the electrolyte component is lithium perchlorate.

In some embodiments, the electrolyte component is tetrabutylammonium hydroxide. In some embodiments, the electrolyte component is dodecyl sulfonic acid.

In some embodiments, the HCF composition further comprises a transition or post-transition metal complex.

In some embodiments, the transition metal is Pd, Ru, V, Fe, Mn or Ni. In some embodiments, the post-transition metal is Al.

In some embodiments, the transition metal complex is palladium pivalate (palladium trimethylacetate).

In some embodiments, the HCF composition further comprises an organic redox mediator.

The term "organic redox mediator" or "catalyst" as used herein includes compounds that form stable organic radicals that act as intermediate electron carriers or reservoirs without changing the final product of the electrochemical reaction of the LOHC. These compounds are regenerated at the electrode surface.

Non-limiting examples of organic redox mediators include quinones (such as benzoquinone, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, naphthoquinone), TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl), N-hydroxyphthalimide, C _1-6 trialkylamines, C _1-6 dialkylamines, C _1-8 diamines, and the like.

In some embodiments, the organic redox mediator is triethylamine, N,N' -dimethyl-1,3-propylenediamine, or N-hydroxyphthalimide.

In some embodiments, the HCF composition comprises a solvent medium. In some embodiments, the solvent medium is water.

The HCF composition may include up to about 90 wt % of a negative LOHC component, up to 60 wt % of an alcohol, up to about 20 wt % of an electrolyte component, and up to 5 wt % of a transition metal or post-transition metal complex/compound, and up to 5 wt % of a redox mediator.

In some embodiments, the composition comprises about 40 wt%-90 wt% of a LOHC-rich component, about 20 wt%-60 wt% of a ketone, a lactone or a mixture thereof, about 1 wt%-20 wt% of an electrolyte component, about 0.5 wt%-5 wt% of a transition metal or a post-transition metal complex/compound, and about 0.5 wt%-5 wt% of a redox mediator.

Without being bound by theory, it is believed that the alcohol can act as a dispersant and/or liquid organic hydrogen carrier; and the electrolyte component can be used to reduce the generation of capacitor charge.

In some embodiments, the alcohol acts as a hydrogen carrier and is reversibly dehydrogenated/hydrogenated between the alcohol and the ketone or lactone form, e.g., butanol to butanone, pentanediol to γ-valerolactone or pentanedione.

In another aspect, the present invention provides the use of HCF compositions for storing and releasing hydrogen in electrocatalytic reactor systems/methods.

When used in an electrocatalytic reactor system and method, the LOHC component of the HCF composition of the present invention can cycle between a hydrogenated form (LOHC-rich) and a dehydrogenated form (LOHC-poor) using a hydrogenation reactor (H-reactor) and a dehydrogenation reactor (D-reactor).

Depending on the end-use application, HCF compositions may be transported via pipeline, truck, train, or individual tanks. Poor LOHC may be re-hydrogenated at a facility or hydrogen refueling center. Rich LOHC may be used on-site to generate hydrogen fuel for use in end applications in electrical power generation, heating, or other hydrogen gas end-use cases.

In some embodiments, the LOHC of the HCF composition of the present invention may be electrochemically dehydrogenated in a dehydrogenation reactor (D-reactor) comprising an anode and a cathode to produce a depleted LOHC.

In some embodiments, the HCF composition of the present invention is converted on-site via a D-reactor to produce hydrogen fuel.

In some embodiments, the HCF composition of the present invention is transported to the site of the D-reactor via pipeline, concentric pipeline, tank truck, personal use tank, concentric personal use tank, or the like.

In some embodiments, the depleted LOHC of the HCF composition is returned via a pipeline, a concentric pipeline, a tank truck, a personal use tank, a concentric personal use tank, or the like for hydrogenation.

In some embodiments, the depleted LOHC is rehydrogenated at a refueling center, or the like, through the use of a hydrogenation reactor (H-reactor).

Although the present invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the present invention. All such modifications apparent to those skilled in the art are intended to be included within the scope of the following claims.

In order to obtain a better understanding of the present invention described herein, the following examples are described. It should be understood that these examples are intended to describe exemplary embodiments of the present invention and are not intended to limit the scope of the present invention in any way. Examples

FIG . 1 depicts a LOHC system involving LOHC compounds of the present invention, wherein during hydrogenation, anemic LOHC (i.e., benzene) and a ketone or lactone react with hydrogen to produce anemic LOHC (i.e., cyclohexane) and an alcohol during hydrogenation, and the reverse occurs during dehydrogenation, wherein the cyclohexane is converted back to cyclohexene and/or benzene, and the alcohol is converted to a ketone or lactone. Example 1

An electrocatalytic HCF formulation comprising a 1:1 mixture by volume of methylcyclohexane and butanol, and 0.1 M tetrabutylammonium hydroxide was used in a parallel flow electrochemical reactor. The electrodes consisted of Ni metal foam coated with a platinum group metal catalyst. The electrodes were connected to a power source so that adjacent electrodes acted as monopolar anodes and cathodes, and with a 0.3 mm separation between the electrodes and a nylon-based flow distributor. The applied potential was ramped up to 2.5 V at a rate of 0.2 V/s. The electrochemical oxidation of methylcyclohexane and butanol was confirmed as the current increased above 0.75 V, the anodic reaction was the oxidation of the liquid organic hydrogen carrier, and the cathodic reaction was the hydrogen evolution reaction (Figure 2).

The system was operated for 2.5 h under chronoamperometric conditions with a fixed current of 20 mA and an average applied potential of 2.6 V, resulting in the conversion of butanol to butanone (>2%) and methylcyclohexane to methylcyclohexene (<1%), with the release of hydrogen gas at the cathode. Example 2

An electrocatalytic HCF formulation comprising a mixture of 40 ml each of n-butanol and methylcyclohexane, 16 g of 4-dodecylbenzenesulfonic acid and 0.15 g of palladium pivalate was used in a beaker type electrochemical reactor. The working and counter electrodes consisted of Ni metal foam coated with a platinum group metal catalyst. The pseudo reference electrode was a silver wire. The electrodes were connected to a voltage regulator (Admiral Ace) so that the electrodes acted as monopolar anodes and cathodes with a 3-5 mm spacing between the electrodes. The applied potential was ramped from -0.15 V to 1.5 V at a rate of 0.2 V/s. Electrochemical oxidation of methylcyclohexane and butanol was established as a current increase starting at -0.15 V, with the anodic reaction being oxidation of the liquid organic hydrogen carrier and the cathodic reaction being a hydrogen evolution reaction (Fig. 3). Due to mass transport limitations of one or more species, a current leveling of 1.6 mA was observed at potentials greater than 0.2 V compared to the Ag pseudo-reference. The system was operated for 4 h under chronoamperometric conditions with a fixed current of 1 mA and an average applied potential of 1 V, resulting in the conversion of butanol to butanone (>5%) and methylcyclohexane to methylcyclohexene (about 1%), with the release of hydrogen gas at the cathode, which was vented to the atmosphere in a laboratory fume hood. Example 3

An electrocatalytic HCF formulation containing 30 mg cyclohexanol, 0.5 M lithium perchlorate and 8 mg redox mediator N-hydroxyphthalimide was diluted in 1.5 ml acetonitrile and tested in a beaker type electrochemical reactor. The electrodes consisted of graphite rods with a platinum group metal catalyst. The electrodes were connected to a power source so that adjacent electrodes acted as monopolar anodes and cathodes with a 0.2 mm gap between them. The applied potential was ramped up to 2 V at a rate of 0.05 V/s. The electrochemical oxidation of cyclohexanol was established as the current increased above 1.1 V, and the anodic reaction was oxidation of the liquid organic hydrogen carrier, and the cathodic reaction was a hydrogen evolution reaction (Fig. 4, HCF with mediator). For comparison, the system was tested with the same electrochemical scan profile without the addition of a redox mediator (Fig. 4, HCF without mediator). This scan shows a significant shift in the onset of oxidation from about 1 V to >1.5 V (indicated by the current increase), highlighting the catalytic nature of the redox mediator for the electrochemical HCF oxidation. The system was operated under chronoamperometric conditions with a fixed current of 2 mA and an average applied potential of 1.8 V for 0.75 h, resulting in the conversion of cyclohexanol to cyclohexanone/cyclohexanol (>10%), cyclohexenone <1%, and phenol <0.1%.

without

Further features and advantages of the present disclosure will become apparent from the following detailed description when read in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic illustration of the hydrogenation and dehydrogenation reactions of the LOHC component of a hydrogen carrier fluid (HCF) composition according to an embodiment of the present invention.

FIG. 2 depicts a cyclic voltammogram associated with the electrochemical dehydrogenation of a LOHC component according to an embodiment of the present invention.

FIG. 3 depicts a linear sweep voltammogram associated with the electrochemical dehydrogenation of a LOHC component according to an embodiment of the present invention.

FIG. 4 depicts a cyclic voltammogram associated with the electrochemical dehydrogenation of a LOHC component according to an embodiment of the present invention.

Domestic storage information (please note in the order of storage institution, date, and number) None Foreign storage information (please note in the order of storage country, institution, date, and number) None

Claims (17)

A hydrogen carrier fluid (HCF) composition, comprising: a) a poor liquid organic hydrogen carrier (poor LOHC) component, which comprises at least one cyclohexyl-based compound having at least one unsaturated bond and, optionally, one or more _C4-12 alkyl alcohols, or a rich liquid organic hydrogen carrier (rich LOHC) component, which comprises at least one cyclohexyl-based compound and, optionally, a _C4-7 ketone, a _C4-6 lactone or a mixture thereof; and b) an electrolyte component. The HCF composition as claimed in claim 1, wherein the LOHC-rich component comprises cyclohexane, methylcyclohexane, cyclohexanol or a mixture thereof. The HCF composition as claimed in claim 1, wherein the poor LOHC component comprises cyclohexene, methylcyclohexene, cyclohexanol, cyclohexanone, phenol or a mixture thereof. The HCF composition as described in any one of claims 1 to 3, wherein the alcohol is butanol, pentanediol, or a mixture thereof. The HCF composition as described in any one of claims 1 to 3, wherein the ketone is butanone, pentanedione, or a mixture thereof, and the lactone is delta-valerolactone. The HCF composition as described in any one of claims 1 to 5, wherein the electrolyte component comprises an alkali metal salt, an alkali earth metal salt, an ammonium salt, a C _6-14 alkyl-C _6-10 aryl sulfonic acid or a mixture thereof. The HCF composition as described in claim 6, wherein one of the relative ions of the alkali metal salt, the alkaline earth metal salt, and the ammonium salt is a hydroxide anion, a perchlorate anion, a borate anion, a carbonate anion, or an acetate anion. The HCF composition as described in claim 6, wherein the electrolyte component is dodecyl sulfonic acid. The HCF composition as described in any one of claims 1 to 8, further comprising a transition metal complex or a post-transition metal complex. The HCF composition as described in claim 9, wherein the transition metal is Pd, Ru, V, Fe, Mn, or Ni, and the post-transition metal is Al. The HCF composition as described in claim 10, wherein the transition metal complex is palladium pivalate (palladium trimethylacetate). The HCF composition as described in any one of claims 1 to 11, further comprising an organic redox mediator. The HCF composition as described in claim 12, wherein the organic redox mediator is benzoquinone, naphthoquinone, N-hydroxyphthalimide, triethylamine, N,N' -dimethyl-1,3-propylenediamine or TEMPO. The HCF composition as described in any one of claims 1 to 8, wherein the composition comprises: About 40wt%-90wt% of the poor LOHC component; About 20wt%-60wt% of the alcohol; and About 1wt%-20wt% of the electrolyte component. The HCF composition as described in any one of claims 1 to 8, wherein the composition comprises: About 40wt%-90wt% of the LOHC-rich component; About 20wt%-60wt% of the ketone, the lactone or a mixture thereof; and About 1wt%-20wt% of the electrolyte component. The HCF composition as described in claim 14 or 15, further comprising: About 0.5wt%-5wt% of the transition metal complex or post-transition metal compound/complex; and/or About 0.5wt%-5wt% of the redox mediator. The use of an HCF composition as defined in any one of claims 1 to 16 for storing and releasing hydrogen.