WO2021181085A1

WO2021181085A1 - Catalyst

Info

Publication number: WO2021181085A1
Application number: PCT/GB2021/050585
Authority: WO
Inventors: David Hodgson; Hubert MEISSEL
Original assignee: Amalyst Limited
Priority date: 2020-03-10
Filing date: 2021-03-09
Publication date: 2021-09-16

Abstract

The invention relates to a catalyst for use in fuel cells, methods of making said catalyst, electrodes and fuel cells comprising said catalyst and the use of said catalyst in fuel cells. In particular, the invention employs a disrupted catalyst-functionalised graphene, using a series of spacers (typically made from non-metallic substances), to optimise the performance of the materials.

Description

Catalyst

Field of Invention

[0001] The invention relates to a catalyst for use in fuel cells, methods of making said catalyst, electrodes and fuel cells comprising said catalyst and the use of said catalyst in fuel cells.

Background

[0002] There has been much research into the utility of graphene in electrochemical systems. The high conductivity and unique structure of graphene make it a uniquely promising material for various electrochemical applications. Graphene has been used to augment electrochemical catalysts, such as those used in fuel cells. For example, platinum nanoparticles have been applied to graphene nanoplatelets with a view to enhancing the catalytic activity of platinum in order to reduce reliance on this precious metal (Ece Arici, et al.; "An effective electrocatalyst based on platinum nanoparticles supported with graphene nanoplatelets and carbon black hybrid for PEM fuel cells'" International Journal of Hydrogen Energy, Vol. 44, 27, 24 May 2019, Pages 14175 - 14183).

[0003] In addition, some work has been done exploring the formulation of graphene based catalysts for optimal performance. In particular, Park et al (Sehkyu Park, et al. "Design of graphene sheets-supported Pt catalyst layer in PEM fuel cells'" Electrochemistry Communications, Vol. 13, 3, March 2011, Pages 258-261) developed a graphene based composition in which carbon spacers were provided so as to reduce aggregation of graphene sheets.

[0004] However, these materials have still not provided sufficient improvement in properties to offer a commercially competitive alternative to conventional platinum catalysts. Accordingly, it is desirable to develop catalysts which are not only (at least) as effective at catalysing electrochemical processes but which provide a commercially viable alternative to platinum on carbon (Pt/C or Pt/graphite catalysts).

[0005]The invention is intended to overcome or at least ameliorate this problem. The project leading to this application has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 649953.

Summary of Invention

[0006] There is provided, in a first aspect of the invention, a composition for use in fuel cells, the composition comprising: a plurality of catalyst-functionalised graphene sheets; and one or more spacer particles; characterised in that the spacer particles partially disrupt the co-ordination between the graphene sheets; and wherein the spacer particles comprise one or more metals.

[0007]The term "catalyst-functionalised" as used herein is intended to refer to the at least partial affixation of a catalytic material to, in the present invention, a graphene sheet. This fixation may be via chemical means (e.g. covalent bonding) or physical means (e.g. through an adsorption type mechanism), provided that the catalytic material is associated with the graphene. The graphene functions as a substrate to which the catalytic material is applied. This enhances the surface area of the catalytic material and governs the resilience. There are numerous techniques in the prior art as to how this can be achieved and the invention is not intended to be limited to any specific technique.

[0008] The term "graphene sheet" is not to be construed as a monolayer of carbon, of one atom's thickness, arranged in a hexagonal fashion i.e. a perfect 2D network of hexagonal carbon. This term is intended to cover both single and multilayer arrangements of hexagonally ordered carbon. Typically, the graphene sheets have a thickness in the range of 1 to 100 layers, more typically 1 to 50, even more typically less than 20, and even more typically still 2 to 10. In some embodiments, the graphene sheets may have 30 to 80 layers, or more typically 40 to 50 layers. However, the graphene sheets in a given composition need not possess the same number of layers. A range of graphene sheets, with greater or fewer layers, may be used in the same compositions. For example, it is typically the case that at least 50% of the graphene sheets present in the composition comprise 10 or fewer layers, more typically at least 75% of the graphene sheets present in the composition comprise 10 or fewer layers, and most typically at least 90% of the graphene sheets present in the composition comprise 10 or fewer layers. In some situations, at least 20% of the graphene sheets present in the composition comprise 5 or fewer layers, more typically at least 40% of the graphene sheets present in the composition comprise 5 or fewer layers, and most typically at least 60% of the graphene sheets present in the composition comprise 5 or fewer layers. Further, it may be the case that 2% or less of the graphene sheets present in the composition comprise 10 or more layers, more typically 5% or less of the graphene sheets present in the composition comprise 10 or more layers, and most typically 10% or less of the graphene sheets present in the composition comprise 10 or more layers.

[0009] The term "spacer particles" is intended to refer to particles that in situ interfere with the assembly of an ordered array of graphene sheets. Without being bound by theory, it is believed that a plurality of 2D graphene sheets will tend towards stacking, with multiple sheets on top of one another i.e. becoming more graphite-like. Again, without being bound by theory, it is believed that this process can be partially interrupted by introducing spacers in order to prevent the close assembly of stacks of graphene sheets. As such, the catalyst-functionalised graphene sheets and the spacer particles form complexes with a large amount of the catalytic material accessible for reactants. This in turn maximises the catalytic surface area (as both faces of the 2D graphene sheets always remain, at least partially, exposed). In particular, gaseous reagents are expected to be better able to penetrate dense lattices of graphene sheets if spacers are provided.

[0010] Reference to "partial" or "partially" interrupted communication between the graphene sheets is intended to mean that the spacers prevent the graphene sheets from assembling into a near perfect graphite-like arrangement, but are not so disruptive as to entirely prevent co-ordination between graphene sheets. Without being bound by theory, it is believed that the graphene sheets are able to stack in a substantially parallel fashion, typically deviating from the parallel by less than 40°, more typically less than 35°, even more typically less than 30°, even more typically still less than 25° and, in some cases, less than 20°. It may be that this angle is even lower than this, such as less than 15° and even as low as less than 10°.

[0011] The term "complex" or "complexes" as used herein is intended to cover the associated combination of the above mentioned catalyst-functionalised graphene sheets and spacer particles. Although the complex will typically possess a sandwich-like structure, i.e. having two graphene sheets separated by one or more spacer particles therebetween, more elaborate arrangements are also envisaged with multiple graphene sheets each separated by multiple sets of one or more spacer particles.

[0012] Although the spacer comprises "one or more metals", this is not intended to be limited to pure or alloyed metallic species. This is to be interpreted as the presence of one or more metal elements. This could be metallic species (such as palladium or platinum), or could also be a compound comprising a metal (such as a metal oxide, metal carbide, metal nitride, or the like). Typically metals include, but are not limited to: Ti, W, Mo, Fe, Cu, Zn, Zr, Ce, Al, Sm, Y, Mn, Co or combinations thereof. Of these, Ti, Fe, Zn, Zr and combinations thereof are often employed.

[0013]The inventors have found that the choice of spacer material used to separate graphene sheets in an electrocatalyst composition is important in optimising the catalytic properties. Often, the spacer material will comprise a metal oxide, metal carbide, metal nitride, or combinations thereof. Usually, the spacer will comprise a metal oxide or metal carbide; most commonly a metal oxide. Whilst the invention is not restricted to a particular material, it is often the case that the spacer comprises a material selected: T1O2, M02C, Fe304, ZnFe204, ZnO, ZrCh, ZrP, CeCh, AlCeCh, SmCh, SnCh, Y2O3, AI2O3, MnO, M^h2q3, C03O4 or combinations thereof. Often, the spacer comprises T1O2, Fe304, Zr02, Ce02, AI2O3, C03O4 or combinations thereof; more typically T1O2, Fe304, Zr02, AI2O3, or combinations thereof; and most typically the spacer comprises T1O2. The inventors have found that metal oxides, in particular T1O2, shows excellent properties. There is no restriction on the type of T1O2 that is used and rutile, anatase, brookite or a combination thereof may be used among others.

[0014]The composition may further comprise other materials other than the species described above. For instance, additional components may be added to further enhance the catalytic properties or to enhance the resilience of the spacers, especially in those fuel cells operating under intense conditions for extended durations. Additional components that may be added to the spacer particles include, but are not limited to: carbon black, carbon nanofibres, silica or combinations thereof.

[0015]The invention is not limited to compositions using only a single spacer material. A range of spacers may be employed as described herein. Further, the spacer particles typically have a particle size of less than 500 pm. The term "particle size" herein refers to the diameter of a particle when approximating the particle to a sphere. It is important that the spacer particles are small enough to be positioned between adjacent graphene sheets, but large enough to effectively disrupt "stacking" of individual graphene sheets. More often, the particles will be less than 200 pm; more typically the particles have a size in the range of 0.01 pm and 100 pm; even more typically 0.1 pm to 80 pm; more typically still in the range of 1 pm to 60 pm; even more typically still 5 pm to 50 pm. In some embodiments, the particle size is in the range of 40 pm to 50 pm. Alternatively, the particles may have a size in the range 0.005 pm to 0.5 pm, or more typically 0.01 to 0.2 pm.

[0016] The particle size distribution of the spacers need not be such that all particles have the same dimensions. As one skilled in the art will appreciate, such highly uniform formulations are very difficult to create. However, the particle size distribution may be a normal distribution (i.e. a Gaussian distribution) or a bimodal distribution.

[0017] In some embodiments, the spacer will comprise an electrically insulating material. It has surprisingly been found that employing an electrically insulating material appears to improve the electrochemical performance. This is counter-intuitive, not only because it was not expected for an insulating material to augment electrochemical processes but, because the presence of insulating materials in electrochemical systems typically reduces the overall efficiency of charge transfer (making the whole electrochemical process less efficient). Even if such an adverse phenomena is occurring in the present invention, as can be seen from the examples, better results are nevertheless obtained with insulating materials as compared to embodiments employing conducting spacers.

[0018] Whilst there is no particular restriction on the choice of catalytic material, beyond the catalytic material being suitable for catalysing fuel cell processes, the catalytic material is typically selected to catalyse cathode reactions, though it may also catalyse anode reactions or both. The catalytic material is typically bound to the graphene sheets by physical means, this typically involves depositing the catalytic material onto the graphene sheets as nanoparticles. Often, the catalyst-functionalised graphene sheets comprise one or more catalytic materials selected from: platinum, palladium, copper, titanium, zinc, rhodium, osmium, gold, silver, nickel, iridium, ruthenium, cobalt or combinations thereof. Of these materials, the catalytic material more typically comprises platinum, palladium and iridium; and most typically, comprises platinum. As one skilled in the art will appreciate, alloys or different metals may be employed or combinations of different catalytic materials can be used. Individual particles comprising a combinations of catalytic materials are also envisaged.

[0019]The catalytic material is typically applied to the graphene sheets as nanoparticles. For the avoidance of doubt, the term "nanoparticle" is intended to take its conventional meaning i.e. having a particle size in the nanometre scale (typically < 1000 nm). Often the particles of catalytic material will have a size in the range of 1 nm to 500 nm, more often 1 nm to 250 nm, more typically 1 nm to 100 nm and even more typically 1 nm to 10 nm. Often, the nanoparticles are in the range of 1 nm to 5 nm, and more typically 1 nm to 3 nm. Usually, the weight ratio of catalytic material to graphene is typically 1% to 95% catalytic material; more typically, 20% to 80% catalytic material, and more typically around 30% to 60% catalytic material. Often the ratio of catalytic material to graphene is equal to or greater than 60% catalytic material, in some embodiments it will be less than 25% catalytic material, more typically less than 15% catalytic material and even more typically less than 10% catalytic material.

[0020]There is no restriction on the area of the graphene sheets that can be employed in the invention. As one skilled in the art will appreciate, the area of the graphene sheets can be controlled so as to tune the available surface area. Usually, the graphene sheets have a surface area in the range of 1 - 2000 m² g ¹. Typically, the graphene sheets have a surface area in the range of 5 - 5000 m² g^_1, more typically 5 - 2000 m² g^_1, more typically still 100 - 100 m² g^_1, and most typically 400 to 800 m² g^_1.

[0021]There is provided in a second aspect of the invention, a method of making the composition according to the first aspect of the invention, comprising the steps of: a) coating one or more graphene sheets with catalytic materials; and b) adding the coated graphene sheets of step a) to a spacer solution.

[0022] Although the coated graphene sheets are added to a "spacer solution", as one skilled in the art would understand, the size of the spacer particles and the solvent used dictates whether the composition containing the spacer particles is a solution (with substantially all of the spacers dissolved) or a suspension (where substantially all of the spacers are merely suspended in solution). Often, the solution is in fact a suspension.

[0023] As one skilled in the art will be aware, there are a number of methods available for coating graphene with catalytic materials. One such method is disclosed in WO 2019/158569 (for instance on pages 32 to 33). Combining catalyst coated graphene sheets with a spacer solution (according to the first aspect of the invention) results in a complex which displays improved electrocata lytic behaviour. The complex can be extracted from the residual spacer solution once combined. Typically, the catalytic materials are nanoparticles. Moreover, the coated graphene sheets are typically coated in situ and, once coated, are isolated from said solution. There is no particular limitation as to how this is accomplished, usually a drying technique is employed to separate the solvent from the catalyst-functionalised graphene sheets.

[0024] Typically, the method of making the composition comprises the steps of: a) preparing an alkaline solution of catalytic material nanoparticles; b) adding graphene sheets to the catalyst solution of step a); c) lowering the pH so as to provoke adsorption of said catalytic material nanoparticles to the graphene sheets; d) extracting the catalyst-functionalised graphene sheets from solution; and e) adding the catalyst-functionalised graphene sheets to a spacer solution.

[0025]The person skilled in the art will be familiar with the preparation of nanoparticle solutions. The alkalinity of the alkaline solution is not particularly limited but is usually in the range of 8 to 14, more typically 9 to 13 and even more typically 10 to 11. The choice of materials used, both in terms of catalytic material and alkaline solution, will naturally influence the pH required in the process. It is desirable to employ alkaline conditions as it encourages the binding of catalytic material to the graphene sheets. The pH is typically lowered to a value in the range of 1 to 7, more typically 2 to 5, and even more typically 3 to 4. Typically, the catalytic material provided in step a) is a salt. Step b) typically includes a heating step in order to dissolve the catalytic material. Usually, the temperature will be in the range of 30°C to 200°C, more typically 70°C to 150°C and most typically in the range of 100°C to 140°C. In one embodiment, the temperature of step b) is in the range of 120°C to 130°C.

[0026] Often, step c) will include a cooling step wherein the temperature of the solution is reduced, typically to the range of 10°C to 30°C. There is no particular duration for each of the steps outlined above and, as one skilled in the art would appreciate, different reactions proceed at different rates. However, it is usually the case that step b) last for less than 10 hours, often in the range of 1 to 8 hours, and usually 3 to 7 hours. Regarding the duration of step c), this typically lasts less than 5 days, usually less than 84 hours, more often in the range of 36 hours and 72 hours.

[0027]Typically, step e) involves agitation of the solution in order to ensure good mixing of the spacer particles and the catalyst-functionalised graphene. This can be done using a variety of means but typically involves sonication.

[0028]The method may also include an additional step, step f), of separating the complex from the spacer solution. Whilst not particularly limited, this typically involves applying the solution (e.g. via spraying) onto a surface and allowing it to dry. The spacer solution is typically adapted for deposition of the complex to a surface used in an electrochemical cell. Accordingly, the spacer solution may include conducting polymers, such as Nation (RTM), and/or other excipients to assist application of the complex.

[0029]There is provided in a third aspect of the invention, an electrode comprising the composition according to the first aspect of the invention. The electrode is typically a cathode, though anodes are also envisaged. The electrode may be part of a membrane electrode assembly (MEA) as would be familiar to one skilled in the art (see, for example, WO213093449). The electrodes may be diffusion electrodes, comprising an electrically conducting support with a diffusion material deposited on the surface comprising the complex.

[0030] There is provided in a fourth aspect of the invention, a fuel cell comprising the composition of the first aspect of the invention or the electrode according to the third aspect of the invention. There is no particular restriction on the type of fuel cell with which the above described complex is compatible. Typically, the fuel cell will be a hydrogen, methanol or ethanol fuel cell; most typically a hydrogen fuel cell. The fuel cell may be polymer electrolyte fuel cell, such as a proton exchange membrane fuel cell (PEMFC) or an anion exchange membrane fuel cell (AEMFC). However, of these two systems, PEMFCs are preferred. Alternatively, the fuel cell may employ a liquid electrolyte; and indeed a hybrid of liquid / polymer electrolyte systems is also envisaged. Typically, the fuel cell is an acidic fuel cell wherein the composition is usually employed on the cathode side of the system.

[0031]There is provided in a further aspect of the invention, the use of a composition according to the first aspect of the invention as an electrocatalyst. Typically, the composition is used as an anodic electrocatalyst. Often, said use will be in connection with fuel cells as described above.

[0032] There is provided in a further aspect of the invention, use of an electrode according to the third aspect of the invention or the fuel cell according to fourth aspect of the invention, in the generation of electricity.

[0033] Unless otherwise stated, each integer described may be used in combination with any other integer as would be understood by the person skilled in the art. Further, although all aspects of the invention typically "comprise" the features described in relation to that aspect, it is specifically envisaged that they may "consist" or "consist essentially" of those features outlined in the claims. In addition, all terms, unless specifically defined herein, are intended to be given their commonly understood meaning in the art.

[0034] Further, in the discussion of the invention, unless stated to the contrary, the disclosure of alternative values for the upper or lower limit of a permitted range of a parameter, is to be construed as an implied statement that each intermediate value of said range parameter, lying between the smaller and greater of the alternatives, is itself also described as a possible value for the parameter. In addition, unless stated otherwise, all numerical values appearing in this application are to be understood as being modified by the term "about".

[0035] In order to aid understanding, preferred embodiments of the invention will now be described with respect to the following figures, preferred embodiments and examples.

Description of Figures [0036] Figure 1 shows cyclic voltammograms of a Pt/graphene nanoplatelets (GNP) catalyst. Electrocatalyst in 0.5M H2SO4 electrolyte solution at a scan rate of 20 mV/s between 0.05V and 1.2V versus a Normal Hydrogen Electrode (NHE).

[0037] Figure 2 shows polarization curves (on a 10 cm² membrane electrode assembly) of the catalyst according to Example 1 without spacers (identified as "HM10") compared to the same catalyst with titanium oxide spacers (identified as "HM10 + PO2"). For comparison purposes, this was contrasted with a commercial MEA made using 40 wt.% Pt on carbon black.

[0038] Figure 3 shows polarization curves (on a 25 cm² membrane electrode assembly) of the reference catalyst (identified as "TKK", a 46.1% Pt on Ketjen Black with a surface area of around 74 m².gPt^_1 sold by Tanaka Kikinzoku Koygo) as compared with the catalyst of Example 1 without spacers ("HM10") and that same catalyst with spacers ("HM10 + T1O2").

[0039] Figure 4 shows polarization curves of the durability testing (AST carbon) of the reference catalyst ("TKK") and the catalyst according to Example X with spacers ("HM10 + T1O2") on a 25 cm² membrane electrode assembly.

[0040] Figure 5 shows polarization curves (on a 25 cm² membrane electrode assembly), of the reference catalyst ("TKK") as compared to the catalyst of Example X without spacers ("HM10"), that same catalyst with spacers ("HM10 + T1O2") that same catalyst again using carbon spacers (Vulcan Carbon); each after 10 cycles.

[0041] Figures 6a and 6b show schematic representations of the complex described above in plan and side on views respectively and Figure 6c shows the intermolecular interactions within the graphene sheets.

Examples

Electrocatalyst Characterisation

[0042] Cyclic Voltammetry (CV) measurements were performed for the determination of the electrocata lytic activity of the synthesized Pt/GNP catalysts. A three-electrode system was used where catalyst ink coated on glassy carbon rotating disk electrode (RDE), Pt wire was the counter electrode and HVH2 was the reference electrode. The catalyst ink was prepared by dispersing the Pt/GNP in isopropanol and Nation® solution (5 wt.%, 2 mg ml_ ^x) and applied drop wise onto the glassy carbon rotating disk electrode (RDE) with a surface area of 0.19625 cm², as the working electrode. CVs were obtained with an electrolyte solution of 0.5M H2SO4 with a potential scan for a range of -0.05 to 1.2 V at 20 mV s ¹ scan rate under N2 atmosphere against a Normal Hydrogen Electrode (NHE).

[0043] Electrochemically Active Surface Area (ECSA) values indicated an activity of 70 to 80 m² g ¹ Pt for the electrocatalyst Pt/GNP (Figure 1).

[0044] By way of comparison, conventional Pt/C catalysts (HiSPEC 4000 obtained from Johnson Matthey) usually achieve activities of approximately 60 m² g^_1 Pt (see for example, "Analytical Procedure for Accurate Comparison of Rotating Disk Electrode Results for the Oxygen Reduction Activity of Pt/C" Yannick Garsany, eta/.; Journal of The Electrochemical Society; 161 (5); F628-F640; 2014).

Example 1 - Method of Pt-Deposition on Graphene

[0045] A solution of hexachloroplatinic acid (H2PtCl6.6H20) in ethylene glycol (EG) was added drop by drop into EG with mechanical stirring for 10 min (one stirring bar). A solution of NaOH (10M in water) was added to adjust the pH of the solution in the range of 11 to 12. Graphene was added to the above solution and stirred for 1 hours. The solution was heated in refluxing conditions at 110 to 120 °C for 5 hours to completely reduce H2PtCl6. After cooling down and stirring for 29 hours, the pH of the reaction solution was adjusted to in the range of 2 to 3 with concentrated HNO3, which promotes the adsorption of the suspended metal nanoparticles onto the carbon support, then stirred for 48 hours. The resulting catalyst (Pt/GNP) was filtered and washed (3 times) with DI water until Cl- was not detected and then dried at 100°C.

Example 2 - Formation of the Membrane Electrode Assembly (MEA)

[0046] A catalyst ink was prepared with the catalyst Pt/GNP (40 wt.% Pt on support) and the spacer (44pm T1O2 particles, 30% wt. catalyst) using the Nation® solution (5 wt.%) with the 2-propanol. The Ti02 was 95% anatase and 5% rutile. The graphene used in the process had a particle size of 2pm, the graphene sheets themselves were several nanometres thick (less than lOnm) and had a surface area of 500 m² g^-1 (xGnP® Graphene Nanoplatelets Grade C, obtained from xG Sciences Limited). The catalyst inks and spacer were sonicated for 2 hours. For the anode, a comparative catalyst ink was prepared with the dispersion of commercially available catalyst powder (40 wt.% Pt on carbon black), and Nation® solution (5 wt.%) in 2-propanol. [0047] The catalyst ink was applied to the gas diffusion layer (GDL) surface by spraying method. Spraying was performed several times until a platinum loading of 0.3 mg cm^-2 was obtained. Sprayed gas diffusion electrodes (GDEs), anodes and cathodes with 25 cm² area, were hot pressed onto Nation® 115 membranes at 135 °C and 2 MPa for 5 min after 10 min pre-heating step at 135 °C without applying pressure.

Example 3 - Fuel Cell Testing

[0048]The catalyst ink was applied to the gas diffusion layer (GDL, Freudenberg H14C7) surface by spraying method. Spraying was performed several times until Pt loading of 0.3 mg. cm^-2 was obtained. Sprayed GDEs (anode and cathode with 25 cm² area) were hot pressed onto Nation® 115 membranes at 135 °C and 2 MPa for 5 min after 10 min pre heating step at 135 °C without applying pressure. [0049] For the electrode performance tests, a Scribner Associates 850e Fuel Cell Test

Station was used. The fuel cell tests were performed in a fully humidified atmosphere at 80 °C with 500 cc min ¹ of Fh and air. The experiments shown Figures 3, 4 and 5 were conducted using 5 cycles with a ratio of 3:3 (at 0,8V 180sec- 0,6V 180sec - 0,4V 180sec - 0,6V 180sec - 0,8V 180sec) and then a final cycle was made with different gases stoichiometry (1.2:2, FteiCh) the Fuel cell was maintained at 80°C with a percentage humidity 100%HR at a back pressure of 1.5bar.

Claims

1) A composition for use in fuel cells, the composition comprising: a plurality of catalyst-functionalised graphene sheets; and one or more spacer particles; characterised in that the spacer particles partially disrupt the co-ordination between the graphene sheets; and wherein the spacer particles comprise one or more metals.

2) A composition according to claim 1, wherein the catalyst-functionalised graphene comprises one or more catalytic materials selected from: platinum, palladium, copper, titanium, zinc, rhodium, osmium, gold, silver, nickel, iridium, ruthenium, cobalt or combinations thereof.

3) A composition according to claim 1 or claim 2, wherein the catalytic material comprises platinum.

4) A composition according to any of claims 1 to 3, wherein the graphene sheets have a surface area in the range of 5 - 5000 m² g ¹.

5) A composition according to any preceding claim, wherein the one or more metals are selected from: Ti, W, Mo, Fe, Cu, Zn, Zr, Ce, Al, Sm, Y, Mn, Co or combinations thereof.

6) A composition according to any preceding claim, wherein the spacer comprises metal oxides, metal carbides or combinations thereof.

7) A composition according to claim 6, wherein the spacer comprises: T1O2, M02C, Fe304, ZNFe₂04, ZnO, Zr02, ZrP, CeCh, AlCeCh, SmCh, SnCh, Y2O3, AI2O3, MnO, M^h2q3, C03O4 or combinations thereof.

8) A composition according to claim 7, wherein the spacer comprises: T1O2, Fe304, ZrCh, Ce02, AI2O3, C03O4 or combinations thereof.

9) A composition according to claim 8, wherein the spacer comprises PO2.

10)A method of making the composition according to any preceding claim, comprising the steps of: a) coating one or more graphene sheets with catalytic materials; and b) adding the coated graphene sheets of step a) to a spacer solution. 11) A method according to claim 10, comprising the steps of: a) preparing an alkaline solution of catalytic material nanoparticles; b) adding graphene sheets to the catalyst solution of step a); c) lowering the pH so as to provoke adsorption of said catalytic material nanoparticles to the graphene sheets; d) extracting the catalyst-functionalised graphene sheets from solution; and e) adding the catalyst-functionalised graphene sheets to a spacer solution.

12)An electrode comprising the composition according to any one of claims 1 to 9.

13)An electrode according to claim 12, wherein the electrode is a cathode.

14)A fuel cell comprising the electrode according to claim 12 or 13.

15)A fuel cell according to claim 14, wherein the fuel cell is a hydrogen or methanol fuel cell.

16)A fuel cell according to claim 14 or 15, wherein the fuel cell is an acidic fuel cell.

17)A fuel cell according to any of claims 14 to 16, wherein the fuel cell is a proton exchange membrane fuel cell.

18) Use of a composition according to any one of claims 1 to 9, as an electrocatalyst.

19)Use of a composition according to claim 18, as an anodic electrocatalyst.

20) Use of the electrode according to claim 12 or 13 or the fuel cell according to any of claims 14 to 17, in the generation of electricity.

21)Use of a composition according to any one of claims 1 to 9 in one or more of the following reactions: a reduction of NO_x; an oxidation of CO to CO2; an oxidation of hydrocarbons to CO2 and water; a hydrogen oxidation reaction; an oxidation reduction reaction; a hydrogen evolution reaction; an oxygen evolution reaction; the chlor-alkali process; nitric acid production; monoethylene glycol synthesis; hydrogenation and dehydrogenation reactions; preparation of anti-microbial coatings; and reinforced fibre glass manufacture. 22) Use of a composition according to any one of claims 1 to 9: as an automotive catalyst; electrolyser; supercapacitor; battery or sensor.