Hydrogen storage material

Abstract

A fuel cell 100 comprises a super structure of composite particles with a scaffold of coalesced carbon nanofoam particles, and where the scaffold is coated with a coating comprising N-doped graphitic

Description

Field 5 The present disclosure relates to a hydrogen storage material for a fuel cell, and in particular to a fuel cell comprising a hydrogen storage material. In particular, the present disclosure relates to a fuel cell configured to operate in both a redox mode and a regenerative mode. The present disclosure also relates to a fuel cell having a fuel storage material integral to the fuel cell and may therefore comprise a fuel cell / based 10 energy storage device. The present disclosure also relates to methods of forming said fuel storage material. Background 15 Conventional electrochemical fuel cells convert fuel and oxidant into electrical energy and a reaction product. A typical layout of a conventional fuel cell comprises a solid polymer ion transfer membrane that is sandwiched between an anode and a cathode. The polymer membrane allows protons to traverse the membrane but blocks the passage of electrons. Typically, the anode and the cathode are both formed from an 20 electrically conductive, porous material such as porous carbon, to which small particles of platinum and / or other precious metal catalyst are bonded. The anode and cathode are often formed at the respective adjacent surfaces of the membrane. This combination is commonly referred to as the membrane-electrode 25 assembly, or MEA. Typically, the polymer membrane and porous electrode layers are sandwiched between flow plates. The flow plates, in a conventional fuel cell, provide for the delivery of reactants to the anode and the cathode and the removal of reaction products. The fuel 30 cell may include porous gas diffusion layers fabricated so as to ensure effective diffusion of gas to and from the anode and cathode surfaces as well as assisting in the management of water vapour and liquid water. Because the voltage produced by a single fuel cell is quite low, conventionally multiple 35 cells are connected in series with the electrically conductive, flow plate on the cathode side of one cell being placed in electrical contact with the adjacent flow plate on the anode side of the next cell. 23 04 25 The present invention is directed to providing improvements in the design of a fuel cell and of a fuel cell stack formed of such fuel cells. Summary 5 The present disclosure relates to a composite material comprising a superstructure of coalesced (N-doped) carbon nanofoam particles that are coated with an N-doped graphitic carbon material, which finds particular use as a fuel storage material. 10 A composite material comprising a superstructure of composite particles, wherein said superstructure comprises: a scaffold of coalesced carbon nanofoam particles; and a coating on the scaffold, said coating comprising N-doped graphitic carbon; wherein the carbon nanofoam particles may optionally be N-doped. 15 According to a second aspect of the present disclosure if provided a fuel storage material comprising a composite material of the first aspect of the disclosure and a proton conducting polymeric material. 20 According to a third aspect of the present disclosure there is provided a fuel cell comprising the fuel storage material of the second aspect of the disclosure as part of or adjacent to an electrode to provide, at least in part, said fuel to the electrode when operating in a redox mode. 25 While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that other embodiments, beyond the particular embodiments described, are possible as well. All modifications, equivalents, and alternative embodiments falling within the scope of the appended 30 claims are covered as well. The above discussion is not intended to represent every example embodiment or every implementation within the scope of the current or future claim sets. The figures and Detailed Description that follow also exemplify various example embodiments. Various 35 example embodiments may be more completely understood in consideration of the following Detailed Description in connection with the accompanying Drawings. Brief Descriotion of the Drawings 23 04 25 One or more embodiments will now be described by way of example only with reference to the accompanying drawings in which: 5 Figure 1 shows an example embodiment of a fuel cell and schematically shows a fuel cell stack formed of such fuel cells; and Figures 2a and 2b show SEM micrographs of the N-doped carbon nanofoam material formed in Example 1. Figures 3a and 3b show TEM micrographs of the composite material. 10 Detailed Description The disclosure provides a composite material and fuel cells in various arrangements which contain the composite material. The composite material comprises a 15 superstructure of composite particles, wherein said superstructure comprises a scaffold of coalesced (N-doped) carbon nanofoam particles and a coating on the scaffold, said coating comprising N-doped graphitic carbon. The scaffold of carbon nanofoam particles itself is optionally N-doped (also referred to as (N-doped) carbon nanofoam). The disclosure also provides various examples of the composite material in different 20 arrangements that find various uses, particularly as a fuel storage material in a fuel cell, particularly a fuel cell that can operate in conventional redox mode and in regenerative mode. Particularly preferred types (N-doped) carbon nanofoam material that finds use in examples of the disclosure will be described in more detail below. 25 Example embodiments of a fuel cell will be described. In one or more embodiments, the fuel cell may be configured to operate in both a conventional redox mode, in which a fuel and an oxidant is consumed to generate an electric current and one or more reaction products, and in a regenerative mode, in 30 which a potential difference is applied to the fuel cell and at least one of the one or more of the reaction products are electrolysed to form said fuel. Thus, one or more example embodiments of the fuel cell comprise a reversible fuel cell. In one or more examples, one or more catalyst layers are provided to enable operation in said redox mode and said regenerative mode. 35 In one or more embodiments, the fuel cell may include a fuel storage material as a structure or layer with, i.e., alongside or forming part of, an electrode of said fuel cell, thereby providing a store of fuel within said fuel cell. In one or more examples, the 23 04 25 fuel storage material is provided between first and second plates that contain an active region of said fuel cell. In one or more examples, the fuel is protons and fuel storage material is configured to 5 store said fuel. In one or more examples, the fuel storage material is electrically connected to an electrode. 10 In one or more examples, the fuel storage material comprises a composite material comprising a superstructure of composite particles, wherein said superstructure comprises: a scaffold of coalesced (N-doped) carbon nanofoam particles; and a coating on the scaffold, said coating comprising N-doped graphitic carbon; 15 and a proton conducting polymeric material, as will be described below. It will be appreciated that the fuel cell may be configured to include said fuel storage material without being configured to operate in said redox and regenerative modes. For example, the fuel cell may be configured to operate only in the regenerative mode 20 and thereby function to store fuel in the fuel storage material for extraction. It will be appreciated that reference to the "fuel cell" can also be understood to refer to a stack of fuel cells given that, generally, the form of the fuel cell is replicated throughout the stack. 25 Figure 1 shows an example fuel cell 100 according to an aspect of the disclosure. The fuel cell 100 comprises a polymer electrolyte membrane 101 or "PEM". The PEM 101 comprises a semipermeable membrane and may be configured to conduct protons while acting as an electronic insulator and a reactant barrier. 30 The first plate 104 is arranged adjacent the first electrode 102, such as directly adjacent. The second plate 105 is arranged adjacent the second electrode 103, such as directly adjacent. In one or more examples, the first plate includes flow channels (not shown in figure 1) formed in a surface 106 thereof facing the first electrode 102. 35 The flow channels may be configured to receive a fluid, such as an oxidant, from one or more fluid inlets (shown schematically at 107) and distribute that fluid over the surface of the first electrode 102. 23 04 25 Each plate 104, 105 may include a current tab 112, 113 through which an electric current may flow during use. The fuel cell 100 may include one or more first catalyst layers 114, 115 between the 5 first plate 104 and the polymer electrolyte membrane 101. The one or more first catalyst layers may be configured to provide an active site for catalytic activity for one or both of an oxygen reduction reaction (ORR) and an oxygen evolution reaction (OER). Suitable catalytic materials for use in the catalyst layers are described in more detail below. 10 In one or more examples, an OER catalyst layer may be provided at a side 114 of the first electrode facing the first plate 104. In one or more examples, an ORR catalyst layer may be provided at a side 115 of the first electrode facing the PEM 101. 15 In this and one or more examples, the first electrode 102 is porous and allows fluids to pass through the electrode to the PEM 101. The fuel cell 100 may include one or more second catalyst layers 116, 117 between the second plate 105 and the polymer electrolyte membrane 101. The one or more 20 second catalyst layers may be configured to provide an active site for catalytic activity for one or both of a hydrogen reduction reaction (HRR) and a hydrogen evolution reaction (HER). In one or more examples, an HER catalyst layer may be provided at a side 116 of the 25 second electrode facing the second plate 105. In one or more examples, an HRR catalyst layer may be provided at a side 117 of the second electrode facing the PEM 101. Suitable catalytic materials for use as HER and HRR catalysts are described in more 30 detail below. In the present and one or more examples, the fuel cell 100 is configured to operate in a redox mode and a regenerative mode. In the redox mode the fuel cell 100 is configured to be provided with a fuel to the second electrode 103 and provided with 35 an oxidant, such as oxygen from air, to the first electrode 102 to generate an electric current between the first and second electrodes 102, 103 and a reaction product at the first electrode 102. 23 04 25 In a hydrogen based fuel cell, the fuel comprises hydrogen, the oxidant comprises oxygen from air or an oxygen source, and the reaction product comprises water. In the regenerative mode the fuel cell is configured to be provided with the reaction 5 product, such as water in the case of a hydrogen based fuel cell, to the first electrode 102. A potential difference is to be provided between the first and second electrodes 102, 103 from an electrical power source (not shown) thereby generating said fuel, e.g., hydrogen, at the second electrode 103. 10 The fuel cell 100 may include a fuel storage material as part of or adjacent to the second electrode 103 to provide, at least in part, said fuel to the second electrode 103 in the redox mode and / or store, at least in part, said fuel generated at the second electrode 103 in the regenerative mode. 15 In this and one or more examples, the second electrode 103 is formed of said fuel storage material. Thus, the fuel storage material may be an integral part of the second electrode 103. In other examples, the fuel storage material may comprise a distinct layer separate 20 from the second electrode 103 but arranged adjacent to the second electrode 103 within the fuel cell 100 i.e., at least partly between the first and second plates 104, 105. In one or more examples, the PEM is bonded to a gas diffusion layer (such as a carbon 25 based conductor, e.g., carbon paper, carbon cloth or carbon fibre, preferably carbon paper), with the other side of the gas diffusion layer being coated with HER catalyst. This catalytic layer is adjacent to the anode, allowing facile transfer of electrons. This configuration has been found to be advantageous when the anode acts as a fuel 30 storage material (for instance the N-doped graphitic coated (N-doped) carbon nanofoam material and a proton conducting polymeric material described herein). In such configurations, the hydrogen evolved by the HER is also captured. If the HER is coated directly on the anode, it has been found that hotspots may occur leading to reduced efficiency of hydrogen storage. 35 In one or more examples, the fuel cell 100 may be part of a fuel cell stack 121 comprising a plurality of fuel cells arranged in series with one another. In figure 1, box 23 04 25 122 schematically represents an adjacent fuel cell to the fuel cell 100 in the fuel cell stack 121. The adjacent fuel cell 122 is substantially identical to fuel cell 100. Figure 1 shows a fuel cell having that capability, by virtue of the provision of appropriate catalyst layers to operate in both a redox mode and a regenerative mode, as well as having an integral fuel storage material. However, in one or more examples only some of the above structures may be provided. In an example, the fuel cell 100 may be configured to include said fuel storage material but only operate in the redox mode. Thus, in one or more examples, only said catalyst(s) that act to promote said redox reaction may be provided. In a further example, the one or more first catalysts may not be provided and the one or more second catalysts may be provided. In such an example, the fuel storage material of the second electrode 103 may be "recharged" from an external fuel source rather than by operation in the regenerative mode. Thus, during "recharging", gaseous hydrogen may be provided to the second electrode 105 via the flow channels of the second plate 105 and the one or more second catalyst layers 117, 116 may provide for reduction of said gaseous hydrogen to protons for storage in the fuel storage material. In a further example, the fuel cell 100 may be configured to include said fuel storage material but only operate in the redox mode. It will be appreciated that the first and second catalyst layers act to improve the reaction rate of the fuel cell, but in some application, this may not be required. Thus, in one or more examples, the fuel cell 100 may include said fuel storage material but not one or more of said first and second catalyst layers 114, 115, 116, 117. In a further example, the fuel cell 100 may be configured to only operate in the regenerative mode. Thus, the one or more first catalyst layers 114 may be provided but the one or more second catalyst layers 116, 117 may be absent. Some of the specific materials that may be used in the fuel cell are described in more detail below. (N-doped) carbon nanofoam material The present disclosure provides an (N-doped) carbon nanofoam material having excellent properties as a component in composite materials and fuel storage materials in fuel cells. 23 04 25 As used herein, the term "(N-doped)" means the material is optionally N-doped. Thus, "(N-doped) carbon nanofoam material" denotes a carbon nanofoam material that may optionally be N-doped. 5 As used herein, "Cnf" may be used to denote a carbon nanofoam material. As used herein, "Cnf-Nx" may be used to denote an N-doped carbon nanofoam material. 10 Carbon materials provide useful electrocatalysts due to their high surface area, high conductivity and cost. Various types of carbon materials suitable for use as electrocatalysts are disclosed in X. Wang etal.,Adv. Energy Mater., 2017, 7, 1700544. Non-metal atoms such as N, P, S and B can be doped into the carbon structure, 15 resulting in multiple possible configurations of doped carbon material. Being more electronegative than carbon, these heteroatoms make neighbouring carbon atoms electron deficient, thereby promoting oxygen adsorption on the carbon nanostructure. Doped carbon structures may take various forms, including nanotubes, sheets or particulate carbon materials. 20 Of these doping atoms, N is advantageous as it provides a stable material having the desired balance of properties. Furthermore, N-doping increases the hydrogen storage properties of a fuel storage material comprising a carbon nanofoam of the disclosure. In contrast, doping with S and P typically acidifies the carbon leading to a material with 25 higher pH sensitivity. The (N-doped) carbon nanofoam material of the present disclosure may be characterised as a scaffold of coalesced (N-doped) carbon nanofoam particles,, said particles having a diameter of from 0.005 pm to 25 pm. 30 Preferably, the nanofoam particles are from 0.01 to 15 pm, preferably from 0.01 to 5 pm, more preferably from 0.01 to 2 pmin diameter. The diameters of the nanofoam particles may be measured by SEM. Typically, in such a process the largest dimension of the particle is measured. 35 The average diameter may be calculated by taking the mean value of the measurement of the largest dimension of ten separate nanofoam particles. 23 04 25 The (N-doped) carbon nanofoam material of the disclosure is a continuous, or semi-continuous, interconnected superstructure of coalesced (N-doped) carbon nanofoam particles. This superstructure may act as a scaffold or support for the N-doped graphitic carbon in the composite material of the disclosure. 5 In an example, the scaffold has a tortuous path of open pores at least 3 times the average diameter of the nanofoam particles, preferably at least 5 times the average diameter of the nanofoam particles, for instance from 5 to 100 times, preferably from 5 to 50 times the average diameter of the nanofoam particles. 10 The open pores typically have an irregular shape, as shown in Figure 2b. The pore size can be determined by SEM, with the average size of any given pore being defined as the mean of the largest and smallest dimension of that pore as determined by SEM. 15 The average size of the pores of the scaffold will vary depending on the size of the particles of the nanofoam particles, and are typically from 10 to 100 pm, such as for nanofoam particles being around 1pm. In an alternative embodiment, the average size of the pores of the scaffold are typically 20 from 0.2 to 2 pm. The mean pore size can be determined by the mean of 10 average pore sizes, as determined by SEM. 25 In an example, the (N-doped) carbon nanofoam material has a density of below 300 mg / cm3, typically from 50 to 200 mg / cm3 and preferably from 50 to 150 mg / cm3. The density of the (N-doped) carbon nanofoam material may be measured by weighing the bulk material and then correlating for the mass of the average element density. 30 Methods for making carbon nanofoams are known in the art, for instance in Sattler et al., Carbon 95 (2015), pp434-441. An example method of forming an (N-doped) carbon nanofoam material comprises: 35 i. forming a mixture of sugar, water and hydrocarbon mediator; ii. heating said mixture to form a carbon nanofoam; and 23 04 25 iii. optionally heating the carbon nanofoam in the presence of an acidic nitrogen source (e.g. nitric acid) to form an N-doped carbon nanofoam. Suitable sugars to use include monosaccharides, disaccharides and trisaccharides, for 5 instance sucrose, glucose or fructose, with sucrose being preferred. The mixture of sugar and water is highly concentrated, namely at least 3 molar, typically at least 4 molar such as about 5 molar. Such high concentrations will typically require heating and vigorous stirring to fully dissolve the sugar, typically from 50°C to 10 85°C, for instance from 60°C to 80°C. Typically, the concentrated sugar solution is cooled before the hydrocarbon mediator is added, for instance cooled to below 50°C. 15 Suitable hydrocarbon mediators include aromatic hydrocarbons such as pyrene, chrysene, benz[a]anthracene, fluoranthene, anthracene, naphthalene, benzene and hexane, with anthracene, naphthalene and benzene being preferred and naphthalene being most preferred. 20 Typically, only a small amount of hydrocarbon mediator (e.g., naphthalene) is required. For instance, the ratio of hydrocarbon mediator (e.g., naphthalene) to sugar (e.g., sucrose) is typically from 1:25,000 to 1:75,000, or 1:50,000 to 1:65,000. Step ii requires heating the mixture to form a nanofoam. The mixture is heated at a 25 temperature and for a time sufficient to carbonise the sugar to form a particulate material. Suitably, the mixture is heated at a temperature of from 100°C to 600°C for 30 minutes to 24 hours. Heating to a higher temperature usually requires a shorter heating time. 30 For instance, the mixture may be heated to 500°C for 1 hour. Alternatively, the mixture may be heated to 155°C for 5 hours. Heating the mixture for longer is of course possible, but this is usually not required. Preferably, the mixture is heated at a temperature of from 350°C to 600°C for 30 35 minutes to 3 hours. Alternatively, the mixture is heated at a temperature of from 100°C to 300°C for 4 hours to 12 hours. 23 04 25 The heating step carbonises the material to form a nanofoam. As such, the heating is typically carried out in a suitably inert vessel, for instance a Teflon coated hydrothermal reactor. 5 The heating step is preferably carried out in a sealed reactor. The resultant nanofoam may optionally be comminuted, for instance by milling. Milling may be carried out in a ball mill. 10 The resultant material is a scaffold of coalesced (N-doped) carbon nanofoam particles. The (N-doped) carbon nanofoam particles are typically mesoporous, i.e., having pores of 2 nm to 50 nm. The nanofoam particles are bound together by covalent interactions, resulting in a scaffold that is surprisingly retained even under mechanical stresses such as during milling. 15 The pore size of the mesopores may be determined by tunnelling electron microscopy. In such a process, the material may be coated with a metal such as titanium by sputtering. After coating, the pore structure can be observed using a tunnelling electron microscope, with the pore size being determinable from the image produced. 20 Although the methodology provides an image of the surface, it is evident from the bulk reactivity of the material that the pores extend beneath the surface into the structure of the carbon. The material is therefore best described as a mesoporous (N-doped) carbon nanofoam. 25 The nanofoam particles may vary in shape, and the shape can be dependent on the sugar and hydrocarbon mediator that are used. For instance, glucose and naphthalene form cube-like structures. Sucrose and naphthalene are preferred and give rise to approximately spherical 30 particles. The nanofoam particles are typically from 0.01 to 15 pm, preferably from 0.01 to 5 pm, more preferably from 0.01 to 2 pm in diameter. 35 Step iii. comprises N-doping by heating the carbon nanofoam with an acidic nitrogen source, such as nitric acid (HNO3), nitrous acid (HNO), hyponitrous acid (H2N2O), or mixtures thereof, with nitric acid being preferred. 23 04 25 Typically, the carbon nanofoam is heated to at least 80°C for at least 2 hours, for instance to at least 90°C for at least 4 hours, preferably 95°C to 115°C for at least 4 hours. 5 The heating is typically carried out in a suitable acid resistant pressure vessel, for instance a Teflon hydrothermal reactor. The acidic nitrogen source (e.g. nitric acid) should be sufficiently concentrated to ensure sufficient levels of N-doping. Suitable concentrations (e.g. of nitric acid) include 10 from 3 molar to 10 molar, preferably from 4 molar to 8 molar. Treatment of the carbon nanofoam particles with nitric acid or an alternative acidic nitrogen source introduces N-doping into the structure, forming a mixture of pyridinic-N, pyrrolic-N and graphitic-N sites. However, when nitric acid, or an alternative acidic 15 nitrogen source, is used, the acid conditions additionally form carboxylate groups at the surface of the material. Moreover, pitting of the surface can occur, resulting in loss of some of the mesoporous structure. The conditions therefore need to be controlled to provide the desired amount of doping while avoiding too much degradation of the mesoporous structure. The process is however mild enough to ensure that the scaffold 20 of coalesced particles is retained. Typically, the surface pore sizes are around 2 to 10% larger after treatment with nitric acid, or alternative acidic nitrogen source. 25 Typically, the N content of the resultant material is from 0.1 to 8 wt%, for example from 0.5 to 6 wt%, or from 1 to 5 wt%. Preferably the N content of the resultant material is 2 wt% or more. The surface area of the resultant material is typically from 200 to 3500 m2 / g, preferably 30 400 to 3000 m2 / g, preferably 800 to 2500 m2 / g, preferably 800-2000 m2 / g. For example, 900 to 2000 m2 / g, preferably 900 to 1500 m2 / g. The surface area may be measured by BET isotherm, for instance at 77 K using nitrogen. 35 The above process is an exemplary way of forming the N-doped carbon nanofoam. Alternative methods are possible. For instance, the mesoporous structure is obtained by heating the mixture of sugar, water and hydrocarbon mediator. If a nitrogen source 23 04 25 is included in the mixture, this can lead to an N-doped carbon nanofoam being formed without the need for step iii (treatment with the acidic nitrogen source). Composite material 5 The disclosure additionally provides a composite material comprising a superstructure of composite particles, wherein said superstructure comprises a scaffold of coalesced (N-doped) carbon nanofoam particles and a coating on the scaffold, said coating comprising N-doped graphitic carbon. The scaffold of coalesced (N-doped) carbon 10 nanofoam particles is as described above, and may optionally themselves be N-doped, for instance as formed by treatment with an acidic nitrogen source such as nitric acid. The N-doped graphitic carbon coating may be formed by treating the scaffold of coalesced nanofoam particles with a structural protein to coat the scaffold of (N-doped) 15 carbon nanofoam with an N-doped graphitic carbon. This step can be carried out on a scaffold of (N-doped) carbon nanofoam particles (e.g. as formed following treatment with an acidic nitrogen source), or on the scaffold of coalesced (N-doped) carbon nanofoam particles (i.e. without N-doped the scaffold material). 20 During formation, the scaffold of (N-doped) carbon nanofoam provides a template for growth of the N-doped graphitic phase. The N-doped graphitic phase is typically located on the surface of the (N-doped) carbon nanofoam scaffold, for example on the external surfaces and internal surfaces, such as within the open pores. 25 The composite material typically retains the same overall structure as the coalesced particles of (N-doped) carbon nanofoam scaffold used as the template prior to coating with N-doped graphitic carbon phase. Consequently, the composite material may be described as comprising composite 30 particles. The composite particles therefore comprise a continuous, or semi-continuous, scaffold of (N-doped) carbon nanofoam that is coated with N-doped graphitic carbon. The N-doped graphitic phase is typically located on the surface of the (N-doped) carbon 35 nanofoam scaffold, for example on the external surfaces and internal surfaces, such as within the open pores. 23 04 25 The composite particles are coalesced via the (N-doped) carbon nanofoam scaffold to form the composite material superstructure. That is, the (N-doped) carbon nanofoam scaffold interconnects the composite particles to form a superstructure. 5 The coalesced superstructure of composite particles may also comprise N-doped graphitic carbon on the available surfaces. In the context of this disclosure, "N-doped graphitic carbon" means graphite-like carbon which contains nitrogen atoms in the graphitic plane. Such nitrogen atoms 10 form graphitic (i.e. replacing a carbon and having three bonds), pyridinic (i.e. replacing a carbon and having two bonds, forming a six membered ring), and pyrrolic sites (i.e. replacing a carbon and having two bonds, forming a five membered ring) within the graphitic plane. Pyridinic and pyrrolic sites within the graphitic plane cause defects or open sites within the plane, owing to the reduced number of atoms. 15 Preferably, the composite particles are from 0.005 pm to 25 pm in diameter. For example, the composite particles are from 0.01 to 15 pm, for instance from 0.01 to 5 pm, or from 0.01 to 2 pm in diameter. 20 Smaller particles have a much higher surface area and are typically preferred. Preferably, the composite particles have a diameter of 100 nm or less, such as 50 nm or less, or 30 nm or less, for instance 25 nm or less, or 20 nm or less. Preferably the composite particles have a diameter of 10 to 30 nm. 25 The composite particles tend to aggregate and form clusters. Typically, the clusters have a diameter of from 1 to 10 pm, for instance from 2 to 8 pm, or 3 to 6 pm. For instance, when the composite particles are around 20 nm, the aggregate clusters 30 may have a diameter of around 3 to 6 pm. The diameters of the composite particles and clusters may be measured by TEM. Typically, in such a process the largest dimension of the particle / cluster is measured. 35 Formation of the composite material typically involves: - heating the (N-doped) carbon nanofoam material with a structural protein in a reduced oxygen environment. 23 04 25 Thus, an example method of forming the composite material comprises: a. forming a mixture of sugar, water and hydrocarbon mediator; 5 b. heating the mixture to form a carbon nanofoam material; c. optionally heating the carbon nanofoam in an acidic nitrogen source (e.g. nitric acid) to form an N-doped carbon nanofoam; d. optionally comminuting the (N-doped) carbon nanofoam material; e. heating the (N-doped) carbon nanofoam material with a structural protein in a 10 reduced oxygen environment to form a composite material; f. optionally treating the composite material with a pitting agent to form an activated composite material; and g. optionally comminuting the composite material. 15 Steps e. to g. may be repeated as necessary until the required amount of N-doped graphitic regions are obtained, and the required active surface area is achieved. Steps a., b. and c. are identical to step i., ii., and iii. of the example method for forming the (N-doped) carbon nanofoam material. 20 Step d. is optional but often done to ensure a more consistent material is used as the scaffold for the formation of N-doped graphitic carbon. Suitable comminuting methods include milling, for instance ball milling. 25 Step e. involves heating the resultant nanofoam with a structural protein in a reduced oxygen environment to form a N-doped graphitic coating on the (N-doped) carbon nanofoam. The reduced oxygen environment can be achieved by any means, although it is 30 preferred to use an inert atmosphere (such as argon gas) or vacuum. The mixture is heated to a high temperature for a relatively short period. Prolonged heating at the temperatures required to effect N-doping is possible, though usually not necessary. 35 Typically, step e. involves heating at a temperature of at least 400°C for at least 10 minutes, for instance from 450°C to 900°C from 10 minutes to 3 hours, preferably from 500 to 600°C from 30 minutes to 90 minutes. 23 04 25 Heating at a higher temperature such as over 1000°C will graphitize the structural protein, leading to formation of large volumes of graphite. The temperatures used in step e. involve a lower temperature, resulting in partial graphitisation. 5 The resultant material contains N-doped graphitic carbon coated over the (N-doped) carbon nanofoam, for example on the external surfaces and internal surfaces, such as within the open pores. 10 Optional step f, involves treating the resultant material with a pitting agent to form an activated composite material. In the context of the disclosure, a "pitting agent" refers to a substance that causes activation of the composite material by e.g., increasing the surface area. For instance, step f. may create pits or indentations in the surface of the composite material, providing a larger active surface area. 15 A composite material that has been pitted may be described as an "activated composite material". Suitable pitting agents include alkali or alkaline earth carbonate, alkali or alkaline earth 20 hydroxide, such as NaOH, KOH, NazCOs, K2CO3, or mixtures thereof. Alternatively, acidic pitting agents such as H2SO4, HCI, HNO3 H3PO4 and mixtures thereof may be used. 25 Preferably, the pitting agent is an alkali or alkaline earth carbonate. When an alkali or alkaline earth carbonate pitting agent is used, regular, consistent pitting is achieved. Typically, alkali or alkaline earth carbonate pitting agents increase the number of mesopores within the material, wherein the mesopores have smooth or rounded edges. Rounded mesopores are particularly advantageous for hydrogen storage via 30 physisorption. In contrast, when an acidic pitting agent is used, the pitting is more random and the newly formed indentations may have jagged edges have an irregular shape. 35 Preferably, the pitting agent is K2CO3. The pitting agent should be included in an amount sufficient to increase the activate the surface, which typically required the pitting agent to be in (weight) excess. For 23 04 25 example, the weight ratio of composite material to pitting agent may be 1:1.5 or more, for instance, 1:2 to 1:10, 1:2.5 to 1:8, or 1:3 to 1:5. Preferably the weight ratio of composite material:pitting agent is 1:3. 5 Step f. should be carried out in a reduced oxygen environment, at high temperature. Typically, step f. is be carried out at a temperature of at least 600°C for at least 10 minutes, for instance, 650-1000°C for 10 minutes to 3 hours, preferably from 750-850°C for 1 hour. 10 The optional step g. may be carried out by milling. This step results in any loosely bound graphitic materials breaking away to leave a superstructure of composite particles comprising a scaffold of coalesced (N-doped) carbon nanofoam and a coating of N-doped graphitic.. 15 The N-doped graphitic material is preferably covalently bound to the scaffold. Typically, the N content of the resultant material is from 0.1 to 8 wt%, for example from 0.5 to 6 wt%, or from 1 to 5 wt%. Preferably the N content of the resultant material is 2 wt% or more. 20 The surface area of the resultant material is typically from 200 to 3500 m2 / g, preferably 400 to 3000 m2 / g, preferably 800 to 2500 m2 / g, preferably 800-2000 m2 / g. For example, 900 to 2000 m2 / g, preferably 900 to 1500 m2 / g. 25 When a pitting agent is used, the surface area of the resultant material may be from 25% to 50% higher than for the same material before pitting. The amount by which the surface area is increased will depend on the volume / concentration of pitting agent, the temperature at which pitting is carried out, the length of the pitting step, and the type of pitting agent used. 30 Any suitable structural protein may be used, such as keratin or collagen, with keratin being preferred. The structural protein should preferably be dried and in a form to allow intimate mixing with the carbon particles, such as in a powdered form. 35 Suitable collagen materials that can be used include gelatine. Any source of keratin may be used, including hair, nails, feathers, horns, claws, baleen or hooves. 23 04 25 Preferably, the structural protein is avian feathers. Avian features are highly porous and it has been found that the resultant material retains porosity after carbonisation to form the N-doped graphitic coating. 5 Any suitable avian features can be used, with farmed birds such as chicken, turkey, duck and goose being particularly suitable due to their availability. Down feathers are preferred, particularly goose down and duck down. 10 Typically, the avian feathers are mixed with the (N-doped) carbon nanofoam in a weight ratio of 2:1 to 1:4 of nanofoam to feathers, preferably a weight ratio 3:2 to 1:3. 15 Following formation of the coating layer, the resultant material can optionally be comminuted, for instance by milling. OER, ORR, HER, HRR Catalytic Materials 20 Various types of catalytic materials are known for use in fuel cells. For instance, X. Wang etal.,Adv. Energy Mater., 2017, 7, 1700544 and C. Zhang etal., Front. Energy., 2017, 11, 268-285 and N. Alonso-Vante et al., catalysts, 2018, 8, 559 provide an overview. 25 In some embodiments, a bifunctional catalyst may be used in the fuel cell. Bifunctional catalysts are catalysts that have the ability to catalyse two different types of reactions. In some instances, the ORR. and the OER may be catalysed by the same bifunctional catalyst. 30 In some instances, the OER and HER may be catalysed by the same bifunctional catalyst. In instances where a bifunctional catalyst is used, a heterojunction may be employed 35 to separate the positive and negative charges in an organic material. Noble metal-based electrocatalysts (Pt, Ir and Ru-based) are well-known to catalyse ORR, OER and HER reactions. 23 04 25 Platinum group metals are known for use as electrocatalysts and the most commonly used in electrocatalysis platinum. However, due to concerns with durability platinum usage worldwide, research has been done into new platinum group metal alloy 5 nanoparticles supported on a conductive substrate, such as, carbon, carbon black, oxides, single-walled carbon nanotubes and carbon nanofibers. Such platinum group metal alloys can be described as Pt-M (wherein M = 3d transition metal) alloy nanoparticles. For example, wherein M is one or more of Ni, Co, Fe, Cu, 10 Pd, Rh, Ti, V, Cr, Mo, W and Re. For example, PtNis, PtxCo (wherein x = 2, 3, 5, 7 and 9), PtaCu, PtCu and PtCus. In some instances, ternary Pt-based systems may also be suitable catalysts. For example, catalysts that may be described as Pt-M-N, wherein M is as defined as above 15 and N is Fe, Cu, Ni or Co. For instance, Pt2CuNi, PtsCoNi, PtsFeNi and PtsFeCo. Transition metal-based catalysts are also known as suitable electrocatalysts for ORR, OER and HER. For example, Ti, V, Mn, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, or mixtures thereof based catalysts such as Mn, Co, Ni and Fe oxides. 20 Preferably, the transition metal is selected from Co, Fe, Ni, or mixtures thereof. Preferably, the transition metal is Co. 25 Suitable cobalt based catalysts include, but are not limited to, cobalt oxide, cobalt phosphides, cobalt halides, cobalt nitrates, cobalt chalcogenides (sulphide and selenides), Co-included layered double hydroxides, Co-N-C, Co-based single atoms, Co-MOFs (metal organic frameworks), cobalt carboxylates, Co-Nx / C and their composites. 30 Fuel Storage Material The disclosure additionally provides a fuel storage material that finds particular use in fuel cells, said fuel storage material comprising a proton conducting polymeric material 35 and composite material comprising a superstructure of composite particles, wherein said superstructure comprises: a scaffold of coalesced (N-doped) carbon nanofoam particles; and a coating on the scaffold, said coating comprising N-doped graphitic carbon.. 23 04 25 The (N-doped) carbon nanofoam material coated with N-doped graphitic carbon is preferably as set out herein. 5 The proton conducting polymeric material is typically capable of conducting protons at room temperature, i.e., at 25°C. By "capable of conducting protons" is meant a proton conductivity of greater than 10-3 S / cm, preferably greater than 10-2 S / cm. Of course, the polymer itself may have very 10 poor proton conductivity in its dry form. The proton conductivity of the polymeric material is measured on the hydrated and (if necessary) acidified polymer. The proton conducting polymeric material may be an acid doped hydrogel. 15 When a hydrogel is doped with a suitable acid, such as phosphoric acid or sulphuric acid, the resultant polymeric material displays very high proton conductivity. Suitable levels of acid dopant in the hydrogel are from 5 to 25 wt%, preferably from 10 to 20 wt%. 20 Suitable hydrogels are selected from polyvinyl alcohol, poly(meth)acrylate, collagen, gelatine and fibrin. Preferred hydrogel polymers are selected from poly(meth)acrylate and gelatine, with 25 polyacrylate being particularly preferred. The fuel storage material typically contains less than 15 wt% acid doped hydrogel, preferably from 0.1 to 12 wt%, more preferably from 0.2 to 10 wt%, more preferably from 0.5 to 8 wt%. 30 The proton conducting polymeric material may be a fluorinated acid polymer, preferably a fluorinated acid polymer as set out herein. Preferably, the fluorinated acid polymer in the fuel storage material has Formula X: (O-CF2CFR{3)a-O-CF2CFRf4SO:iE' (X) where each c is independently 0 or an integer from 1 to 3; n is at least 4; 5 Rd and Rf4 are independently selected from F, Cl or a highly- fluorinated alkyl group having 1 to 10 carbon atoms, a = 0, 1 or 2, and E5 is selected from hydrogen or a cation such as Li, Na, or K. 23 04 25 10 Preferably the fluorinated acid polymer in the fuel storage material comprises a perfluorocarbon backbone and the side chain represented by the formula -O-CF2CF(CF3)-O-CFzCF2SO3E5 15 where E5 is selected from hydrogen or a cation such as Li, Na, or K, Preferably, the fluorinated acid polymer in the fuel storage material has formula XI: --!CF,-CF AHCFj-OH-- o O-CF2CF(CF>)-O-CF-.CF-.SO,E5 (XI) 20 where each c is independently 0 or an integer from 1 to 3; n is at least 4; and E5 is selected from hydrogen or a cation such as Li, Na, or K. 25 The fuel storage material typically contains less than 5 wt% fluorinated acid polymer, for instance from 0.05 to 5 wt%, preferably from 0.1 to 4 wt%, more preferably from 0.1 to 3 wt%, more preferably from 0.2 to 2 wt%. In an example, a method of making the fuel storage material comprises: 23 04 25 forming a paste of composite material, proton conducting polymeric material and a dispersing agent, said composite material comprising a superstructure of composite particles, wherein said superstructure comprises a scaffold of coalesced (N-doped) carbon nanofoam particles and a coating on the scaffold, said coating comprising N-doped graphitic carbon ; pressing the paste into a compacted form; and drying the compacted form. Typically, the paste is formed using water as the dispersing agent. When the proton conducting polymeric material is an acid doped hydrogel, the forming step may comprise: forming a mixture of hydrogel-forming polymer, acid dopant and composite material ; lyophilising the mixture; and adding water for form a paste of lyophilised conducting polymeric material and composite material.. The lyophilising step increases the structural integrity of the hydrogel, allowing it to retain better proton conductivity when incorporated into the fuel storage material. Typically, the drying step involves heating the compacted form at a temperature high enough to facilitate removal of the dispersing agent, but low enough not to damage the proton conducting polymeric material. Suitable temperatures include from 50 to 250°C, such as from 100 to 200°C when fluorinated acid polymer is used as the proton conducting material. The heating may be carried out in a flowing air stream to facilitate removal of the dispersing agent. When acid doped hydrogel is used as the proton conducting material, it is usually preferred to avoid heating to a high temperature during the drying step, as these hydrogels tend to be less stable at higher temperatures. Preferably, the drying step comprises drying at a temperature no higher than 75°C. Optionally, after drying the material may be degassed, for instance in a vacuum furnace. 23 04 25 The fuel storage material may additionally comprise an Arrhenius acid to facilitate uptake and storage of protons. Any Arrhenius acid may be used, with suitable acids including sulphuric acid, phosphoric acid, and nitric acid. The Arrhernius acid added to the fuel cell may also be called an "polymer activating agent". 5 For hydrogel-based proton conducting materials, the acid is preferably phosphoric acid. For fluorinated polymeric sulfonic acid-based proton conducting materials, the acid is preferably sulphuric acid. 10 The material may be loaded with Arrhenius acid by soaking in a solution of the acid for a sufficient period (e.g., for at least 4 hours). Once loaded with the acid, the material can be dried to remove most of the water, 15 however it is beneficial to retain a low degree of hydration to ensure sufficient proton conductivity. Residual water within the material aids in transport and retention of hydrogen ions, which interact with the water to form hydronium ions. Typically, the fuel storage material contains at least 0.01 wt% water, preferably at 20 least 0.1 wt% water, for instance from 0.01 to 5 wt% water, preferably from 0.1 to 2 wt% water. Without wishing to be bound by theory, the N-doped graphitic carbon phase facilitates chemisorption of hydronium ions within the fuel storage material, with the nitrogen 25 sites (particularly the pyridinic and pyrrolic sites) able to hydrogen bond to the ions immobilising them on the surface of the material. By "hydronium ion" is meant protonated water, i.e. H3O+. The fuel storage material of the disclosure may store hydronium itself, or solvated forms of hydronium such as 30 HsO2+, H?O3+, HgO4+, or mixtures thereof. Charge balance is believed to be achieved by the negative charge being stored in the graphitic material, which is further facilitated and stabilised by the electronegativity of the nitrogen atoms and overall high conductivity of the material. 35 In the operating fuel cell, the released hydronium ions migrate to the PEM, with the protons passing through the PEM to the counter electrode where they react with oxygen to form water. 23 04 25 Without wishing to be bound by theory, the fuel storage material also stores hydrogen via physisorption within the mesopores of the (N-doped) carbon nanofoam. Thus, when the concentration of hydronium ions increases, it becomes less preferable to 5 store additional hydrogen as hydronium with the charge balance residing within the graphitic material. Instead, dihydrogen is formed, and once the pressure increases to a sufficient level (for instance above about 5 bar), this condenses inside the mesopores of the (N-doped) carbon nanofoam. Inside the mesopores, the hydrogen is in a pseudo-liquid state. The liquified hydrogen is affixed to the fuel storage material by 10 physical adsorption to the surfaces of mesopores. Typically, liquification of hydrogen occurs at high pressures (e.g. 300 bar), however, confinement liquification occurs within the mesopores of the (N-doped) carbon nanofoam, which facilitates liquification at a much lower pressure (e.g., around 5 bar). 15 N-doping of the carbon nanofoam further promotes physisorption due to the electronegativity of the N atoms promoting the formation of van der Waals interactions between the hydrogen and the N-doped carbon nanofoam. In order to increase hydrogen storage properties of the fuel storage material, an increase in the number of mesopores within the carbon nanofoam is beneficial, as well as increasing the degree 20 of N-doping. The dominant hydrogen storage mechanism within the fuel storage material depends on the temperature and pressure of the system. Typically, chemisorption dominates at pressures below 5 bar, and typically temperature below 80 °C, and physisorption 25 dominates at pressure of 5 bar and above, and typically at temperatures of 80 °C and above. However, it is common that hydrogen is stored via both chemisorption and physisorption simultaneously. Surprisingly, the fuel storage material is capable of storing hydrogen at levels of above 30 1 wt%, for instance above 1.5 wt%, or above 1.8 wt%, or even above 2 wt%. Protocols for measurements Calculation of Pore Size 35 To calculate pore diameters of micropore levels and smaller, the inventors have used the protocol set out in Kawazoe et al., J. Chern. Eng. Japan, 16 (6), 1983, 470-475. 23 04 25 The above protocol describes a method for the calculation of effective pore size distribution from adsorption isotherms. Calculation of the pore size distribution was done from N2 isotherms at 77 K. 5 For measurement of the N2 isotherms at liquid N2 temperature a sample (~0.3g) was put into a sample holder and degassed at 200°C and 10 5 Torr (1.33x10 3Pa) pressure for at least 48 hours. A Cahn electrobalance provided highly accurate mass measurement. For the measurement of pressure ULVAC ionization vacuum gauges and MKS Baratron sensors were used (pressure ranges 1.33xl0-6 - S.SSxlO^Pa; 10 1.33x10 1 - 105 Pa). To calculate pore volumes greater than 1.5nm, the inventors have used the following protocol: Dollimore, D. and G. R. Heal et al., J. AppL Chern., 14, 1964, 109-114. 15 The above protocol describes a method for calculating the pore size distribution from adsorption isotherms on porous solids. Herein, the total amount of nitrogen taken up at a pressure of 1 atmosphere and a temperature of 77K gave the total pore volume. With the model of cylindrical pores 20 the total pore volume was calculated using: l / 4*pi*d*d*l, where d is the mean pore diameter and I is the total length of the pores. 25 If the BET surface area measured the total surface area of the pores, the BET surface area S(BET) = pi*d*l. From the two equations I was eliminated and the average diameter d was calculated. 30 The Barrett-Joiner-Halenda (BJH) procedure assumes capillary condensation of the liquid nitrogen within the pores and calculates from the relative pressures and the amount of nitrogen taken up at a given relative pressure of the sorption isotherm taking into account the adsorbed layer of nitrogen and the capillary condensed nitrogen the pore size distribution. The adsorption and the desorption branch lead to different 35 pore size distributions. Therefore, the desorption branch was usually employed. Surface Area 23 04 25 Samples were treated at elevated temperatures (120°C) and reduced pressures for at least 8 hours before nitrogen sorption to remove any bound gases and adsorbed water from the materials. 5 The N2 sorption analysis may be performed using a Belsorp Mini (Bel Japan, Inc.) apparatus at 77K, using liquid gas for each respective test, and surface areas calculated using the Brunauer-Emmett-Teller (BET) theory using sorption data. Calculation of Density for Carbon Nanofoams 10 The following methods were used: Displacement density method: using water as the displacement medium, density is calculated at 22°C, latm of pressure and using the equation D = m / v (mass divided 15 by volume). TAP density method, as described by: • The International Pharmacopoeia, s.3.6. Bulk Density and Tapped Density of Powders, QAS11^450 FINAL (modified March 2012). The tapped density is an 20 increased bulk density attained after mechanically tapping a container containing the powder sample. Here, the tapped density is obtained by mechanically tapping a graduated cylinder containing the sample until little further volume change is observed. 25 The tapping can be performed using different methods. The tapped density is calculated as mass divided by the final volume of the powder. A mean average was subsequently taken of the two measurement methodologies. 30 Conductivity of the pulverized material samples Spin coating was used to prepare the material samples. The material samples were prepared in the same manner as the preparation steps for making electrodes. Namely, a silver foil in a solution containing the material samples and a 5% addition of binder. 35 If the resistance of the material samples was of a magnitude of kiloohms or more, a two-point probe was used. 23 04 25 The spin coated film is mounted in a metallic sample holder and a vacuum is created inside to get rid of moisture. 2-Point and 4-Point probe tests may be used. The conductivity of the samples that was measured was on average 0.4 S / cm to 100 S / cm depending on layer thickness and conductivity of the carbon support utilized. Preferences, options and embodiments for a given aspect, feature or parameter of the invention should, unless the context indicates otherwise, be regarded as having been disclosed in combination with any and all preferences, options and embodiments for all other aspects, features and parameters of the invention. Example 1 - Preparation of N-Doped Carbon Nanofoam 171g of table sugar was dissolved in 100ml deionized (DI) water. The mixture was heated and stirred to dissolve the sugar until fully dissolved. The final temperature when the sugar becomes fully dissolved was approximately 60°C - 80°C. The mixture was allowed to cool to approximately 45°C, and 3mg of naphthalene was added. The mixture was stirred to dissolve the naphthalene. The resultant mixture was added to a Teflon lined hydrothermal reactor. The reactor was sealed and placed into oven at 155°C for 5 hours. The resultant mixture was allowed to cool, then the carbonaceous material was removed and thoroughly cleaned using physical dissolution, decanting, and DI filtering of the material, sequentially in that order. The filtrate was dried under vacuum in an oven at 50°C for 6-12 hrs. The material was then milled in a ball mill for 24+hrs using 5mm - 10mm steel bearings (other bearings such as alumina or zirconium may also be used), then sieved through a 43 - 63 micron polyamide filter. The resultant material was nitrogen doped by treating with 6 M HNOs for 8 h at 100°C, then neutralized using mild sodium bicarbonate solution and rinsing in DI water until pH of 6.5 - 7 is reached. The material was then dried under vacuum at 50°C for 6 -12hrs. 23 04 25 SEM micrographs of the resultant material are shown in Figures 2a and 2b. The material is a scaffold of small particulate material having diameters of approximately 1-2 pm, which are coalesced to form a foamed porous material. 5 Example 2 - Preparation of a carbon nanofoam material coated with N-doped graphitic carbon (composite material) 171g of table sugar was dissolved in 100ml deionized (DI) water. The mixture was 10 heated and stirred to dissolve the sugar until fully dissolved. The final temperature when the sugar becomes fully dissolved was approximately 60°C - 80°C. The mixture was allowed to cool to approximately 45°C, and 3mg of naphthalene was added. The mixture was stirred to dissolve the naphthalene. 15 The mixture was added to a Teflon lined hydrothermal reactor. The reactor was sealed and heated in an oven at 69°C for 5 hours. The material was nitrogen doped by mixing with avian feathers (goose down) in a 20 50:50 (carbon material to feathers). The mixture was heated in a reduced oxygen environment (under argon flow) at 550°C for Ihr. Once a composite material was formed, a pitting agent (K2CO3) was added to the mixture at a mass ratio of 1:3 composite material:pitting agent. The material was then 25 dried and heated in a nitrogen environment at 800°C for 1 hour. Once done, the mixture was cooled and the carbonaceous material was removed. The material was thoroughly cleaned using physical dissolution, decanting, and DI filtering of the material, sequentially in that order. The filtrate was dried under vacuum in an 30 oven at 50°C for 6-12 hrs. The material was then milled in a ball mill for 12hrs using 5mm - 10mm steel bearings (other bearings such as alumina or zirconium may also be used), then sieved through a 43 - 63 micron polyamide filter. 35 Cleaning and milling can optionally be repeated to provide the final product. 23 04 25 TEM micrographs of the resultant material, are shown in Figures 3a and 3b. The material is a superstructure of small particulate material having diameters of approximately 10-30 nm, which aggregate to form clusters of around 4-5 pm, shown in Figures 3a and 3b respectively. 5 In order to disperse the aggregates and image the individual particles, an ionic solvent is added to the sample, for example isopropyl alcohol. Example 3 - Fuel Storage Material 10 20ml of DI water was added to 100 g of composite material from Example 2. 1% wt of 60% EtOH Nation® 212 solution is added to carbon nanofoam solution. The material is paddle mixed to ensure a consistent dispersion. 15 The solution was pressed into sheets of 2 - 3mm in thickness (depending on the active surface area of the end battery model). Electrode sheets were then exposed to a dehumidified dry-air stream at 150°C with a residence time of 2 minutes. Infrared Radiant Heating is used as the heating mechanism. 20 The pre-heated electrode sheets were then passed into a vacuum furnace at 70°C for 6hrs at 101 kPa to de-gas the material. After de-gassing the material the sheets were soaked in IM H2SO4 for 8 - 12hrs. After the soaking stage the material is dried at ambient temperature for 24hrs to evaporate 25 the excess water, but not to remove all the water content. An estimated minimum of 5000ppm of water content is required for proton conductivity. The material was then cut into the required shape. 30 Example 4 - Estimation of storage potential The hydrogen storage potential of the N-doped carbon nanofoam with N-doped graphitic carbon (composite material) was estimated from the discharge time of a fuel cell comprising the composite material in a fuel storage electrode. The result was 35 compared to other known carbon nanofoam materials. Storage material                            Details 23 04 25 A -Carbon nanofoam According to steps i and ii (no N-doping) B - Activated carbon Powder Activated Carbon 80 Mesh from Carbon Activated Corp; Thornbury, Bristol C - Black Pearls® 2000 Commercially available form of carbon black D - Composite material N-doped carbon nanofoam treated with structural protein according to steps a-e and g E - Activated composite material N-doped carbon nanofoam treated with structural protein and pitting agent according to Example 2 Table 1. Details of fuel storage materials A-E To form the electrodes, each of the materials was combined with Nation® 212 (5-10%) 5 and soaked in IM H2SO4 to activate the Nation. The amount of fuel storage material in each test cell was standardized at 1g. • Test cell dimensions: 3cm x 3cm • Active surface area: 9cm2 10 • Catalyst: Pt-C, 20% platinum on carbon (purchased from fuelcellstore: 20% Platinum on Vulcan XC 72, Product Code: 591278)% • Polymer activating agent: IM H2SO4 • PEM: Nation® 115 • Fuel: 10mL water 15 • Exacting time: Imin • Load: 100mA Table 2 shows the discharge time for each of the carbon nanofoam materials. Storage materials D and E show a significantly longer discharge time than materials A, B and C. This is indicative of a higher hydrogen storage capacity for materials D and E, with material E having the best performance. 5 Without wishing to be bound by theory, it is thought that materials D and E have better hydrogen storage capabilities due to a higher surface area and a degree high N-doping. The high degree of N-doping allows for easy absorption of the hydronium form of hydrogen. For example, the hydrogen may be stored as H3O+, HsO2+ or HgO3+, wherein 10 temporary ions bonds are formed between the ions and the storage material. 23 04 25 Storage Material Discharge Current Discharge Time A 0.7V x 100mA / 0.07W 4 min 11 sec B 0.7V x 100mA / 0.07W 4 min 38 sec C 0.7V x 100mA / 0.07W 5 min 45 sec D 0.7V x 100mA / 0.07W 7 min 44 sec E 0.7V x 100mA / 0.07W 10 min 32 sec Table 2. Discharge time for fuel storage materials A-E 15 Based on the discharge time, it is estimate that samples D and E store around 1-2% hydrogen. 03 03 25

Claims

1. A fuel cell comprising a fuel storage material, wherein the fuel storage material comprises:(i) a proton conducting polymeric material; and(ii) a composite material comprising a superstructure of composite particles, wherein said superstructure comprises:a scaffold of coalesced carbon nanofoam particles; anda coating on the scaffold, said coating comprising N-doped graphitic carbon; wherein the carbon nanofoam particles may optionally be N-doped.

2. The fuel cell of claim 1, wherein the fuel storage material is part of or adjacent to an electrode to provide, at least in part, said fuel to the electrode when operating in a redox mode.

3. The fuel cell of any preceding claim, wherein the composite material comprises composite particles, the composite particles having a diameter of from 0.005 to 25 pm.

4. The fuel cell of any preceding claim, wherein the N-doped graphitic carbon is covalently bound to the (N-doped) carbon nanofoam scaffold.

5. The fuel cell of any preceding claim, wherein the (N-doped) carbon nanofoam particles are N-doped carbon nanofoam particles.

6. The fuel cell of any preceding claim, wherein the composite material has an N content of from 1 to 5 wt%.

7. The fuel cell of any preceding claim, the scaffold of coalesced (N-doped) carbon nanofoam particles having a tortuous path of open pores at least 3 times the average diameter of the nanofoam particles.

8. The fuel cell of claim 7, wherein the composite material has N-doped graphitic regions that are located in the open pores of the scaffold of coalesced (N-doped) carbon nanofoam particles.

9. A fuel cell as defined in any preceding claim, wherein the composite material has a surface area of from 900 to 2000 m2 / g.03 03 2510. The fuel cell as defined in any preceding claim, wherein the proton conducting polymeric material is an acid doped hydrogel.

11. The fuel cell as defined in any of claims 1-9, wherein the polymeric material is a fluorinated acid polymer.

12. A fuel cell stack comprising a plurality of fuel cells arranged in series, said plurality of fuel cells comprising at least one fuel cell according to any of claims 1-11.

13. A method of making a composite material as used in any of claims 1-11, the method comprising the steps of:a. forming a mixture of sugar, water and hydrocarbon mediator;b. heating the mixture to form a carbon nanofoam material;c. optionally heating the carbon nanofoam in the presence of an acidic nitrogen source (such as nitric acid) to form an N-doped carbon nanofoam;d. optionally comminuting the (N-doped) carbon nanofoam material;e. heating the (N-doped) carbon nanofoam material with a structural protein in a reduced oxygen environment to form a composite material;f. optionally treating the composite material with a pitting agent to form an activated composite material; andg. optionally comminuting the material.

14. The method of claim 13, wherein the structural protein is collagen, gelatine or keratin, preferably wherein the structural protein is feathers, even more preferably wherein the structural protein is avian feathers.

Images