This invention relates to a fuel cell and, in particular, to a strip of fuel cell components for forming a fuel cell or fuel cell stack. The invention also relates to a method of manufacturing a fuel cell stack.

Typically, fuel cells comprise a proton exchange membrane (PEM) sandwiched between two porous electrodes, together comprising a membrane-electrode assembly (MEA). The MEA may include a catalyst layer. The MEA itself is conventionally sandwiched between: (i) a cathode diffusion structure (such as a cathode gas diffusion layer) having a first face adjacent to the cathode face of the MEA and (ii) an anode diffusion structure (such as an anode gas diffusion layer) having a first face adjacent the anode face of the MEA. The anode and cathode diffusion structures may each comprise a gas diffusion layer and a microporous layer. The second face of the anode diffusion structure contacts an anode fluid flow field plate for current collection and for distributing hydrogen to the second face of the anode diffusion structure. The second face of the cathode diffusion structure contacts a cathode fluid flow field plate for current collection, for distributing oxygen to the second face of the cathode diffusion structure, and for extracting excess water from the MEA. The anode and cathode fluid flow field plates conventionally each comprise a rigid, electrically conductive, material having fluid flow channels in the surface adjacent the respective diffusion structure for delivery of the reactant gases (for example, hydrogen and oxygen) and removal of the exhaust gases (for example, unused oxygen and water vapour).

According to a first aspect of the invention we provide a strip of fuel cell components for use in forming a fuel cell comprising:

a substrate, extending in a first direction, comprising a film having a layer of graphene at least partially extending over said film; and

a plurality of fuel cell components, each component formed on one or more of a plurality of substrate regions, the substrate regions spaced apart along the first direction and separated by fold regions which extend in a direction perpendicular to the first direction, wherein the strip is configured to be folded along said fold regions.

This is advantageous as the strip provides for easy assembly of the fuel cell stack. The use of a thin film, which may be of a polymer, and a graphene layer provides a flexible, lightweight substrate on which the fuel cell components can be applied to form efficient micro-fuel cells. Further, the layer of graphene provides for efficient control of the conductivity between the fuel cell components. The strip may contain fuel cell components for forming a single fuel cell or a fuel cell stack comprising a plurality of fuel cells or a subset of the components for forming a fuel cell or stack. The film may be of a polymer material, such as Polydimethylsiloxane (PDMS) or Poly(methyl methacrylate). The film may be porous. This is advantageous as the film does not hinder flow through the fuel cell when the strip is assembled and the film acts as a support for the graphene layer.

The plurality of fuel cell components may be formed by printing. This is advantageous as the strip can be fed through a printer which prints the fuel cell components onto the strip. The printer may be an additive printer such as a 3D printer or an ink-jet printer. The plurality of fuel cell components comprise at least one or more of a first membrane; a catalyst layer; a first microporous layer; a first gas diffusion layer; a bi-polar plate; a second gas diffusion layer; a second microporous layer; a second membrane; and a second catalyst layer. The components may be combined and formed on one or more of the substrate regions. For example, a combined membrane and catalyst layer may be provided which includes a proton exchange membrane having the catalyst layer thereon formed on one or more substrate regions.

The strip of fuel cell components may be configured such that, when folded, the strip of fuel cell components comprises at least a portion of a fuel cell stack or a fuel cell. Thus, the strip may include all of the components required to form the fuel cell or stack. Alternatively it may comprise a subset of said components and the missing components may be inserted into the folded or unfolded strip in a further manufacturing step.

The strip may include electrically conductive fold regions and non-electrically conductive fold regions. The conductive fold regions may comprise regions over which the layer of graphene extends and the non-conductive regions may comprise regions where the layer of graphene is absent. Thus, the non-conductive regions comprise an insulator region to prevent a flow of current between adjacent components under normal operating conditions of the assembled cell. The conductive regions may have a resistivity of less than 100 nDm. The non-conductive regions may have a resistivity of greater than 100 Dm. The strip of fuel cell components may comprise a plurality of portions of a fuel cell stack, wherein successive portions are connected to each other by electrically non-conductive fold regions, such that the strip of fuel cell components is configured to comprise a fuel cell stack when folded.

At least one of the fuel cell components may extend over a plurality adjacent substrate regions. This is advantageous as the thickness of a fuel cell component can be controlled by the number of adjacent substrate regions it is distributed over. When the strip is folded the adjacent components will be brought together to form the complete fuel cell component layer.

The fuel cell components may include at least a first combined membrane and catalyst layer. The first membrane and catalyst layer may be formed over a plurality of adjacent substrate regions. The combined membrane and catalyst layers may be formed by printing a catalyst onto a membrane layer. The membrane of the combined membrane and catalyst layer may include graphene oxide, such as a coating of graphene oxide. The layer may include conductive ribbons extending therefrom. The membrane may comprise graphene oxide printed with conductive ribbons. The ribbons provide a convenient way of connected a current path to the fuel cell or fuel cell stack.

The strip may include holes formed through at least one of the fuel cell components for controlling the porosity through the component.

The layer of graphene may include a plurality of holes such that the graphene layer is porous. The membrane and catalyst layers may comprise an array of holes such that the combined membrane and catalyst layers are porous. The film of polymer and the graphene layer may comprises an array of holes such that the film with the graphene layer is porous. Thus, the layer of graphene, membrane, catalyst and other components and substrate, may include holes that provide the layer with porosity such that when folded, the layer does not detrimentally affect the transport of fluids through the assembled fuel cell/fuel cell stack. The holes in the gas diffusion layers may have a larger diameter than holes in the microporous layers.

According to a further aspect of the invention we provide a method of manufacturing a strip of fuel cell components comprising:

providing a substrate, extending in a first direction, comprising a film coated with graphene,

forming on regions of the substrate a plurality of fuel cell components, wherein the regions of the substrate are spaced apart along the first direction and separated by a plurality of fold regions.

The plurality of fuel cell components may comprise at least one or more of: a first membrane; a first catalyst layer; a first microporous layer; a first gas diffusion layer; a bi-polar plate; a second gas diffusion layer; a second microporous layer; a second membrane; and a second catalyst layer.

The step of forming may comprise printing the fuel cell components onto the substrate. The method may include the step of forming holes or pores through at least one of the fuel cell components for controlling the porosity through the component and possibly the film. The holes may extend through the film or may extend through both the fuel cell component and the film. The holes may be formed by lithography. The method may include the step of folding the strip to assemble a fuel cell. Adjacent components may advantageously be brought into face to face contact when the strip is fan-folded to form a fuel cell or fuel cell stack.

There now follows, by way of example only, a detailed description of embodiments of the invention with reference to the following figures, in which:

Figure 1 shows a side view of a strip of fuel cell components;

Figure 2 shows a plan view of the strip shown in Figure 1 ;

Figure 3 shows the strip shown in Figure 1 folded to form part of a fuel cell stack;

Figure 4 shows a diagrammatic view of the strip showing the control of porosity along the strip;

Figure 5 shows a cross section through the strip; Figure 6 shows a further example of the strip; and

Figure 7 shows a flow chart illustrating an example method of assembling a fuel cell using the strip of fuel cell components.

Figures 1 and 2 show a strip 1 of fuel cell components for forming a fuel cell or fuel cell stack comprising a plurality of fuel cells stacked together. The fuel cell components described in this embodiment comprise a plurality of layers. The layers form a fuel cell having a proton exchange membrane (PEM) between an anode and a cathode, which together form a membrane electrode assembly (MEA). The anode and cathode may include a catalyst material and therefore form a catalyst later. Also, the anode and cathode each have an associated gas diffusion structure, which may comprise one or more layers, such as a gas diffusion layer and a microporous layer. A flow field plate or bipolar plate may deliver fuel and/or oxidant to the gas diffusion structures. However, it will be appreciated that the strip 1 may contain one or more or all of these fuel cell components.

The strip 1 includes a plurality of fuel cell components 2, 3, 4, 5, 6, 7, 8 arranged side by side. The strip 1 comprises a substrate 10, extending in a first direction, X. The substrate 10 comprises a film of a polymer material, such as Polydimethylsiloxane (PDMS) or Polymethyl methacrylate (PMMA). The film has a layer of graphene 9 at least partially extending over said film. The film may be porous and acts as a support for the graphene layer. The film has a thickness of between 0.05 pm and 1 pm and the graphene layer may have a thickness of 0.001 pm and 0.01 pm.

The plurality of fuel cell components 2, 3, 4, 5, 6, 7, 8 are each formed on a respective substrate region 12, 13, 14, 15, 16, 17, 18. The substrate regions are spaced apart along the first direction, X, and separated by fold regions 22, 23, 24, 25, 26, 27, 28, 29 which extend in a direction, Y, perpendicular to the first direction, X. The strip 1 is configured to be folded along said fold regions 22, 23, 24, 25, 26, 27, 28, 29 when forming a fuel cell or fuel cell stack. In this example, the strip 1 shown in Figures 1 and 2 comprises a repeating unit, n, of fuel cell components 2, 3, 4, 5, 6, 7, 8 which are intended to be folded and form a plurality of fuel cells arranged in a stack configuration. The strip thus extends further, as represented by component 2 _n +i and component 8 _n -i in dashed lines. Fuel cell component 2 is located on substrate region 12 and comprises a membrane which includes a catalyst layer. The fuel cell component 2 thus forms the proton exchange membrane and catalyst layer of the resulting fuel cell. The membrane may comprise a polymer such as Nation and is preferably non-electrically conductive. The catalyst layer may be coated or printed onto the membrane. A graphene layer (distinct from graphene layer 9 which extends over the substrate) may be provided over the membrane. The graphene layer and catalyst layer may be porous and may include holes. The holes may be formed by lithography or other micro/nano fabrication techniques. The membrane and catalyst layer is shown diagrammatically in Figure 4 where holes 40 are shown extending through the catalyst layer and graphene layer 2. Rather than a graphene layer, a graphene oxide layer may cover the membrane. Alternatively, a graphene oxide layer may replace the Nafion membrane. The use of graphene oxide is advantageous as it has similar properties to Nafion in that it is proton conductive, electrically non- conductive and water permeable. Terminal ribbons (not shown) of graphene may be formed, which receive the current generated by the cell and thereby provide a current flow path. The terminal ribbons may be formed by nano-heaters to reduce the graphene oxide to graphene on the graphene oxide layer. The catalyst layer can then be formed over the ribbons by coating the surface with catalyst particles, if present. The catalyst layer may comprise any suitable catalyst, such as platinum.

Fuel cell component 3 is located on substrate region 13 and forms a microporous layer (MPL) of the fuel cell. The MPL may be formed of a graphene material, although other materials may be used. The MPL is shown diagrammatically in Figure 4. The MPL may be porous and the porosity may be determined by a plurality of holes formed in the MPL. Figure 4 shows a plurality of holes 41 formed in the MPL, which provide transport of fluids to and from the membrane and catalyst layer 2. The holes may be formed through the substrate 10 as well as the MPL 3. Fuel cell component 4 is located on substrate region 14 and forms a gas diffusion layer (GDL) of the fuel cell. The GDL is shown diagrammatically in Figure 4. The GDL is formed of a graphene material, although other materials could be used. The GDL may be porous and the porosity may be determined by a plurality of holes formed in the GDL. Figure 4 shows a plurality of holes 42 formed in the GDL, which provide transport of fluids to and from the membrane and catalyst layer 2 through the MPL 3. The holes 42 may be larger than the holes 41 of the MPL. Thus, the porosity of the layers will increase with distance from the membrane and catalyst layer 2. The holes may be formed through the substrate 10 as well as the GDL 4. Further, the GDL provides transport of fluid in a direction perpendicular to the thickness of the layer (i.e. in the X and Y directions) while the MPL provides transport substantially through the thickness of the layer with less transport in the perpendicular directions.

Fuel cell component 5 is located on substrate region 15 and forms a bipolar plate of the fuel cell. With reference to Figure 5, the bipolar plate contains at least one track 43 for transporting fluid to and from the GDL 4. The bipolar plate 5 contains at least one further, separate track on its opposite side for transporting fluid to and from the fuel cell component 6. The bipolar plate 5 may be of a conductive non-porous material such as graphene sheet. Further, the bipolar plate may be of two halves; with one half provided on one side of substrate 10 and the other half provided on the other side of substrate 10. Each half of the plate may be configured to provide a track for transporting fluids to the respective fuel cell component 4 or 6.

Fuel cell component 6 is located on substrate region 16 and forms a gas diffusion layer (GDL) of an adjacent fuel cell in the fuel cell stack (when considering the bipolar plate as providing the boundary between adjacent fuel cells in the stack). The GDL 6 is of the same construction as GDL 4.

Fuel cell component 7 is located on substrate region 17 and forms a microporous layer (MPL) and has the same construction as MPL 3. The fuel cell component 8 is located on substrate region 18 and forms a membrane which includes a catalyst layer. The component 8 has the same construction as fuel cell component 2.

The fold regions 22 to 29 comprise portions of the strip 1 that are foldable and in this example are absent of fuel cell components. The fold regions 23 to 28 are electrically conductive due to the graphene layer 9 extending between components 2 and 3, 3 and 4, 4 and 5, 5 and 6, 6 and 7, and 7 and 8. Thus, these components are electrically connected together by the graphene layer 9. The fold regions 22 and 29 are non-conductive and the graphene layer 9 does not extend over said regions (shown as boxes in Figure 1 for purposes of clarity). The non-conductive fold region 22 extends between membrane/catalyst layer 2 and a component 8 _n -i of an adjacent unit along the strip 1. The component 8 _n -i also comprises a membrane/catalyst layer 2. The non-conductive fold region 29 extends between membrane/catalyst layer 8 and a component 2 _n +i of an adjacent unit along the strip 1. The component 2 _n +i also comprises a membrane/catalyst layer 2. Thus, no current flow path is provided through the membrane. Instead, the current flow path is provided by the ribbons, which extend from the catalyst layer and are insulated from the membrane by the layer of graphene oxide, as described above. The width of the fold regions may not be constant. Depending how the strip is to be folded, the fold regions may alternate between narrow and wide along the strip depending on whether faces of the substrate will be brought together at a particular fold or whether faces of the adjacent fuel cell components will be brought together. The wider fold regions would thus need to accommodate the thickness of the adjacent fuel cell components to allow them to come together face to face when the strip is folded.

Figure 3 shows the strip 1 when folded to form part of a fuel cell 30. The strip 1 is fan-folded in concertina fashion. Thus, adjacent fold regions 22 to 29 are folded in opposite directions. The strip is shown spaced apart for clarity and it will be appreciated that when folded the fuel cell components 2, 3, 4, 5, 6, 7, 8 and substrate 10 are in face-to-face contact. Thus, the membrane with catalyst layer 2 contacts the microporous layer 3. The microporous layer 3 contacts the gas diffusion layer 4 (through the substrate 10). The gas diffusion layer 4 contacts the bipolar plate 5. The bipolar plate 5 contacts the gas diffusion layer 6 (through the substrate 10). The gas diffusion layer 6 contacts the microporous layer 7. The microporous layer 7 contacts the membrane with catalyst layer 8 (through the substrate 10). As the substrate 10 is porous, it does not hinder the flow of fluid between the fuel cell components.

Figure 5 shows a cross-section through part of the strip 1 showing the holes or pores visible in Figure 4. The fold regions are narrow in this figure such that the fuel cell components appear to extend continuously over the substrate. Figure 5 shows the substrate 10 and the fuel cell components 2 to 8. The membrane 50 of the membrane and catalyst layer 2 is shown without holes formed therethrough. However, the catalyst layer 51 that lies on the membrane 50 has pores 40 formed therethrough. The MPLs 3 and 7 and GDLs 4 and 6 both have holes 41 and 42 respectively that extend through the strip 1. The holes 42 of the GDL are larger in area and/or diameter than the holes 41 of the MPL. The bipolar plate 5 has a track 43 on one side and a separate track 53 on its opposite side. The tracks 43, 53 are arranged to deliver fluid to the gas diffusion layers 4 and 6 respectively.

Figure 6 shows an alternative arrangement of the membrane/catalyst layer 2. In this example, the membrane/catalyst layer is formed over a plurality of substrate regions, each substrate region defined between two fold regions. Thus, several substrate regions with membrane material and catalyst material formed thereon make up the complete membrane and catalyst layer in the assembled fuel cell/fuel cell stack. Figure 6 shows a first membrane/catalyst sub-component 60' formed on a substrate region 61. The membrane/catalyst component has the same form as discussed above in relation to fuel cell component 2. A second membrane/catalyst sub-component 60" is formed on a substrate region 62 adjacent the first component 60, separated by the fold region 63. Likewise, further membrane/catalyst sub-components up to 60" are provided. When folded together in fan-like manner, the membrane/catalyst sub-components 60 to 60" form the complete membrane/catalyst layer of the resulting fuel cell.

It will be appreciated that any of the other fuel cell layers may be provided over one or more adjacent substrate regions. When the strip is folded, the component layers are brought together to form a complete layer of the resultant fuel cell. This provides a convenient way of forming the fuel cell component layers of a desired thickness. Thus, the fuel cell layers may be formed by a fuel cell component on a single substrate region or the fuel cell component may be distributed over multiple adjacent substrate regions. If, for example, a thicker gas diffusion layer is required, several adjacent substrate regions in the strip are formed with gas diffusion layer material thereon, which when folded together forms the gas diffusion layer.

Figure 7 shows a flow chart illustrating the formation of a fuel cell or fuel cell stack using the strip 1. Step 70 comprises receiving the substrate 10. Step 71 comprises applying the fuel cell components to the substrate regions of the substrate. Step 72 comprises providing the required porosity through the substrate and/or components, possibly by the formation of holes. Step 73 comprises the step of fan-folding the strip 1 to form a fuel cell or fuel cell stack.

In the above examples, the fuel cell components are formed by printing onto one side of the substrate. However, the components may be applied to the strip by other techniques. Also, the fuel cell components may be formed on both sides of substrate.