WO2014167306A2

WO2014167306A2 - Fuel cells

Info

Publication number: WO2014167306A2
Application number: PCT/GB2014/051084
Authority: WO
Inventors: Robert Longman
Original assignee: Acal Energy Limited
Priority date: 2013-04-08
Filing date: 2014-04-07
Publication date: 2014-10-16
Also published as: GB2515994A; GB201306326D0; WO2014167306A3

Abstract

A liquid-distributing channel (222, 224, 226) having an aperture (232, 234, 236) transports liquid electrolyte to and from a porous cathode (218) in a cation exchange membrane (CEM) fuel cell, the porous cathode (218) being adjacent the channel's aperture. The channel has a width greater than the width of its aperture so as to provide reduced flow resistance of the channel. The aperture (232, 234, 236) is wide enough to allow the liquid electrolyte to pass between the channel (222, 224, 226) and the porous cathode and small enough to inhibit ingress of the porous cathode (218) into the channel (222, 224, 226) due to the porous cathode (218) being compressed against the channel (222, 224, 226), or due to the porous cathode (218) being forced against the channel (222, 224, 226) by flow of the liquid into the channel from the porous cathode (218).

Description

FUEL CELLS

The present invention relates to fuel cells and redox batteries. In particular, but not exclusively, the present invention relates to apparatus for distributing a liquid through a fuel cell or redox battery.

A fuel cell typically comprises an anode and a cathode separated by a membrane such as a cation exchange membrane and/or an anion exchange membrane. The electrodes and the membrane together form a or a part of a membrane electrode assembly (MEA) of a fuel cell. A fuel cell allows a chemical reaction to be split into two half-reactions, one taking place at the anode, and the other taking place at the cathode, such that electrically charged particles are carried through the electrolyte between the two electrodes, whereas electrons are unable to flow through the fuel ceil but instead flow through an external circuit thereby providing an electric current. The overall effect is indirectly to combine hydrogen with oxygen to produce water thereby providing an electrical current. In many types of fuel cell, the hydrogen fuel and oxidant (usually oxygen or air) are fed respectively to catalysing, diffusion-type electrodes separated by a membrane electrolyte which carries electrically charged particles between the two electrodes. At the anode, hydrogen gas is catalytically converted to protons and electrons. The protons pass through the polymer electrolyte membrane to reach the cathode side. The electrons also reach the cathode, but need to do so via an external circuit (thereby generating electricity) because the fuel cell Is electrically insulating. At the cathode, oxygen gas reacts with the protons and electrons to produce water.

Typically fuel cells are stacked electrically in series to form a so-called fuel-cell stack. Heat generated in the process may be transported away from the MEA for example by fluid e.g. water, channelled through bipolar plates which separate individual cells or by the air flow on the cathode side of the MEA to the ambient environment surrounding the fuel cell. In the case of a water cooled fuel cell stack required for high power fuel cell systems the cooling water Is passed through an external heat exchanger where heat is dissipated to the surrounding environment. Published international patent applications WO2010/128333, WO2011 /107794 and

WO2011/107795 disclose redox fuel cells in which a regeneration zone is provided for the oxidative regeneration of a redox active species which has been reduced at the cathode in operation of the cell. These fuel cells may use hydrogen as a fuel with air or oxygen as oxidant. The operation of indirect redox fuel cells of these types is such that the oxidant is not supplied directly to the electrode but instead reacts with the reduced form of a redox couple in the catholyte to oxidise the redox couple, and this oxidised species is fed to the cathode of the fuel cell. In the regenerator, the catholyte comes into contact with an oxidant such as air or oxygen and is regeneratively oxidised before flowing back to the fuel cell. The available power output from the fuel cell depends on the rate of transport of catholyte through the fuel cell i.e. past the cathode. Therefore, it is desirable to maximise the flow rate of catholyte through the fuel cell.

Aspects and embodiments in accordance with the present invention were devised with the foregoing in mind. Although the specific description which follows is primarily concerned with fuel cells it will be appreciated that the liquid distribution arrangements described herein may, optionally with suitable adaptation, be utilised also in redox batteries.

Viewed from a first aspect there is provided apparatus for distributing a liquid in a fuel cell, or in a redox battery comprising: a plate including at least one liquid distribution channel for distributing a liquid through the fuel cell or redox battery, wherein the at least one liquid distribution channel comprises one or more apertures in a wall of the channel for providing liquid communication in a direction transverse to a liquid flow direction defined by the channel.

Viewed from a second aspect there is provided a method of distributing a liquid in a fuel cell, or in a redox battery the method comprising providing at least one liquid distribution channel in a plate of the fuel cell or redox battery, providing one or more apertures in a wall of the at least one liquid distribution channel and passing liquid into the at least one liquid distribution channel such that it may flow through the one or more apertures. In particular, the at least one liquid distribution channel has a width greater than the width of the one or more apertures. Since at least a portion of the channel has a width greater than the width of the aperture, there may be reduced resistance to liquid flow in the channel and hence increased liquid flow rate in the channel compared to a configuration in which the aperture is substantially the same width as the channel.

Also the channel may be less deep or tall for a given cross section area providing a desired flow rate compared to a configuration in which the aperture is substantially the same width as the channel, which allows for a more compact, or at least slimmer, design and may allow easier manufacturing of a bipolar plate incorporating the channel. The width of the channel being greater than the width of the aperture provides for a channel of reduced height-to- width ratio (aspect ratio) and may therefore make it easier to form part of the channel (a lower part comprising bottom and side walls) as part of a pressed, moulded or machined plate, the top wall of the channel being provided by a substantially planar element or plate that interfaces with the lower part to define the upper wall of the channel. The term

"substantially" is used to indicate that the element may not be exactly flat or indeed planar but may vary from flat or planar at least within the realms of manufacturing tolerance if not more. The top plate may be uneven even to the extent of being undulating or corrugated. The undulations or corrugations may be formed in the upper wall of the channel and/or on the top side of the plate.

The one or more apertures may be sized to allow the liquid to pass between the channel and the porous element and to inhibit ingress of the porous element into the channel. In particular, the aperture may be sized to inhibit ingress of the porous element into the channel, in particular to inhibit ingress resistive to compression of the porous element against the channel and/or due to the porous element being forced against the channel by flow of the liquid into the channel from the porous element and/or internal pressure required to establish good electrical contact at the various interfaces within the apparatus. Thus, occlusion of the channel may be inhibited thereby avoiding increased flow resistance due to occlusion of the channel by the porous element.

The apparatus may further comprise a plurality of apertures spaced apart at intervals arranged in accordance with a flow rate profile of the liquid through respective apertures. In one or more embodiments a plurality of apertures are sized and distributed in the wall to distribute substantially evenly the flow of liquid between the channel and the porous element. Typically, the flow rate profile is for substantially equal flow of the liquid through respective apertures. Since the liquid pressure is likely to decrease the further from the input of the channel an aperture is, a typical configuration is to have the spacing between apertures gradually decreasing the further away from the input they are and/or the size of the aperture increasing the further away from the input the apertures are, e.g. the aperture width increasing.

According to one or more embodiments, the aperture may comprise at least one elongate aperture or slot extending along the channel longitudinally along at least part of the length of the channel. It may extend along most or all of the length of the channel and may be of uniform width or varying width. One or more embodiments may comprise differently configured apertures.

In one or more embodiments, the at least one liquid distribution channel comprises a separate liquid input channel and liquid output channel, the one or more apertures respectively comprising one or more input apertures and one or more output apertures for providing communication of the liquid from the liquid input channel to a porous element and for providing communication of the liquid from a porous element to the liquid output channel respectively. In this way, respective input and output channels may be arranged to optimise the input and output of liquid and/or to promote an even distribution of liquid through the porous element. Such an output channel may not be necessary since the liquid

communicated to the porous element could leak from the edges of the porous element and be collected in an output channel acting as a form of "gutter". In this arrangement the one or more output apertures may be in the form of an opening along part or all of the length of the gutter.

In one or more embodiments the liquid input channel and liquid output channel are interdigitated with respect to each other. Such a configuration may bring respective input and output channels into close cooperation with each other thereby promoting communication of liquid from the input channel through the porous element and into the output channel.

Suitably, the liquid input channel is coupled to a reservoir of the liquid. Optionally or additionally, the liquid output channel is coupled to a repository for the liquid. In apparatus providing a closed system for the liquid, the reservoir and the repository may be the same receptacle. That Is to say, from a single receptacle liquid is communicated to the input channel and returned to the receptacle from the output channel. In an embodiment utilising a single inflow channel for providing liquid to the porous element, such as the arrangement in which liquid is collected from the edges of the porous element in a gutter-like arrangement, liquid may be returned to the receptacle from the gutter-like arrangement.

For apparatus in which the liquid has been reduced at some point from leaving the receptacle to arriving back at the receptacle, the receptacle may comprise a reaction chamber for oxidising the liquid.

One or more of the one or more apertures may have a periphery extended towards the porous element. The extended periphery may direct liquid between the liquid distribution channel and a region of the porous element distal from the channel and proximal to a CEM at the side of the porous element furthest away from the channel. The extended periphery may extend sufficiently to engage with a porous element compressed against a side of the plate comprising the one or more apertures to provide a mechanical engagement between the channel wall and the porous element, or at least assist or enhance any mechanical engagement.

The liquid may be an electrolyte, in particular a catholyte. Thus, a synergistic benefit may be obtained in that the electrolyte is also used for cooling the apparatus and conducting heat away from the MEA of a fuel cell. In particular, in an embodiment utilising a receptacle the heat is conducted away from the apparatus as a whole and may be subjected to cooling, for example the receptacle may be fitted with cooling fins. In a closed liquid system, liquid may conduct heat away from the apparatus, be cooled in the receptacle and then returned to the apparatus after oxidation. The apparatus may comprise a plate which is a bipolar plate for a fuel cell configured to have at least one liquid distribution channel therein. The apparatus may further comprise a porous element disposed against a side of the p!ate comprising the one or more apertures, the porous element may comprise an electrode for example a cathode. A plate, such as a bipolar plate, may be formed of metal which may be thin and may potentially offer less resistance to the flow of liquid through the aperture into or out from the channel due to thinness of the wall section of the channels. On the other hand, part or all of the plate may be formed of carbon. Carbon has good chemical properties and can be produced in small volumes by machining - for higher volumes the tooling cost is much lower than metal press tools.

Viewed from another aspect there is provided a fuel cell comprising the apparatus provided by the first aspect, wherein the porous element comprises an electrode. The fuel cell may comprise a bipolar plate configured to have the at least one liquid distribution channel therein.

One or more embodiments may be applicable to redox battery configurations, for example a vanadium redox battery or a redox battery comprising a polyoxometallate as at least one redox couple.

The fuel cell may be used in electronic or automotive equipment or for generating combined heat and power.

A fuel cell stack may be formed from plural fuel cells, arranged adjacent to one another. Since the overall volume of the apparatus may be minimised a more compact fuel cell stack may be provided. Such a stack may be constructed so that at least one fuel cell of the stack has apparatus according to the first aspect of the invention summarised above, with a porous element on (a) the cathode side, or (b) the anode side, or (c) both the cathode and the anode sides of the cell, the porous element(s) forming porous electrode(s).

Viewed from another aspect, there is provided an electronic, automotive or combined heat and power equipment comprising the fuel cell. For example the fuel cell may be incorporated in a motor vehicle. The above aspects and features could be applied in applications other than fuel cells, for example to provide apparatus for distributing another type of liquid, or gas. The porous element could be used to perform filtering of liquid or gas containing particles or impurities, for example. Further aspects will become apparent from the more detailed description of one or more embodiments provided below, by way of example only and with reference to the accompanying drawings. It should be understood that the scope of protection sought by the applicant is defined by the appended claims and should not be considered as limited to any one of the described and illustrated embodiments. In the drawings:

FIG. 1 is a simplified perspective view of a known MEA fuel cell;

FIG. 2 is a cross sectional view of a fuel cell apparatus according to an embodiment;

FIG. 3 is a cross sectional view of a fuel cell apparatus listing typical parts and dimensions for an embodiment;

FIG. 4 is a view of different cross-sectional configurations of liquid distribution channel; FIG. 5 is a plan view of a serpentine liquid distribution channel;

FIG. 6 is a plan view of serpentine input and output liquid distribution channels;; FIG. 7 is a plan view of interdigitated inlet and outlet liquid distribution channels; .

FIG. 8 is an extended side cross sectional view of the fuel cell apparatus illustrated in FIG. 2;

Fig 9 shows an extended aperture periphery protruding into a porous electrode element. In the fuel cell illustrated in FIG. 1 an ionic transport membrane, or cation exchange membrane (CEM), 102 with opposed catalytic surfaces (incorporating platinum) is located between two electrically conductive planar electrodes (cathode 104 and anode 106 respectively) to form a membrane electrode assembly (MEA). The MEA is located between channelled plates 108, 110 of electrically conducting material such as metal or graphite. The planar electrodes 104, 106 are electrically insulated from each other by the CEM.

Respective cathode and anode gas diffusion layers 105 and 107 are located between the electrodes 104, 06 and the CEM 102. The cathode 104 and anode 106 are separated from the respective channelled metal plates 108 and 1 10 by respective backing/gas diffusion layers 1 12 and 1 14.

Each plate has channels 1 16 and 1 18, shown in the figure as having rectangular cross section. The channels 1 18 of the anode plate 1 0 on the anode side of the cell have open sides facing the anode 106 and the CEM 102 by which the hydrogen contacts the anode via the anode backing/gas diffusion layer 1 14. The anode channels thus serve to provide hydrogen gas to the backing/gas diffusion layer 1 14 in which the gas is spread out over the surface of the anode 106 facing away from the CEM 102. Part of the hydrogen gas is used in the redox reaction that occurs at the membrane 102. The remainder of the hydrogen gas is output from the cell via the channels 1 18. The channels 116 of the cathode plate 108 on the cathode side of the cell have open sides facing the cathode 104 by which oxygen contained in air, passed into the channels 116, is provided to the outer surface of the backing/gas diffusion layer 1 12. Some of this oxygen passes through the backing/gas diffusion layer 1 12 and is spread out to contact across the surface of the cathode 104. Water is produced at the cathode by a redox reaction. The cathode channels thus serve to provide oxygen to the surface of the cathode facing away from the CEM, and to direct unused oxygen, air and water (as vapour) out of the cell.

The plates 108 and 110 described briefly above are sometimes referred to as bipolar plates, and they may comprise one or other or both of carbon and metal which are both electrically conductive.

US patent 5108849 (see FIG. 2 thereof and accompanying description) discloses anode and cathode plates which each have a single meandering gas-conducting channel having a gas input at one end and a gas output at another end. Hydrogen gas is input to one end of the "anode" channel of the anode plate and unused hydrogen exits the other end of the anode channel. Air enters one end of the "cathode" channel of the cathode plate, and water and unused air exit the other end of the cathode channel. The channel of each plate traverses the central area of the plate surface in a 'serpentine' manner, causing the gas at each, i.e. respective cathode-facing and anode-facing, side of the membrane to be distributed on respective sides of the membrane. The gas inlet and gas outlet at the respective ends of the channels are directly connected to common gas supply (input) and exhaust (output) openings respectively.

US 5108849 (see FIG. 4 thereof and accompanying description) also discloses that the meandered flow channel may comprise a plurality of meandered flow channels (44) alongside one another, supply and exhaust openings being common to each of the channels. Another patent, US 5641586, discloses a cathode plate separated from a so-called polymer electrolyte membrane (PEM) by a 'macroporous flow field' , which is stated to increase reactant gas (air/oxygen) availability at a catalytic layer of the PEM and support reduced- thickness gas diffusion backing located between the macroporous flow field and the PEM. The reactant gas may be directly introduced into the macroporous flow field (US 5108849 FIG. 1 C and accompanying description) or may be introduced by means of a channel (FIG. 1 B and accompanying description) having an open side facing the macroporous flow field. The open-sided flow channel may follow a serpentine path or it may comprise two interdigitated fluid flow channels (FIG. 2 and accompanying description).

Published international patent application WO2010/128333 discloses a platinum-free, liquid electrolyte-based CEM fuel cell technology. Hydrogen is catalysed on the anode to form a proton (cation) and an electron. The proton passes across the membrane to the cathode and the electron passes directly via an electrical circuit to the cathode. In the liquid electrolyte-based CEM fuel cell the electron and proton at the cathode are absorbed into a liquid electrolyte (which can be termed 'catholyte') solution containing redox catalyst systems (redox couples), flowing from the cathode of the fuel cell to an external oxidation system termed by the applicant as a "regeneration system" or "regenerator". The electrolyte is reduced at the cathode. In the regenerator, the catholyte comes into contact with air containing oxygen, and so the catholyte and protons react together with oxygen to form water which exits the regenerator as vapour. The process of regeneration acts to re-oxidize the reduced catholyte. The re-oxidized catholyte then flows back to the cell so that it can again be reduced and accept protons to balance the charge.

The liquid electrolyte can provide 'liquid cooling' of a fuel cell stack by conduction of heat into the liquid and transfer of the heat from the liquid, by conduction or radiation, out from the fuel cell stack. The extracted heat may be used as a by-product for example in a combined heat and power system.

The plate channels in the fuel cell illustrated in Fig. 1 are used to transport gas reactants. However, plate channels in a liquid electrolyte-based CEM fuel cell are used to transport primarily liquid (catholyte). Since the viscosity of a liquid is greater than the viscosity of a gas, the viscosity of the liquid catholyte in the cathode plate channels is greater than the viscosity of the air in the cathode plate channels of the solid electrolyte-based CEM fuel cell. The greater viscosity of the liquid catholyte limits its flow rate through the cell for a given pressure forcing the catholyte across the cathode region.

The flow resistance to liquid catholyte passing through the fuel cell determines the catholyte flow rate past the cathode. The higher the liquid catholyte flow rate the higher the rate of redox reaction and consequently the higher the power output from the cell.

Additionally, increasing the catholyte flow rate may result in a greater rate of heat transfer out from the fuel cell due to the heat-conducting action of the catholyte liquid. This allows increased cooling of the fuel cell reducing risk of overheating and, potentially, greater generation of heat as a by-product of the electrical power generation of the fuel cell. Such generation of heat may be used in a heating system of a vehicle for example.

Distributing catholyte within the cell should be achieved whilst keeping the thickness of the fuel cell, and therefore the thickness of the bipolar plate, as low as possible to minimise the space requirements of the fuel cell (i.e. its overall height/depth and its occupied volume). Open-sided fluid channels defined in a cathode plate for distributing liquid catholyte, rather than gas, through the cathode side of the membrane are described in the applicant's published patent application WO2011/148198, the contents of which are incorporated herein by reference, in particular FIG.s 1 to 4, FIG. 6 and accompanying description.

In accordance with an embodiment of the present invention, a porous element is located between, and thus separates, the plate and the membrane of the configuration disclosed in WO2011/148198. Such a porous element potentially may act to increase the amount of contact of catholyte with the membrane. The catholyte may contact portions of the membrane that are distal from the open side of the channel due to the porous element acting as a catholyte distribution medium in the space between the plate and the membrane, allowing the catholyte to migrate laterally to regions of the membrane's surface that are not directly opposite the open side of the channel.

However, the inventors have found that the use of such a porous element typically requires restriction of channel widths to less than around 1 or 2 millimetres depending on the porous element's mechanical properties, for example its stiffness when wet with liquid catholyte. This is because if the width of the flow channel(s) in the plate were not limited in this way, then portions of the porous element spanning the open face of the channel would be squeezed or extruded into the channel due to the porous element being compressed against the channel wall. This is because the porous element may be made of flexible or soft material that may deform under compression. Such ingress of the porous element into the channel would inhibit liquid flow through the catholyte-carrying channels and therefore increase flow resistance i.e. resistance to flow of liquid in the channel.

In FIG. 2 an embodiment of a fuel cell apparatus 200 is illustrated comprising lower and upper EA cell elements 210, 260 respectively stacked in parallel, relative to a liquid flow direction, against one another and Illustrated in the figure one above the other. The MEA cell elements 210, 260 are connected electrically in series. The fuel cell apparatus 200 may be used in other orientations than that illustrated in FIG. 2, including a vertical orientation in which the MEA cell elements may be placed side by side.

The lower MEA cell element 210 comprises a lower metal bipolar plate 212 comprising a shaped portion 214 and a flat plate 216 which are attached together to define liquid-carrying channels. The shaped portion 214 and a flat plate 216 may be attached together by welding, screwing or riveting the two portions to each other, or by some other suitable method. Optionally, the shaped portion 214 and flat plate 216 may be integrally formed of one piece of material such as a metal e.g. by extrusion, moulding or machining. Adjacent and above the lower metal bipolar plate 212 is a substantially planar cathode electrode 218 which is formed of a porous element comprising a material such as carbon felt, cloth or paper and an electrode contact layer of a conductive material disposed between the bi[polar plate 212 and the porous material. Examples of porous material type, thickness and permeability are set out in Table 1.

Table 1

Adjacent and above the cathode electrode 218 is a CEM 220. Adjacent and above the CEM 220 is an anode electrode 221 and gas diffusion layer 223. The shaped portions 214 of the bipolar plate 212, together with the flat plate 216, define liquid channels 224 and 228 which are used to distribute catholyte between the cathode 218 and catholyte-distributing channels 222, 224, 226 and 228. Each wall section 256 of the flat plate 216 which defines a catholyte-distributing channel 222, 224, 226, 228 has apertures 232, 234, 236 and 238 forming the liquid interface between the bipolar plate 216 and the cathode 218. Catholyte can flow through the apertures across the wall section 256 of the plate 216 between respective catholyte-distributing channels and the porous cathode 218. In the arrangement illustrated in FIG. 2 the catholyte-distributing channels 222, 224, 226 and 228 are arranged so that they are alternately catholyte inflow channels (input channels) 224, 228 and catholyte outflow channels (output channels) 222, 226. That is, channels adjacent to inflow channels are outflow channels and channels adjacent to outflow channels are inflow channels. Other arrangements are possible, so long as there is at least one inflow channel and at least one outflow channel. The catholyte may flow through the porous cathode and exit at its edges and therefore a different outflow channel arrangement may be provided for directing liquid away from the bipolar plate, for example providing a gutter-like arrangement at or around the edge of the bipolar plate. If there are an input channel and an output channel within the plate, then only one such input channel and output channel might be present. The general directions of liquid flow from catholyte inflow channels, through the cathode region, to catholyte outflow channels, are indicated by curved arrows 205.

As can be seen from FIG. 2, the upper MEA cell element 260 is substantially identical to the lower MEA cell element 210. in the upper MEA cell element 260 there is a membrane 220a, an anode 221 a, a gas diffusion layer 223a and a cathode 218a. These elements are similar or identical to respective elements 220, 221 , 223 and 218 of the lower MEA cell element 210. In the arrangement illustrated in FIG. 2, the spaces between catholyte-distributing liquid channels 272, 274, 276 and 278 of the upper MEA cell element 260 and bounded by the flat plate 266 of the upper MEA cell element 260 synergistically define anode fluid flow channels, which may act as anode fluid electrolyte (usually hydrogen in a fuel cell ^distributing channels, bounded by outer (vertical) walls of the catholyte-conducting liquid channels 272, 274, 276 and 278 of the upper MEA cell element 260, the flat plate 266 of the upper MEA cell element 260, and the anode 221 of the lower MEA cell element 210. The anode electrolyte flow channels can conduct anode electrolyte to and from the surface of the anode 221.

In this arrangement, an anode fluid flow field or channel is created by the lower profile of the upper bipolar plate assembly 260 and the anode surface of the lower bipolar plate assembly 210, making it possible to have at least one catholyte-distributing channel and at least one anode flow field channel located in the same plane. This may allow simpler and potentially lower cost manufacture of a bipolar plate comprising both the catholyte-distributing channels and anode flow field channels. The anode flow field channels may distribute reactant gas to the anode. Optionally, the anode flow field channels may distribute anode electrolyte in the form of a liquid. Plural MEA cell elements 210 and 260 may be stacked to form a multiple-element stack, as illustrated for the two MEA cell elements illustrated in FIG. 2 and described above.

Flow distribution of the catholyte may be controlled by the size and distribution of apertures in the channel walls so as to match the permeability of the chosen cathode material. Illustrated in FIG. 3 are some example dimensions for one or more embodiments. The height 355 of the catholyte-distributing channels may typically be around 0.4mm and in the range 0.2 tO 0.6 mm. The thickness of the cathode electrode layer 218a may also be around 0.4mm and in the range 0.1 to 1.0 mm. The thickness of the anode region 221 a is around 0.2mm and in the range 0.1 to 0.5 mm. The thickness of the membrane 220a is typically around 25-microns, but may be in the range 15 - 30 microns, possibly within the range 10 - 50 microns and even up to 100 microns (0.1 mm). The thickness 214, 256 of the electrolyte- distributing channel walls is around 0.1 mm and in the range 0.05 to 2.5 mm ( the latter being more typical if Carbon is used to manufacture plates. The total 'cell pitch' is around 1 .3 - 1.4 mm and may be in the range 1.0 to 5.0 (e.g. when carbon plates would be used). In this example, the channel wails are made of a metal such as stainless steel or other corrosion resistant materials. Naturally, the whole of the plate in which the channels are formed may be made of the metal or something else and coated with metal. Optionally, the plate may be made of metal and coated with a corrosion resistant metal or material.

The catholyte distribution channels may use a large proportion of the available plan area of the liquid-distributing apparatus (see the cross section area of the apparatus illustrated in FIG.s 2, 3 and 4).

As shown in the various parts of FIG. 4, part of the liquid channel (a lower part comprising bottom and side walls) can be formed as part of a pressed, moulded or machined plate 310, the top wall of the channel being provided by a planar or substantially planar element or interfacing plate 320 that interfaces with the lower part to define the upper wall of the channel and can interface with a porous element. It should be noted that plate 310 may have an upper side 325 which may be uneven, corrugated or undulating. In the figure, three arrangements are shown: (a), (b); (c), (d); and (e), (f) having rectangular, trapezoidal and curved channel cross sections, respectively. Each arrangement Is shown with the interfacing plate and lower part separated and joined, respectively. FIG. 5 is a plan view of a serpentine (meandering) liquid distribution channel 10. Side walls 20 of the channel 10 are indicated by shaded regions 20. The channel 10 is closed at one end.. A channel may be interleaved with another channel, as shown in FIG. 6 (the channels being shown as solid lines) to form input and output channels. In FIG. 6, input channel 502 has an input end 504 and a closed end 506 and is interleaved with output channel 512 having an output end 514 and a closed end 516.

The channel may comprise interdigitated inlet and outlet channels. An example is illustrated in FIG. 7 in which inlet channel 12' is interdigitated with outlet channel 18'. Each channel comprises fingers which are defined by side walls 20'. Each channel has a wall, comprising one or more apertures in it, facing the porous element (not shown). Liquid enters the fingers of the inlet channel (as shown by downward arrows 14'), passes through the one or more apertures into the porous element, and then passes from the porous element, through the one or more apertures in the outlet channel, into the outlet channel.

The embodiments illustrated in FIG.s 3 to 7 are for illustration only, and the channels may be configured differently, more closely spaced to each other and/or cover a larger area in practice to encourage transfer of liquid from the inlet channel to the outlet channel via the porous element.

FIG. 8 is another side cross sectional view of the fuel cell apparatus illustrated in FIG. 2. In FIG. 8, the general directions of flow from catholyte inflow channels, through the cathode region 218 and 218a, to electrolyte outflow channels, are indicated by curved arrows 305. FIG. 9 is another side cross sectional view of the fuel cell apparatus illustrated in FIGs 2 and 5, illustrating further channels to the left and right of the channels of FIG. 2. FIG. 10 is an illustrative side cross sectional view of an upwardly extending aperture in an upper wall of the catholyte channel. Such an aperture may be produced by piercing the wall from what will be the channel side. The aperture side wall extends (protrudes) towards the membrane. Such a protruding aperture would be in a position indicated by the locations of apertures 234 and 236 in the figure, for example.

The protruding aperture may direct the catholyte into the bulk of the membrane minimising dead zones with low catholyte turnover i.e. enhancing catholyte passing through the aperture either to or from the membrane. Also, the protruding walls of the apertures may provide mechanical engagement between the plate and the porous cathode.

In the case of a metal plate implementation, the apertures may be produced by piercing of the metal plate, as explained above.

The various apparatus described herein are also suitable for providing a moulded plate as the 'aspect ratio' of the features is much lower for a given cross section of liquid flow, which makes manufacture of the plate by moulding easier.

Additionally, it is possible to utilise a substantially fiat pierced metal plate and a second half manufactured from moulded carbon. This has the advantages of a lower tooling cost while maintaining the ability to incorporate small accurately formed holes with minimal pressure drop and reducing the risk of erosion by liquid flow.

Additionally, the design may permit the cathode electrode to be supported over a large area minimising extrusion of the porous cathode material into the catholyte-distributing channels. This is facilitated by configuring the apertures to be relatively narrow and hence the total surface area of the plate supporting the cathode is relatively large. Furthermore, the porous element may be made of a conductive material thereby providing a bulk electrode for contact with the CEM.

Although a specific embodiment has been described utilising a gas diffusion layer associated with the anode of the MEA cell element one or more embodiments in accordance with the present invention may be implemented without a gas diffusion layer and utilise a liquid anolyte.

In an implementation, all of the catholyte may be returned within the electrode material or distributed by several adjacent channels and returned likewise. As will be apparent to those skilled in the field of the invention, there are many possible flow possibilities giving a great freedom of design in flow fields.

Although it is said that the upper and lower CEM cell elements are substantially identical when describing FIG. 2, the cells may be different from each other, such differences not being limited to manufacturing tolerances.

Although one or more embodiments have been described with a lower metal bipolar plate 212, bipolar plate 212 can be of any electrically conductive material, for example carbon.

One or more embodiments described herein may also be applicable to redox battery configurations, for example a vanadium redox battery or a redox battery comprising a polyoxometallic as at least one redox couple.

One or more embodiments may provide for one or more of the following features: a. A bipolar plate for a liquid catholyte fuel cell comprising two halves forming catholyte distribution channels.

b. A channel design in which the inverted form of the liquid distribution channels forms an anode flow field.

c. Distribution and sizes of holes in the cathode side of the bipolar plate designed to ensure uniform distribution of catholyte.

d. Pierced holes with elevated peripheries to direct catholyte towards the membrane thus minimising regions of low liquid turn over.

e. A fuel cell stack using multiple plates according to the above.

f. The use of pressed metal bipolar plates according to the above designs g. The use of moulded carbon plates according to the above designs

g. A composite bipolar plate using a low cost "flat" apertured metal plate forming an upper boundary of the channels and a moulded carbon portion incorporating lower portions of the flow channels.

h. The metal plate may be pierced, providing for low-cost manufacture and providing for an aperture that extends towards the centre of the channel, as explained in further detail herein.

As used herein any reference to "one embodiment" or "an embodiment" means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment. As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, "or" refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

In addition, use of the "a" or "an" are employed to describe elements and components of the invention. This is done merely for convenience and to give a general sense of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

The scope of the present disclosure includes any novel feature or combination of features disclosed therein either explicitly or implicitly or any generalisation thereof irrespective of whether or not it relates to the claimed invention or mitigate against any or all of the problems addressed by the present invention. The applicant hereby gives notice that new claims may be formulated to such features during prosecution of this application or of any such further application derived therefrom. In particular, with reference to the appended claims, features from dependent claims may be combined with those of the independent claims and features from respective independent claims may be combined in any appropriate manner and not merely in specific combinations enumerated in the claims.

Claims

CLAIMS:

1. Apparatus for distributing a liquid in a fuel cell or in a redox battery, comprising: a plate including at least one liquid input channel and at least one separate liquid output channel for distributing a liquid through the fuel cell or redox battery,

wherein

the at least one liquid input channel comprises one or more input apertures and the at least one output channel comprises one or more output apertures in a wall of the respective channels for providing liquid communication in a direction transverse to a liquid flow direction defined by the channel.

2. Apparatus as claimed in claim 1 , wherein the at least one liquid input channel and/or the at least one liquid output channel has a width greater than the width of the one or more apertures.

3. Apparatus as claimed in Claim 2, wherein the one or more apertures are sized to allow liquid communication between the channel and a porous element adjacent the channel and to inhibit ingress of the porous element into the channel.

4. Apparatus as claimed in Claim 3, wherein the one or more apertures are sized to inhibit ingress of the porous element into the channel resistive to compression of the porous element against the plate.

5. Apparatus as claimed in any preceding claim, wherein the one or more apertures comprise a plurality of apertures spaced apart at intervals arranged in accordance with a flow rate profile of the liquid through respective apertures.

6. Apparatus as claimed in any preceding claim, wherein the one or more apertures comprise a plurality of apertures sized in accordance with a flow rate profile of the liquid to respective apertures.

7. Apparatus as claimed in claim 5 or 6, wherein the flow rate profile is for substantially equal flow of the liquid through respective apertures.

8. Apparatus as claimed in any preceding claim, wherein the one or more input apertures and one or more output apertures provide communication of the liquid from the liquid input channel to a porous element and provide communication of the liquid from a porous element to the liquid output channel respectively.

9. Apparatus as claimed in claim 8, wherein the liquid input channel and liquid output channel are interdigitated with respect to each other.

10. Apparatus as claimed in claim 8 or claim 9 wherein the liquid input channel is coupled to a reservoir of the liquid.

11. Apparatus as claimed in any of claims 8 to 10, wherein the liquid output channel is coupled to a repository for the liquid.

12. Apparatus as claimed in claim claim 11 , wherein the reservoir and the repository are the same receptacle.

13. Apparatus as claimed in claim 12, wherein the receptacle comprises a reaction chamber for oxidising the liquid.

14. Apparatus as claimed in any preceding claim, wherein the one or more apertures have a periphery extending away from the channel.

15. Apparatus as claimed in claim 1 , wherein the periphery extends sufficiently to engage with a porous element compressed against a side of the plate comprising the one or more apertures.

16. Apparatus as claimed in any preceding claim, wherein the liquid is an electrolyte.

17. Apparatus as claimed in claim 16, wherein the electrolyte is a catholyte.

18. Apparatus as claimed in any preceding claim, wherein the plate is a bipolar plate for a fuel cell configured to have the at least one liquid input channel therein.

19. Apparatus as claimed in any preceding claim, further comprising a porous element disposed against a side of the plate comprising the one or more apertures.

20. Apparatus as claimed in claim 19, wherein the porous element comprises an electrode.

21. Apparatus as claimed in claim 20, wherein the electrode is a cathode.

22. A fuel cell comprising apparatus as claimed in claim 20 or 21.

23. A redox battery comprising apparatus as claimed in claim 20 or 21 , for example a vanadium redox battery and/or a redox battery comprising a polyoxometallate as at least one redox couple.

24. A channel plate for forming a part of the apparatus as claimed in any of claims 1 to 21 and comprising at least one liquid distribution trench formed therein.

25. A top plate for forming a part of the apparatus as claimed in any of claims 1 to 21 and comprising one or more apertures configured to have a smaller width than the at least one trench.

26. A plate assembly, comprising:

the channel plate of claim 24; and

the top plate of claim 25;

wherein the top plate is disposed over the channel plate such that the one or more apertures are superposed over the at least one trench thereby forming apparatus in accordance with any of claims 1 to 9.

27. Use of a fuel cell as claimed in claim 23 and/or use of a redox battery as claimed in claim 23 in electronic or automotive equipment or for generating combined heat and power.

28. An electronic, automotive or combined heat and power equipment comprising a fuel cell as claimed in claim 22 and/or a redox battery as claimed in claim 23.

29. An automotive vehicle comprising a fuel cell as claimed in claim 22 and/or a redox battery as claimed in claim 23.

30. A method of distributing a liquid in a fuel cell, the method comprising providing at least one liquid input channel in a plate of the fuel cell and a separate liquid output channel, providing one or more apertures in a wall of each of the liquid input and output channels and passing liquid into the at least one liquid input channel such that it may flow through the one or more apertures.

31. A method as claimed in claim 30, further comprising providing the at least one liquid input channel and/or the at least one liquid output channel with a width greater than the width of the one or more apertures.

32. A method as claimed in claim 31 , further comprising configuring the width of the one or more apertures such that the liquid may be passed between the at least one channel and a porous element adjacent the at least one channel and ingress of the porous element into the at least one channel is inhibited.

33. A method as claimed in claim 32, further comprising compressing the porous element against a side of the plate comprising the one or more apertures.

34. A method as claimed in any of claims 30 to 33, further comprising spacing the one or more apertures at intervals arranged in accordance with a flow rate profile of the liquid through respective apertures.

35. A method as claimed in any of claims 30 to 34, further comprising sizing the one or more apertures in accordance with a flow rate profile of the liquid through respective apertures.

36. A method as claimed in claim 34 or claim 35, wherein the flow rate profile is for substantially equal flow of the liquid through respective apertures.

37. A method as claimed in any of claims 29 to 36, wherein the one or more input apertures and one or more output apertures provide communication of the liquid from the liquid input channel to a porous element and provide communication of the liquid from a porous element to the liquid output channel respectively.

38. A method as claimed in claim 37, further comprising interdigitating the liquid input channel and liquid output channel with respect to each other.

39. A method as claimed in claim 37 or claim 38, further comprising coupling the liquid input channel to a reservoir of the liquid.

40. A method as claimed in claim 37 to claim 39, further comprising coupling the liquid output channel to a repository for the liquid.

41. A method as claimed in claim 40, wherein the reservoir and the repository are the same receptacle.

42. A method as claimed in claim 41 , further comprising oxidising the liquid in a reaction chamber forming part of the receptacle.

43. A method as claimed in any of claims 30 to 42, wherein the liquid is an electrolyte.

44. A method as claimed in 43, wherein the electrolyte is a catholyte.

45. A method of manufacturing apparatus according to any of claims 1 to 19, the method comprising:

forming a channel plate including at least one liquid distribution trench; forming a top plate including one or more apertures having a width less than the width of the at least one trench; and

disposing the top plate over the channel plate such that the one or more apertures are superposed over the at least one trench.

46. Apparatus substantially as hereinbefore described with reference to respective embodiments and corresponding figures of the drawings.

47. A method substantially as hereinbefore described with reference to respective embodiments and corresponding figures of the drawings.