WO2021111137A1

WO2021111137A1 - Reactant gas plates, electrochemical cells, cell stacks and power supply systems

Info

Publication number: WO2021111137A1
Application number: PCT/GB2020/053101
Authority: WO
Inventors: Christopher Reynolds; Roland BLANCH OJEA; Neill Maynard; Richard Cartwright
Original assignee: Afc Energy Plc
Priority date: 2019-12-04
Filing date: 2020-12-03
Publication date: 2021-06-10
Also published as: GB2589611A; GB2606890A; GB201917740D0; GB2606890A8; GB202209282D0

Abstract

A reactant gas plate (200, 300) for conveying a reactant gas in an electrochemical cell (100), comprises a reactant gas volume (210, 310) having an inflow array (224, 324) of spaced- apart inflow apertures (222, 322), to allow reactant gas to flow into the reactant gas volume (210, 310); and an outflow array (234, 334) of spaced-apart outflow apertures (232, 332), to allow reactant gas to flow out of the reactant gas volume (210, 310), the outflow array (234, 334) having a proximal end (227, 327) and a distal end (228, 328); a collector channel (240, 340) having a proximal end (215, 315) and a distal end (216, 316), extending adjacent the outflow array (234, 334) and in fluid communication with the reactant gas volume (210, 310) through the outflow apertures (232, 332); and an exhaust port (250, 350) in fluid communication with the collector channel (240, 340) at the distal end (216, 316), to allow reactant gas to flow out of the reactant gas plate (200, 300). The outflow array (234, 334) has a proximal half (221, 321) coterminous with the proximal end (227, 327), and a distal half (223, 323) coterminous with the distal end (228, 328). The outflow apertures (232, 332) are arranged to reduce the hydrodynamic resistance for reactant gas flowing through the proximal half (221, 321) of the outflow array (234, 334) relative to the hydrodynamic resistance for reactant gas flowing through the distal half (223, 323), operable to bias the flow of reactant gas towards the proximal end (215, 315) of the collector channel (240, 340).

Description

REACTANT GAS PLATES, ELECTROCHEMICAL CELLS, CELL STACKS AND POWER

SUPPLY SYSTEMS

FIELD

This disclosure relates generally to electrochemical cells and stacks comprising electrochemical cells, preferably but not exclusively to alkaline fuel cells and/or electrolytic cells, and to plates for containing and conveying reducing or oxidising gas for electrochemical cells; as well as to power supply systems comprising said electrochemical stack, such as for charging electric vehicles or powering an electrical device.

BACKGROUND

WO/2011/015842 discloses a liquid electrolyte fuel cell comprising an electrolyte volume having a removable electrode on either side. Each electrode comprises a sheet of electrically conductive material including through-pores and having a peripheral margin without through-pores. WO 2012/104599 discloses an electrode which includes a perforated metal sheet, and a gas-permeable layer of fibrous or particulate electrically conductive material bonded onto the metal sheet and provided with a catalytic material at its outer surface.

Fuel cell stacks comprise an arrangement of fuel cells in series. Each fuel cell may comprise an electrolyte plate, a pair reactant gas plates and a pair of flat electrodes, one electrode being an anode and the other a cathode. One of the reactant gas plates conveys a fuel gas such as hydrogen and the other conveys an oxidising gas such as oxygen within the air. The electrolyte and reactant gas plates and the electrodes may be provided in bipolar or mono-polar arrangements, and each may produce an electromotive force of about 1 23V (Lower Heating Value of Hydrogen at 25°C and 1atm.).

There is a need for electrochemical cells and cell stacks, particularly but not exclusively fuel cells and stacks, particularly but not exclusively alkaline fuel cells and stacks exhibiting increased chemical reaction and thermal uniformity, so as to minimise the oversupply (over stoichiometry) of the fuel and oxidant gasses and/or a reduced frequency and magnitude of thermal spikes, and/or reduced overall residual reaction heat generation. It may also be desirable to have enhanced efficiency of electric power generation. There is also a need for electrical power supply systems, particularly but not exclusively for charging batteries, such as electrical vehicle batteries, or for powering electrical apparatuses in operation.

SUMMARY

Viewed from a first aspect, for conveying a reactant gas in an electrochemical cell, comprising: a reactant gas volume having an inflow side and an opposite outflow side, each having a respective proximal and distal end; an inflow array of spaced-apart inflow apertures, extending along the inflow side, to allow reactant gas to flow into the reactant gas volume; and an outflow array of spaced-apart outflow apertures, extending along the outflow side, to allow reactant gas to flow out of the reactant gas volume, the outflow array having a proximal end and a distal end; a collector channel having a proximal end and a distal end, extending adjacent the outflow array and in fluid communication with the reactant gas volume through the outflow apertures; and an exhaust port in fluid communication with the collector channel at the distal end, to allow reactant gas to flow out of the reactant gas plate; the outflow array having a proximal half coterminous with the proximal end, and a distal half coterminous with the distal end; wherein the outflow apertures are arranged to reduce the hydrodynamic resistance for reactant gas through the proximal half of the outflow array relative to the hydrodynamic resistance for reactant gas through the distal half of the outflow array, operable to bias the flow of reactant gas towards the proximal end of the collector channel.

Viewed from a second aspect, there is provided an electrochemical cell comprising an oxidising gas plate, to convey oxidising gas (such as air or oxygen); a fuel gas plate, to convey fuel gas (such as hydrogen); an electrolyte plate, to convey an electrolyte fluid; an anode electrode and a cathode electrode; the electrolyte plate including an electrolyte volume for conveying electrolyte fluid; wherein the cathode electrode is arranged between the electrolyte volume and the reactant gas volume of the oxidising gas plate, and the anode electrode is arranged between the electrolyte volume and the reactant gas volume of the fuel gas plate; operable to generate a potential difference between the anode electrode and the cathode electrode; wherein at least one of the oxidising gas plate and the fuel gas plate comprises an example disclosed reactant gas plate according to the first aspect. In some example arrangements, the electrochemical cell may be configured as a fuel cell for generating electrical energy, or as an electrolytic cell for using electrical energy to cause chemical reactions. Viewed from a third aspect, there is provided an electrochemical cell stack comprising a plurality of example disclosed electrochemical cells according to the second aspect, electrically connected to each other in series, operable to generate a potential difference across the electrochemical stack.

Viewed from a fourth aspect, there is provided a power supply system for charging or powering an electrical device, comprising an example disclosed electrochemical stack according to the third aspect, and a power supply control system electrically connected to the electrochemical stack and having a connector mechanism for allowing the power supply control system to be electrically connected to an electrical device, operable to charge or power the electrical device. For example, the power supply system may be configured for charging the battery of an electric vehicle (EV); or for an uninterrupted power supply (UPS), operable to power an electrical apparatus; or for generating power for a cellular telecommunications transmitter; or for some other stationary power system. In some example arrangements, the power supply system may comprise an ammonia cracker system for processing ammonia to produce hydrogen gas; and a fuel conveyor channel connecting the ammonia cracker system to the electrochemical stack, operable to convey the hydrogen gas from the ammonia cracker system to the electrochemical stack. The fuel gas may consist predominantly of hydrogen, where 99.999% is hydrogen. Alternatively, the percentage of hydrogen might be 99.95%, or 99%. It is also envisaged that the fuel could be -75% hydrogen, -25% nitrogen with up to 1 ,000 parts per million of ammonia. The hydrogen may be supplied by an ammonia cracker system, as mentioned above, or it may be supplied by a steam methane reformer, which can utilise methane or biomethane. The hydrogen may also be supplied by an electrolyser. Hydrogen produced using an ammonia cracker system might have a composition of -75% hydrogen, -25% nitrogen and 0 to -1 ,000 parts per million of residual ammonia.

These aspects and various additional features of electrochemical cells, stacks and power supply systems are set out in the appended claims.

This disclosure envisages various non-limiting non-exhaustive example arrangements of electrochemical cells and stacks, and various combinations of features, some of which are described below.

In some example arrangements, the proximal half of the outflow array may include a greater number of outflow apertures than the distal half of the outflow array. For example, the proximal half of the outflow array may include at least about 50% more outflow apertures than the distal half, or at least twice the number outflow apertures than the distal half; and/or the number of outflow apertures in the proximal half may be at most about 5 times, or at most about 3 times the number of outflow apertures in the distal half of the outflow array.

In some examples, the number of outflow apertures in the distal half of the outflow array may be 0 or 1 , or at least 2; and/or the number of outflow apertures in the proximal half may be at least 2. The number of outflow apertures in the proximal half of the outflow array may be about 15 to about 40; and/or the number of outflow apertures in the distal half may be about 5 to about 20.

In some example arrangements, each pair of successive outflow apertures may be spaced apart by a respective outflow spacing; the proximal half of the outflow array may have a first mean outflow spacing between successive outflow apertures, and the distal half of the outflow array having a second mean outflow spacing between successive outflow apertures; wherein the first mean outflow spacing is less than the second mean outflow spacing. For example, the first mean outflow spacing between successive outflow apertures may be at most 50% of the second mean outflow spacing; and/or the mean spacing between successive outflow apertures in the distal half may be at most about 5 times, or at most about 3 times the mean spacing between successive outflow apertures in the proximal half.

In various example arrangements, the mean spacing between successive outflow apertures in the distal half may be at least about 5 mm, or at least about 8 mm, or at least about 15 mm; and/or at most about 20 mm, or at most about 15 mm; and/or the mean spacing between successive outflow apertures in the proximal half may be at least about 1 mm, or at least about 2 mm, and/or at most about 8 mm, or at most about 5 mm. In some example arrangements, successive outflow spacings may increase incrementally from the proximal end to the distal end; and/or successive outflow spacings between a plurality of successive outflow apertures may be equal.

In some example arrangements, each outflow aperture has a respective cross-sectional area; and the outflow apertures in the proximal half may have a first mean cross-sectional area, and the outflow apertures in the distal half may have a second mean cross-sectional area; wherein the first mean cross-section area may be greater than the second mean cross- section area. For example, the first mean cross-section area of the outflow apertures may be at least about 10% greater than the second mean cross-section area.

In some example arrangements, at least some of the outflow apertures may have substantially the same mean cross-sectional area; or the mean cross-sectional areas of the outflow apertures may be substantially invariant. In some examples, the widths of the outflow apertures (that is, the dimension of the aperture perpendicular to the plane of the reactant gas plate), and/or the breadths of the outflow apertures (that is, the dimension of the aperture parallel to the plane of the reactant gas plate), may be substantially invariant along the outflow array. In various examples, the outflow apertures may have a mean breadth of at least about 1 mm, or at least about 2 mm, or at least about 5 mm; and/or at most about 6 mm; and/or the mean width of the outflow apertures may be about 1 mm to about 1.5 mm. In some example arrangements, the mean cross-sectional area of any outflow aperture may be varied by providing an insert or protrusion into the aperture which effectively reduces the mean cross-sectional area.

In some example arrangements, each outflow aperture has a respective length; and the outflow apertures in the proximal half of the outflow array may have a first mean length, and the outflow apertures in the distal half may have a second mean length; wherein the first mean length of the outflow apertures may be less than the second mean length. For example, the first mean length of the outflow may be at most about 90%, or at most about 80% of the second mean length; and/or the second mean length may be at most about 100%, or at most about 50% greater than the first mean length. The lengths of the outflow apertures may increase incrementally with increasing distance from the proximal end; and/or, at least some, or all, successive outflow apertures may have substantially the same length_. In some example arrangements, the length of any outflow aperture may be varied by providing an insert or protrusion into or abutting the outflow array proximal to the outflow aperture which effectively increases or reduces the length. In some example arrangements, the inflow array may have a proximal end and a distal end; a proximal half of the inflow array being coterminous with the proximal end and a distal half being coterminous with the distal end; wherein the inflow apertures may be arranged to increase the hydrodynamic resistance for reactant gas flowing through the proximal half of the inflow array relative to the hydrodynamic resistance for reactant gas flowing through the distal half of the inflow array, operable to bias the flow of reactant gas into the reactant gas volume towards the exhaust port.

In some example arrangements, the distal half of the inflow array may include a greater number of inflow apertures than the proximal half. For example, the distal half of the inflow array may include at least about 10% more inflow apertures than the proximal half.

In some examples, the number of inflow apertures in the proximal half of the inflow array may be 0 or 1 , or at least 2; and/or the number of inflow apertures in the distal half of the inflow array may be at least 2. In various examples, the inflow array may comprise at least about 5, or at least about 10 inflow apertures; and/or at most about 50, at most about 20, or at most about 15 inflow apertures.

In some example arrangements, the spacing between neighbouring inflow apertures may decrease with increasing distance along the inflow array from the proximal end to the distal end; or the spacing between successive inflow apertures may be substantially invariant along the inflow array.

In some example arrangements, each inflow aperture has a mean cross-sectional area; and the inflow apertures in the proximal half of the inflow array may have a first mean cross- section area, and the inflow apertures in the distal half may have a second mean cross- section area; wherein the second mean cross-section area may be greater than first mean cross-section area. For example, the second mean cross-section area of the inflow apertures may be at least about 10% greater than the first mean cross-section area.

In some example arrangements, the inflow apertures may have a mean breadth (in a plane parallel to the reaction gas volume, through the proximal end and the distal end of the inflow array) of at least about 1 mm, or at least about 2 mm, or at least about 5 mm; and/or at most about 6 mm; and/or the mean width of the inflow apertures may be about 1 mm to about 1.5 mm. The sum of the mean breadths of all the inflow apertures may be expressed as a percentage of the length of the inflow side of the reactant gas volume, and may be at least about 5%, or at least about 10%, or at least about 15%; and/or at most about 50%, or at most about 40%, or at most about 20% of the length of the inflow side. This percentage depends on the combination of the number of inflow apertures and the mean breadths of the inflow apertures. In some example arrangements, the inflow apertures in the proximal half of the inflow array may have a first mean length, and the inflow apertures in the distal half of the inflow array may have a second mean length; wherein the first mean length may be greater than the second mean length. For example, the first mean length of the inflow apertures may be at least about 10% greater than the second mean length. In some example arrangements, the lengths of the inflow apertures may decrease with increasing distance from the proximal end, towards the distal end; or the lengths of the inflow apertures may be substantially invariant.

In some example arrangements, the mean cross-sectional area, breadth, or length of each inflow aperture may be varied by providing inserts which effectively reduce the dimensions of the aperture, and/or otherwise by providing a protrusion within the aperture which reduces these dimensions. In some example arrangements, the length of the aperture may be increased with the inclusion of one or more inserts which abut the inflow array proximal to the aperture.

In some example arrangements, the number of outflow apertures may be greater than the number of inflow apertures.

In some example arrangements, the collector channel may comprise a recess into the reactant gas plate, the recess having a recess side opposite the outflow array; wherein the recess side may diverge from the outflow array with distance along the outflow array, from the proximal end of the collector channel towards the distal end. For example, the recess side may diverge from the outflow array at angles that vary with distance along the outflow array; for example, the recess side may diverge from the outflow array at one or more angle of 2° to 10°.

In some example arrangements, the reactant gas plate may have a plate thickness adjacent the collector channel, and the recess may have a mean collector depth of at least about 50%, or at least about 70% of the plate thickness. For example, the mean collector depth may be greater than 1 mm, or at least about 2.5 mm; and/or at most about 5 mm. The plate thickness may be about 2 mm to about 10 mm; or at most about 7 mm, or at most about 5 mm. In some example arrangements, the depth of the collector recess may be substantially invariant. The depth of the collector recess may be as great as possible, without extending all the way through the reactant gas plate and whilst ensuring that the reactant gas plate has sufficient strength.

In some example arrangements, the reactant gas plate may include a plurality of reinforcement bosses arranged within the collector channel, to support the portion of the plate within the collector recess, where the plate has a substantially reduced thickness. Additional reinforcement bosses may be provided adjacent the exhaust port, arranged along an arc adjacent a circular exhaust port, for example. The reinforcement bosses may have the aspect of allowing the collector depth to be as great as possible, whilst achieving sufficient strength and robustness of the reactant gas plate.

In some example arrangements, the hydrodynamic resistance across either the inflow or outflow array is varied by the inclusion of one or more bosses proximal to the inflow or outflow aperture. These bosses would be positioned so as to restrict the flow of fluids at one or more of the inflow apertures and/or outflow apertures. In some example arrangements, the one or more bosses restrict more than one inflow aperture and/or outflow aperture. In some example arrangements, the one or more bosses vary in proximity to the inflow apertures and/or outflow apertures to produce a variation in the fluid flow restriction across the inflow apertures or outflow apertures.

In some example arrangements, the exhaust port may be a circular or polygonal through- hole through the reactant gas plate, having a mean diameter of at least about 60 mm; and/or at most about 90 mm.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be more particularly described byway of example only, with reference to the accompanying drawings, of which:

Figure 1 shows a schematic illustration of an example alkaline fuel cell;

Figure 2A shows a schematic front view of an example reactant gas plate, for conveying oxidising gas in an electrochemical cell;

Figure 2B shows an expanded view of the portion A of the example reactant gas plate, including the proximal end of the outflow array;

Figure 2C shows an expanded view of the portion B of the example reactant gas plate, including the distal end of the outflow array; and

Figure 2D shows a schematic back view of the example reactant gas plate shown in Figure 2A;

Figure 3A shows a schematic front view of an example reactant gas plate, for conveying hydrogen fuel gas in an electrochemical cell;

Figure 3B shows an expanded view of the portion B of the example reactant gas plate, including the proximal end of the outflow array;

Figure 3C shows an expanded view of the portion C of the example reactant gas plate, including the distal end of the outflow array;

Figure 3D shows an expanded view of the portion A of the example reactant gas plate, including the proximal end of the inflow array; and

Figure 3E shows a schematic back view of the example reactant gas plate shown in Figure 3A;

Figure 4A shows a schematic front view of an example outflow array and collector channel of an example reactant gas plate; and

Figure 4B shows a schematic front view of an example inflow array of the example reactant gas plate in Figure 4A;

Figure 5A shows a schematic front view of an example outflow array and collector channel of an example reactant gas plate; and

Figure 5B shows a schematic front view of an example inflow array of the example reactant gas plate in Figure 5A;

Figure 6 shows a schematic illustration of common features of the inflow array and outflow array, showing certain dimensions.

Figure 7 (left) shows a schematic front view of an area of an example reactant gas plate, including part of the collector channel at the distal end, and several outflow apertures; and (right) a schematic cross-section through the collector channel and an outflow aperture, in the plane X-X indicated on the front view;

Figure 8 shows a graph of example spacings between neighbouring outflow apertures, and of aperture lengths of outflow apertures, versus distance along an example outflow array, from the proximal end to the distal end;

Figure 9A shows a schematic front view of an example electrolyte plate for an electrochemical cell; and

Figure 9B shows a schematic rear view of the example reactant gas plate; and

Figure 10 shows a block diagram of an example power supply system for charging an electric vehicle. DETAILED DESCRIPTION

With reference to Figure 1 , an example electrochemical cell 400 may comprise a first reactant gas plate 200, for conveying oxidising gas such as air 430, a second reactant gas plate 300, for conveying a fuel gas such as hydrogen 440, a first electrode 410, a second electrode 420 and an electrolyte plate 100. The first electrode 410 (cathode) is arranged between the first (oxidising) reactant gas plate 200 and the electrolyte plate 100, and the second electrode 420 (anode) is arranged between the electrolyte plate 100 and the second (fuel) reactant gas plate 300. The electrolyte plate 100 comprises an electrolyte volume 110, an electrolyte inlet 126 for conveying electrolyte liquid 450 such as potassium hydroxide (KOH) into the electrolyte volume 110, and an electrolyte outlet 128 for conveying the electrolyte liquid 450 out of the electrolyte volume 110. The first and second reactant gas plates 200, 300 each comprises a respective reactant volume 210, 310, a respective inlet 226, 326 and a respective outlet 236, 336. The inlets 226, 326 convey air 430 and hydrogen gas 440, respectively, into the reactant volume 210, 310. The outlet 236 of the of the first reactant gas plate 200 conveys air and potentially liquid condensate out of the first reactant gas volume 210; and the outlet 336 of the second reactant gas plate 300 conveys water or other reactant product from the second reactant gas plate 300. In example electrochemical cells, reactions between the electrolyte liquid 450 and the hydrogen gas 440 at the anode 420, and between the electrolyte liquid 450 and the oxygen in the air 430 at the cathode 410 generate a flow of electrons 480 from the anode 420 to the cathode 410, through a load 470.

An example electrolyte stack 500 (in Figure 10) comprises a plurality of electrochemical cells 400 that are electrically connected to each other in series, to generate a combined potential difference across the electrochemical stack. The electrochemical cells 400 may comprise fuel cells, in particular but not exclusively alkaline fuel cells 400, in which the electrolyte liquid may comprise, or consist essentially of, potassium hydroxide (KOH) and the fuel gas may comprise, or consist essentially of, hydrogen gas (H2).

An example alkaline fuel cell assembly may comprise an alkaline fuel cell stack 500 (in Figure 10) and a system 620 (in Figure 10) for processing a forming gas to generate hydrogen fuel gas. An example forming gas is ammonia (NH3) and the process of generating the hydrogen gas from ammonia may be referred to as “ammonia cracking”, wherein 2 NH3 3 H2 + N2. Alkaline fuel cell assemblies that include a system for generating hydrogen gas from ammonia may be used to provide an alternative to off-grid power generators that produce harmful emissions. Such fuel cell assemblies may also have the advantage that it is generally easier to obtain and store ammonia than high grade hydrogen almost anywhere in the world. Known fuel cell components are shown in, for example, GB2540592 A and WO 02/37592 A1.

Example arrangements of reactant gas plates 200, 300 will be described with reference to Figures 2A to 3E. A further example combination of an outflow array 234 and a collector channel 240 is shown in Figure 4A, and a further example inflow array 224 is shown in Figure 4B. An additional further example combination of an outflow array 334 and a collector channel 340 is shown in Figure 5A, and an additional example combination of an inflow channel 325 and inflow array 324 is shown in Figure 5B.

Example reactant gas plates 200, 300 may comprise a substrate body formed of moulded polymer such as plastic, including a reactant gas volume 210, 310 having an inflow side 220, 320 and an opposite outflow side 230, 330. In the illustrated examples, each reactant gas volume 210, 310 is a substantially rectangular through-aperture, having an area of about 680 cm² to about 750 cm². Each of the example reactant gas plates 200, 300 includes an inflow array 224, 324 of spaced-apart inflow apertures 222, 322, an outflow array 234, 334 of spaced-apart outflow apertures 232, 332, a collector channel 240, 340 and an exhaust port 250, 350. The inflow array 224, 324 extends along the inflow side 220, 320 of the reactant gas volume 210, 310 and has a proximal end 217, 317 and a distal end 218, 318. The outflow array 234, 334 extends along the outflow side 230, 330 and has a proximal end 227, 327 and a distal end 228, 328. The collector channel 240, 340 extends adjacent the outflow array 234, 334, in fluid communication with the reactant gas volume 210, 310 through the outflow apertures 232, 332, and has a proximal end 215, 315 and a distal end 216, 316. The exhaust port 250, 350 is in fluid communication with the collector channel 240, 340 at the distal end 216, 316, to allow reactant gas to flow out of the reactant gas plate 200, 300. The exhaust port 250, 350 is substantially circular in the illustrated example and may be polygonal in other examples. The reactant gas plate 200, 300 may also include a sealing gasket 260, 360 that extends around an area that includes the reactant gas volume 210, 310 and the outflow manifold 236, 336.

Example reactant gas plates illustrated in Figure 3A and partially in Figure 5B may comprise an inflow access channel 325 and an inlet port 352, in which the inflow access channel 325 is provided as a recess into the reactant gas plate 300. The inflow access channel 325 has a proximal end 321 and a distal end 323, and extends adjacent the inflow array 324, in fluid communication with the inflow apertures 322. The inlet port 352 may be positioned at the proximal end 321 of the inflow access channel 325, to allow reactant gas such as hydrogen or air to flow from a source (not shown) into the inflow access channel 325. The inflow access channel 325 has a width Wi between the inflow array 324 and an opposite side 319 of the recess 325. In the illustrated examples, the opposite side 319 tapers towards the inflow array 324 with decreasing distance from the inlet port 352 at the distal end 323 to the proximal end 321, the width Wi decreasing linearly with increasing distance from the inlet port 352.

When the reactant gas plate 200, 300 is oriented as in use, the inflow side 220, 320 and the outflow side 230, 330 extend horizontally, the inflow side 220, 320 being above the outflow side 230, 330, so that the direction of gravity is from the inflow side 220, 320 towards the outflow side 230, 330. Reactant gas will enter the reactant gas volume 210, 310 at the inflow side 220, 320, move downwards through the reactant gas volume 210, 310 and exit the reactant gas volume 210, 310 at the outflow side 220, 320.

When assembled in an electrolytic cell 400, the first and second reactant gas plates 200, 300 will be arranged back-to-back, and the first and second reactant gas plates 200, 300 are arranged such that their respective exhaust ports 250, 350 are separated. In electrolytic cell stacks 500 (in Figure 10) comprising a plurality of example electrolytic cells 400, the exhaust ports 250 of all the first reactant gas plates 200 are aligned with each other to provide a channel for removing air from the cell stack 500; and, similarly, the exhaust ports 350 of all the second reactant gas plates 300 are aligned with each other to provide a channel for removing the second reactant gas from the cell stack 500.

With reference to Figures 2A, 3A, 4B and 5B, example inflow arrays 224, 324 may be considered to have a proximal half 211 , 311 and a distal half 213, 313, on either side of an imaginary central dividing line Hi of the inflow array 224, 324; that is, the central line Hi is midway between the proximal end 217, 317 and the distal end 218, 318 of the inflow array 224, 324. The inflow apertures 222, 322 may be equidistant from each other, the respective distances Di between successive inflow apertures 222, 322 being substantially equal.

With reference to Figures 2A, 3A, 4A and 5A, example outflow arrays 234, 334 may be considered to have a proximal half 221 , 321 and a distal half 223, 323, on either side of an imaginary central dividing line Ho of the outflow array 234, 334; in other words, the imaginary central line Ho is midway between the proximal end 227, 327 and the distal end 228, 328.

There are substantially more outflow apertures 232, 332 in the proximal half 221 , 321 , which is remote from the exhaust port 250, 350, than in the distal half 223, 323. The mean spacing Do between successive outflow apertures 232, 332 in the proximal half 221 , 321 is substantially less than the mean spacing Do between successive outflow apertures 232, 332 in the distal half 223, 323. In the outflow array 224 shown in Figure 4A, there are 15 outflow apertures 232 in the proximal half 221 and 6 outflow apertures 232 in the distal half 223. In the outflow array 324 shown in Figure 5A, there are 14 outflow apertures 332 in the proximal half 321 and 8 outflow apertures 332 in the distal half 323. All else being equal, the greater number of outflow apertures 232, 332 in the proximal half 221 , 321, relative to the number in the distal half 223, 323, results in the proximal half 221 , 321 providing a substantially lower hydrodynamic resistance for reactant gas flowing through the proximal half 221 , 321 than for reactant gas flowing through the distal half 223, 323. This may have the effect of biasing the flow of reactant gas within the reactant gas volume 210, 310 towards the proximal half 221 , 321 and away from the exhaust port 250, 350.

Figure 6 shows a schematic drawing of part of an example array 270 of spaced-apart apertures 272, illustrating certain common features and dimensions of example inflow arrays 224 324 and outflow arrays 234, 334. Each of the apertures 272 is provided as a recess 272 having a depth W (defining the width W of the aperture 272, as used herein). The apertures 272 are separated by bosses 274, the apertures 272 and bosses 274 being arranged sequentially along an axis X. Each aperture 272 has an open inflow side Z_\ for receiving reactant gas and an opposite open outflow side Zo through which the reactant gas exits the aperture 272. Each boss 274 has a breadth D along the axis X, defining the spacing between neighbouring apertures 272. Each aperture 272 may have a mean breadth B along the axis X between successive bosses 274, and a length L through the array 270. The breadth B and/or the width W of an aperture 272 may vary along length L, the mean breadth B and width W being calculated over the entire length L. Each aperture 272 has a mean cross-sectional area over the length L, and the mean cross-sectional area of more than one aperture 272 is calculated as the average of their mean cross-section areas. Although example apertures 272 are shown as being substantially rhombohedral, apertures 272 having more complex shapes. In some examples, the apertures 272 may be substantially cylindrical in shape, and the open inflow and outflow sides Zi, Zomay be substantially circular or elliptical, or have some other shape.

While wishing not to be bound by a particular theory, the dimensions of the cross-sectional area of the outflow apertures 232, 332 (for example, the length L and breadth B of a rectangular aperture, or the diameter of a circular aperture) may be a factor determining the capillary force on liquid moving through the outflow aperture 232, 332. Relatively narrow outflow apertures 232, 332 may increase the magnitude of the capillary effect on condensed liquid and/or liquid reaction product, such as water. For example, water may arise within a reactant gas plate 200, 300 by condensation, or as a chemical reaction product within a fuel gas (for example, hydrogen) plate 200, 300. The shape and dimensions of the outflow apertures 232, 332 may allow liquid condensate such as water to be drained relatively quickly from the reactant gas volume 210, 310 into the collector channel 240, 340. If an outflow aperture 232, 332 is too narrow (that is, if the breadth B and/or the width W are too small), and/or if an outflow channel 232, 332 is too long (that is, if the length L is too great), then liquid condensate may be retained within the outflow aperture 232, 332. Liquid may be drawn into the outflow aperture 232, 332 by capillary force and fail to drain through it, thus potentially blocking the outflow aperture 232, 332, which may deleteriously affect the flow of reactant gas within the reactant gas volume 210, 310, as well as through to the collector channel 240, 340. The dimensions of the outflow apertures 232, 332 should be selected so that liquid condensate will pass through them relatively easily, given the operating pressure of the reactant gas within the reactant gas volume 210, 310.

The effective dimensions of one or more of the inflow apertures and/or one or more of the outflow apertures may be varied by using one or more inserts into any one aperture, having the effect of reducing the dimensions of said aperture. The respective length of any aperture may be increased using one or more inserts which abut the inflow or outflow array and provide an extension to the aperture. In some embodiments two or more inserts may form an extended aperture, and/or a single insert may have an integral aperture, positioned to extend an inflow aperture and/or an outflow aperture. In addition, or alternatively, one or more of the inflow apertures and/or one or more of the outflow apertures may be varied by providing protrusions in the aperture to effectively reduce the dimension of one or more of the apertures. The inserts would be fitted to the reactive gas plate, and may be made of the same or different materials as the reactive gas plate, or composites of the two. It will be understood that ‘fitted’ in this context means retrofitted to the plate following first assembly (and disassembly), or fitted to the plate during first assembly of the fuel cell and/or fuel cell stack. The protrusions achieve the same effect, but are monolithic to the respective plate. Monolithic in this context means that both the reactive gas plate and the protrusions are one piece e.g. manufactured from a single injection moulding process. Various arrangements of inserts and/or protrusions could be provided based on the required change to any one inflow aperture and/or outflow aperture, and these would be readily derivable by the skilled person. In some exemplary arrangements, one or more inflow apertures and/or outflow apertures could be completely blocked by said insert and/or protrusion. In some example arrangements, the inserts and/or protrusions may act increase the length of each aperture. In some example embodiments, the one or more inserts may be porous inserts which partially or fully span the one or more inflow apertures and/or one or more outflow apertures. This has the effect of restricting the flow through those one or more inflow apertures and/or out flow apertures.

With reference to Figure 7, an example reactant gas plate 200, 300 has a front side 202, 302 and an opposite rear side 204, 304, and a thickness T between the front side 202, 302 and the rear side 204, 304. The collector channel 240, 340 is provided as a recess into the reactant gas plate 200, 300, the recess 240, 340 having a depth Tc and a varying collector width Wc from the outflow array 234, 334 to an opposite recess side 242, 342. The collector recess 240, 340 may have a substantially invariant collector depth Tc greater than 1 mm; for example, about 1.5 mm to about 2 mm. The collector depth Tc may be at least 50% or at least 75% of the thickness T of the reactant gas plate 200, 300; in general, the collector depth Tc may be as great as possible without substantially weakening the reactant gas plate 200, 300.

The reactant gas plate 200, 300 may include a plurality of reinforcement bosses 241, 341 , arranged within the collector channel 240, 340, to strengthen the portion of the reactant gas plate 200, 300 within the collector recess 240, 340, where the reactant gas plate 200, 300 has a substantially reduced thickness, T - Tc. Additional reinforcement bosses 251, 351 may be provided adjacent the exhaust port 250, 350, arranged along an arc adjacent a circular exhaust port 250, 350, for example. The reinforcement bosses 251 , 351 may reduce deformation of the collector channel 240, 340.

In some example arrangements, one or more bosses may be provided proximal to one or more of the inflow apertures and/or one or more of the outflow apertures. These bosses would restrict the flow either into or out of the one or more inflow and/or one or more outflow apertures in order to restrict the flow of fluid through said aperture. Such one or more bosses may restrict the fluid flow through more than one inflow aperture and/or more than one outflow aperture. Where multiple inflow apertures and/or outflow apertures are restricted by a single boss, the restriction can be varied across the multiple inflow apertures and/or outflow apertures to which that boss is proximal. For example, this could be achieved by varying the distance between the boss and each aperture, or by providing an aperture through the boss more proximal to one of the inflow apertures and/or outflow apertures when compared to another. In addition, these one or more bosses could be on either side of the inflow and/or outflow array, or on both sides of each array. That is to say, when one or more bosses is used to restrict the flow of one or more inflow apertures, the bosses may be on the inlet side of the inflow array, and/or on the reactive volume side of the inflow array. Further when one or more bosses is used to restrict the flow of one or more outflow apertures, the bosses may be on the reactive volume side of the outflow array, and/or in the collector channel or exhaust side of the outflow array.

The skilled person would understand that there are various ways in which the arrangement of these bosses could be varied in order to alter the hydrodynamic resistance across the inflow array and/or the outflow array, and such routine variations fall within the scope of the present invention. In one example arrangement, the one or more bosses may fitted to the reactive gas plate. Fitted in this context means retrofitted to the plate following first assembly (and disassembly) or fitted to the plate during first assembly of the fuel cell and/or fuel cell stack. In such an arrangement, the one or more bosses may be made of the same and/or different materials to the plate, or a composite thereof. In some example arrangements the bosses are monolithic with the plate, meaning made of a single piece (e.g. manufactured in a single injection moulding process).

The example collector channels 240, 340 shown in Figures 2A, 3A, 4A and 5A have a recess side 242, 342 that diverges from the respective outflow array 234, 334, providing a collector width Wc that increases with distance from the proximal end 215, 315 to the exhaust port 250, 350 at the distal end 216, 316. In some example arrangements, the recess side 242, 342 may diverge from the outflow array 234, 334 at a uniform angle in the range of about 4° to about 10°, or at various angles within this range, depending on the position along the outflow array 234, 334. Some example reactant gas plates 200, 300 comprising a collector channel 240, 340 having widths Wc that diverge towards the exhaust port 250, 350 may have the aspect of improved draining of liquid condensate such as water (condensed from air) to the exhaust port 250, 350. Divergent configurations of example collector channels 240, 340 may accommodate an increasing cumulative quantity of reactant gas flowing through the outflow array 234, 334 and increase the uniformity of the reactant gas flow rate through the collector channel 240, 340.

The example collector channels 240, 340 illustrated in Figures 4A and 5A comprise a recess side 242, 342 that diverges from the outflow array 234, 334 at various angles, dependent on the distance along the outflow array 234, 334 from the proximal end 215, 315 to the proximal end 216, 316. The recess side 242, 342 may include an acceleration portion 243, 343 that diverges from the outflow array 234, 334 at an angle of about 10° to about 80°, the increase in the collector width Wc over the acceleration portion 243, 343 being substantially greater than the increase over any other portion of the recess side 242, 342 having the same length. This may result in accelerated flow of reactant gas through the collector channel 240, 340 adjacent the acceleration portion 242, 342, which may increase the uniformity of reactant gas flow within the reactant gas volume 210, 310, along the outflow array 234, 334. While wishing not to be bound by a particular theory, this may result from improved balance of the hydrodynamic resistance through the collector channel 240, 340, in relation to the varying mean hydrodynamic resistance through the outflow array 234, 334, which differs between the proximal half 221 , 321 and the distal half 223, 323 of the outflow array 234, 334.

With reference to Figures 2A, 3A, 4B and 5B, each inflow aperture 222, 322 has a respective length U, and in some example arrangements, the mean length U in the distal half 213, 313 of the inflow array 224, 324 may be less than or equal to the mean length U in the proximal half 211, 311. The mean widths W and breadths B of the inflow apertures 222, 322 may be substantially invariant along the inflow array 224, 324.

Figure 8 shows a graph of example spacings Do between successive outflow apertures 232, 332, as well as the corresponding outflow aperture lengths l_o, versus the distance of the outflow apertures 232, 332 from the proximal end 227, 327 of the outflow array 234, 334. In this example, the length l_o of the first outflow aperture 232, 332 adjacent the proximal end 227, 327 is about 8 mm and the lengths of successive outflow apertures 232, 332 increases by an incremental amount such that the length l_o of the last outflow aperture 232, 332, adjacent the distal end 228, 328 is about 15 mm. In the proximal half 221 , 321 of the outflow array 234, 334, the inter-aperture spacings Do increase by about 0.15 mm for each successive pair of outflow apertures 232, 332, from 2 m adjacent the proximal end 227, 327 to about 7 mm adjacent the half-way line Ho; and in the distal half 223, 323, the inter aperture spacings Do increase stepwise in three incremental amounts, to about 13 mm at the distal end 228, 328. In this example, the mean spacing distance Do between successive outflow apertures 232, 332 in the proximal half 221 , 321 may be about 4.6 mm; and the mean spacing distance Do between neighbouring outflow apertures 232, 332 in the distal half 223, 323 may be about 11.7 mm.

In use, reactant gas will flow from the reactant gas volume 210, 310 through the outflow apertures 232, 332 and into the collector channel 240, 340. Each inflow aperture 222, 322 and outflow aperture 232, 332 will provide a hydrodynamic resistance to the reactant gas flowing through them, dependent on their shape, dimensions and surface texture. Variation of these characteristics, as well as the arrangement of the outflow apertures 232, 332 along the outflow array 224, 324, have the combined effect of causing the proximal half 221, 321 and distal half 223, 323 of the outflow array 234, 334 each to provide a substantially different mean dynamic resistances for the reactant gas flowing through the respective half. In other words, each of the proximal half 221, 321 and distal half 223, 323 of the outflow array 234, 334 provides a substantially different aggregate dynamic fluid resistance for the reactant gas. In the disclosed examples, the aggregate dynamic fluid resistance provided by the proximal half 221 , 321 of the outflow array 234, 334 is substantially less than that of the distal half 223, 323.

As a consequence of the distal half 223, 323 of the outflow array 234, 334 having substantially fewer outflow apertures 232, 332 than the proximal half 221 , 321, and the mean length of the outflow apertures 232, 332 being substantially greater in the distal half 223, 323 than in the proximal half 221, 321 (all else being substantially equal), the distal half 223, 323 will present a substantially greater hydrodynamic resistance to the reactant gas than the proximal half 221, 321. Consequently, the distal half 223, 323 can sustain a greater difference in reactant gas pressure than the proximal half 221 , 321 , the difference in pressure increasing from the proximal end 227, 327 to the distal end 228, 328; and the rate at which reactant gas flows through the outflow array 234, 334 will vary along the outflow side 230, 330.

As used herein, a fluid may be said to experience ‘hydrodynamic resistance’ when it loses mechanical energy as it flows through an aperture, channel or chamber, or through an array of apertures. While wishing not to be bound by any particular theory, the hydrodynamic resistance R of an aperture having a length L and a rectangular cross-section of width W and breadth B may be approximated as follows under certain simplifying assumptions (for example, including that the reactant gas flowing through them is substantially incompressible): (12· m· R

147. (1 - 0.63 ) where m is the viscosity of the flowing reactant gas and B £ W. The dynamic resistance R of a cylindrical aperture having a cross-section of radius r may be approximated as:

Consequently, the hydrodynamic resistance of an inflow or outflow aperture can be increased by increasing the length L of the aperture, and/or by decreasing the breadth B or the radius r of the aperture cross-section.

In a first order approximation, which may be more accurate for laminar flow, the volumetric flow rate Q at which reactant gas flows through an aperture, or an array of apertures, can be expressed as being proportional to a pressure drop DR across the aperture as follows:

AP = R.Q

Volumetric flow rate Q of a fluid is the volume (V) of the fluid that flows through a surface area (A) per unit time.

The mean hydrodynamic resistance R across an array of apertures, for a given reactant gas at a given temperature and pressure, may be determined empirically by measuring the mean flow rate Q of the reactant gas across the array, as well as the difference in pressure P of the reactant gas on either side of the array; that is as the difference in the mean pressure P divided by the mean flow rate Q.

While wishing not to be bound by a particular theory, an outflow array 234, 334 (and, similarly, of the inflow array 224, 324) including N spaced-apart outflow apertures 232, 332 can be considered to comprise N hydrodynamic resistors arranged in parallel, each having a respective hydrodynamic resistance R, (for i = 1... N), and the combined dynamic resistance R_T of which may be expressed as:

Since the mean spacing distance Do between successive outflow apertures 232, 332 in the distal half 223, 323 of the outflow array 234, 334 is substantially greater than mean spacing distance Do in the proximal half 221, 321, there are substantially fewer outflow apertures 232, 332 in the distal half 223, 323 than in the proximal half 221, 321. Consequently, all else being equal, the combined dynamic resistance R_T of the distal half 223, 323 is substantially greater than the combined dynamic resistance R_T of the proximal half 221 , 321. The combined dynamic resistance R_T of the distal half 223, 323, for example, can be increased by increasing the mean spacing distance Do between successive outflow apertures 232, 332, and thus reducing the number of outflow apertures 232, 332 in that half. This can be considered to have the effect of increasing a mean effective dynamic resistance R of each outflow aperture 232, 332, being the combined dynamic resistance R_T in the distal half 223, 323 divided by the number of outflow apertures 232, 332 in the distal half 223, 323. Similarly, the combined dynamic resistance R_T of the proximal half 221 , 321 can be reduced by reducing the mean spacing distance Do between successive outflow apertures 232, 332, and thus increasing the number of outflow apertures 232, 332 in that half.

Arranging the outflow apertures 232, 332 such that the mean spacing between outflow apertures 232, 332 in the distal half 223, 323 of the outflow array 234, 334 is substantially greater than that in the proximal half 221, 321 may have the aspect of allowing the hydrodynamic resistance of the distal half 223, 323 to be substantially greater than that of the proximal half 221, 321, without necessarily varying the cross-sectional dimensions W, B, and/or the lengths l_o of the respective outflow apertures 232, 332. Substantially varying the cross-sectional dimensions W, B, and/or the lengths l_o of the respective outflow apertures 232, 332 may have undesirable consequences for other aspects of the reactant gas plate 200, 300 configuration, and potentially for the flow of reactant gas. For example, if the length l_o of an outflow aperture 232, 332 is too great, and/or the cross-sectional area is too small, then condensed liquid may become trapped within the outflow aperture 232, 332 by capillary forces, thus blocking the outflow aperture 232, 332.

The effect of the configuration and arrangement of the outflow apertures 232, 332 according to example arrangements may be to bias the flow of reactant gas within the reactant gas volume 210, 310 towards the proximal end 227, 327 of the outflow array 234, 334. This may result in a more uniform reactant gas flow rate across the reactant gas volume 210, 310, potentially reducing the size of “dead spots”, in which reactant gas flows slowly relative to the rate of chemical reactions involving the reactant gas, resulting in reduced chemical activity and generation of heat within the dead spot. An indicator of the uniformity of the reactant gas flow rate along the outflow array may be expressed as the ratio of the maximum volumetric flow rate (C ) to the minimum volumetric flow rate (Qmin), and example outflow array configurations may substantially reduce the ratio CW/ Qmin.

A substantial improvement of the uniformity of the reactant gas flow rate may result from the combined, potentially synergistic, effects of the depth Tc and divergence angle(s) of the width Wc of the collector channel 240, 340, and the arrangement, shape(s) and dimensions of the outflow apertures 232, 332. In general, greater depth Tc of the collector channel 240, 340 may result in improved uniformity of reactant gas flow rate.

With reference to Figures 9A and 9B, an example electrolyte plate 100 for conveying an electrolyte fluid comprises an electrolyte volume 110, being a substantially rectangular through-aperture extending all the way through the electrolyte plate 100. The electrolyte volume 110 has an inflow side 120, at which electrolyte fluid enters the electrolyte volume 110, and an outflow side 130, at which electrolyte fluid exits the electrolyte volume 110. On the inflow side 120, the electrolyte plate 100 comprises an inlet port 152, a pair of ionic resistance ducts 127A, 127B, an inflow access channel 125 and an electrolyte inflow array 124 of spaced-apart inflow apertures 122, arranged to allow electrolyte fluid to enter through the inlet port 152 and flow (under pressure) into the electrolyte volume 110. On the outflow side 130, the electrolyte plate 100 comprises an array of outflow apertures 132 and an outflow manifold 136, to allow electrolyte fluid to flow out of the electrolyte volume 110.

Wth reference to Figure 10, an example electric vehicle (EV) charging system 600 may comprise a charging terminal 610, to which an electric vehicle (not shown) can be electrically connected by a cable 612, a stack 400 of alkaline fuel cells is connected to a balance of plant and power electronics 500 as disclosed herein, a battery storage system 630 may or may not be connected , either an ammonia cracking system, a hydrogen gas storage system or a direct hydrogen feed from another source 620 is connected via a tube 622 for conveying a hydrogen gas blend, e.g. a blend of hydrogen and nitrogen from the ammonia cracking or hydrogen system 620 to the stack of alkaline fuel cells 400. Some example EV charging systems 600 may have the aspect of allowing EVs to be charged in remote locations, in which there is little or no access to an electricity grid.

Various additional non-limiting examples of parameter values for the inflow arrays 224, 324, the outflow arrays 234, 334 and the collector channel 240, 340 will be given. Example reactant gas plates 200, 300 may have a thickness T of about 2 mm to about 3 mm (at least adjacent the collector channel 240, 340). The inflow side 220, 320 and the outflow side 230, 330 of the reactant gas volume 210, 310 may be about 470 mm to about 490 mm. A pair of lateral sides of the reactant gas volume 210, 310, connecting the inflow side 220, 320 and the outflow side 230, 330 at the proximal ends and the distal ends, respectively, may be about 140 mm to about 150 mm.

In example reactant gas plates 200 suitable for oxidising gas such as air, the number of inflow apertures 222 in the inflow array 224 may be about 20 to about 40; the mean breadth of the inflow apertures 222 may be about 2 mm to about 5 mm; the sum of the mean breadths of the inflow channels 222 as a percentage of the length of the inflow side 220 may be about 8% to about 40% (in which the inflow side 220 is 490 mm). In example reactant gas plates 300 suitable for fuel gas such as hydrogen, the number of inflow apertures 322 in the inflow array 324 may be about 10; the mean breadth of the inflow apertures 322 may be about 2 mm to about 5 mm; the inflow side 320 of the reactant gas volume 310 may be about 490 mm; the sum of the mean breadths of the inflow channels 322 as a percentage of the length of the inflow side 320 may be about 4% to about 10%. The mean width W of the inflow apertures 222, 322 may be about 1 mm to about 1.5 mm. The widths W and breadths B of the inflow apertures 222, 322 may be substantially invariant along the inflow array 224, 324, or at least the mean breadths B may increase from the proximal end 217, 317 to the distal end 218, 318 of the inflow array 224, 324.

In example reactant gas plates 200, 300, the number of outflow apertures 232, 332 may be about 15 to about 40 in the proximal half 221 , 321; and about 5 to about 20 in the distal half 223, 323. For example, the number of outflow apertures 232, 332 in the proximal half 221 of the outflow array 224, 324 may be at least about 1.5* (times), or at least about 2* the number in the distal half 223, 323. The mean breadth of the outflow apertures 232, 332 may be about 2 mm to about 5 mm (for example, about 2.5 mm); and the mean width W may be about 1 mm to about 1.5 mm. The outflow apertures 232, 332 may have one or more lengths L of about 5 mm to about 20 mm. For example, the outflow aperture 232, 332 adjacent the proximal end 227, 327 and distal end 228, 328 of the outflow array 224, 324 may have lengths L of about 8 mm and about 15 mm, respectively; the lengths L of the outflow apertures 232, 332 may increase incrementally from the proximal end 227, 327 to the distal end 228, 328.

In example reactant gas plates 200, 300 for either oxidising gas or fuel gas, the collector channel 240, 340 may have a minimum width Wc (at the proximal end 215, 315) of about 1 mm to about 2 mm (for example, about 1.5 mm); the collector depth Tc may be about 1 mm to about 2 mm (for example, about 1.5 mm); the recess side 242, 342 of the collector channel 240, 340 may diverge from the outflow array 234, 334 at an angle of about 2° to about 10° (which may be referred to as the “collector slope”). Example reactant gas plates 200 for air may have a collector slope substantially greater than that in example reactant gas plates 300 for hydrogen gas. For example, the collector slope in reactant gas plates 200 for air may be about 8°and the collector slope in reactant gas plates 300 for hydrogen may be about 4.5°.

Some example electrochemical cell arrangements may have the aspect of generating less residual heat, and/or improved uniformity of heat generation within reactant gas volumes and the temperatures over the electrodes in use, and enhanced efficiency of conversion between chemical and electrical energy, and potentially greater durability of the electrochemical cell. Some example arrangements may have the aspect of more uniform reaction rates over the reaction volume, and/or reduced or more uniform generation of evaporated water. Some or all these effects may result from disclosed arrangements of the outflow array; and/or disclosed arrangements of the inflow array. In some example electrochemical cells, disclosed arrangements of the outflow array, particularly but not exclusively in combination with disclosed configurations of the collector channel, may result in more substantial advantageous effects than example arrangements of the inflow array.

While wishing not to be bound by a particular theory, certain advantageous effects may result from increased uniformity and stability of reactant gas flow speed throughout the reactant gas volume, and consequently over the corresponding electrode; the recirculation and/or stagnation of reactant gas within regions of respective reactant gas volumes may be reduced and substantially laminar or near-laminar flow may be increased.

In example use cases where air is used as a source of oxygen, reduced air flow rates in a region of the reactant gas volume may result in the oxygen component of the air being consumed in chemical reactions more rapidly than it can be supplied, leaving an excessive proportion of nitrogen gas in the region. The rate of chemical reactions in the region will decrease, resulting in reduced heat generation in the region, thus increasing the non uniformity of heat generation across the reactant gas volume. For example, oxygen depletion may arise if outflow apertures become blocked by water or other liquid, potentially resulting in rapid reduction in performance. Certain disclosed examples may have the aspect of reduced blockage of outflow apertures by liquid condensate, which may reduce the risk of reactant gas taking a path of least resistance into another plate and may improve the performance of electrolytic cells.

In some example fuel cells, a large percentage of the heat generated may be absorbed by the electrolyte liquid; for example, approximately 80% - 90% of the heat generated may be absorbed by KOH electrolyte. Improved uniformity of reactant gas flow rate may result in increased uniformity of temperature of electrolyte fluid contained within the electrolyte volume, when in use. While wishing not to be bound by a particular theory, liquid water produced during operation of a fuel cell may evaporate in response to absorbing generated heat, which may improve the performance of some example fuel cells.

While wishing not to be bound by a particular theory, uniform generation of reaction heat may result in improved operational efficiency of electrochemical cells, particularly but not exclusively fuel cells, at least over some range of operating conditions. In general, electrical performance may be better when the operating voltage is not too low, at least over a range of voltages; for example, the electrochemical performance per cell is more electrically efficient at a high cell voltage of 0.8V rather than a low voltage of 0.3V.

While wishing not to be bound by a particular theory, increased uniformity of the flow rate of electrolytic fluid may improve the uniformity of temperature throughout the electrolyte volume, potentially reducing the instances and magnitude of thermal spikes (‘hot spots’) within electrodes and the electrolytic fluids. In some example arrangements, the temperature of reactant gas at a respective outlet, and/or of electrodes, may be no more than about 80°C (for example, about 50°C to about 80°C).

Claims

1. A reactant gas plate (200, 300) for conveying a reactant gas in an electrochemical cell (100), comprising: a reactant gas volume (210, 310) having an inflow side (220, 320) and an opposite outflow side (230, 330), each having a respective proximal and distal end; an inflow array (224, 324) of spaced-apart inflow apertures (222, 322), extending along the inflow side (220, 320), to allow reactant gas to flow into the reactant gas volume (210, 310); and an outflow array (234, 334) of spaced-apart outflow apertures (232, 332), extending along the outflow side (230, 330), to allow reactant gas to flow out of the reactant gas volume (210, 310), the outflow array (234, 334) having a proximal end (227, 327) and a distal end (228, 328); a collector channel (240, 340) having a proximal end (215, 315) and a distal end (216, 316), extending adjacent the outflow array (234, 334) and in fluid communication with the reactant gas volume (210, 310) through the outflow apertures (232, 332); and an exhaust port (250, 350) in fluid communication with the collector channel (240, 340) at the distal end (216, 316), to allow reactant gas to flow out of the reactant gas plate (200, 300); the outflow array (234, 334) having a proximal half (221, 321) coterminous with the proximal end (227, 327), and a distal half (223, 323) coterminous with the distal end (228, 328); wherein the outflow apertures (232, 332) are arranged to reduce the hydrodynamic resistance for reactant gas through the proximal half (221, 321) of the outflow array (234, 334) relative to the hydrodynamic resistance for reactant gas through the distal half (223, 323) of the outflow array (234, 334), operable to bias the flow of reactant gas towards the proximal end (215, 315) of the collector channel (240, 340).

2. A reactant gas plate (200, 300) as claimed in claim 1 , wherein the proximal half (221 , 321) of the outflow array (234, 334) includes a greater number of outflow apertures (232, 332) than the distal half (223, 323) of the outflow array (234, 334); optionally, the proximal half (221, 321) of the outflow array (234, 334) includes at least 50% more outflow apertures (232, 332) than the distal half (223, 323).

3. A reactant gas plate (200, 300) as claimed in claim 1 or claim 2, each pair of neighbouring outflow apertures (232, 332) being spaced apart by a respective outflow spacing (Do); the proximal half (221, 321) of the outflow array (234, 334) having a first mean outflow spacing and the distal half (223, 323) of the outflow array (234, 334) having a second mean outflow spacing; wherein the first mean outflow spacing is less than the second mean outflow spacing; optionally, the first mean outflow spacing between successive outflow apertures (232, 332) is at most 50% of the second mean outflow spacing.

4. A reactant gas plate (200, 300) as claimed in any of the preceding claims, each outflow aperture (232, 332) having a respective mean cross-sectional area; the outflow apertures (232, 332) in the proximal half (221, 321) having a first mean cross- sectional area, and the outflow apertures (232, 332) in the distal half (223, 323) having a second mean cross-sectional area; wherein the first mean cross-sectional area is greater than the second mean cross-sectional area; optionally, the first mean cross-sectional area of the outflow apertures (232, 332) is at least 10% greater than the second mean cross-section area.

5. A reactant gas plate (200, 300) as claimed in any of the preceding claims, each outflow aperture (232, 332) having a length (l_o); the outflow apertures (232, 332) in the proximal half (221, 321) having a first mean length, and the outflow apertures (232, 323) in the distal half (223, 323) having a second mean length; wherein the first mean length of the outflow apertures (232, 332) is less than the second mean length; optionally, the first mean length of the outflow apertures (232, 332) is at most 90% of the second mean length.

6. A reactant gas plate (200, 300) as claimed in any of the preceding claims, the inflow array (224, 324) having a proximal end (217, 317) and a distal end (218, 318); a proximal half (211, 311) of the inflow array (224, 324) being coterminous with the proximal end (217, 317) and a distal half (213, 313) being coterminous with the distal end (218, 318); wherein the inflow apertures (222, 322) are arranged to increase the hydrodynamic resistance for reactant gas flowing through the proximal half (211, 311) of the inflow array (224, 324) relative to the hydrodynamic resistance for reactant gas flowing through the distal half (213, 313) of the inflow array (224, 324), operable to bias the flow of reactant gas into the reactant gas volume (210, 310) towards the exhaust port (250, 350).

7. A reactant gas plate (200, 300) as claimed in claim 6, wherein the distal half (213, 313) of the inflow array (224, 324) includes a greater number of inflow apertures (222, 322) than the proximal half (211, 311); optionally, the distal half (213, 313) of the inflow array (224, 324) includes at least 10% more inflow apertures (222, 322) than the proximal half (211, 311).

8. A reactant gas plate (200, 300) as claimed in claim 6 or claim 7, each inflow aperture (222, 322) having a respective mean cross-sectional area; the inflow apertures (222, 322) in the proximal half (211, 311) of the inflow array (224, 324) having a first mean cross-sectional area, and the inflow apertures (222, 322) in the distal half (213, 313) having a second mean cross-sectional area; wherein the second mean cross- sectional area is greater than first mean cross-sectional area; optionally, the second mean cross-sectional area of the inflow apertures (222, 322) is at least 10% greater than the first mean cross-section area.

9. A reactant gas plate (200, 300) as claimed in any of claims 6 to 8, each inflow aperture (222, 322) having a length (U); the inflow apertures (222, 322) in the proximal half (211 , 311) of the inflow array (224, 324) having a first mean length, and the inflow apertures (222, 322) in the distal half (213, 313) of the inflow array (224, 324) having a second mean length; wherein the first mean length is greater than the second mean length; optionally, the first mean length of the inflow apertures (222, 322) is at least 10% greater than the second mean length.

10. A reactant gas plate (200, 300) as claimed in any of the preceding claims, the collector channel (240, 340) comprising a recess (240, 340) into the reactant gas plate (200, 300), the recess (240, 340) having a recess side (242, 342) opposite the outflow array (234, 334); wherein the recess side (242, 342) diverges from the outflow array (234, 334) with distance along the outflow array (234, 334), from the proximal end (215, 315) of the collector channel (240, 340) towards the distal end (216, 316); optionally, the recess side (242, 342) diverges from the outflow array (234, 334) at one or more angle of 2° to 10°.

11. A reactant gas plate (200, 300) as claimed in claim 10, having a plate thickness (T) adjacent the collector channel (240, 340), and the recess (240, 340) having a mean collector depth (Tc) of at least 50% of the plate thickness (T); optionally, the mean collector depth (Tc) is greater than 1 mm and the plate thickness (T) is 2 mm to 10 mm.

12. A reactant gas plate (200, 300) as claimed in any of the preceding claims, wherein the collector channel (240, 340) includes a plurality of reinforcement bosses (241 , 341).

13. An electrochemical cell (400) comprising an oxidising gas plate (200, 300), to convey oxidising gas; a fuel gas plate (300, 200), to convey fuel gas; an electrolyte plate (100), to convey an electrolyte fluid; an anode plate (420) and a cathode plate (410); the electrolyte plate (100) including an electrolyte volume (110); the cathode plate (410) arranged between the electrolyte volume (110) and the reactant gas volume (210, 310) of the oxidising gas plate (200, 300), and the anode plate (420) arranged between the electrolyte volume (110) and the reactant gas volume (310, 210) of the fuel gas plate (300, 200); operable to generate a potential difference between the anode plate (420) and the cathode plate (410); wherein one or both of the oxidising gas plate (200, 300) and the fuel gas plate (300, 200) is as claimed in any of claims 1 to 12.

14. An electrochemical cell stack (500) comprising a plurality of electrochemical cells (400) as claimed in claim 13, electrically connected to each other in series, operable to generate a potential difference across the electrochemical stack (500).

15. A power supply system (600) for charging or powering an electrical device, comprising an electrochemical stack (500) as claimed in claim 14, and a power supply control system (610) electrically connected to the electrochemical stack (500), and having a connector mechanism (612), operable to electrically connect the power supply control system (610) to an electrical device.

16. A power supply system (600) as claimed in claim 15, comprising an ammonia cracker system (620), for processing ammonia to produce hydrogen gas; and a fuel conveyor channel (622) connecting the ammonia cracker system (620) to the electrochemical stack (500), operable to convey the hydrogen gas from the ammonia cracker system (620) to the electrochemical stack (500).

17. A power supply system (600) as claimed in claim 15 or 16, configured to charge an electric vehicle.