Electrochemical cell

Abstract

An electrochemical cell comprising a non-electrically conductive structural frame for supporting components of the electrochemical cell and a pressure ring, wherein the structural frame comprises a border defining an electrochemical active area and the pressure ring comprises a border defining the electrochemical active area, wherein the inner face of the structural frame border comprises a rebate comprising an inner riser, a landing and an outer riser, wherein the pressure ring is adapted to reside adjacent the landing and retain at least one of the components of the electrochemical cell between the pressure ring and the structural frame landing and wherein the depth of the structural frame landing is greater than the width of the pressure ring border.

Description

Electrochemical CellTECHNICAL FIELD

[0001] The present invention relates to electrochemical cells and more particularly, electrochemical flow cells, electrochemical fuel cells and electrolyser cells for electrolysis of water or other electrolytes.BACKGROUND ART

[0002] Due to its potentially lower carbon footprint, the use of hydrogen as a clean and sustainable energy source is increasingly attracting attention. Accelerating hydrogen energy industrialisation is a strategic initiative for many countries and participants.

[0003] The electrolysis of water is emerging as an alternative source of hydrogen compared to the currently employed extraction of hydrogen from petrochemical sources.

[0004] Classified by the electrolyte, there are three established electrolytic hydrogen production technologies using proton exchange membrane electrolysers, alkaline water electrolysers and anion exchange membrane electrolysers. The electrolysers generally comprise a membrane separating the anode and the cathode along with gas diffusion and catalyst layers. Each membrane type offers particular advantages over the others.

[0005] A proton-exchange membrane (PEM), is a semipermeable membrane adapted to conduct protons and insulate hydrogen and oxygen. They produce high-purity hydrogen gas without the need for additional purification steps and can produce hydrogen gas at higher pressures, reducing the need for additional compression steps. Electrolysers using proton exchange membranes are generally more compact and suitable for applications with space constraints and have faster response times to changes in electrical load.

[0006] Proton exchange membranes have higher catalyst costs than other membranes, requiring expensive platinum-based catalysts for the hydrogen evolution reaction. The membranes are more sensitive to impurities in the water feedstock, requiring extensive water purification systems.

[0007] An anion exchange membrane (AEM) is a semipermeable membrane adapted to conduct anions by reject gases hydrogen and oxygen. AEM membranes use less expensive catalysts such as nickel than proton exchange membranes.

[0008] Alkaline electrolysis membranes do require the use of alkaline electrolytes, which can be corrosive to some materials and usually produce hydrogen gas at relatively lower pressures than proton exchange electrolysers. They have a larger physical footprint compared to other types of electrolysers and have slower response times to changes in electrical load. Alkaline electrolysers can utilise a wider range of feedstocks, including purified water, brackish water, and wastewater, caustic solutions such as sodium hydroxide and potassium hydroxide.

[0009] An alkaline water electrolyser is characterised by having two electrodes operating in a liquid alkaline electrolyte solution of potassium hydroxide or sodium hydroxide. These electrodes are separated by a separator, separating the product gases and transporting the hydroxide ions (OH") from one electrode to the other.

[0010] A fuel cell is an electrochemical device that converts the chemical energy of a fuel, typically hydrogen, into electrical energy. They comprise an electrolyte that allows the movement of ions between the anode and the cathode. It can be a solid, liquid, or polymer membrane, depending on the type of fuel cell. The anode is the electrode where the fuel (usually hydrogen) is oxidised, releasing electrons and generating positively charged ions and the cathode is the electrode where the oxidant (often oxygen from the air) is reduced, accepting electrons and reacting with the ions from the anode.

[0011] Different types of fuel cells, such as proton exchange membrane fuel cells (PEMFC), solid oxide fuel cells (SOFC), alkaline fuel cells (AFC) and molten carbonate fuel cells (MCFC) are known. The specific components and configurations may vary depending on the type of fuel cell technology.

[0012] A flow battery is an electrochemical energy storage device that uses two electrolyte solutions stored in separate tanks. When the battery is charging or discharging, the electrolytes flow through the battery cell stack.

[0013] Flow batteries consist of two separate electrolyte storage tanks, typically containing different redox-active species dissolved in a supporting electrolyte. The tanks may be made of various materials, such as plastic or metal, and their structural problems can include leakage, corrosion, or degradation over time.

[0014] Flow batteries use a membrane to separate the positive and negative electrolyte solutions while allowing the flow of ions.

[0015] Electrolysers, fuel cells and flow batteries all can experience mechanical stress due to factors such as fluid flow, pressure variations, thermal expansion, or vibrations. Excessive mechanical stress can result in structural damage, degradation, or even catastrophic failure.

[0016] Inadequate sealing in stacks of electrolysers, fuel cells and flow batteries can result in gas or electrolyte crossover, reduced efficiency and decreased performance of the overall device.

[0017] All three of these electrolysis technologies have aspects in common and can all act as a pressure vessel albeit with differing internal pressures. They all utilise electrically non-conductive structural frames, made of for example, plastics, to retain various electrolysis cell components. The operating conditions of the electrolysis cell as well as the inherent strength of the plastics, impacts on the sizes of the frames. For example, higher operating pressures conditions generally require thicker frames to reduce frame distortion.

[0018] The preceding discussion of the background to the invention is intended to facilitate an understanding of the present invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge as at the priority date of the application.

[0019] Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0020] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referenced to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.

[0021] The present invention is not to be limited in scope by the specific embodiments described herein, which are intended for the purpose of exemplification only. Functionally equivalent products, compositions and methods are clearly within the scope of the invention as described herein. The entire disclosures of all publications (including patents, patent applications, journal articles, laboratory manuals, books, or other documents) cited herein are hereby incorporated by reference.SUMMARY OF INVENTION

[0022] In accordance with the present invention, there is provided an electrochemical cell comprising a non-electrically conductive structural frame for supporting components of the electrochemical cell and a pressure ring, wherein the structural frame comprises a border defining an electrochemical active area and the pressure ring comprises a border, wherein the inner face of the structural frame border comprises a rebate comprising an inner riser, a landing and an outer riser, wherein the pressure ring is adapted to reside adjacent the structural frame landing and retain at least one of the components of the electrochemical cell between the pressure ring and the structural frame landing and wherein the depth of the structural frame landing is greater than the width of the pressure ring border.

[0023] It will be appreciated that the border of the pressure ring defines an electrochemical active area.

[0024] As a result of the difference in the depth of the structural frame landing and the width of the pressure ring border, the electrochemical active area defined by the pressure ring is larger than the electrochemical active are defined by the structural frame.

[0025] Electrochemical cells are known to operate under pressure with a pressure differential between the cathode and anode sides separated by the membrane.

[0026] Proton exchange membrane electrolysers typically operate at a high differential pressure to improve their performance and efficiency. The high differential pressure refers to the pressure difference between the hydrogen and oxygen sides of the electrolyser. Advantages include improved mass transport or reactant gases to the catalyst layers allowing for more efficient electrochemical reactions. The pressure gradient helps ensure a steady supply of reactant gases to the catalyst sites, reducing concentration polarization and improving the overall reaction kinetics.

[0027] The high differential pressure effective gas diffusion through the GDLs and PTLs. It aids in maintaining a uniform gas distribution across the electrode surfaces, preventing localised gas depletion or stagnation. Improved gas diffusion provides better utilisation of the catalyst materials and facilitates optimal electrochemical reactions.

[0028] Operating at high differential pressure aids in effective water management within the electrolyser. It helps remove water produced at the cathode during the oxygen evolution reaction (OER) and prevents flooding or accumulation of water in the electrode assembly. Efficient water management is crucial for maintaining the proton conductivity of the membrane and avoiding performance degradation.

[0029] High differential pressure reduces ohmic losses associated with proton transport through the membrane. By operating at higher pressures, the proton exchange membrane experiences better contact with the catalyst layers,reducing the resistance to proton conduction. This leads to lower voltage losses and improved overall electrolyser efficiency.

[0030] Hydrogen is typically used at high pressures, so outputting a higher hydrogen pressure reduces the cost / need for additional compressors to get to the needed hydrogen pressure for transportation.

[0031] Advantageously, the pressure ring allows for localised sealing pressure nearer the active area, which reduces the chance of fluid crossover between anodic and cathodic chambers of an electrolyser cell assembly.

[0032] Preferably, the pressure ring releasably engages the structural frame.

[0033] Advantageously, the pressure ring and the structural frame are not bonded together.

[0034] The releasable pressure ring allows for simpler assembly of an electrolyser cell.

[0035] In one form of the invention, the pressure ring is dimensioned to provide a pressure fit with the structural frame.

[0036] In the context of the present specification, the term inner riser shall be understood to refer to the riser at the inner periphery of the structural frame, nearest the active area of the electrochemical cell.

[0037] In the context of the present specification, the term outer riser shall be understood to refer to the riser between the landing and the upper surface of the structural frame.

[0038] In the context of the present specification, the terms riser and landing are used to distinguish between the various surfaces of a rebate and may be in any spatial orientation, particularly when in use.

[0039] It will be appreciated that the width of the pressure ring border should be such that it can provide sufficient length of components of the electrochemical cell to be trapped, causing a seal between the pressure ring and the structural frame. If the width is too small, the components of the electrochemical cell could potentially slip out from under the pressure ring.

[0040] In one form of the invention, the depth of the structural frame landing is 200 % of the width of the pressure ring border. In an alternate form of the invention, the depth of the structural frame landing is 190 % of the width of the pressure ring border. In an alternate form of the invention, the depth of the structural frame landing is 180 % of the width of the pressure ring border. In an alternate form of the invention, the depth of the structural frame landing is 170 % of the width of the pressure ring border. In an alternate form of the invention, the depth of the structural frame landing is 160 % of the width of the pressure ring border. In an alternate form of the invention, the depth of the structural frame landing is 150 % of the width of the pressure ring border. In an alternate form of the invention, the depth of the structural frame landing is 140 % of the width of the pressure ring border. In an alternate form of the invention, the depth of the structural frame landing is 130 % of the width of the pressure ring border. In an alternate form of the invention, the depth of the structural frame landing is 120 % of the width of the pressure ring border. In an alternate form of the invention, the depth of the structural frame landing is 110 % of the width of the pressure ring border.

[0041] It will be appreciated that said components may comprise one or more of a membrane, a membrane electrode assembly (MEA), a separator and a gasket.

[0042] In one form of the invention, a gap is provided between the outer edge of the pressure ring and the outer riser of the structural frame.

[0043] In one form of the invention, a gap is provided between the outer edge of the cathode and the inner riser of the structural frame.

[0044] In one form of the invention, a gap is provided between the inner edge of the pressure ring and the outer edge of the anode.

[0045] Where provided, gaps allow for differential thermal expansion of the various adjacent components.

[0046] In one form of the invention, the structural frame comprises at least one sealing ridge. The sealing ridge is adapted to engage with at least one of the retained components of the electrochemical cell between the pressure ringand the structural frame landing. The sealing ridge is an elongate protrusion on the structural frame landing surface and serves to increase the pressure applied to the components when the pressure is applied to the stack by the tie rods. In one form of the invention, a gasket is provided between the pressure ring and the structural frame landing and is engaged by the structural frame sealing ridge.

[0047] Preferably, the at least one sealing ridge is integral with the structural frame.

[0048] In one form of the invention, the pressure ring comprises at least one sealing ridge. The sealing ridge is adapted to engage with at least one of the retained components of the electrochemical cell between the pressure ring and the structural frame landing. The sealing ridge is an elongate protrusion on the pressure ring surface and serves to increase the pressure applied to the components when the pressure is applied to the stack by the tie rods. In one form of the invention, a gasket is provided between the pressure ring and the structural frame landing and is engaged by the pressure ring sealing ridge.

[0049] Preferably, the at least one sealing ridge is integral with the pressure ring.

[0050] The electrochemical cell may be provided in the form of a flow cell, a fuel cell or an electrolyser cell.

[0051] In one form of the invention, the pressure ring is non electrically conductive.

[0052] In an alternate form of the invention, the pressure ring is electrically conductive.

[0053] The structural frame may be prepared by any method known in the art, including but not limited to injection molding, blow molding, thermoforming, compression molding, rotation molding or 3D printing.

[0054] The pressure ring may be prepared by any method known in the art, including but not limited to injection molding, blow molding, thermoforming, compression molding, rotation molding or 3D printing.

[0055] The pressure ring preferably comprises the same material as the structural frame. The pressure ring is preferably prepared by the same method as the structural frame.

[0056] The structural frame and the pressure ring should have as high a compressive, tensile strength as possible or at least adequate margin of safety for applied forces in whatever configuration to reduce the likelihood of plastic deformation or rupture. Preferably, the thermal coefficients of expansion of adjacent materials such as those comprising the structural frame and the pressure ring are as close as possible.

[0057] Preferably, the structural frame is plastic including but not limited to polysulfones, polyphenylsulfones, polyether ether ketones, polyphenylene sulfides, polyphenylene sulfones, polyamideimides, polyamides, polybutylterephthalates and polyethyl imides.

[0058] Preferably, the pressure ring is plastic including but not limited to polysulfones, polyphenylsulfones, polyether ether ketones, polyphenylene sulfides, polyphenylene sulfones, polyamideimides, polyamides, polybutylterephthalates and polyethyl imides.

[0059] Advantageously, the pressure ring reduces the material requirements of electrolyser cell membranes. Generally, membranes and separators in electrochemical cells are approximately the same size as the structural frame. The present invention enables a membrane or a separator to be smaller than the structural frame and only as large as the pressure ring.

[0060] It will be appreciated that the structural frame and pressure ring are substantially planar and should be the same plan view shape as each other. However, given that the pressure ring is adapted to reside inside the structural frame, it will be appreciated that they will have different sizes despite having the same shape.

[0061] In the context of the present specification, reference to the sizes of the structural frame and the pressure ring shall be understood to refer to their outer dimensions.

[0062] Where the structural frame is a quadrilateral, the pressure ring is a smaller quadrilateral. Where the structural frame is a square, the pressure ring is a smaller square. Where the structural frame is a rectangle, the pressure ring is a smaller rectangle. Where the structural frame and the pressure ring are both rectangles, the length to width ratio of the structural frame is preferably the same as the length to width ratio of the pressure ring.

[0063] Where the structural frame is circular, the pressure ring is circular with a smaller outer radius.

[0064] A circular structural frame would be provided with three different radii. The largest radius would be to the periphery of the structural frame border. The middle radius would be the radius to the outer riser, and the smallest radius would be to the inner riser.

[0065] A circular pressure ring would be provided with two radii. The largest radius would be to the outer face of the pressure ring and the smaller radius to the periphery of the pressure ring border.

[0066] It will be appreciated that the pressure ring border periphery radius will be smaller than the structural frame middle radius.

[0067] Similarly, a square structural frame will comprise a first distance between opposing inner risers, a second distance between opposing outer risers and a third distance between opposing frame sides.

[0068] Similarly, a square pressure ring will comprise a first distance between opposing inner faces and a second distance between opposing outer faces.

[0069] The structural frame second distance is larger than the pressure ring second distance.

[0070] It will be appreciated that a similar concept will apply for rectangular frames, noting the shorter and longer distances of opposing sides of both the structural frame and the pressure ring.

[0071] It will be appreciated that the pressure ring will be provided with an outer face and an inner face irrespective of the shape of the pressure ring.

[0072] The electrochemical cell assembly may further be provided with at least one flow field.

[0073] It is known to provide flow fields as a metallic mesh that allows passage of the oxygen and hydrogen gases whilst also being electrically conductive.

[0074] The upper surface of the pressure ring and the upper surface of the structural frame are substantially coplanar in an assembled electrochemical cell.

[0075] In one form of the invention, the thickness of the pressure ring is approximately equal to the combined height of all layers above the membrane electrode assembly, compensating for compression as required.

[0076] In an alternate form of the invention, the thickness of the pressure ring and the thickness of the gasket is approximately equal to the combined height of all layers above the membrane electrode assembly, compensating for compression as required.

[0077] It will be appreciated that the thicknesses of certain layers in an electrochemical cell may change on compression into a stack. It is within the scope of the skilled addressee to predict and account for compression in determining the preferred heights of inner and outer structural ring risers.

[0078] In one form of the invention, the thickness of the pressure ring is approximately the same as the combined thicknesses of the anode gas diffusion layer and the porous transport layer.

[0079] In an alternate form of the invention, the thickness of the pressure ring is approximately the same as the thickness of the anode gas diffusion layer.

[0080] In one form of the invention, the pressure ring is between about 1 mm and 20 mm thick. In an alternate form of the invention, the pressure ring is between about 1 mm and 10 mm thick. In an alternate form of the invention, the pressure ring is between about 1 mm and 5 mm thick. In an alternate form of the invention, the pressure ring is between about 2 mm and 5 mm thick. In an alternate form of the invention, the pressure ring is between about 3 mm and5 mm thick. In an alternate form of the invention, the pressure ring is between about 4 mm and 5 mm thick.

[0081] In one form of the invention, the pressure ring is at least 1 mm thick. In an alternate form of the invention, the pressure ring is at least 2 mm thick. In an alternate form of the invention, the pressure ring is at least 3 mm thick. In an alternate form of the invention, the pressure ring is at least 4 mm thick. In an alternate form of the invention, the pressure ring is at least 5 mm thick. In an alternate form of the invention, the pressure ring is at least 10 mm thick.

[0082] In one form of the invention, the pressure ring is less than 1 mm thick.In an alternate form of the invention, the pressure ring is less than 2 mm thick.In an alternate form of the invention, the pressure ring is less than 3 mm thick.In an alternate form of the invention, the pressure ring is less than 4 mm thick.In an alternate form of the invention, the pressure ring is less than 5 mm thick.In an alternate form of the invention, the pressure ring is less than 10 mm thick.

[0083] In one form of the invention, the pressure ring is about 1 mm thick. In an alternate form of the invention, the pressure ring is about 2 mm thick. In an alternate form of the invention, the pressure ring is about 3 mm thick. In an alternate form of the invention, the pressure ring is about 4 mm thick. In an alternate form of the invention, the pressure ring is about 5 mm thick. In an alternate form of the invention, the pressure ring is about 10 mm thick.

[0084] In one form of the invention, the pressure ring is between about 5 mm and 30 mm wide. In an alternate form of the invention, the pressure ring is between about 5 mm and 20 mm wide. In an alternate form of the invention, the pressure ring is between about 5 mm and 10 mm wide.

[0085] In one form of the invention, the pressure ring is at least 5 mm wide.In an alternate form of the invention, the pressure ring is at least 10 mm wide.In an alternate form of the invention, the pressure ring is at least 20 mm wide.

[0086] In one form of the invention, the pressure ring is less than 5 mm wide.In an alternate form of the invention, the pressure ring is less than 10 mm wide.In an alternate form of the invention, the pressure ring is less than 20 mm wide.In an alternate form of the invention, the pressure ring is less than 30 mm wide. In an alternate form of the invention, the pressure ring is less than 40 mm wide.

[0087] In one form of the invention, the pressure ring is about 5 mm wide. In an alternate form of the invention, the pressure ring is about 10 mm wide. In an alternate form of the invention, the pressure ring is about 20 mm wide. In an alternate form of the invention, the pressure ring is about 30 mm wide. In an alternate form of the invention, the pressure ring is about 40 mm wide.

[0088] The pressure ring may be provided with a plurality of channels for fluid flow. It will be appreciated that where the pressure ring comprises a plurality of channels, it will the thickness of the pressure ring will need to accommodate the channels.

[0089] In one form of the invention, the channels are between 0.5 mm and 10 mm deep. In an alternate form of the invention, the channels are between 0.5 mm and 5 mm deep. In an alternate form of the invention, the channels are between 1 mm and 5 mm deep. In an alternate form of the invention, the channels are between 1 mm and 3 mm deep. In an alternate form of the invention, the channels are between 1 mm and 2 mm deep.

[0090] In one form of the invention, the channels are at least 0.5 mm deep. In an alternate form of the invention, the channels are at least 1 mm deep. In an alternate form of the invention, the channels are at least 2 mm deep. In an alternate form of the invention, the channels are at least 3 mm deep. In an alternate form of the invention, the channels are at least 5 mm deep. In an alternate form of the invention, the channels are at least 10 mm deep.

[0091] In one form of the invention, the channels are about 0.5 mm deep. In an alternate form of the invention, the channels are about 1 mm deep. In an alternate form of the invention, the channels are about 2 mm deep. In an alternate form of the invention, the channels are about 3 mm deep. In an alternate form of the invention, the channels are about 5 mm deep. In an alternate form of the invention, the channels are about 10 mm deep.

[0092] In one form of the invention, the height of the inner riser is between 1 mm and 20 mm. In an alternate form of the invention, the height of the innerriser is between 1 mm and 10 mm. In an alternate form of the invention, the height of the inner riser is between 1 mm and 5 mm. In an alternate form of the invention, the height of the inner riser is between 2 mm and 5 mm. In an alternate form of the invention, the height of the inner riser is between 3 mm and 5 mm. In an alternate form of the invention, the height of the inner riser is between 4 mm and 5 mm.

[0093] In one form of the invention, the height of the inner riser is at least 1 mm. In an alternate form of the invention, the height of the inner riser is at least 2 mm. In an alternate form of the invention, the height of the inner riser is at least 3 mm. In an alternate form of the invention, the height of the inner riser is at least 4 mm. In an alternate form of the invention, the height of the inner riser is at least 5 mm. In an alternate form of the invention, the height of the inner riser is at least 10 mm.

[0094] In one form of the invention, the height of the inner riser is less than 1 mm. In an alternate form of the invention, the height of the inner riser is less than 2 mm. In an alternate form of the invention, the height of the inner riser is less than 3 mm. In an alternate form of the invention, the height of the inner riser is less than 4 mm. In an alternate form of the invention, the height of the inner riser is less than 5 mm. In an alternate form of the invention, the height of the inner riser is less than 10 mm.

[0095] In one form of the invention, the height of the inner riser is about 1 mm. In an alternate form of the invention, the height of the inner riser is about 2 mm. In an alternate form of the invention, the height of the inner riser is about 3 mm. In an alternate form of the invention, the height of the inner riser is about 4 mm. In an alternate form of the invention, the height of the inner riser is about 5 mm. In an alternate form of the invention, the height of the inner riser is about 10 mm.

[0096] In one form of the invention, the height of the outer riser is between 1 mm and 20 mm. In an alternate form of the invention, the height of the outer riser is between 1 mm and 10 mm. In an alternate form of the invention, the height of the outer riser is between 1 mm and 5 mm. In an alternate form of the invention, the height of the outer riser is between 2 mm and 5 mm. In analternate form of the invention, the height of the outer riser is between 3 mm and 5 mm. In an alternate form of the invention, the height of the outer riser is between 4 mm and 5 mm.

[0097] In one form of the invention, the height of the outer riser is at least 1 mm. In an alternate form of the invention, the height of the outer riser is at least 2 mm. In an alternate form of the invention, the height of the outer riser is at least 3 mm. In an alternate form of the invention, the height of the outer riser is at least 4 mm. In an alternate form of the invention, the height of the outer riser is at least 5 mm. In an alternate form of the invention, the height of the outer riser is at least 10 mm.

[0098] In one form of the invention, the height of the outer riser is less than 1 mm. In an alternate form of the invention, the height of the outer riser is less than 2 mm. In an alternate form of the invention, the height of the outer riser is less than 3 mm. In an alternate form of the invention, the height of the outer riser is less than 4 mm. In an alternate form of the invention, the height of the outer riser is less than 5 mm. In an alternate form of the invention, the height of the outer riser is less than 10 mm.

[0099] In one form of the invention, the height of the outer riser is about 1 mm. In an alternate form of the invention, the height of the outer riser is about 2 mm. In an alternate form of the invention, the height of the outer riser is about 3 mm. In an alternate form of the invention, the height of the outer riser is about 4 mm. In an alternate form of the invention, the height of the outer riser is about 5 mm. In an alternate form of the invention, the height of the outer riser is about 10 mm.

[0100] In one form of the invention, the width of the landing is between 5 mm and 30 mm. In an alternate form of the invention, the width of the landing is between 5 mm and 20 mm. In an alternate form of the invention, the width of the landing is between 5 mm and 10 mm.

[0101] In one form of the invention, the width of the landing is at least 5 mm. In an alternate form of the invention, the width of the landing is at least 10 mm. In an alternate form of the invention, the width of the landing is at least 20 mm.In an alternate form of the invention, the width of the landing is at least 30 mm. In an alternate form of the invention, the width of the landing is at least 40 mm.

[0102] In one form of the invention, the width of the landing is less than 5 mm. In an alternate form of the invention, the width of the landing is less than 10 mm. In an alternate form of the invention, the width of the landing is less than 20 mm. In an alternate form of the invention, the width of the landing is less than 30 mm. In an alternate form of the invention, the width of the landing is less than 40 mm.

[0103] In one form of the invention, the width of the landing is about 5 mm. In an alternate form of the invention, the width of the landing is about 10 mm. In an alternate form of the invention, the width of the landing is about 20 mm. In an alternate form of the invention, the width of the landing is about 30 mm. In an alternate form of the invention, the width of the landing is about 40 mm.

[0104] The electrochemical active area defined by the pressure ring is larger than the electrochemical active area defined by the structural frame. As a consequence, the anode is larger than the cathode.

[0105] In one form of the invention, the size of the electrochemical active area defined by the structural frame is about 50 % of the size of the electrochemical active area defined by the pressure ring. In an alternate form of the invention, the size of the electrochemical active area defined by the structural frame is about 55 % of the size of the electrochemical active area defined by the pressure ring. In an alternate form of the invention, the size of the electrochemical active area defined by the structural frame is about 60 % of the size of the electrochemical active area defined by the pressure ring. In an alternate form of the invention, the size of the electrochemical active area defined by the structural frame is about 65 % of the size of the electrochemical active area defined by the pressure ring. In an alternate form of the invention, the size of the electrochemical active area defined by the structural frame is about 70 % of the size of the electrochemical active area defined by the pressure ring. In an alternate form of the invention, the size of the electrochemical active area defined by the structural frame is about 75 % of the size of the electrochemical active area defined by the pressure ring. In analternate form of the invention, the size of the electrochemical active area defined by the structural frame is about 80 % of the size of the electrochemical active area defined by the pressure ring. In an alternate form of the invention, the size of the electrochemical active area defined by the structural frame is about 85 % of the size of the electrochemical active area defined by the pressure ring. In an alternate form of the invention, the size of the electrochemical active area defined by the structural frame is about 90 % of the size of the electrochemical active area defined by the pressure ring. In an alternate form of the invention, the size of the electrochemical active area defined by the structural frame is about 95 % of the size of the electrochemical active area defined by the pressure ring. In an alternate form of the invention, the size of the electrochemical active area defined by the structural frame is about 96 % of the size of the electrochemical active area defined by the pressure ring. In an alternate form of the invention, the size of the electrochemical active area defined by the structural frame is about 97 % of the size of the electrochemical active area defined by the pressure ring. In an alternate form of the invention, the size of the electrochemical active area defined by the structural frame is about 98 % of the size of the electrochemical active area defined by the pressure ring. In an alternate form of the invention, the size of the electrochemical active area defined by the structural frame is about 99 % of the size of the electrochemical active area defined by the pressure ring.

[0106] In one form of the invention, the pressure ring retains the membrane electrode assembly of the electrolyser cell assembly.

[0107] In an alternate form of the invention, the pressure ring retains the porous transport layer and the membrane electrode assembly of the electrolyser cell assembly.

[0108] The electrochemical cell of the present invention may further be provided with at least one overmoulded gasket.

[0109] In one form of the invention, the gasket is overmoulded onto the structural frame to mechanically interlock the structural frame and the conductive layer. In an alternate form of the invention, the gasket isovermoulded onto the conductive layer to mechanically interlock the structural frame and the conductive layer. Suitable materials in include ePDM, or a fluoroelastomer such as FKM dependant on electrolyte and temperature its subject to.

[0110] Advantageously, an overmoulded gasket can reduce the surface area requiring compression.

[0111] Advantageously, an overmoulded gasket can reduce the individual number of parts to assemble.

[0112] The structural frame further comprises water inlet and water outlet apertures. It will be appreciated that said apertures are different to the tie rod apertures.

[0113] It will be appreciated that in some applications such as proton exchange membrane electrolysis, the pressure ring could be provided in the form of an electrically conductive material such as a metal given that the flowing liquid is non-conductive and the surrounding components are insulators.

[0114] It will be appreciated that electrolyser cell assembly may further comprise a separator selected from the group comprising proton exchange membranes, anion exchange membranes and alkaline separators.

[0115] The separator may form part of a membrane electrode assembly comprising a catalyst-coated membrane and an anode and a cathode on opposing sides of the membrane.

[0116] Alkaline electrolysis separators are known to include porous nickel materials such as nickel foam or mesh coated in a thin layer of nickel hydroxide, which would act as both the electrode and separator or Zirfon, which is a zirconium oxide based ceramic material, or porous ceramics like aluminium oxide or porous ceramic composites.

[0117] It will be appreciated that the membrane should have good mechanical stability, high porosity for efficient ion transport and chemical resistance to alkaline electrolytes.

[0118] Proton exchange membranes are usually perfluorosulfonic acid polymers such as Nation. Other materials include PBI and SPEEK (sulfonated polyether ether ketone), PES (poly ether sulfone), PI (Polyimide).

[0119] It will be appreciated that the membrane should have excellent chemical and thermal stability, high proton conductivity and resistance to chemical degradation operable at elevated temperatures which allow for improved water management and higher system efficiency.

[0120] Anion exchange membranes are typically an anion conducting polymer membrane. Such as quaternary ammonium functionalised polymers like PVam, PPO, PS.

[0121] It is known to coat the separators with catalysts. Alkaline electrolysis separators are typically coated with nickel, nickel oxide or nickel based alloys such as nickel-cobalt or nickel-iron. Proton exchange membranes are typically coated with platinum on the cathode side and iridium oxide or ruthenium oxide at the anode side. Anion exchange membranes are typically coated with platinum or palladium.

[0122] Fuel cells use catalysts to facilitate the electrochemical reactions that occur at the electrodes. In a fuel cell, the anode catalyst facilitates the oxidation reaction of the fuel, such as hydrogen gas (H2) or a hydrocarbon, to release electrons and generate positively charged ions (e.g., H+). The cathode catalyst facilitates the reduction reaction of the oxidant, typically oxygen gas (O2), where the ions and electrons combine to form water (H2O) or other reaction byproducts.

[0123] The most commonly used catalyst material in fuel cells is platinum or platinum-based alloys due to their high catalytic activity and stability. These catalysts are typically applied as a thin layer or coating onto the electrode surfaces, increasing the surface area available for the electrochemical reactions and enhancing the efficiency of the fuel cell.

[0124] Flow batteries typically do not use catalysts in the same way as fuel cells. In flow batteries, the redox reactions occur directly between the electrolyte solutions rather than at specific catalyst-coated electrodes. Theredox-active species in the electrolytes undergo reversible oxidation and reduction reactions during the charging and discharging processes.

[0125] Flow batteries employ different redox couples as the active species in the electrolyte solutions. These redox couples can consist of metal ions, organic compounds, or other electroactive species. The reactions between these species can occur without the need for catalysts.

[0126] However, some flow battery chemistries may utilise catalysts, albeit in a different context. For example, certain types of flow batteries, such as the vanadium redox flow battery (VRFB), may use catalysts in the electrode materials to enhance the kinetics of reactions occurring at the electrode surfaces. These catalysts are typically used to improve the efficiency and performance of the electrode reactions, rather than directly facilitating the redox reactions in the electrolyte.

[0127] In one form of the invention, the electrochemical cell comprises a bipolar plate. In one form of the invention, the electrochemical cell comprises a current collector.

[0128] It is known to use bipolar plates in electrochemical cell assemblies for a variety of purposes. They allow even gas distribution over the electrode surface are and provide electrical conductivity and assist in heat management by facilitating water outtake. They provide support to the membrane electrochemical assemblies and provide mechanical stability to a stack of cells.

[0129] Bipolar plates are generally alternately stacked with membrane electrochemical assemblies so that each plate provides electrical connection on one side for the anode of one membrane electrolyser assembly and on the second side for the cathode of the neighbouring membrane electrochemical assembly.

[0130] The electrochemical cell assembly may further comprise at least one gas diffusion layer. It is known to use a gas diffusion layer for each electrode. They are porous, conductive materials that facilitate the reactant gas distribution, provide a pathway for electron flow and allow efficient water management within the electrolyser. The anode gas diffusion layer distributesthe hydrogen gas evenly across the surface of the electrode, while the cathode gas diffusion layer facilities the distribution of the oxygen gas in the same way. The gas diffusion layers also assist in the removal of water produced during the reactions and provide some mechanical support to the catalyst layers.

[0131] In one form of the invention, the electrochemical cell assembly comprises a gas diffusion layer and a porous transport layer.

[0132] In proton exchange membrane technology, both a porous transport layer and a gas diffusion layer may be provided. They have different functions and are positioned differently within the assembly. The porous transport layer is a thin, porous layer that is typically located between the catalyst and the gas diffusion layer. It acts as a transport medium for reactant gases and facilitates the movement of protons (H+) and water molecules within the electrode assembly. The primary functions of the PTL are proton transport and water management

[0133] The gas diffusion layer is generally a thicker and more porous layer typically positioned between the catalyst layer and the flow field or bipolar plate. The main functions of the GDL are gas distribution and electron conduction.

[0134] It is known to coat gas diffusion layers and porous transport layers to enhance their performance and functionality. The coatings applied to these layers serve various purposes depending on the specific requirements of the electrolyser.

[0135] Gas diffusion layers and porous transport layers may be coated with hydrophobic materials to improve water management within the electrolyser. These coatings repel water and help prevent flooding or blockage of the porous layers, ensuring efficient gas and proton transport. Hydrophobic coatings can also enhance the overall stability and performance of the electrolyser by preventing water buildup and enabling better reactant gas access to the catalyst layers.

[0136] Gas diffusion layers and porous transport layers may be coated with catalyst materials to enhance the electrochemical reactions at the electrode interfaces. The catalyst coatings facilitate faster and more efficient reactions,such as the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. Common catalyst materials used for coating include without being limited to precious metals like platinum (Pt), palladium (Pd), or non-precious metals like nickel (Ni) or cobalt (Co).

[0137] To enhance proton conductivity within the electrode assembly, gas diffusion layers and porous transport layers may be coated with proton- conductive materials. These coatings assist in the efficient transport of protons from the catalyst layers to the proton exchange membrane. Materials such as perfluorosulfonic acid (PFSA) or other ionomer coatings can enhance proton conduction, enabling better performance and higher efficiency of the electrolyser.

[0138] It will be appreciated that the specific choice of coating depends on the electrolyser design, the desired performance characteristics, and the compatibility with the operating conditions. Coatings are applied to gas diffusion layers and porous transport layers to optimise their functionality, improve water management, enhance catalytic activity, or facilitate proton transport, all of which contribute to the overall efficiency and performance of the electrolyser.BRIEF DESCRIPTION OF THE DRAWINGS

[0139] Further features of the present invention are more fully described in the following description of several non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:Figure 1 is an exploded isometric view of an electrolyser cell assembly in accordance with an embodiment of the invention;Figure 2 is an isometric view of a structural frame in accordance with an embodiment of the invention;Figure 3 is an isometric view of a structural frame and pressure ring in accordance with an embodiment of the invention.DESCRIPTION OF EMBODIMENTS

[0140] Those skilled in the art will appreciate that the invention described herein is amenable to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.

[0141] Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0142] Those skilled in the art will appreciate that the invention described herein is amenable to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more steps or features.

[0143] In Figure 1 there is provided an exploded isometric view of an electrolyser cell assembly in accordance with an embodiment of the present invention. The assembly 10 comprises a gasket 12, a structural frame 14, a cathode gas diffusion layer 16, a cathode microporous layer 18, a membrane 20, an anode gas diffusion layer 22, a pressure ring 24 overlaying the edge of the membrane, an anode porous transport layer 26 and a gasket 28. Bipolar plates (not shown) will be provided as is known in the art.

[0144] In Figure 2 there is provided an isometric view of a structural frame 14 in accordance with an embodiment of the present invention. The structural frame 14 comprises a plurality of tie rod apertures 30 for receiving tie rods as isknown in the art. The structural frame 14 may further comprise water inlet apertures (not shown) and water, oxygen and hydrogen outlet apertures (not shown).

[0145] In Figure 3 there is provided a side view of a portion of an electrolyser cell assembly in accordance with an embodiment of the present invention. The Figure depicts the structural frame 14 supporting a membrane 20 and an anode gas diffusion layer 22. The pressure ring 24 overlays the anode gas diffusion layer 22 to retain it and the membrane 20. The cathode gas diffusion layer 16 and the cathode microporous layer 18 reside inside the electrochemical active area defined by the structural frame 14. The anode porous transport layer 26 overlays the anode gas diffusion layer 22 and resides inside the electrochemical active area defined by the pressure ring 24.

[0146] It will appreciated that the anode and cathode components may be reversed such that cathode gas diffusion layer is numbered 26, the anode porous transport layer is numbered 16, the cathode microporous layer is numbered 22 and the anode gas diffusion layer is numbered 18.

[0147] The structural frame 14 comprises a series of sealing ridges 30 to engage the membrane 20.

[0148] Other components of an electrolyser cell assembly such as separators, flow fields, electrodes, hydrophobic layers and hydrophilic layers may be provided as required.

[0149] The present invention enables the use of smaller membranes than cells of the prior art that require a membrane to extend the full width of the structural ring.

[0150] In use, electrolyte (either water or alkaline solution depending on the separator type) passes through the electrolyte inlet into the one or more of the chambers either side of the separator. The electrolyte reacts with the electrode / s passing ions through the separator and excess electrolyte flows out electrolyte outlet and then through all of the adjacent cells to the end plate and out of the system. Oxygen and hydrogen exit the respective outlets as is known in the art.

[0151] To assemble a cell assembly 10, the structural ring 14 is placed on a hard clean surface, and the parts are placed in the order as shown in exploded view of cell assembly in Figure 1 .

[0152] To assemble a stack, the parts are laid vertically as shown in Figure 1. The structural frame is placed on top of a bipolar plate. The outer dimensions of the structural frame should be approximately the same as the outer dimensions of the bipolar plate.

[0153] The cathode gas diffusion layer is placed inside the structural frame in the active area followed the membrane electrode assembly. The pressure ring is placed on top of the MEA inside the outer riser of the structural frame followed by the anode gas diffusion layer and the porous transport layer to provide an electrolysis cell. The above procedure has been described in terms of a proton exchange membrane. It is within the scope of the skilled addressee to understand that variations may occur for other electrolysis designs of fuels cells or flow batteries.

[0154] The end plate should be made of a material that is suitably strong to maintain internal pressure of the stack and compressive forces applied to the tie rods. It will be appreciated that if the end plate doubles as the current collector, then the material has to be electrically conductive. End plates are commonly made of Stainless Steel 316.

[0155] The tie rods act as guiding rods to accurately place parts on top of each other. Finally, a tensioner system is used to pull the stack together and place the nuts on the tie rods.

Claims

CLAIMS1. An electrochemical cell comprising a non-electrically conductive structural frame for supporting components of the electrochemical cell and a pressure ring, wherein the structural frame comprises a border defining an electrochemical active area and the pressure ring comprises a border defining the electrochemical active area, wherein the inner face of the structural frame border comprises a rebate comprising an inner riser, a landing and an outer riser, wherein the pressure ring is adapted to reside adjacent the landing and retain at least one of the components of the electrochemical cell between the pressure ring and the structural frame landing and wherein the depth of the structural frame landing is greater than the width of the pressure ring border.

2. An electrochemical cell in accordance with claim 1 , wherein the pressure ring releasably engages the structural frame.

3. An electrochemical cell in accordance with claim 1 or claim 2, wherein a gap is provided between the outer edge of the pressure ring and the outer riser of the structural frame.

4. An electrochemical cell in accordance with any one of the preceding claims, wherein a gap is provided between the outer edge of the cathode and the inner riser of the structural frame.

5. An electrochemical cell in accordance with any one of the preceding claims, wherein a gap is provided between the inner edge of the pressure ring and the outer edge of the anode.

6. An electrochemical cell in accordance with any one of the preceding claims, wherein the structural frame comprises at least one sealing ridge.

7. An electrochemical cell in accordance with claim 6, wherein the at least one sealing ridge is integral with the structural frame.

8. An electrochemical cell in accordance with any one of the preceding claims, wherein the structural frame and pressure ring are the same shape as each other.

9. An electrochemical cell in accordance with any one of the preceding claims, wherein the pressure ring resides inside at least a portion of the structural frame.

10. An electrochemical cell in accordance with any one of the preceding claims, wherein the pressure ring comprises the same material as the structural frame11. An electrochemical cell in accordance with any one of the preceding claims, wherein the pressure ring and the structural frame are plastic.

12. An electrochemical cell in accordance with any one of the preceding claims, wherein the pressure ring is adapted to retain at least a portion of an electrochemical cell membrane or separator between the pressure ring and the structural frame landing.

13. An electrochemical cell in accordance with any one of the preceding claims, wherein the pressure ring comprises at least one flow field in fluid communication with at least one flow field on the structural frame.

14. An electrochemical cell in accordance with any one of the preceding claims, wherein the electrochemical cell is provided in the form of a flow cell, a fuel cell or an electrolyser cell.

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