Electrochemical cell and method for processing hydrogen-contained gas flow

Abstract

To provide an electrochemical cell that electrochemically compresses and refines hydrogen, and a method for processing a hydrogen-contained gas flow.SOLUTION: There is provided an electrochemical cell or a stack of electrochemical cells. Each electrochemical cell in the stack comprises at least a membrane electrode assembly (MEA) and means of providing the electrochemical cell with the necessary power, and the MEA comprises at least an anode, a cathode, an anion exchange membrane located between the anode and the cathode, an inlet for introducing hydrogen at a first pressure into the anode half-cell, and an outlet for transferring hydrogen at a second pressure from the cathode half-cell.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electrochemical cell and a method for treating a hydrogen-containing gas stream, optionally by using one or more electrochemical cells arranged in a stack. The cells or stacks may be used, for example, for detecting hydrogen in the stream, purifying and compressing hydrogen, and generating electricity. [Background technology]

[0002] Hydrogen is used in many ways, such as an industrial feedstock or as a means of long-term energy storage. Certain applications, such as fuel cells in vehicles, require high pressures, such as 350 or 700 bar. Higher pressures may be desirable for some applications. It is essential that the hydrogen stored is dry, as residual moisture can damage components, reduce efficiency, or have other undesirable consequences.

[0003] Hydrogen is becoming more widely adopted as both a long-term and short-term energy storage means. It can also be used in existing natural gas pipelines to provide heat and when used in fuel cells to provide electricity. Hydrogen also has many industrial applications.

[0004] Electrolysers are devices used to split water to produce hydrogen and oxygen. Such systems are generally one of three main technologies currently available: Anion Exchange Membrane (AEM) systems, Proton Exchange Membrane (PEM) systems, and liquid alkaline systems. Other systems, such as solid oxide electrolysis, are also available.

[0005] As disclosed in WO 2011 / 004343, hydrogen can be produced from hydrocarbons or by electrolysis in an environmentally friendly manner. It is preferable to produce "green" hydrogen without relying on fossil fuels.

[0006] Conventional hydrogen compression methods include mechanical and non-mechanical means. Mechanical compression has many problems, such as energy required, contamination of hydrogen with oil / lubricants in the compressor, and the need for pre-drying. Additionally, powering such compressors and the cost of the compressor are also considerations.

[0007] In PEM electrochemical compression, low pressure hydrogen reacts with water and splits into hydronium ions and electrons, which pass through a membrane before recombining to form hydrogen gas and water. The following reactions occur in a PEM system: PEM Anode H 2 +2H 2 O→2H 3 O + +2e - PEM cathode 2H 3 O + +2e - →H 2 +2H 2 O

[0008] Water is present at the cathode in a PEM electrochemical compression system, observing fundamental differences to the reaction pathways seen in the present invention. Thus, while hydrogen may be compressed in a PEM electrochemical cell, hydrogen inherently contains water and is therefore an impurity, so a dryer must be used in PEM electrochemical compression prior to storage.

[0009] Furthermore, the acidic environment of PEM means that platinum group metal (PGM) catalysts must use expensive metals / coatings (e.g. titanium), which is an obstacle to widespread application for a number of reasons. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2011 / 004343 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention aims to provide a means and method for electrochemically compressing and purifying hydrogen. [Means for solving the problem]

[0012] According to the present invention, there is provided an electrochemical cell comprising: an anode half-cell having an inlet configured to receive hydrogen at a first pressure; a cathode half-cell having an outlet configured to transport hydrogen at a second pressure; a membrane electrode assembly (MEA) separating the anode half-cell and the cathode half-cell; and a power source, wherein the MEA comprises at least an anode electrode, a cathode electrode, and an anion exchange membrane (AEM) disposed between the anode electrode and the cathode electrode.

[0013] As used herein, the term "cell" refers to an electrochemical cell. Although a stack is typically considered to be multiple cells, the term "cell" may be used to describe a single cell within a stack or the entire stack.

[0014] As used herein, with respect to anion exchange membranes, the terms "humid," "hydrated," and "humidified" are used interchangeably.

[0015] As used herein, the terms "moisture sensor" and "humidity sensor" are used interchangeably and are intended to cover all sensors capable of detecting the presence of water.

[0016] As used herein, the terms "anode and cathode" may be used interchangeably to refer to an anode half-cell and a cathode half-cell.

[0017] As used herein, the term "anion exchange membrane (AEM)" may be used for any ion exchange material that has anion exchange properties, but may or may not have cation exchange properties (e.g., potassium ions added by KOH doping PBI-based materials, or mixtures of cationic and anionic polymers and / or functionalities). The additional cationic groups may or may not be involved in either or both half-reactions.

[0018] As used herein, the term "compression" generally means an increase in pressure, although it is contemplated that in some embodiments a reduction in pressure may be desired and the term "compression" may be used synonymously with decompression. Although an electrochemical cell may be referred to as a compressor, this does not exclude variations in which the cell operates as a sensor or means solely for purification.

[0019] As used herein, the term "destination" refers to the end use of the refined and / or compressed hydrogen, such as, but not limited to, refueling or storage.

[0020] Not described is the Balance Of Plant (BOP), including temperature and pressure regulation means, valves, wiring, etc. The connections between the power supply and the electrochemical cells are also not described herein.

[0021] Since hydrogen is often required at pressures higher than a single cell compressor can achieve, more than one cell may be used in series, assuming multiple cells form a stack. More than one stack may be used in the compressor. Additionally, more than one cell may be desirable if impurity concentrations are above a certain level.

[0022] According to the present invention, there is provided in a second embodiment an electrochemical cell assembly, generally as described above, comprising at least a first electrochemical cell and a second electrochemical cell arranged in a stack, the electrochemical cells being in fluid communication with an outlet of a cathode half-cell of the first electrochemical cell and an inlet of an anode half-cell of the second electrochemical cell.

[0023] As used herein, the term "stage of cells" means one or more cells whose anodes are generally similar in pressure and whose cathode outlets from each cell in a stage are combined to feed the anodes of the cells in the next stage. The stages may be connected in parallel, in series, or in a combination of parallel and series.

[0024] When compressing a fluid, it is common practice to compress in multiple stages. The same approach can be applied to electrochemical compression. In one embodiment of the present invention, it is assumed that multiple stage compression is achieved by providing one or more cells in each stage as described above. Hydrogen enters the anodes of the cells in the first stage at a first pressure, while the cathode outlets from the cells of the first stage are at a second pressure and the multiple outlets are combined. The cathode outlet from the first stage at the second pressure typically serves as the inlet to one or more anode half-cells of the second stage, or, if there is only one compression / purification stage, the outlet leads to storage.

[0025] It is envisioned that the cells or stacks of each stage may be arranged in parallel, or as a space saving measure, in series with piping and the BOP allowing for multiple stages. The figures show various arrangements. Means may be provided to separate and / or insulate each cell.

[0026] The total current applied to a cell or stack of cells for each group or stage of cells being compressed is generally approximately the same as the total current applied to the next group or stage of cells being compressed. If the pressure difference across each cell at a given stage is different from the pressure difference at other stages, there will be a variation in the current required across the membrane at each stage. As the pressure difference increases, a higher current density is required to overcome the reverse diffusion (crossover) of hydrogen. However, as a result, the efficiency of the sensing current may decrease. This embodiment is shown in the figures.

[0027] Typically, purification occurs simultaneously with compression. In such embodiments, the second pressure is higher than the first pressure. At each cathode outlet, any known means for adjusting the pressure may be used so that hydrogen flows out of the cathode outlet at high pressure. In another embodiment, it may be necessary to reduce the pressure of hydrogen, and the pressure adjustment means may be manufactured as appropriate.

[0028] In an AEM compressor equipped with a single cell or stack of cells, hydrogen flows into the anode half-cell of the first cell at the first pressure and is pressurized until it reaches the second pressure at the first cathode half-cell. The hydrogen stream at the second pressure is sent from the first cathode half-cell to the anode half-cell of the second cell. The hydrogen is pressurized until it reaches the third pressure at the second cathode half-cell, and so on. In a series of cells, the pressure increases progressively, for example, P1 < P2 < P3 < P4, etc. The pressure in the cathode half-cell is higher than the pressure in the anode, and the hydrogen contained in the cathode half-cell is assumed to be of higher purity than the hydrogen in the corresponding anode and the hydrogen in the previous cell.

[0029] The AEM system is hydroxide OH - and passes through the membrane instead of hydronium (solvated protons), which is essentially different from PEM. Therefore, the operating mechanism is different, and new problems must be overcome. The reaction is as follows. AEM anode H 2 + 2OH - → 2H2 O+2e - AEM cathode 2H 2 O+2e - →H 2 +2OH -

[0030] With electrochemical compression in AEM-based systems, no additional drying step is required since water is consumed at the cathode in parallel with hydrogen compression. A clear advantage over other options is realized in current practice.

[0031] The reaction pathway is fundamentally different from PEM and contradicts the commonly held view in the electrochemical field that hydrogen always splits into two hydrogen ions.

[0032] It is understood that hydrogen electrochemically compressed in an AEM system is dry. As water is produced in the anodic reaction and consumed in the cathodic reaction, the nearly dry hydrogen may migrate from the first cell to the second cell, etc. Preferably, an MEA is applied to retain the water by the water management means described herein.

[0033] In PEM systems, platinum or platinum group metals (PGMs) are required as catalysts at both the anode and cathode. In the AEM electrochemical compression of the present invention, PGM catalysts may be used, but may not be required if the system can be made more sustainable in nature. Any known catalyst for the Hydrogen Evolution Reaction (HER) and / or Hydrogen Oxidation Reaction (HOR) may be used, but it is not intended that the present invention be limited by the aforementioned catalysts. The anode catalyst and cathode catalyst may be the same or different.

[0034] The MEA may be free of ionomer and / or binder. Alternatively, the MEA may include ionomer and / or binder. In one embodiment, the MEA is envisioned to include a substrate with conductive whiskers and a thin catalyst layer sputtered onto the substrate to maximize surface area and minimize catalyst required. The large surface area and intimate contact reduces the need for ionomer.

[0035] The anion exchange membrane may be any membrane with the desired properties. The required properties are primarily high ionic conductivity, low gas permeability, high mechanical strength, and hydrophilicity. However, it is envisioned that the membrane may be a composite membrane. The composite membrane may comprise an inorganic filler consisting of hygroscopic particles, such as, but not limited to, clay nanoparticles, such as montmorillonite, an organic filler, such as, but not limited to, any ionomer nanoparticles or fibers produced by electrospinning, or a combination of inorganic and organic fillers. The ionomer may be an anion ionomer.

[0036] It is envisioned that the membrane has a polymer backbone with hydrophilic inorganic and / or organic fillers. The hydrophilicity ensures that the water is retained and the high pressure hydrogen remains dry. It is envisioned that the polymer may be polybenzimidazole (PBI), preferably modified to improve alkali resistance and / or covalent bonding with positive charges, although this is not intended to be a limiting feature. Additionally, the membrane has the advantage that it has the ability to exchange excess OH, as compared to the ion exchange capacity derived from covalently bonded positive charges (e.g., quaternary ammonium salts) and / or neutralization of acid hydrogen (e.g., pyrrole hydrogen in PBI) using, but not limited to, highly concentrated alkaline solutions (e.g., KOH). - It is assumed that doping with OH - The source may be in any form, but is preferably aqueous.

[0037] When electrochemically compressing hydrogen, the pressure difference across the membrane must be considered. If the pressure difference is too large, the membrane or other components may be damaged. Increasing the mechanical strength of the membrane may reduce performance in other areas, such as ionic conductivity. The pressure difference in a single cell is theoretically unlimited, but in practice is limited due to component integrity and crossover. It is assumed that a pressure rise of 1 bar-2000 bar, more preferably 1 bar-1000 bar, can be observed in each cell. The pressure difference may be in the range of 10 bar-500 bar, 10 bar-100 bar, 10 bar-80 bar, 20 bar-50 bar, 30 bar-40 bar. The AEM electrochemical compressor assumes a rise of about 35 bar per cell in a stack.

[0038] It is envisaged that the electrochemical compressor will function with hydrogen produced by any known means such as steam reforming, but preferably a green hydrogen source is used. To achieve this, the inlet air stream is preferably the outlet air stream from an electrolyser, more preferably an AEM electrolyser. Impurities may be present, but should be limited to water and oxygen. Other impurities, if present, should not be likely to impair the operation of the catalyst, excluding impurities such as carbon monoxide. Other impurities, e.g. OH - Acids or salts containing anions different from OH - It can react with CO 2 , S.O. 3 , NO 3 Situations may arise where gaseous acids such as argon, argon, and argon gas are acceptable. If the catalyst is only temporarily impaired, gaseous acids may be acceptable because they can be converted to their acidic form on the anode side of the reaction that consumes hydroxy ions to remove the acid. In embodiments where hydrogen from steam reforming is compressed, impurities are assumed to be removed.

[0039] According to the present invention, hydrogen is pressurized and purified and does not pass any impurities that are permitted through the first half-cell. Water should retain membrane binding and OH generated at the cathode is removed. -When the water moves to the anode, it is consumed by the anodic reaction. - Water may be transported from the cathode to the anode along with the water vapor. The water flux across the membrane depends in both magnitude and direction on the applied current.

[0040] It is contemplated that power may be supplied as DC, AC, pulsed current, or reverse pulsed current. However, in a preferred embodiment, the supplied power is either DC, pulsed current, or reverse pulsed current. The advantage of reverse pulsed current is that harmful substances are removed from the electrodes when the current is temporarily reversed.

[0041] All cell membranes must be kept sufficiently humidified. With the membrane selected for its properties, the water generated in the anode reaction serves the above purpose. The water produced should be in sufficient quantity to keep the membrane hydrated without flooding the cathode or being carried away by the cathode hydrogen stream. Water management means are used to limit / prevent unwanted water movement. Water management means are disclosed herein.

[0042] For example, a microporous layer (MPL) may be used that is porous enough to allow hydrogen transport but prevents water from flowing across the MPL in either direction. Additionally, the membrane may have a hydrophilic component, which maintains water membrane binding but allows it to be used for the cathode reaction.

[0043] The MEA may include an anode, an anion exchange membrane, and a cathode, but typically includes additional layers. Any one or more of the following may be included at one or both poles, alone or in combination: A gas diffusion layer (GDL) may be provided at one or both of the cathode and anode. If a GDL is provided, the anode GDL, the anode catalyst layer, the membrane, the cathode catalyst layer, and the cathode GDL constitute the MEA. In another embodiment, an MPL may be used. The MPL is generally provided only on the cathode side, but may be provided only on the anode side, or may be provided on both sides if one or more MPLs are used, and in this case the MPLs may be the same or different. The MPL is selected because it has porosity and hydrophobicity. As further described below, a water management membrane may be used on the anode side, the cathode side, or both sides.

[0044] It is envisioned that the MPL may be provided on the membrane of each cell on the cathode side, or on only one or some of the membranes. Alternatively, the MPL may be provided on the anode side or on both the anode and cathode sides. It is further envisioned that, if an MPL is used, the MPL may have different properties at various positions in the stack, such as being more hydrophobic in later cells. A more hydrophobic MPL in the final cell would prevent (excess) water from being present at the final outlet, which may be undesirable in the first cell, since the varying MPL properties will affect other properties of the membrane. MPLs are generally produced by casting a slurry containing a conductive material and a binder onto a substrate. The conductive material may be, but is not limited to, carbon black or nickel nanoparticles. The binder is a hydrophobic polymer, such as, but not limited to, PTFE or FEP. The pore size, distribution, distribution of pore sizes, hydrophobicity, and other physiochemical properties can be tailored by varying the components, the ratio of each component, and / or the manufacturing method.

[0045] Another means of water management is to include an ionomer in the MEA on one or both sides of the AEM, i.e., on one or both of the anode and cathode sides. It is preferred that the ionomer is included on both the cathode and anode sides of the membrane. Typically, for water management, there is relatively more ionomer included on the cathode side than on the anode side. Alternatively, it is contemplated that the anode side of the AEM may not include an ionomer, while the other side of the membrane may include an ionomer.

[0046] Yet another means for water management in the membrane is to include a water management membrane in the MEA. The water management membrane is preferably hygroscopic and on the cathode side of the MEA. Also, the water management membrane is preferably highly ionically conductive and / or highly electrically conductive. The water management membrane may be on the anode side, the cathode side, or on both sides. In yet another embodiment, the water management membrane may be located between two AEMs, and the water management membrane in any of the previous embodiments is part of the MEA. The water management membrane may be, for example, an ionomer mixed with carbon black.

[0047] Yet another means for water management is to use an anion exchange membrane composite, where the filler particles / nanoparticles / microparticles are hygroscopic. It is assumed that the filler particles / nanoparticles / microparticles may have a concentration gradient within the membrane, or may be separate layers on one or both sides of the AEM, not necessarily adjacent to the AEM. The cathode side of the membrane, which has a relatively high concentration of particles, is compared to the anode side.

[0048] It is contemplated that any one of the water management mechanisms described herein may be used alone or in combination.

[0049] According to the present invention, there is provided a method of treating a hydrogen-containing gas stream, the method comprising the steps of providing an electrochemical cell as generally described above, supplying a hydrogen-containing gas stream to an inlet of an anode half-cell, and delivering hydrogen from an outlet of the cathode half-cell.

[0050] All of the structural limitations associated with the device apply to the method of operating the cells, and therefore the same applies to the method of using a compressor with a stack of cells.

[0051] The methods for operating a single cell compressor are generally applicable to operating a compressor comprising a stack of cells.

[0052] According to the present invention, there is provided a method of treating a hydrogen-containing gas stream, the method comprising the steps of providing an electrochemical cell assembly substantially as described above, supplying a hydrogen-containing gas stream to an inlet of an anode half-cell of a first electrochemical cell in the stack, transferring hydrogen from an outlet of the cathode half-cell of each electrochemical cell in the stack to an inlet of an anode half-cell of another electrochemical cell, and transporting hydrogen from an outlet of the cathode half-cell of a final electrochemical cell in the stack to an external destination.

[0053] In the electrochemical cells, electrochemical cell assemblies, and methods described above, the inlet gas stream may be delivered directly from an electrolyser, a hydrogen storage tank, or any suitable source of hydrogen of suitable purity.

[0054] The only possible impurities, especially from the electrolytic production of hydrogen, are water and oxygen. Water should combine with the membrane and oxygen reacts with hydrogen in the first anode half-cell to produce water. The catalyst is not active for ORR and any oxygen present is preferably pumped out of the anode half-cell. Therefore, these impurities are not expected to be a problem. However, CO 2 , NO 2 , S.O. 3 Since other impurities such as ruthenium oxide, arsenic oxide, and niobium oxide may be present and these impurities may reduce the efficiency of the first few cells, a means may be provided to purge the anode half-cell.

[0055] All of the above architectural limitations related to the device also apply to the method of operating the cell or stack and should be addressed accordingly.

[0056] It is assumed that the final outlet of the stack is connected to one or more storage tanks suitable for containing hydrogen at the desired pressure, which can be anywhere from 30 bar-1000 bar. The pressure can be increased to any required level, including industry standards of 300 bar, 700 bar, and 1000 bar. It is assumed that the pressurized hydrogen from the outlet can be directed to any system or means for using, transporting, or storing the pressurized hydrogen.

[0057] As water is consumed in each cathode compartment, the hydrogen is effectively dried while being compressed. This is fundamentally different from PEM electrochemical compression, where water is involved in the form of hydronium (solvated protons). In PEM systems, water is transported to the cathode in the form of hydronium along with the hydrogen ions. Thus, the hydrogen produced is essentially humid. It is important to ensure that each membrane in the stack is properly hydrated to maintain the required membrane conductive properties. If insufficient water is generated in the anode half-cell, it is assumed that the moisture content of the membrane can be stabilized by adding water to the hydrogen inlet to ensure the feed is moist. However, adding too much water to the hydrogen stream can result in the outlet stream becoming humid or flooding the anode half-cell and preventing the hydrogen from contacting the anode catalyst. This achieves the goal of pressurizing the hydrogen, but the hydrogen is not dried, or the cell efficiency can be reduced due to mass transport overpotential. A control system may be used to pressurize and dry the hydrogen, as described below.

[0058] It is envisaged that at least two moisture sensors will be used to control moisture in the system. A first moisture sensor will be installed on the feed stream, a second on each outlet stream, but most importantly on the hydrogen outlet of the last cell. One or all cells in the stack can also be provided with a moisture sensor that determines the saturation of the membrane at a given point in the stack, allowing an operator to determine if the membrane is too dry to operate in the stack, or if the humid hydrogen from the outlet can be vented or, preferably, reduced pressure and recycled to the inlet, as described below. Alternatively, a thermal conductivity sensor can be used instead of a moisture sensor. Any suitable sensor alternative can be used.

[0059] The two or more sensors are operatively connected to a control module, such as, but not limited to, a PID controller. When the moisture content falls below a predetermined threshold, water is introduced to one or more water inlets. Multiple inlets for introducing water can be provided to the stack, typically leading to either the cathode compartment, the anode compartment, or between the cells. However, since pressure increases along the stack, it is preferred to provide a single inlet for additional water on the feed stream at a first pressure. The inlets are then provided after the first sensor, and the water inlet is provided before the stack or leading into the first anode compartment.

[0060] Problems can arise if moist hydrogen escapes the final cell of the compressor. Moist hydrogen may not be fit for purpose and therefore should not be stored. It is therefore envisaged that if moist hydrogen escapes the stack, the hydrogen may be vented. In a preferred embodiment, the moist hydrogen may be recirculated from the outlet before it reaches its destination. It is envisaged that the pressurised hydrogen is recirculated from the outlet to the inlet via a means of reducing the pressure to a suitable level for reintroduction at an earlier stage of the compressor stack.

[0061] It is envisioned that a temporary holding tank would be provided on the recirculating air stream to minimize the need for venting in the event of excess moisture. It is envisioned that the temporary holding tank would have a means to drain concentrated moisture so that it can be removed from the tank. Ideally, there would be a means to direct the water for reuse in this or another system.

[0062] Green hydrogen is produced by utilizing excess energy from renewable sources, usually produced by electrolysis. This necessarily results in discontinuous hydrogen generation and therefore a discontinuous feed stream for the electrochemical compression stack. The electrochemical refinery and compressor are adapted for intermittent operation. Using a buffer tank between the electrolyser and the compressor to store hydrogen at an intermediate pressure, e.g. 35 bar, allows a more consistent supply of hydrogen to the AEM compressor.

[0063] It is contemplated that while the membranes may all be the same, the membranes may vary between cells in the stack. In one embodiment, the first cell may have the thickest membrane, and subsequent cells may have thinner membranes. Alternatively, the first cell may have a thinner membrane, and subsequent cells may have progressively thicker membranes. In another embodiment, the membrane thickness may vary non-linearly, i.e., the membrane may go from relatively thin to thick and then back to thin, or from thick to thin and then back to thick, or any variation of these. Thicker membranes retain more water, and therefore are more resilient to fluctuations in moisture content, thus ensuring that the conductive properties are maintained and that the likelihood of the hydrogen outlet being moist is reduced. Thicker membranes may be more resilient to larger pressure differences, thereby requiring fewer cells to make the same step change in pressure difference.

[0064] Thicker membranes are generally more resilient to larger pressure differentials and higher pressures. It is contemplated that supports may be provided on either side of the membrane. The supports may be of any suitable material, i.e., materials that do not adversely react with the system. Any suitable membrane support may be used, such as, but not limited to, nickel foam. The supports may have a mesh or other suitable structure that promotes membrane resilience to pressure. Additionally, membrane supports are useful in preventing creep deformation of the membrane due to high pressure differentials.

[0065] In a preferred embodiment, thermal management means are provided for the cell or stack of cells. Heating and / or cooling can ensure that an optimum temperature is reached, which is assumed to be above room temperature but below 100°C, more preferably 40°C-80°C, substantially 60°C.

[0066] It is envisaged that means may be provided for thermal management of the cells or stacks. For example, heating and / or cooling may be achieved using heating cartridges or radiators mounted on each end plate and / or intermediate frame of the stack or cells. Another option is a liquid circulating within or in contact with any of the aforementioned components, but preferably without contacting any components that may affect the reaction or stack efficiency.

[0067] While it is assumed that the stack is made up of cells with substantially the same cross-sectional area, the stack may also include cells with various cross-sectional areas. In such an embodiment, the cross-sectional area is gradually reduced from the first cell to the last cell, and the current density increases accordingly to maintain the same hydrogen flow rate in proportion to the total current, and the reduced volume passively promotes pressure build-up, thereby improving water management by increasing the electro-osmotic resistance as the cathode hydrogen stream transports excess water from one cell to the next. The opposite, i.e., the cross-sectional area is gradually increased from the first cell to the last cell, and the current density is correspondingly reduced, and water management is promoted by progressively dehydrating from one cell to the next. The cross-section of each cell may vary, or multiple cells in the stack may have the same cross-sectional area before the area reduction. In another embodiment, the cross-section may vary non-linearly, i.e., from relatively large to small and then back to large, or from small to large and then back to small.

[0068] The cross section of the cell or stack of cells may be any shape. It is contemplated that the shape may be circular, square, or rectangular. Alternatively, other shapes may be used, such as, but not limited to, pentagonal, hexagonal, heptagonal, octagonal, or any other regular or irregular cross-sectional shape.

[0069] It is envisioned that various combinations of membrane cross-sectional areas and membrane thicknesses may be used, in addition to other previously mentioned variations such as MPL or GDL. In one embodiment where the cross-sectional area decreases along the stack, the membrane thickness may increase along the stack. Such a configuration facilitates increased pressure due to reduced volume, and also facilitates reduced water content in the cathode hydrogen stream by increasing electro-osmotic resistance at higher current densities and reducing water transport through thicker membranes. In other embodiments, any combination of the previously mentioned variations may be used.

[0070] It is important to ensure that there is sufficient water in each membrane at start-up, and compressor assembly and standby conditions should be taken into account to ensure that the membranes, typically the MEAs, are largely saturated at the time of assembly. Means for adding water may also be provided to each anode cell.

[0071] The present invention is not intended to be limited by the catalyst or the method of depositing the catalyst, but it is contemplated that the catalyst may be applied to the conductive substrate using a catalyst slurry or spray. The catalyst typically comprises nanoparticles, and the conductive catalyst layer substrate may be carbon cloth or Ni foam, etc. Another catalyst substrate may be Ce or nano / micro particles of Ce.

[0072] Moreover, electrochemical compression requires no moving parts, with all the associated advantages. Moreover, electrochemical compression has much lower energy than alternative compression methods and is therefore more environmentally sound, improving the overall efficiency when considering hydrogen production and management. Compression may be done in a single stage, depending on the elasticity of the membrane used. Furthermore, the process can be performed at constant temperature rather than adiabatic.

[0073] As described herein, electrochemical compressors may also be used in other applications with generally similar configurations.

[0074] The hydrogen to be compressed is preferably obtained via electrolysis or another green hydrogen source. In this case, the electrochemical cell may be operated intermittently, although this is applicable to all scenarios. Instead of maintaining the pressure gradient, the pressure gradient is equalized in the stack during the transition to the ramp down / standby procedure. Energy can be obtained from the cell by reversing the current to the stack during the transition to the standby state. The generated power may be stored by any known means for later use. Such operation minimizes energy wastage. Energy is obtained as a result of depressurizing the pressurized hydrogen by utilizing the pressure difference to generate an electromotive force.

[0075] While it is envisioned that the pressurized hydrogen exiting the cell or stack will be stored, in accordance with another embodiment, it may be directly refueled into devices requiring hydrogen, such as, but not limited to, automobiles, forklifts, boats, buses, or other hydrogen powered devices. In such an embodiment, appropriately rated pipelines and nozzles should be used.

[0076] As mentioned above, another application for an electrochemical cell or stack is as a hydrogen sensor. The presence of hydrogen gas in a stream may be sensed by feeding a gas potentially containing hydrogen to the anode of the cell and applying a voltage to the cell or stack. If hydrogen is present, a current is measured. The measured current is proportional to the partial pressure. Conversely, a current may be applied and the measured voltage indicates the presence of hydrogen in the gas stream. To prevent pressure build-up at the anode of a cell used as a hydrogen sensor, an outlet from the anode is required to prevent undesired pressure build-up. Without the anode outlet, the stream being tested for the presence of hydrogen would have no route to exit the cell. This is discussed further below in another application. At high anode flow rates, with high % hydrogen in the stream, the electrochemical cell may be configured to function as a sensor only or as both a sensor and a compressor. As in other embodiments, pressure regulation means and a control system would be required for any of the above configurations.

[0077] Another means of passively sensing hydrogen is to measure the cell open circuit voltage. The catalyst can be the same or different on each side. The open circuit potential can be measured passively since it is directly proportional to the partial pressure of the impurity gas present. The sensor of such an embodiment would require calibration by introducing a gas stream of known composition into the electrochemical cell.

[0078] Another application for a single cell or stack of cells according to the invention is to separate and compress hydrogen from a stream containing hydrogen gas. This is envisioned to be applied to a natural gas stream containing hydrogen, but any gas containing hydrogen may be used. That is, some gases, such as but not limited to carbon monoxide, carbon dioxide, or ammonia, may adversely affect the life of the cell or stack. Impurities do not pass through the membrane, electrochemically or otherwise, and therefore remain in the anode half-cell. To prevent pressure build-up at the anode of the first cell, an outlet is provided for the removal of gas impurities. It is envisioned that some hydrogen may remain in the anode outlet stream, and therefore the gas may be recycled to the anode for further purification. A hydrogen sensor as described above may be used to detect the presence of hydrogen and determine the need for recycling.

[0079] In either embodiment, an anode outlet may be provided on any cell in the stack, but is most preferably provided in the first cell or stage of cells to allow removal of impurities from the anode half-cell, although this does not exclude the inclusion of an anode outlet in subsequent cells.

[0080] Pressure regulating means may be provided at one or more of the inlet to the anode cell, the outlet of the anode cell if present, and the outlet of the cathode cell. Pressure regulating means may include, but are not limited to, a valve. [Brief description of the drawings]

[0081] [Figure 1] FIG. 1 shows a single cell AEM electrochemical compressor. [Diagram 2] FIG. 2 shows multiple cells forming an AEM electrochemical stack. [Figure 3A] FIG. 3A shows a single AEM electrochemical cell. [Figure 3B] FIG. 3B shows multiple cells forming an AEM electrochemical stack. [Figure 4] FIG. 4 shows an MEA suitable for use in the present invention. [Diagram 5] FIG. 5 illustrates an electrochemical cell according to the present invention suitable for use as a hydrogen sensor or for removing hydrogen from a hydrogen-containing gas stream. [Figure 6] FIG. 6 shows the electrochemical cell of FIG. 5 with an additional cell to further compress hydrogen. [Figure 7A] FIG. 7A shows an electrochemical compressor with multiple cells as the first stage of compression. [Figure 7B] FIG. 7B shows an alternative arrangement of an electrochemical compressor with multiple cells as the first stage of compression. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0082] In order that the invention may be more readily understood, specific embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings in which:

[0083] In FIG. 1, a single cell AEM electrochemical compressor 1 is shown. It is provided with an inlet 2 and an outlet 3. A stream consisting primarily of hydrogen from an electrolyser or other hydrogen source is fed via inlet 2 to an anode half-cell 5. An MEA 4 separates the anode half-cell 5 from the cathode half-cell 6. The hydrogen is pumped through a first pressure P 1 into the anode half-cell 5 at a first pressure P 2 The pressure is increased until the reaction in the anode and cathode half cells is: AEM Anode H 2 +2OH - →2H 2 O+2e - AEM cathode 2H 2 O+2e - →H 2 +2OH -

[0084] The MEA 4 separates the two half-cells and includes at least an anode, a cathode, and an AEM between the anode and cathode. As mentioned above, additional layers such as a GDL or MPL may be used with varying properties as needed. Figure 4 shows a close-up of the MEA 4.

[0085] Water generated at the anode combines with the membrane and is therefore consumed in the cathode reaction. - The electrons from the anode are consumed at the cathode.

[0086] It should be noted that impurities such as water or oxygen may be present at the hydrogen inlet, and as previously mentioned, it is not a problem that water may act and that oxygen, depending on the catalyst, may react with hydrogen in the first anode half-cell to produce water.

[0087] A single cell AEM electrochemical compressor will most likely be insufficient to reach the desired pressure, therefore multiple cells may be used in series to form a stack, as shown in FIG. 2.

[0088] FIG. 2 (BOP not shown) shows a number of cells 1a, 1b, 1c forming a stack 10. The brackets around 1b indicate that more than three cells may be included in a stack. The number of cells in a stack is not intended to be a limiting feature of the invention. Hydrogen from an electrolyser, temporary storage, or other source is introduced into the P 1 While the anodic reaction occurs, P 2 Hydrogen is generated at the cathode in the cathode reaction until the P from the first cathode 6a is reached. 2 The hydrogen of P is introduced through the outlet 3a connected to the inlet 2b. 2 The hydrogen is delivered to the anode of the second cell 5b as is. The second anode reaction and the second cathode reaction occur in the half-cell 5b and the half-cell 6b, respectively. Meanwhile, the hydrogen is delivered to the anode of the second cell 5b as is. 3In FIG. 2, 1c, the above process continues until the last cell in the stack. At this point, hydrogen is produced in the second cathode compartment 6b until a final pressure P 4 and final outlet 3c to storage tanks or other destinations requiring pressurized hydrogen. The control system and BOP are not shown.

[0089] In Figures 3A and 3B, cells with various MEA cross-sectional areas are shown. Figure 3A shows a single cell 11 with a constriction 7 narrowing towards the MEA 4, while Figure 3B shows two such cells arranged in series. The two dotted lines X---X indicate that the MEA 4 of the second cell is smaller than the MEA 4 of the first cell. Such variations are useful to manage the pressure difference observed at each cell in the stack and are intended to improve water management. Other means disclosed include varying the mechanical properties of the membrane, in addition to its chemical and physiochemical properties.

[0090] In FIG. 4, a schematic of an MEA 4 with its various components is shown. From left to right, there is an anode GDL 45a, an anode catalyst 42, an anion exchange membrane 41, a cathode catalyst 43, an MPL 44, and a cathode GDL 45c. The core components are the two catalysts and the membrane, other components may improve the functionality of the system. The MPL 44 may vary between cells to have different properties and achieve the desired results, but such differences are not shown. The more hydrophobic MPL in the later cells of the stack minimizes water desorbing from the membrane, ensuring that the compressed hydrogen leaving the stack is as dry as possible.

[0091] 5 shows a diagram of an electrochemical cell 21 according to the present invention. The electrochemical cell 21 is suitable for compressing hydrogen while separating hydrogen from a hydrogen-containing gas stream or functioning as a hydrogen sensor. First, its operation as a means for removing hydrogen will be described.

[0092] The anode 25 in this embodiment comprises an inlet 22 for introducing a hydrogen-containing fluid stream, and an outlet 27 for transporting other impurity gases to prevent pressure build-up in the anode half-cell 25. An outlet regulation means, typically a valve, at the outlet 27 is not shown. When an electric current is applied to the cell, the hydrogen reacts as disclosed in the previous embodiment, while the remaining gases do not react. This means that the hydrogen passes through the AEM 24 to the cathode half-cell 26, while the impurity gases remain in the anode 25. From the cathode 26, the hydrogen is passed to the high pressure P 2 In this embodiment and in any other embodiment, the pressure P 2 may be adjusted to increase the pressure by any known pressure adjusting means, such as a valve.

[0093] A cell such as that shown in FIG. 5 may be used as a hydrogen sensor. In such an embodiment, a gas stream, in which hydrogen may or may not be present, is fed to the cell 21 via the inlet 22. A low voltage is applied to the cell, and if hydrogen is present, a current can be detected. The measured current should be proportional to the partial pressure or concentration of hydrogen in the stream. An anode outlet 27 allows other gases to be removed, preventing unwanted pressure build-up due to other impurity gases remaining at the anode. Via a cathode outlet 23, a cell suitable for detecting hydrogen may pump hydrogen out of the cell for further compression or other purposes. The sensor may be used only to detect the presence of hydrogen and to notify the user of its presence, and thus compression may not be desired in such an embodiment.

[0094] FIG. 6 shows the cell 21a of FIG. 5 with a cathode outlet 23a connected to the anode inlet 22b of the second cell 21b of the stack. Note that more cells may be connected to allow further compression of hydrogen. The procedure largely mirrors that described for the other stacks, with the difference being the removal of hydrogen from the impure air stream in cell 21a. The purified and compressed hydrogen in cathode 26a is sent to anode 25b via outlet 23a / inlet 22b. Cell 21b further compresses the hydrogen as it passes through membrane 24b to cathode 26b. Note that more cells may be used in series if further compression is desired.

[0095] Figures 7A and 7B show two embodiments of alternative arrangements of electrochemical stacks. First, referring to Figure 7A, at least two electrochemical cells 31a, 31b forming a stack for the first stage of compression are connected in parallel. Hydrogen flows into each anode 35a, 35b at a first pressure, and upon application of an electric current, the above-mentioned anode and cathode reactions occur. At the cathodes 36a, 36b, the hydrogen is reformed and is sent from the cathode outlets 33a, 33b at a second pressure by pressure regulation means (not shown). The cathode outlets of each stage are then combined, as shown in pipe 37, and the hydrogen at the second pressure forms the feed to the anode inlet 32c of the cells in the next compression stage. The number of cells in each stage or the number of compression stages is not limited. The pressure difference of each cell in one stage will generally be the same, but may differ between stages.

[0096] Finally, in FIG. 7B, an electrochemical compressor is shown with a number of cells 51a, 51b forming stages. As before, three or more cells are provided in each stage. Hydrogen enters through the anode inlet 52a, 52b at a first pressure, passes through the membrane 54a, 54b via the reaction mechanism previously described and is reformed at the cathode 56a, 56b. Hydrogen at a second pressure leaves the cathode through the cathode outlet 53a, 53b into the tube 57, and the air stream forms the feed for the next compression stage. Hydrogen enters the cell in the next compression stage 51c through the anode inlet 52c. The cells 51a, 51b, 51c are separated by an insulating membrane 58.

[0097] Although not shown, the supply device 57 includes a pressure adjusting means and other functions constituting a BOP.

[0098] For clarity, in the above example, cells 31a, 31b form one stage and cell 31c forms one stage. Similarly, in Fig. 7B, cells 51a, 51b form one stage and cell 51c forms its own stage. In Fig. 2, cells 1a, 1b, 1c each form their own stage. Stages may have the same or different number of cells depending on requirements. Each stage may have two or more cells forming the stage.

[0099] To maintain a constant flow rate, the sum of the current densities on the membranes of the cells of each stage will be approximately similar if the pressure difference across each cell is the same. If there is a larger pressure difference across the cells of one stage, the current density will be proportionately higher, resulting in backflow etc. as discussed above.

[0100] It is not intended that the invention be limited to the details of any of the foregoing embodiments, for example, any electrochemical compressor for hydrogen that uses one or more cells with an AEM is encompassed by the present invention.

[0101] The method of manufacturing the components of the electrochemical compressor is not intended to limit the present invention.

[0102] The hydrogen leaving the compressor should be essentially dry, however a dryer may be provided at the final outlet to ensure that the hydrogen is nearly dry before storage under pressure.

[0103] It is not intended that the invention be limited by the catalyst used, although non-PGM, membrane composition, final pressure, or other such components may be preferred.

[0104] Although it is assumed that a pH gradient having acidic and alkaline regions at both ends may occur at extreme current densities, the pH in the present invention is preferably about 7 or higher, more preferably about 9 to 14, and even more preferably about 12 to 13. In any case, the present invention does not depend on a pH gradient.

[0105] While it is often necessary to compress the hydrogen, it is envisioned that the present invention may be applied to only purifying a hydrogen stream, without further compression being desired. In such an embodiment, a cell or stack of cells according to the present invention may be used without the flow of hydrogen between the cells and the pressure regulation means, such as but not limited to valves, between the cells that cause the purification of the hydrogen stream. The disclosed water management means are useful for drying the hydrogen. Cells as described and illustrated above may be configured with any of the disclosed functions, i.e., sensors, compressors, dryers, or combinations thereof.

[0106] Impurities typically remain in the first anode half-cell. For impurities other than water and oxygen, an anode outlet is preferred to prevent pressure build-up in the first cell. In addition, the outlet allows water to be removed to prevent flooding of the anode.

[0107] While it is envisioned that compressed hydrogen will be used for energy storage or in fuel cells, other uses for compressed hydrogen include refrigeration.

[0108] A stack can have many cells, but it is not expected that more than roughly 1000 bar of hydrogen will be required. If we increase the pressure to 35 bar per cell, it is expected that each stack will have no more than 30 cells.

[0109] The present invention can be arranged in a number of ways. Where one or more cells form a compression stage, each stage may be considered as a stack. Such stacks may be arranged in series or in parallel.

[0110] The present invention allows for simultaneous compression and drying of hydrogen without moving parts. The system also does not rely on acidic environments or PGM catalysts and has no moving parts. Thus, the system improves green hydrogen qualification inherently more efficiently than known options.

Claims

1. an anode half-cell having an inlet configured to receive hydrogen at a first pressure; a cathode half-cell including an outlet configured to transfer hydrogen at a second pressure; a membrane electrode assembly (MEA) separating the anode half-cell and the cathode half-cell; A power source; and The MEA includes at least An anode electrode; A cathode electrode; an anion exchange membrane (AEM) provided between the anode electrode and the cathode electrode; With The power source is a reverse pulse. Electrochemical cell characterized in that

2. At least one anode outlet; It is made of 2. The electrochemical cell of claim 1.

3. the inlet of the anode half-cell; the outlet of the cathode half-cell; If present, the outlet of the anode half-cell; and a pressure adjusting means provided in any one or more of the above; It is made of 3. An electrochemical cell according to claim 1 or 2.

4. the pressure regulating means at the outlet of the cathode half-cell is configured, in use, to maintain a gas pressure in the cathode half-cell higher than a gas pressure in the anode half-cell; 4. The electrochemical cell of claim 3.

5. The MEA comprises one or more catalysts.

5. An electrochemical cell according to any one of claims 1 to 4.

6. the one or more catalysts are not platinum group metals; 6. The electrochemical cell of claim 5.

7. The MEA is An anode gas diffusion layer (GDL: Gas Diffusion Layer); A cathode GDL; and A microporous layer (MPL) provided on the anode side and / or the cathode side; A water management membrane provided on the anode side and / or the cathode side; A membrane support provided on the anode side and / or the cathode side; Among these, one or more of them are provided.

7. An electrochemical cell according to any one of claims 1 to 6.

8. The AEM comprises a composite membrane.

8. An electrochemical cell according to any one of claims 1 to 7.

9. The AEM is OH － doped with a source, 9. An electrochemical cell according to any one of the preceding claims.

10. At least one of the cathode side of the AEM and the anode side of the AEM includes an ionomer; 10. An electrochemical cell according to any one of the preceding claims.

11. The MEA does not include an ionomer and / or a binder on at least one of the anode side and the cathode side of the AEM; 11. An electrochemical cell according to any one of claims 1 to 10.

12. The AEM comprises hygroscopic particles.

12. An electrochemical cell according to any one of the preceding claims.

13. The hygroscopic particles are arranged in a concentration gradient; the concentration of the hygroscopic particles is higher on the cathode side of the AEM; 13. The electrochemical cell of claim 12.

14. the pressure regulating means is configured to maintain, in use, a pressure differential across the cell in the range 1-1000 bar. Electrochemical cell according to claim 3 or any one of claims 4 to 13 dependent thereon.

15. a moisture sensor coupled to the outlet of the cathode half-cell; It is made of 15. An electrochemical cell according to any one of the preceding claims.

16. an output means configured to communicatively couple to an external hydrogen fueled device; and The output means supplies fuel directly to the external device.

16. An electrochemical cell according to any one of the preceding claims.

17. In use, power generated by the cells during gradient ramp down is stored.

16. An electrochemical cell according to any one of the preceding claims.

18. At least one of the components according to claim 1 to 15 arranged in a stack. A first electrochemical cell; A second electrochemical cell; and and the outlet of the cathode half-cell of the first electrochemical cell is in fluid communication with the inlet of the anode half-cell of the second electrochemical cell; Electrochemical cell assembly comprising:

19. A plurality of electrochemical cells according to any one of claims 1 to 15 arranged in series as a stack, the outlet of the cathode half-cell of each electrochemical cell other than the final electrochemical cell in the stack is in fluid communication with the inlet of the anode half-cell of an adjacent electrochemical cell in the stack; the outlet of the cathode half-cell of the last electrochemical cell in the stack is configured to transport hydrogen to an external destination; 20. The electrochemical cell assembly of claim 18.

20. 1. A method for treating a hydrogen-containing gas stream, comprising the steps of: Providing an electrochemical cell according to any one of claims 1 to 15; providing a hydrogen-containing gas stream to the inlet of the anode half-cell; delivering hydrogen from the outlet of the cathode half-cell; Including, A method comprising:

21. 1. A method for treating a hydrogen-containing gas stream, comprising the steps of: Providing an electrochemical cell assembly according to claim 18 or 19; providing a hydrogen-containing gas stream to the inlet of the anode half-cell of the first electrochemical cell in the stack; transferring hydrogen from the outlet of the cathode half-cell of each of the electrochemical cells in the stack to the inlet of the anode half-cell of another of the electrochemical cells; transporting hydrogen from the outlet of the cathode half-cell of the final electrochemical cell of the stack to an external destination; Including, A method comprising:

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