Electrochemical device and fuel cell system

Abstract

The invention relates to an electrochemical device and a fuel cell system. An electrochemical device including an electrochemical pump (ECP) and a fuel cell system including a fuel cell and an ECP are disclosed. Specifically, the electrochemical device may be an ECP comprising an anode, a cathode, and an anion exchange polymer separating the anode from the cathode. The ECP may be coupled to a hydroxide exchange membrane fuel cell (HEMFC) disclosed herein as a fuel cell system. These devices can be used in methods for removing carbon dioxide from air and generating electricity.

Description

[0001] This application is a divisional application of patent application number 2019800890593, filed on November 20, 2019, entitled “Electrochemical Devices and Fuel Cell Systems”. TECHNICAL FIELD

[0002] Disclosed are electrochemical devices, specifically electrochemical pumps (ECPs), and fuel cell systems comprising a hydroxide exchange membrane fuel cell (HEMFC) and an ECP. These ECPs and systems can be used in methods for removing carbon dioxide from air and generating electricity by running a fuel cell with C02-containing air. BACKGROUND

[0003] Carbon dioxide (C02) is an acidic gas, present in the atmosphere at about 400 ppm. As an acidic gas, C02reacts with strong bases, such as hydroxide anions, to form carbonate and bicarbonate anions.

[0004]

[0005] Alkaline fuel cells and hydroxide exchange membrane fuel cells (HEMFCs) use a hydroxide conducting electrolyte and suffer a significant loss of efficiency when exposed to C02. Liquid alkaline fuel cells are affected by carbonate precipitation, which clogs gas pores and can be fatal to the cell. HEMFCs have a constrained cation that cannot form carbonate precipitates, but the efficiency of the HEMFC decreases due to a concentration gradient of carbonate anions in the cell. When run in steady state in C02-containing air, the anode consumes hydroxide and accumulates bicarbonate until the local pH drops low enough for the bicarbonate to decompose. The cell reaches a steady state in which C02is captured by the cathode at the same rate that it is released from the anode, and the pH gradient between the anode and the cathode typically causes a loss of several hundred mV. When the cathode gas contains 400 ppm C02, the loss is typically 100-300 mV.

[0006] HEMFCs have a potential cost advantage over the more common proton exchange membrane fuel cells (PEMFCs), largely due to the better corrosion resistance of many metals in alkaline electrolytes than in acidic electrolytes. This makes possible non-precious metal catalysts, especially at the cathode, and cheaper bipolar plate materials. However, as noted above, achieving good HEMFC performance and efficiency requires supplying air to the cathode with a low concentration of C02. Therefore, a compact and low-cost device for generating a stream of air with a low C02concentration is important for a commercially viable HEMFC technology.

[0007] The prior art for generating an air stream with low concentration of carbon dioxide for a HEMFC is to use two or more layers of renewable polymeric amine sorbents as disclosed in U.S. Patent No. 9,368,819. These layers are thermally regenerated and require a minimum of two layers to provide continuous operation such that one layer is on-line while the other is being regenerated. This design is complex and bulky and can not be suitable for transportation uses or other space-limited HEMFC applications.

[0008] Additionally, the system for removing carbon dioxide from a gas stream has many applications outside of the HEMFC field. Other applications include: CO2 removal for metal-air batteries, breathing gas purification for diving, submersibles, or space applications; CO2 enrichment of greenhouses to accelerate plant growth; capture of CO2 from flue gas or air for subsequent use or sequestration; and gas separation in industrial applications.

[0009] Accordingly, there is a need for a more efficient and cost-effective device and method for removing carbon dioxide from a carbon dioxide-containing gas that can be used with additional devices, such as a fuel cell. SUMMARY

[0010] The present disclosure relates to fuel cell systems, electrochemical pumps, and methods of using them to reduce carbon dioxide concentration in air and generate electricity.

[0011] For example, the present disclosure relates to a fuel cell system comprising a hydroxide exchange membrane fuel cell (HEMFC) and an electrochemical pump (ECP) for separating carbon dioxide from a carbon dioxide-containing gas, the ECP comprising a cell comprising an anode, a cathode, and a membrane. The anode comprises an anode electrocatalyst for oxidizing a reagent to form a proton or consume a hydroxide ion; the cathode comprises a cathode electrocatalyst for reducing oxygen to form a hydroxide ion; and the membrane is adjacent to and separates the anode and the cathode. The carbon dioxide-containing gas is supplied to the cathode, and the carbon dioxide reacts with the hydroxide ions formed at the cathode to form bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions. The bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions are transported through the membrane to the anode; and the bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions react at the anode to form carbon dioxide and water. The carbon dioxide-containing gas is air, and after the air passes through the cathode of the ECP to reduce the concentration of carbon dioxide, the air with reduced carbon dioxide concentration is directed to the cathode inlet of the HEMFC.

[0012] Further, the present disclosure relates to an internal current electrochemical pump (iECP) for separating carbon dioxide from a carbon dioxide-containing gas, comprising a cell, the cell comprising an anode, a cathode, and a membrane. The anode comprises an anode electrocatalyst for oxidizing a reagent to form protons or consume hydroxide ions. The cathode comprises a cathode electrocatalyst for reducing a reagent to form hydroxide ions. The membrane is adjacent to and separates the anode and the cathode. The carbon dioxide-containing gas is supplied to the cathode, and the carbon dioxide reacts with the hydroxide ions formed at the cathode to form bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions. The bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions are transported through the membrane to the anode; and the bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions react at the anode to form carbon dioxide and water. The anode and the cathode are electronically connected through the membrane.

[0013] Further, the present disclosure relates to an electrochemical pump (ECP) for separating carbon dioxide from air, comprising a cell, the cell comprising an anode, a cathode, and a membrane, and the cathode is supplied with air and the anode is supplied with hydrogen gas. The anode comprises an anode electrocatalyst for oxidizing the hydrogen gas to form protons or consume hydroxide ions. The cathode comprises a cathode electrocatalyst for reducing oxygen in the air to form hydroxide ions. The membrane is adjacent to and separates the anode and the cathode. Carbon dioxide in the air supplied to the cathode reacts with the hydroxide ions to form bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions. The bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions are transported through the membrane to the anode; and the bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions react at the anode to form carbon dioxide and water.

[0014] Further, the present disclosure relates to a method for separating carbon dioxide from a carbon dioxide-containing gas or air, comprising supplying the carbon dioxide-containing gas or air to a cathode of an electrochemical pump (ECP) of a fuel cell system described herein, and supplying a hydrogen-containing gas to an anode of the ECP.

[0015] The present disclosure also relates to an electrochemical pump (ECP) for separating carbon dioxide from a carbon dioxide-containing gas, comprising a cell comprising a membrane and two electrodes capable of functioning as an anode or a cathode. Each of the two electrodes independently comprises a charge storage compound that reacts to form hydroxide when functioning as a cathode and reacts to consume hydroxide or generate protons when functioning as an anode. The membrane is adjacent to and separates the two electrodes. The carbon dioxide-containing gas is in contact with the electrode functioning as a cathode, and the carbon dioxide reacts with the hydroxide ions to form bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions; the bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions are transported through the membrane to the electrode functioning as an anode; and the bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions react at the electrode functioning as an anode to form carbon dioxide and water. The ECP further comprises means for reversing the direction of the current and simultaneously alternating the electrodes in contact with the carbon dioxide-containing gas, thereby allowing each electrode to function in turn as an anode and a cathode.

[0016] The present disclosure further relates to a system comprising a metal-air cell and an electrochemical pump (ECP) described herein, wherein the carbon dioxide-containing gas is air, and after the air is supplied to the cathode of the ECP to reduce the concentration of carbon dioxide, the carbon dioxide-concentration-reduced air is directed to the cathode inlet of the metal-air cell.

[0017] Further disclosed is a battery system comprising a metal-air cell and an electrochemical pump (ECP) for separating carbon dioxide from a carbon dioxide-containing gas, the ECP comprising a cell comprising an anode, a cathode, and a membrane. The anode comprises an anode electrocatalyst for oxidizing a reagent to form protons or consume hydroxide ions. The cathode comprises a cathode electrocatalyst for reducing oxygen to form hydroxide ions. The membrane is adjacent to and separates the anode and the cathode. The carbon dioxide-containing gas is supplied to the cathode, and the carbon dioxide reacts with the hydroxide ions formed at the cathode to form bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions. The bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions are transported through the membrane to the anode; and the bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions react at the anode to form carbon dioxide and water. The carbon dioxide-containing gas is air, and after the air passes through the cathode of the ECP to reduce the concentration of carbon dioxide, the carbon dioxide-concentration-reduced air is directed to the cathode inlet of the metal-air cell.

[0018] Preferably, the ECP, iECP, or fuel cell system comprises at least one of:

[0019] (a) the anode and the cathode are electronically connected by the membrane to form an internal current ECP (iECP), and the membrane comprises an anion exchange polymer and a conductive material or a conductive anion exchange polymer; or

[0020] (b) the porous structure-ionomer interlayer separates the membrane from the cathode; or

[0021] (c) based on platinum as catalyst, the catalyst loading at the anode and cathode is less than 0.4 mg catalyst per square centimeter; or

[0022] (d) the membrane resistance of the ECP is between 0.5 and 20 Ohm-cm 2 ; or

[0023] (e) the cathode further comprises a catalyst consisting of a primary, secondary, or tertiary amine.

[0024] Other objects and features will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a schematic of a fuel cell system comprising a hydroxide exchange membrane fuel cell (HEMFC) and an electrochemical pump (ECP). Air is supplied to the cathode of the ECP, where carbon dioxide reacts with electrochemically generated hydroxide. After the air passes through the cathode of the ECP, the concentration of CO2 has been reduced, and the air with reduced CO2 concentration is fed into the cathode inlet of the HEMFC. For illustrative purposes, the system is drawn with hydrogen as the anode reagent in the ECP and hydrogen supplied from a purge stream of the HEMFC.

[0026] Figure 2 is a schematic of an ECP operating with oxygen as the cathode reagent and hydrogen as the anode reagent, showing the electrochemical and chemical reactions responsible for CO2 capture and release. Electron current is shown as taking an internal path (iECP) or an external path (eECP). The inset shows a stylized representation of one possible embodiment of the cathode or anode, comprising an electrocatalyst and an ionomer in a porous structure.

[0027] Figure 3 and Figure 4 are schematics of different planar hydrogen / air ECP configurations.

[0028] Figure 5 is a schematic of a spiral wound module, showing an example of a possible cell stack configuration.

[0029] Figure 6 is also a schematic of a spiral wound module, showing an example of a possible configuration including two cells stacked and a current collector for the stack.

[0030] Figure 7 is a schematic of a spiral wound module with an external current path, and shows an axial cross section of the module.

[0031] Figure 8is a schematic of a possible hydrogen inlet for the modules described herein.

[0032] Figure 9 is a schematic of an iECP and details the cell stack of the module.

[0033] Figure 10 is a schematic of a spiral wound module with Figure 9 is a schematic of a spiral wound module with details of the cell stack in

[0034] Figure 11 is a schematic of the hollow fibers of an iECP manufactured in a housing.

[0035] Figure 12 is a schematic of a module containing multiple hollow fibers as shown in Figure 11

[0036] Figure 13 is a simulated concentration profile of anions in a membrane electrode assembly (MEA) at 20 mA / cm 2 . The cell temperature is 70 °C and the gases supplied to the anode gas flow layer and the cathode gas flow layer are hydrogen containing 100,000 ppm CO2 and air containing 400 ppm CO2, respectively, both at 2 bar.

[0037] Figure 14A is a simulated anion concentration profile (in units of 20 mA / cm 2 ) through the thickness of the MEA at a location corresponding to the cathode outlet at 99.9% CO2 removal. The cell temperature is 70 °C and the gases supplied to the anode gas flow layer and the cathode gas flow layer are hydrogen containing 100,000 ppm CO2 and air containing 0.4 ppm CO2, respectively, both at 2 bar.

[0038] Figure 14B is a simulated CO2 reaction rate profile. Positive rates indicate CO2 capture and negative rates indicate CO2 release. The cell temperature is 70 °C and the gases supplied to the anode gas flow layer and the cathode gas flow layer are hydrogen containing 100,000 ppm CO2 and air containing 0.4 ppm CO2, respectively, both at 2 bar.

[0039] Figure 15A and 15B are plots of the cathode outlet CO2 concentration measured from a 25 cm 2 ECP (cell #2) operated in H2 / air mode at a range of air flow rates. Figure 15A shows the results at a constant current density of 10 mA / cm 2 . Figure 15B shows the results at a constant current density of 20 mA / cm 2 ​CO2 concentration as a function of air flow rate. The anode flow rate was 50 seem, the relative humidity (RH) was 80%, and the outlet pressure was ambient pressure. The average value of the CO2 concentration was taken over the last 30 minutes of the 60-minute hold.

[0040] Figure 16A and 16B are plots of the CO2 ECP performance measured at 70°C, 80% RH, 20 mA / cm 2 for low-loading cells with and without ionomer interlayers and regular high-loading cells. The high-loading cells were tested at 80°C, 90% RH, and 5 cm 2 effective area. Figure 16A shows the cathode outlet CO2 concentration as a function of air flow rate. The anode flow rate was 50 seem, the relative humidity (RH) was 80%, and the outlet pressure was ambient pressure. The average value of the CO2 concentration was taken over the last 30 minutes of the 60-minute hold. 2 MEA flow rate (high-loading) was converted to 25 cm 2 equivalent to make comparisons. Figure 16B shows the calculated average mass transfer resistance as a function of outlet CO2 concentration. Results below 1 ppm were excluded due to excessive measurement uncertainty. All measurements were averaged over the last 30 minutes of the 60-minute hold.

[0041] Figure 17 are plots of the measured performance of iECPs operated with hydrogen as the anode reagent and oxygen as the cathode reagent. CO2 concentrations were measured at the anode and cathode outlets at a gas flow rate of 0.1 L min -1 , 90% relative humidity, and ambient pressure. The cathode feed gas was air containing 350 ppm CO2. The anode gas was either N2 or H2 as indicated (to control the cell output). When N2 was used as the anode gas, no significant current was generated in the cell and little CO2 transport occurred. When H2 was used as the anode gas, the current generated resulted in electrochemical pumping of CO2, which was able to “uphill” CO2 pumping. “Uphill” CO2 pumping refers to the cathode gas stream transporting CO2 having a lower CO2 concentration than the anode gas stream transporting CO2. Such transport cannot be driven by a concentration gradient alone, the concentration gradient points in the wrong direction, and must be the result of electrochemical pumping.

[0042] Figure 18 is a schematic of the iECP cell configuration used in Example 4. A compressed porous ePTFE sheet (0.7 mm thick) was used to create a gas diffusion barrier at the anode. A septum pump was connected between the anode outlet and the anode inlet to dilute the hydrogen gas supply with the CO2-rich anode product gas mixture to reduce the partial pressure of hydrogen.

[0043] Figure 19This is a graph illustrating the measurement performance of the iECP in Example 4, using an anode gas diffusion barrier and a recirculation loop to maintain good CO2 separation performance at low hydrogen supply rates. The legend indicates the cathode air flow rate (containing 400 ppm CO2) and the anode recirculation configuration. The case labeled "No Recirculation" uses a single-pass configuration at the anode, with the hydrogen supply indicated on the x-axis. The case labeled "Anode Recirculation" uses a diaphragm pump to recirculate gas from the anode outlet to the anode inlet at a flow rate of 500 mL / min. A mixture of fresh hydrogen supplied to the anode inlet and recirculated gas from the anode outlet is supplied at the rate shown on the x-axis. Each data point represents the average cathode outlet CO2 concentration maintained over the last 30 minutes from 120 or 180 minutes.

[0044] Figure 20 It is 25cm in Example 5. 2 Performance stability curves of a single-cell eECP. The battery was operated at 60°C and 70% RH, with an anode hydrogen supply of 10 sccm and a cathode air flow rate of 1250 sccm containing 400 ppm CO2. The cathode was pressurized to 50 kPa. g .

[0045] Throughout the accompanying drawings, the corresponding reference numerals indicate the corresponding parts. Detailed Implementation

[0046] This disclosure relates to an electrochemical pump (ECP) for separating carbon dioxide from a carbon dioxide-containing gas. The ECP includes an anode, a cathode, and an anion-exchange polymer membrane adjacent to and spaced apart from the anode and cathode. The ECP can be coupled to a hydroxide exchange membrane fuel cell (HEMFC) to form a system disclosed herein as a fuel cell system. Figure 1 A schematic diagram of an example of a fuel cell system is shown. Fuel cell systems can be used to generate electricity.

[0047] The ECP described herein can be used to remove CO2 from a gas stream using a membrane electrode assembly (MEA), wherein hydroxide is generated electrochemically at the cathode and consumed electrochemically or protons are generated at the anode. Figure 2 An embodiment of the ECP is illustrated. CO2 is captured at the cathode via a reaction with hydroxide, according to Equation 1. Carbonate and bicarbonate anions are driven to the anode by an electric field, where CO2 is released throughout the reaction.

[0048]

[0049] The entire reaction can occur in two steps, with proton transfer occurring either before or after CO2 release.

[0050] Many anodic and cathodic reactions can generate protons and hydroxide, respectively. Preferred anodic reactions include hydrogen oxidation reactions (HOR),

[0051] or,

[0052]

[0053] ammonia oxidation reactions (AOR),

[0054] or,

[0055]

[0056] oxygen evolution reactions (OER),

[0057] or,

[0058]

[0059] and nickel oxyhydroxide oxidation reactions (NiOR),

[0060]

[0061] Preferred cathodic reactions include hydrogen evolution reactions (HER),

[0062]

[0063] oxygen reduction reactions (ORR),

[0064]

[0065] and nickel oxyhydroxide reduction reactions (NiRR),

[0066]

[0067] Using the NiOR and NiRR (equations 7 and 10) or other charge storage electrode reactions, nearly pure CO2 product streams can be recovered. Continuous operation can be achieved by periodically reversing the cell current and simultaneously switching the gas connections when the electrodes become fully or nearly fully charged / discharged.

[0068] Also disclosed is a fuel cell system comprising a HEMFC and an ECP comprising a cell for separating carbon dioxide from a carbon dioxide-containing gas, the cell comprising an anode, a cathode, and a membrane. The anode comprises an anode electrocatalyst for oxidizing a reagent to form protons or consume hydroxide ions; the cathode comprises a cathode electrocatalyst for reducing oxygen to form hydroxide ions; and the membrane is adjacent to and separates the anode and the cathode. The carbon dioxide-containing gas is supplied to the cathode of the ECP, and the carbon dioxide reacts with the hydroxide ions formed at the cathode to form bicarbonate ions, carbonate ions, or both bicarbonate and carbonate ions; the bicarbonate ions, carbonate ions, or both bicarbonate and carbonate ions are transported through the membrane to the anode; and the bicarbonate ions, carbonate ions, or both bicarbonate and carbonate ions react at the anode to form carbon dioxide and water. The carbon dioxide-containing gas is typically air, and after the air is supplied to the cathode of the ECP to reduce the concentration of carbon dioxide, the air with the reduced concentration of carbon dioxide is directed to the cathode inlet of the HEMFC.

[0069] Figure 1 A schematic of a fuel cell system is shown.

[0070] The fuel cell systems described herein can have a carbon dioxide- containing gas supplied to the cathode of the HEMFC containing less than about 20 ppm, 18 ppm, 16 ppm, 15 ppm, 12 ppm, 10 ppm, 8 ppm, 6 ppm, 5 ppm, 4 ppm, 3 ppm, or 2 ppm of carbon dioxide, where these reduced levels are achieved by the reaction of CO2 with hydroxide ions at the cathode of the ECP.

[0071] Additionally, the fuel cell systems described herein can have a reagent oxidized at the anode electrocatalyst of the ECP be hydrogen, and less than about 5%, 4%, 3%, or 2% of the hydrogen consumed by the ECP for separating carbon dioxide from air is consumed by the HEMFC.

[0072] For applications where CO2-free air is generated for the HEMFC, the best choice of electrode processes in the ECP is HOR at the anode (Equation 4) and ORR at the cathode (Equation 9) because oxygen is available in the air stream to be purified, and hydrogen gas can be purged from the stack to supply the anode. Another advantage of these reactions is that they generate enough electromotive force to power the cell without the need for an external power source.

[0073] The core component of an ECP is an MEA, which contains a membrane with an electrode on each side. Both electrodes contain an electrocatalyst and an anion exchange polymer with sufficient porosity for gas transport. The electrodes are electronically conductive to both electrons and anions. The membrane contains an anion exchange polymer and can optionally include a reinforcing polymer or an electronic conduction additive. If the membrane conducts both electrons and anions, no external electrical connections are required, and the MEA can be used in any module configuration, similar to a non-electrochemical membrane. An ECP with a membrane that conducts both electrons and anions is referred to herein as an internal current electrochemical pump (iECP). If the membrane conducts only anions and not electrons, an external current path must be included in the module. An ECP that requires an external current path is referred to herein as an external current electrochemical pump (eECP).

[0074] The present disclosure also relates to an iECP for separating carbon dioxide from a carbon dioxide-containing gas having an anode and a cathode electronically connected by an anion exchange membrane. When a potential difference is present across this type of cell, both ionic and electronic currents are generated that pass through the membrane. The iECP comprises a cell comprising an anode, a cathode, and a membrane. The anode comprises an anode electrocatalyst for oxidizing a reagent to form protons or consume hydroxide ions; the cathode comprises a cathode electrocatalyst for reducing a reagent to form hydroxide ions; and the membrane is adjacent to and separates the anode and the cathode. A carbon dioxide-containing gas is supplied to the cathode, and the carbon dioxide reacts with the hydroxide ions formed at the cathode to form bicarbonate ions, carbonate ions, or both bicarbonate and carbonate ions; the bicarbonate ions, carbonate ions, or both bicarbonate and carbonate ions are transported through the membrane to the anode; and the bicarbonate ions, carbonate ions, or both bicarbonate and carbonate ions react at the anode to form carbon dioxide and water; and the anode and the cathode are electronically connected by the membrane.

[0075] Figure 2 A schematic of an ECP with an internal current path (iECP as just described above) or an external current path (eECP) is shown.

[0076] The iECPs disclosed herein can have a membrane comprising an anion exchange polymer and an electronically conductive material or an electronically conductive anion exchange polymer.

[0077] The iECPs can have an anion exchange polymer comprising quaternary ammonium or imidazolium groups and a polymer backbone that does not have ether groups.

[0078] Preferably, the iECPs described herein can comprise anion exchange polymers comprising poly(aryl piperidinium), alkylammonium-functionalized poly(aryl alkylene), substituted imidazolium-functionalized poly(aryl alkylene), alkylammonium-functionalized polystyrene, substituted imidazolium-functionalized polystyrene, alkylammonium-functionalized poly(styrene-co-divinylbenzene), substituted imidazolium-functionalized poly(styrene-co-divinylbenzene), alkylammonium-functionalized poly(styrene-block-ethylene-co-butadiene-block-styrene), substituted imidazolium-functionalized poly(styrene-block-ethylene-co-butadiene-block-styrene), alkylammonium-functionalized polyethylene, substituted imidazolium-functionalized polyethylene, alkylammonium-functionalized poly(tetrafluoroethylene), substituted imidazolium-functionalized poly(tetrafluoroethylene), alkylammonium-functionalized poly(ethylene-co-tetrafluoroethylene), substituted imidazolium-functionalized poly(ethylene-co-tetrafluoroethylene), polyethyleneimine, poly(diallyl ammonium), or combinations thereof.

[0079] The electrically conductive material can comprise carbon, nickel, stainless steel, silver, electrically conductive polymers, or combinations thereof. Additionally, the electrically conductive material comprises nanowires or nanotubes.

[0080] These electrically conductive materials, which are metals, can also be alloys with other metals.

[0081] The iECPs can comprise one or more batteries arranged in a hollow fiber configuration.

[0082] The hollow fiber will have a cathode on the inside (lumen) and an anode on the outside (shell). The CO2-containing gas will pass through the lumen, and the anode reactant will be fed to the shell side.

[0083] The module can be constructed from one or more fibers encased in a cylindrical shell, the fibers being encapsulated in a sealing compound, typically an epoxy, forming a barrier near each end. The lumen is in fluid communication with the ends of the module outside the barrier, while the shell space is between the two barriers and isolated from the ends. The inlet and outlet for the CO2-containing gas are at both ends. The inlet and outlet for the anode reactant and separated CO2 are between the two barriers. Countercurrent flow is advantageous, but not strictly required.

[0084] One method by which such a hollow fiber configuration can be arranged is shown in the schematic diagram of Figure 11 and 12

[0085] ​In a hollow fiber configuration, the lumen of the fiber is the cathode side and the outer shell of the fiber is the anode side. The hollow fibers are bundled and placed in a cylindrical housing, the ends are encapsulated in epoxy and slit. Ports are added to the housing above and below each of the epoxy plugs to allow gas to enter the lumen and shell side of the fibers. The hollow fibers can be made in several configurations, such as disclosed above, Figure 11 and 12 A specific example of this type of configuration is shown.

[0086] The iECP can contain one or more additional cells and these cells can contain an anode gas flow layer adjacent to one or both anodes, an anode adjacent to a membrane, a membrane adjacent to an anode and a cathode, a cathode gas flow layer adjacent to one or both cathodes, the configuration is represented as follows:

[0087] [- AG - A - M - C - C - G - C - M - A -]

[0088] where AG is an anode gas flow layer, A is an anode, M is a membrane, C is a cathode, and CG is a cathode gas flow layer.

[0089] More specifically, for the iECP, both planar and spiral wound configurations as well as hollow fiber configurations are possible. There is no need for electrical connections to individual cells, which expands the possibilities. For the planar and spiral wound configurations, the cells do not need bipolar plates, but can be arranged in a pattern of CMA|AG|AMC|CG|CMA|AG|AMC|CG|... where CMA is an MEA with a cathode on the left and an anode on the right, AMC is an MEA with an anode on the left and a cathode on the right, CG is a cathode gas flow layer, and AG is an anode gas flow layer. The spiral wound module uses one or more leaves of CMA|AG|AMC|CG and winds them in a spiral pattern such that the CG of one winding or leaf contacts the CMA of the next winding or leaf.

[0090] The advantage provided by this configuration is that adjacent cells can share a cathode gas flow layer or an anode gas flow layer. This configuration is enabled by the iECP design. Figure 10 A schematic of this configuration is shown.

[0091] The iECP described herein can also be incorporated into a fuel cell system containing a HEMFC. The carbon dioxide containing gas is air and after the air passes through the cathode of the iECP to reduce the concentration of carbon dioxide, the air with the reduced concentration of carbon dioxide is directed from the cathode exhaust of the iECP to the cathode inlet of the HEMFC.

[0092] Further, the present disclosure relates to an ECP for separating carbon dioxide from air having hydrogen directed to the anode and air directed to the cathode and using an anion exchange polymer membrane as an electrolyte placed between and adjacent to the anode and the cathode.

[0093] The ECP comprises a cell, and the cell comprises an anode, a cathode, and a membrane. The cell supplies air to the cathode and hydrogen gas to the anode. The anode comprises an anode electrocatalyst for oxidizing hydrogen gas to form protons or consuming hydroxide ions; the cathode comprises a cathode electrocatalyst for reducing oxygen in the air to form hydroxide ions; and the membrane is adjacent to and separates the anode and the cathode. Carbon dioxide in the air supplied to the cathode reacts with the hydroxide ions to form bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions; the bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions are transported through the membrane to the anode; and the bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions react at the anode to form carbon dioxide and water.

[0094] Figure 2 A general schematic of the ECP is shown. Figure 3 and 4 Schematics of some planar hydrogen / air ECP configurations are shown.

[0095] The fuel cell systems comprising HEMFCs and ECPs or ECPs described herein can have the reagent oxidized by the anode electrocatalyst be hydrogen, ammonia, hydrazine, methanol, ethanol, urea, or combinations thereof. Preferably, the reagent oxidized at the anode of the ECP comprises hydrogen or ammonia. More preferably, the reagent oxidized at the anode electrocatalyst comprises hydrogen.

[0096] The HEMFC and ECP fuel cell systems or ECPs described herein can have the reagent reduced at the cathode electrocatalyst of the ECP comprise oxygen, hydrogen peroxide, or combinations thereof. Preferably, the reagent at the cathode comprises oxygen.

[0097] The fuel cell systems comprising HEMFCs and ECPs or ECPs described herein can have the anode electrocatalyst of the ECP comprise platinum, platinum alloys, carbon-supported platinum, carbon-supported platinum alloys, nickel, nickel alloys, carbon-supported nickel, carbon-supported nickel alloys, ruthenium, ruthenium alloys, carbon-supported ruthenium, carbon-supported ruthenium alloys, iridium, iridium alloys, carbon-supported iridium, carbon-supported iridium alloys, palladium, palladium alloys, carbon-supported palladium, carbon-supported palladium alloys, or combinations thereof. Preferably, the anode electrocatalyst comprises carbon-supported platinum.

[0098] The HEMFC and ECP fuel cell systems or ECPs described herein can have the cathode electrocatalyst of the ECP comprise silver, a silver alloy, carbon-supported silver, carbon-supported silver alloy, platinum, a platinum alloy, carbon-supported platinum, carbon-supported platinum alloy, palladium, a palladium alloy, carbon-supported palladium, carbon-supported palladium alloy, manganese oxide, carbon-supported manganese oxide, cobalt oxide, carbon-supported cobalt oxide, a heteroatom-doped carbon (X-C, where X comprises one or more of N, C, B, P, S, Se, or O), a metal-heteroatom-carbon (M-X-C, where X comprises one or more of N, C, B, P, S, Se, or O, and M comprises one or more of Fe, Ce, Cr, Cu, Co, Mo, Ni, Ru, Pd, Pt, Ir, Rh, Os, Ag, Au, Re, Ta, Ti, V, W, Mn, Zn, Sn, Sb, In, Ga, Bi, Pb, or Zr), a perovskite (ABX3, where A comprises one or more of Ca, Sr, Ba, Sc, Y, La, Ce, Zr, Cu, Zn, Sb, Bi, B comprises one or more of Al, Ti, Mn, Fe, Co, Ni, W, and X comprises one or more of O, Se, S), a carbon-supported perovskite (ABX3, where A comprises one or more of Ca, Sr, Ba, Sc, Y, La, Ce, Zr, Cu, Zn, Sb, Bi, B comprises one or more of Al, Ti, Mn, Fe, Co, Ni, W, Pd, and X comprises one or more of O, Se, S), or a combination thereof. Preferably, the cathode electrocatalyst comprises silver.

[0099] The HEMFC and ECP fuel cell systems or ECPs described herein can have the membrane of the ECP comprise an anion exchange polymer.

[0100] The anion exchange polymer can comprise a poly(arylpiperidinium), an alkylammonium-functionalized poly(arylene alkyl ene), a substituted imidazolium-functionalized poly(arylene alkyl ene), an alkylammonium-functionalized polystyrene, a substituted imidazolium-functionalized polystyrene, an alkylammonium-functionalized poly(styrene-co-divinylbenzene), a substituted imidazolium-functionalized poly(styrene-co-divinylbenzene), an alkylammonium-functionalized poly(styrene-block-ethylene-co-butadiene-block-styrene), a substituted imidazolium-functionalized poly(styrene-block-ethylene-co-butadiene-block-styrene), an alkylammonium-functionalized polyethylene, a substituted imidazolium-functionalized polyethylene, an alkylammonium-functionalized poly(tetrafluoroethylene), a substituted imidazolium-functionalized poly(tetrafluoroethylene), an alkylammonium-functionalized poly(ethylene-co-tetrafluoroethylene), a substituted imidazolium-functionalized poly(ethylene-co-tetrafluoroethylene), a polyethyleneimine, a poly(diallyl ammonium), or a combination thereof. Preferably, the anion exchange polymer comprises a poly(arylpiperidinium).

[0101] The ECP MEA can be combined with gas flow layers, optional gas diffusion layers, and optional separators to produce a cell of the ECP. One or more cells are packaged with gas manifolds, a housing, and seals to make an ECP module. The ECP module is combined with a controller to form a complete ECP. Finally, the ECP can be integrated with HEMFC stacks and other system balancing components to form an air-fed ECP-HEMFC system, depending on the application. Figure 1 An example of an air-fed ECP-HEMFC system is shown.

[0102] The eECPs described herein, and used in fuel cell systems, can have current supplied to them by an external power source, or it can have current drawn through a load if the electromotive force of the electrochemical cell is sufficient to drive the current.

[0103] The fuel cell systems or ECPs described herein containing HEMFCs and ECPs can have one or more additional cells.

[0104] The ECPs described herein, and in fuel cell systems, can have one or more additional cells electrically connected in series.

[0105] There can be several cell and module configurations for the eECP. The module structure can be planar or spirally wound. Planar modules contain a stack of planar cells, with manifolds incorporated into the boundary regions outside the active areas to distribute gas to each cell. The cells can be separated by bipolar plates containing flow channels, or the cells can be separated by planar bipolar plates with conductive mesh feed separators to provide flow paths. This type of configuration is shown in Figure 3 .

[0106] The HEMFC and ECP fuel cell systems or ECPs described herein can have the cells electrically connected in series through conductive bipolar plates.

[0107] The ECPs described herein, and in fuel cell systems, can have each cell further containing an anode gas flow layer and a cathode gas flow layer.

[0108] The ECPs described herein, and in fuel cell systems, can have the anode gas flow layer, the cathode gas flow layer, or both the anode gas flow layer and the cathode gas flow layer containing a flow field of one or more flow channels alternating with conductive material to provide electrical connections between the anode, the cathode, or both the anode and the cathode and the bipolar plates.

[0109] A typical bipolar plate is a thin sheet of stainless steel. One side is electrically connected to the anode, and the other side is electrically connected to the cathode of the adjacent cell.

[0110] The bipolar plate can be integrated with one or both adjacent gas flow layers. In this case, the bipolar plate is typically stamped to form flow channels (corrugated structure) on both sides.

[0111] The ECPs described herein, and in fuel cell systems, can have two or more flow channels of the cathode gas flow layer, or two or more flow channels of the anode gas flow layer arranged in a substantially parallel configuration.

[0112] The ECPs described herein, and in fuel cell systems, can have two or more flow channels of the cathode gas flow layer or two or more flow channels of the anode gas flow layer arranged in a cross configuration.

[0113] The ECPs described herein, and in fuel cell systems, can have the bipolar plate integrated with an adjacent anode gas flow layer or an adjacent cathode gas flow layer.

[0114] The ECPs described herein, and in fuel cell systems, can have the bipolar plate integrated with an adjacent anode gas flow layer and an adjacent cathode gas flow layer.

[0115] The ECPs described herein, and in fuel cell systems, can have the anode gas flow layer, the cathode gas flow layer, or both the anode gas flow layer and the cathode gas flow layer comprise an electrically conductive feed spacer.

[0116] The fuel cell systems comprising HEMFCs and ECPs, or the ECPs, described herein can have the electrically conductive feed spacer made of a mesh made of nickel, a nickel alloy, stainless steel, an electrically conductive polymer, carbon fiber paper, or a combination thereof.

[0117] The ECPs described herein, and in fuel cell systems, can have the electrically conductive feed spacer comprise a perforated metal sheet.

[0118] The ECPs described herein, and in fuel cell systems, can have the cells be substantially planar and arranged in a stacked manner.

[0119] The HEMFCs and ECP fuel cell systems, or the ECPs, described herein can have the cells in a stacked form and formed around an inner tube to form a spiral stack.

[0120] The ECPs described herein, and in fuel cell systems, can have each cell comprise a cathode gas flow layer, and the cathode gas flow layer fluidically connected to an axial end of the spiral stack.

[0121] The ECPs described herein, and in fuel cell systems, can have each cell comprise an anode gas flow layer, and the anode gas flow layer fluidically connected to an inner surface of the tube and an outer radial surface of the spiral stack. As Figure 7 and 10 shown, air can enter and exit the axial ends of the spiral stack.

[0122] Figure 5 A spiral wound module with specific cell stack details is shown. Figure 6 An additional configuration for a cell stack is shown, detailing the stack of two cells and including current collectors for the stack.

[0123] Figure 7 An example of a spiral wound module with external current paths is shown, and the module axial section is shown. One of ordinary skill in the art will know that fewer or more cells can be stacked in series before winding the module.

[0124] Additionally, the inner tube can be split for hydrogen inlet and outlet for carbon dioxide rich hydrogen. For example, the HEMFC and ECP fuel cell systems or ECP described herein can have a cell comprising an anode gas flow layer, and the anode gas flow layer is in fluid connection with a first manifold and a second manifold in the inner tube. Additionally, the anode gas flow layer can comprise a flow directing element that causes gas to flow outwardly from the first manifold in the inner tube through a portion of the anode gas flow layer, and then inwardly through a second portion of the anode gas flow layer to the second manifold in the inner tube. This configuration is shown in detail in Figure 8 .

[0125] A spiral wound module configuration contains a stack of several cells that are wound into a spiral wound cylindrical module form. Each cell contains a MEA sandwiched between an anode and a cathode feed spacer, bipolar plates made of metal foil, and gaskets that seal the cell edges, providing an axial flow path on the cathode side and a radial flow path on the anode side. There are two configurations for the anode inlet and outlet. The spiral wound module is made by winding the cell stack around an inner tube and inserted into a cylindrical housing. The anode inlet and outlet ports can be located at either the inner or outer radial end of the spiral, in either order. Alternatively, both the anode inlet and outlet ports can be the inner tube, with a partition separating the two ports. Flow directing elements can then be added to the anode feed spacer to direct the gas in a U-shaped pattern out the end of the vane and back in. The simplest flow directing element would be a bead of sealant or gasket that is applied in the line from the partition outward to almost the end of the vane, around which the gas must flow. However, there can be some stagnation zones near the outer corners of the vane, so it can be better to use multiple gaskets or beads of sealant to create nested U-shaped flow channels.

[0126] For the iECP, the spiral wound module can have a cell stack as shown in Figure 9 and a spiral wound module as shown in Figure 10 . The spiral wound module can also have a hydrogen inlet as shown in Figure 8 .

[0127] The HEMFC and ECP fuel cell systems or ECPs described herein can have a cell pitch of less than about 2 mm, less than about 1.5 mm, or less than about 1 mm.

[0128] The iECPs described herein can use air as the carbon dioxide containing gas.

[0129] The ECPs described herein, and the ECPs in the fuel cell systems, can have a membrane area / air flow rate ratio of less than or equal to 50 cm 2 / standard liters per minute (SLPM) at 1 atmosphere.

[0130] The ECPs described herein, and the ECPs in the fuel cell systems, can have a cell volume / air flow rate ratio of less than or equal to 10 cm 3 / SLPM.

[0131] Also disclosed is a method for separating carbon dioxide from air or another carbon dioxide containing gas, comprising supplying a carbon dioxide containing gas to the cathode of an ECP or an ECP in a HEMFC fuel cell system described herein, and supplying a hydrogen containing gas to the anode of the ECP.

[0132] The method can further comprise causing the current I CO2 , i.e., the number of moles of CO2 per second per cell that enters the cathode inlet, to be proportional to the current I cell , where I cell is defined as:

[0133] I cell = nF N CO2

[0134] where n is a number in the range of 2 to 50, and F is the Faraday constant. Operating the ECP in this range of n can achieve nearly complete removal of CO2 from an air stream while minimizing the use of hydrogen gas. For the methods described herein, the carbon dioxide containing gas can be air.

[0135] Further, for the methods described herein, the carbon dioxide containing gas can be flue gas.

[0136] Additionally, the carbon dioxide in the ECP anode outlet stream can be collected. When the carbon dioxide is collected as a mixture with hydrogen gas, the hydrogen gas:carbon dioxide ratio can be between about 1 : 1 and about 4: 1.

[0137] A hydrogen and carbon dioxide mixture (e.g., syngas) can be fed to a downstream reactor, where the desired ratio depends on the downstream product. For example, the hydrogen:carbon dioxide ratio can be about 4: 1 for the Sabatier process (methane), about 3: 1 for methanol, about 2: 1 for the Fischer-Tropsch process, or about 2: 1 for the Bosch reaction (for oxygen recycling on a spacecraft (e.g., CO2+ 2H2= C + 2H20).

[0138] Also disclosed is an ECP for separating carbon dioxide from a carbon dioxide containing gas, comprising a cell, the cell comprising a membrane and two electrodes each capable of functioning as an anode or a cathode; each of the two electrodes independently comprising a charge storage compound that reacts to form hydroxide when functioning as a cathode and reacts to consume hydroxide or produce protons when functioning as an anode; the membrane being adjacent to and separating the two electrodes; wherein the carbon dioxide containing gas is in contact with the electrode functioning as a cathode, and the carbon dioxide reacts with the hydroxide ions to form bicarbonate ions, carbonate ions, or both bicarbonate and carbonate ions; the bicarbonate ions, carbonate ions, or both bicarbonate and carbonate ions are transported through the membrane to the electrode functioning as an anode; the bicarbonate ions, carbonate ions, or both bicarbonate and carbonate ions react at the electrode functioning as an anode to form carbon dioxide and water; wherein the ECP further comprises a means for reversing the direction of the current and simultaneously alternating the electrodes in contact with the carbon dioxide containing gas, thereby allowing each electrode to function in turn as an anode and a cathode.

[0139] The above ECP can have one or both electrodes comprising a metal oxide, a metal hydroxide, a metal oxyhydroxide, or a hydrogen storage alloy. The metal oxyhydroxide can comprise nickel oxyhydroxide. The metal oxide can comprise manganese dioxide. The hydrogen storage alloy can comprise lanthanum nickel hydride.

[0140] Also disclosed is a method of separating carbon dioxide from a carbon dioxide containing gas, comprising supplying the carbon dioxide containing gas to the cathode of the electrochemical pump (ECP) described above having one or both electrodes, the electrodes comprising a metal oxide, a metal hydroxide, a metal oxyhydroxide, or a hydrogen storage alloy.

[0141] Preferably, for the method just described above, the carbon dioxide containing gas is flue gas.

[0142] The current in the ECP is provided by a power source, and the power source can directly reverse its output current, or a double pole double throw switch / relay can be used to reverse the connection between the terminals of the ECP and the terminals of the power source.

[0143] For gas flow, four-way valves need to be provided at the inlet and outlet. For example, the gas flow can be arranged such that in mode A, electrode 1 has CO2-containing gas flowing in and CO2-lean gas flowing out, and electrode 2 has sweep gas (optional) flowing in and CO2-rich gas flowing out. In mode B, electrode 1 has sweep gas (optional) flowing in and CO2-rich gas flowing out, and electrode 2 has CO2-containing gas flowing in and CO2-lean gas flowing out.

[0144] Further disclosed is a battery system comprising a metal-air battery and an electrochemical pump (ECP) for separating carbon dioxide from a carbon dioxide-containing gas, the ECP comprising a cell, the cell comprising an anode, a cathode, and a membrane. The anode comprises an anode electrocatalyst for oxidizing a reagent to form protons or consume hydroxide ions. The cathode comprises a cathode electrocatalyst for reducing oxygen to form hydroxide ions. The membrane is adjacent to and separates the anode and the cathode. The carbon dioxide-containing gas is supplied to the cathode, and the carbon dioxide reacts with the hydroxide ions formed at the cathode to form bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions. The bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions are transported through the membrane to the anode; and the bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions react at the anode to form carbon dioxide and water. The carbon dioxide-containing gas is air, and after the air passes through the cathode of the ECP to reduce the concentration of carbon dioxide, the air with reduced carbon dioxide concentration is directed to the cathode inlet of the metal-air battery.

[0145] When considering the following equation:

[0146] I cell = nF N CO2 ,

[0147] It is desirable to operate at low n values to reduce energy consumption, but the rate of carbon dioxide capture decreases at low n values. The reason this occurs is because the hydroxide:carbonate ratio in the cathode decreases (i.e., less hydroxide is generated). Hydroxide is the active agent for CO2 capture, so lower hydroxide concentrations will reduce the capture rate. When the hydroxide concentration is reduced, the kinetics of CO2 capture decrease before the equilibrium partial pressure of CO2 becomes significant, meaning that the same high fraction of CO2 capture is possible, but the ECP area required is larger. Using a suitable catalyst, the CO2 capture rate can be maintained at low values of n (e.g., n = 2-10), reducing energy (e.g., hydrogen) consumption without requiring a larger ECP.

[0148] Primary, secondary, and tertiary amines are active for CO2 capture. CO2 and water react with tertiary amines to form tertiary ammonium bicarbonate (R3NH + HCO3 -). If the tertiary amine is incorporated into the ionomer (physically or chemically), the bicarbonate can be shifted into the ionomer and the ammonium can be quickly neutralized by hydroxide, making it active for CO2 capture again. The key advantage is that the concentration of tertiary amine can be very high, even if significant carbonate accumulation has occurred, and there is only a small amount of hydroxide present.

[0149] Primary and secondary amines can form bicarbonate, but primarily form carbamate - R2HNH + R2HNCOO - .

[0150] In terms of construction, one approach is to incorporate branched polyethyleneimine with the ionomer into the cathode structure. A second approach is to use an ionomer with a combination of quaternary ammonium and primary-tertiary amine.

[0151] Similar to the basic principles of CO2 hydration catalysts, it is expected that performance will improve at low n values (low current density). As carbonate accumulates in the cathode and lowers the hydroxide concentration, the CO2 capture rate decreases. For sufficiently high membrane resistance values, the ratio of carbonate to hydroxide in the cathode will be determined by the ratio of their generation rates and their electrochemical mobility in the ionomer. At this limit, anion transport through the ionomer is dominated by migration.

[0152] However, for lower membrane resistance values, the potential gradient is smaller and diffusion plays a role. The concentrations of carbonate and bicarbonate are very high near the anode, and diffusion will push hydroxide toward the anode and carbonate back toward the cathode, resulting in more carbonate accumulation and a lower CO2 capture rate. Thus, given other competing requirements, including mechanical performance and gas permeability, it is not desirable to use a membrane with the lowest possible resistance, as is typically used for fuel cells and electrolyzers. Rather, it is desirable for the membrane to have high resistance, to reduce the back diffusion of carbonate and bicarbonate, regardless of gas permeation or mechanical performance considerations.

[0153] If the membrane resistance is too high, there will not be enough electromotive force to drive the current. Ideally, the ohmic (iR) losses are kept between 10 mV and 300 mV. If the design current is 5-30 mA / cm 2 , the membrane resistance can be a minimum of 2 Ohm-cm 2 and a maximum of 10 Ohm-cm 2 . More broadly, membrane resistances between 0.5 and 20 Ohm-cm 2 can be considered. These ranges are significantly higher than the membrane resistance values typically practiced in the field of polymer electrolyte fuel cells and electrolyzers.

[0154] For the iECPs described herein, there is no method to directly control the cell current density. One possible method to control the hydrogen consumption is to intentionally limit the supply of hydrogen to the cell to produce a low average cell current by fuel starvation, although fuel starvation will provide a non-uniform current density profile and poor CO2 capture performance. Even with proper adjustment of the cell resistance to provide the optimum current density at one air flow rate, the application of the HEMFC fuel cell system requires an increase or decrease in the flow rate to the iECP as the flow rate to the HEMFC increases or decreases. If the flow rate is not correspondingly increased and decreased, then excessive hydrogen will be consumed at partial load.

[0155] Since the anode and cathode flow rates are the only parameters that need to be controlled in the iECP, and the cathode flow rate is matched to the HEMFC load, the anode gas supply can be the target for control of the internal current density.

[0156] To control the rate of hydrogen supply from the anode gas stream layer to the anode, a diffusion barrier can be added to the anode and then operated at a diffusion-limited current density determined by the barrier. Typically at the iECP operating current density, the mass transfer is fast and there is essentially no hydrogen concentration gradient between the anode gas stream layer and the anode electrocatalyst surface. This negligible hydrogen concentration gradient does not result in a significant voltage loss and does not affect the cell current density.

[0157] One method to control the cell current density of the iECP is to place a microporous or partially gas permeable barrier between the anode and the anode gas stream layer. Advantageously, such a barrier will block hydrogen transport except for a small amount of hydrogen that can diffuse through the barrier (e.g., on the order of 10 mA / cm 2 When the cell approaches this current density, the anode will be starved of hydrogen and the cell voltage will drop to zero. The flux of hydrogen through the ionomer membrane and the limiting current density are described as follows:

[0158]

[0159] where N H2 is the flux of hydrogen, i is the limiting current density, D is the diffusivity of hydrogen in the barrier, R is the gas constant, T is the temperature, p H2 is the partial pressure of hydrogen, and L film is the thickness of the barrier. If we can control p H2 , then we can control i lim . The partial pressure of hydrogen can be controlled by changing the total pressure, by recycling the CO2-rich, hydrogen-lean exit gas, or by mixing in some air or HEMFC exhaust gas (e.g., less oxygen). The latter strategy will consume some of the hydrogen by catalytic combustion, but will dilute the remaining hydrogen with nitrogen.

[0160] A diffusion barrier will result in CO2accumulating to a higher concentration in the anode. Here, it can be advantageous to use a diffusion barrier selective to carbon dioxide over hydrogen (such as an ionomer membrane). Increasing carbon dioxide permeation over hydrogen gas will minimize the carbon dioxide gradient from the anode to the anode gas flow layer. However, the sensitivity of hydrogen and carbon dioxide permeation rates to temperature and relative humidity must also be considered. It is preferable to minimize this sensitivity to achieve more predictable control of the cell current density from the hydrogen gas partial pressure.

[0161] The basic control method for the HEMFC and ECP described herein is to adjust the current density and hydrogen flow rate to be proportional to the air flow rate required by the HEMFC. In the case of reduced air demand, it can be advantageous to reduce the current and hydrogen supply above 1 : 1 as the required ECP performance is also lower and so additional carbonate buildup can be tolerated. This will reduce parasitic hydrogen consumption when the HEMFC is at partial load.

[0162] For the iECP cell, the hydrogen recycling and hydrogen dilution strategies are expected to only apply with a hydrogen diffusion barrier. A pulsed hydrogen flow is an alternative method that can work without a hydrogen diffusion barrier, with the advantage that most PEMFC system implementations use pulsed purging rather than continuous purging. The advantages of this method can also apply to HEMFC systems.

[0163] If the cell is consistently starved of hydrogen, the result is a high current density near the anode inlet and a very low current near the anode outlet, where the hydrogen is depleted. Conversely, if the hydrogen is pulsed at high flow, the entire anode gas flow layer can be filled with a high concentration of hydrogen. Under these conditions, the cell will reach its maximum design current density (e.g. 30 mA / cm 2 ). Then, when the hydrogen supply is turned off, the hydrogen will be consumed uniformly from the anode gas flow layer across the cell. The current will remain at 30 mA / cm 2 , until the hydrogen is depleted, and then the cell current will rapidly drop to zero. When the current reaches zero, carbonate will accumulate in the cathode and also begin to diffuse from the anode. The stored hydroxide will continue to capture CO2until the hydroxide is completely consumed. As long as the next hydrogen pulse occurs before the hydroxide concentration is too low, sufficient iECP performance is maintained. The current pulse pumps the accumulated carbonate to the anode and replaces it with hydroxide, and then the cycle begins again.

[0164] The ECP described herein can be applied to remove carbon dioxide from a gas stream containing electrochemically reducible components and remove carbon dioxide into a gas stream containing electrochemically oxidizable components. Possible cathode reactions include oxygen reduction, proton reduction (i.e. hydrogen evolution). Possible anode reactions include hydrogen oxidation, water oxidation (i.e. oxygen evolution) and ammonia oxidation.

[0165] The ECPs described herein can be used to remove, in whole or in part, acid gases that dissolve, react, or dissociate in water to form anions and protons from a stream containing the acid gases. These acid gases can include sulfur dioxide and hydrogen sulfide.

[0166] The ECPs described herein can be used to remove, in whole or in part, basic gases that dissolve, react, or dissociate in water to form cations and hydroxide from a stream containing the basic gases. Basic gases can include ammonia and organic amines. In this case, anion exchange polymers are replaced by cation exchange polymers and the gas to be purified must be introduced to the anode. Hydrogen oxidation, ammonia oxidation, and water oxidation (i.e., oxygen evolution) can be included as anode reactions compatible with this cell. Oxygen reduction, proton reduction (i.e., hydrogen evolution) are non-exhaustive lists of cathode reactions compatible with this cell.

[0167] Battery electrode reactions can be used in place of fuel cell reactions for the anode and cathode. In these cases, a cyclic operation is required in which the current and gas supply connections are periodically reversed to alternate which electrode is the cathode and captures carbon dioxide, and which electrode is the anode and concentrates carbon dioxide.

[0168] Definitions

[0169] As used herein, “cell pitch” is the shortest distance from the anode-membrane interface of one cell to the anode-membrane interface of the adjacent cell. Alternatively, it is the combined thickness of the anode, membrane, cathode, anode gas flow layer, cathode gas flow layer, and bipolar plate.

[0170] “Bipolar plate” is a component that separates adjacent cells in a stack of cells connected in series and provides an electrical connection between the cathode of one cell and the anode of the adjacent cell while maintaining separation of the gas flow layers.

[0171] “Gas flow layer” is a layer of a cell through which a gas flows and with which the gas can exchange with the anode or cathode (the “anode gas flow layer” and “cathode gas flow layer”, respectively).

[0172] “CO2 mass transfer resistance” is a performance metric for an ECP defined as the average CO2 concentration in the cathode gas transport layer divided by the CO2 removal rate per unit MEA area. Mathematically, the CO2 mass transfer resistance (R MT ) is calculated as

[0173]

[0174] where A is the total MEA area in the ECP (in m 2 ), v is the volumetric flow rate of CO2-containing gas to the ECP (in m 3 / s), and x in and x outis the mole fraction of CO2 in the CO2 containing gas at the inlet and outlet of the ECP, respectively (unitless).

[0175] “sccm” is a unit of gas flow rate corresponding to 1 cm 3 / minute at standard conditions of 0 °C and 1 atm pressure.

[0176] “slpm” is a unit of gas flow rate corresponding to 1 L / minute at standard conditions of 0 °C and 1 atm pressure.

[0177] Many modifications and variations of this application can be made in the light of the above detailed description. The embodiments described hereinbefore are illustrative only and changes can be made to the specifications without departing from the scope of the present application, which is defined in the following claims.

[0178] Examples

[0179] The following non-limiting examples are provided to further illustrate the application.

[0180] Example 1 Modeling of ECP for CO2 removal

[0181] The ECP mechanism for carbon dioxide can be understood by combining a one-dimensional membrane electrode assembly (MEA) model for electrochemical transport and reactions. The conversion between carbon dioxide, bicarbonate, and carbonate is handled using rate constants and activation energies from literature lists, assuming water in the ionomer behaves as a dilute aqueous electrolyte. The key reactions are

[0182]

[0183] where reaction

[12] dominates in the cathode and reaction

[11] dominates in the anode. Carbonic acid, bicarbonate, and carbonate can interconvert according to two acid-base equilibria,

[0184]

[0185] The net rate of CO2 hydration i is given by

[0186]

[0187] where k1k -1 k2, k -2 are the forward and reverse rate constants for the neutral (Equation 11) and basic (Equation 12) CO2 hydration mechanisms, respectively, ε ion is the volume fraction of ionomer in the electrode, φ Η2O is the volume fraction of water in the ionomer, K H,CO2 is the Henry’s law constant for CO2 in water, p CO2 is the partial pressure of CO2 in the gas pore, c i is the concentration of ion i, and Kb2 This is the acid-base equilibrium constant between carbonic acid and bicarbonate (Equation 13). The three key ions are represented by the subscripts H for hydroxide, C for carbonate, and B for bicarbonate. Electrochemical transport is modeled using the Nernst-Planck equation.

[0188]

[0189] Where N i It is flux, D i It is the diffusivity, z i Φ is the charge of all ions i. Φ2 is the ionic potential, and x is the spatial coordinate. For a low conductivity film with a diameter of 20 μm (4 Ω·cm) 2 ), 0.01 mg Pt / cm 2 Anode (5wt% Pt / C) and 1 mg / cm 2 The simulated concentration curves of hydroxide, carbonate, and bicarbonate in the MEA at the cathode are shown below. Figure 13 As shown. The one-dimensional model was run with a fixed flow channel composition as boundary conditions—in this case, 400 ppm for the cathode and 10,000 ppm for the anode. The electric field generated at the low current density was sufficient to maintain a pH gradient of approximately 6 units, which produced a very large difference in the equilibrium CO2 concentrations at the anode and cathode, thereby driving a nearly irreversible CO2 pumping.

[0190] Figure 14 illustrates the ability of the CO2 ECP to remove >99.9% of CO2 from the air, showing simulated results for a cathode flow channel concentration of 0.4 ppm and an anode flow channel concentration of 100,000 ppm. Figure 14A The anion concentration curve is shown, and Figure 14B The figures show the values ​​at open circuit, 10 and 20 mA / cm. 2 The CO2 hydration / dehydration rate (e.g., capture / release, respectively). In open circuit, CO2 is transported according to the concentration gradient, but only in the range of 10 to 20 mA / cm². 2 At that time, CO2 is captured from the cathode.

[0191] Calculations estimate that the characteristic length scale for CO2 reaction / diffusion into the hydroxide ionomer is only 50 nm at 70 °C. Within this length scale, any CO2 diffusing through the membrane from the anode to the cathode will react with the hydroxide before reaching the cathode.

[0192] Example 2 eECP operates in air / hydrogen mode

[0193] A single air / hydrogen cell experiment was used to demonstrate the proof of concept of ECP to investigate the effect of operating temperature and current density on the performance of ECP in removing CO2 from an air stream to a hydrogen stream. The cathode or anode outlet gas was monitored by a CO2 sensor (Vaisala GMP252). The first experiment was at 5 cm 2 of 0.4 mg Pt / cm 2 of 5 wt. % Pt / C and demonstrated CO2 levels in the exhaust below 100 ppm at low current densities (≤ 40 mA / cm 2 ). Given this initial success and the stringent cost requirements of the end application, a 25 cm 2 cell (#2) was fabricated with 0.013 mg Pt / cm 2 of 5 wt. % Pt / C for the anode and 0.6 mg / cm 2 of unsupported Ag for the cathode. The second cell was investigated over a wider range of flow rates and demonstrated CO2 removal rates down to the ppm level (the measurement was limited by the accuracy of the CO2 sensor). To demonstrate the room for performance improvement, a cell #3 was fabricated using the same gas diffusion electrodes as cell #2, but a porous carbon- ionomer interlayer was applied directly to the cathode side of the membrane. Such an interlayer provides a more accessible ionomer volume for the CO2 and hydroxide reaction. All experiments used a PAP membrane and ionomer. The PAP membrane and ionomer are described in U.S. Application No. 16 / 146,887, which is incorporated herein by reference.

[0194] When the cathode hydroxide concentration is sufficiently high, the cathode OH - trapped CO2 is a first order irreversible process and the CO2 concentration is expected to exponentially decrease along the length of the cathode flow channel. Under these conditions, there should be a log-linear relationship between the outlet CO2 concentration and the reverse flow rate. Such a relationship implies that if we need 1 m 2 of effective ECP area to achieve a 90% CO2 removal rate, we can achieve a 99% removal rate with 2 m 2 and a 99.9% removal rate with 3 m 2 . This favorable characteristic needs experimental evidence to have been provided.

[0195] Figure 15 depicts a 25 cm 2CO2 removal capability of a single air / hydrogen cell (cell #2) of the PAP membrane, used as an ECP. CO2 levels in the exhaust were measured as a function of air flow rate at temperatures between 50 °C and 70 °C. The results show that at low flow rates, CO2 removal rates can be reduced to single digit ppm CO2. Based on an anode flow rate of 50 seem, the anode outlet CO2 concentration should be in the range of 700 to 3000 ppm, which indicates that CO2 can be pumped against a concentration gradient of about 3 orders of magnitude without performance loss. Except in cases of suspected flooding, the CO2 pump exhibits first order irreversible behavior, with CO2 removal rates up to 99%, where the limit of sensor accuracy is reached.

[0196] Figure 16 shows CO2 removal rates and calculated CO2 mass transfer resistances for cells #2 and #3 at 70 °C and for cell #1 at 80 °C, all at 20 mA / cm2. 2 Cell #2 has lower performance than cell #1, which can be due to lower ionomer loading in the cathode, which limits the reaction with hydroxide. Cell #3 exhibits the best performance, with a mass transfer resistance that is half that of cell #2. Cell #3 uses a multi-layer cathode structure that combines more ionomer volume for CO2 capture without using thick electrocatalyst layers. Thinner electrocatalyst layers would be particularly advantageous if the electrocatalyst is expensive. The mass transfer specific resistance is nearly constant with CO2 concentration (Figure 16b), indicating an ideal first order process. Under these conditions, a three-fold increase in membrane area is required to achieve CO2 removal rates from 90 to 99.9%, making it possible to achieve air purity specifications for HEMFC stacks.

[0197] Example 3 : iECP operated in air / hydrogen mode

[0198] In addition, the iECP concept, which aims to achieve the simplest operation, possibly the cheapest ECP, was demonstrated experimentally. A PAP membrane was cast with 30 wt% carbon nanotubes to create internal electronic shorts and 0.4 mg Pt / cm2was used in the Pt / C catalytic electrodes to make an MEA. A 5 cm2 2 cell was assembled and tested over a range of cell temperatures, with hydrogen or nitrogen on the anode side and 350 ppm CO2 containing air on the cathode side. The results are shown in 2 and match roughly the performance of a similar non-shorted 5 cm2 2 MEA. Due to the smaller total area of the cell, the CO2 content in the air outlet did not reach ultra-low levels, but similar mass transfer coefficients were calculated compared to the cell using the non-shorted MEA. Figure 17

[0199] Example 4 ​: iECP operated in air / hydrogen mode with an anode gas diffusion barrier and recirculation loop

[0200] A composite membrane was prepared by adding carbon nanotubes to a solution of poly(arylpiperidinium) (PAP-TP-85) in dimethylsulfoxide solution (bromide counterion). The weight ratio of carbon nanotubes to PAP-TP-85 polymer was 30:70. The mixture was cast on a glass plate and dried at 50 °C until visibly dry, then at 120 °C for at least 8 hours to remove residual solvent. The membrane was ion exchanged to bicarbonate counterions by repeated immersion in sodium bicarbonate solution at room temperature. The thickness of the membrane was 80 pm. The membrane was cut to 7.5 cm x 7.5 cm.

[0201] An anode catalyst ink was prepared by mixing 12.5 mg of 40 wt% Pt / C catalyst, 30 mg of water, 93.5 mg of poly(arylpiperidinium) (PAP-TP-100) polymer solution (3.5 wt% in ethanol), and 1.25 mL of isopropanol. A cathode catalyst ink was prepared by mixing 12.6 mg of 40 wt% Pt / C catalyst, 30 mg of water, 94 mg of PAP-TP-100 polymer solution (3.5 wt% in ethanol), and 1.25 mL of isopropanol. A cathode interlayer ink was prepared by mixing 25 mg of carbon black (Vulcan XC-72), 483.5 mg of PAP-TP-100 polymer solution (3.5 wt% in ethanol), and 1.67 mL of isopropanol. The inks were sonicated in an ice bath for 1 hour. After mixing, the inks were sprayed onto the composite membrane in the following order using an airbrush. The cathode interlayer ink was sprayed first onto the cathode side of the membrane. The cathode catalyst ink was sprayed second onto the dried cathode interlayer. The anode catalyst ink was sprayed third onto the anode (opposite) side of the membrane. All layers were 5.0 cm x 5.0 cm as defined by the template. Approximately 50% of the total ink solution was deposited within the active area, with the remainder lost due to over-spraying, resulting in catalyst loadings of 0.1 mg Pt / cm 2 , 0.1 mg Pt / cm 2 , and 0.5 mg C / cm 2 in the anode, cathode, and cathode interlayer, respectively.

[0202] The catalyst-coated membrane was dried overnight at room temperature. A 1.6 mm thick porous ePTFE gasket material sheet was compressed to a thickness of 0.7 mm and cut into 5.2 cm x 5.2 cm pieces to serve as the anode gas diffusion barrier layer. A carbon paper gas diffusion layer (Toray TGP-H-030, 0.1 mm thick) without a microporous layer was cut into 5.0 cm x 5.0 cm pieces to serve as the cathode gas diffusion layer. The anode gasket, made of PTFE, was 7.5 cm x 7.5 cm with a 5.2 cm x 5.2 cm opening to seal around the anode gas diffusion barrier layer. The cathode gasket, made of FEP, was 7.5 cm x 7.5 cm with a 5.0 cm x 5.0 cm opening to seal around the cathode gas diffusion layer.

[0203] Battery configuration such as Figure 18 As shown. Single-cell iECPs are assembled into a commercial 25cm stack via stacking. 2 The fuel cell test hardware (fuel cell technology) consists of the following components in sequence: anode end plate, anode current collector, anode flow field (single serpentine flow pattern), anode gasket, ePTFE anode gas diffusion barrier layer, catalyst coating membrane, cathode gasket, cathode gas diffusion layer, cathode flow field (cross-flow pattern), cathode current collector, and cathode end plate. The battery is connected to a fuel cell test station (Scribner 850e) to control gas flow, temperature, and humidity. On the anode side, a diaphragm pump is connected between the anode outlet and anode inlet to recirculate the anode product gas back to the anode inlet.

[0204] The battery was tested at 60°C, with hydrogen fed to the anode at 70% relative humidity (RH) and air containing 400 ppm CO2 fed to the cathode at 70% RH. The cathode outlet was passed through a condenser to remove water and directed to a Teledyne TML20 CO2 analyzer to measure CO2 removal rate. The battery was tested at various anode and cathode flow rates, with the anode circulation flow rate set to 0 or 500 mL / min. Results are shown below. Figure 19 .

[0205] First, the results without anode recirculation were observed. For anode flow rates ranging from 50 to 200 sccm, CO2 removal was high and constant, with an average residual CO2 of 5 ppm at a cathode flow rate of 1000 sccm and 4 ppm at a cathode flow rate of 500 sccm. However, when the anode hydrogen supply was between 7 and 25 sccm, the CO2 removal performance of the iECP was very poor because the hydrogen supply was lower than that required to support a uniform cell current density throughout the active region.

[0206] Due to the anode gas diffusion barrier, the cell current density can be uniformly reduced throughout the active area by lowering the hydrogen partial pressure. An anode recycle flow of 500 mL / min was used to dilute the incoming hydrogen supply with a C02-rich product gas mixture. In these cases, the C02separation was significantly improved at hydrogen flow rates of 7 to 25 seem compared to the results obtained without an anode recycle flow. Even at a hydrogen supply rate of 4 seem, 91% and 95% C02removal was observed for air flow rates of 2000 seem and 1000 seem, respectively. These results demonstrate that the combination of an anode gas diffusion barrier with means to lower the hydrogen partial pressure can enable successful high C02separation performance in iECPs with low hydrogen consumption.

[0207] Example 5 : Running eECP with a cross-flow field and low cathode catalyst loading in air / hydrogen mode

[0208] An anode catalyst ink was prepared by mixing 13.6 mg of 40 wt% Pt / C catalyst, 30 mg of water, 102.1 mg of poly(arylpiperidinium) (PAP-TP-100) polymer solution (3.5 wt% in ethanol), and 1.25 mL of isopropanol. A cathode catalyst ink was prepared by mixing 13.6 mg of 40 wt% Pt / C catalyst, 30 mg of water, 97.3 mg of PAP-TP-100 polymer solution (3.5 wt% in ethanol), and 1.25 mL of isopropanol. A cathode interlayer ink was prepared by mixing 26.9 mg of carbon black (Vulcan XC-72), 520 mg of PAP-TP-100 polymer solution (3.5 wt% in ethanol), and 1.67 mL of isopropanol. The inks were sonicated in an ice bath for 1 hour. After mixing, the inks were sprayed onto a poly(arylpiperidinium) membrane (PAP-TP-85, 22 pm thickness) in the following order by airbrush. The cathode interlayer ink was sprayed first onto the cathode side of the membrane. The cathode catalyst ink was sprayed second onto the dried cathode interlayer. The anode catalyst ink was sprayed third onto the anode (opposite) side of the membrane. All layers were 5.0 cm x 5.0 cm as defined by the template. Approximately 50% of the total ink solution was deposited within the active area, with the remainder lost due to overspray, resulting in catalyst loadings of 0.1 mg Pt / cm 2 , 0.1 mg Pt / cm 2 , and 0.5 mg C / cm 2 of catalyst loading in the anode, cathode, and cathode interlayer, respectively.

[0209] The catalyst-coated membrane was dried overnight at room temperature. A microporous carbon paper gas diffusion layer (Toray TGP-H-030, 0.1 mm thick) was used for both the anode and cathode gas diffusion layers, and 0.09 mm thick FEP gaskets were used for both the anode and cathode. Single-cell eECPs were assembled into a commercially available 25 cm² configuration via stacking. 2 The fuel cell test hardware (fuel cell technology) consists of the following components in sequence: anode end plate, anode current collector, anode flow field (single serpentine flow pattern), anode gasket, anode gas diffusion layer, catalyst coating film, cathode gasket, cathode gas diffusion layer, cathode flow field (cross-flow pattern), cathode current collector, and cathode end plate. The battery is then connected to a fuel cell test station (Scribner 850e) to control gas flow, temperature, and humidity.

[0210] The battery operated for 100 hours at 60°C and 70% RH, using hydrogen at an anode flow rate of 10 sccm and air containing 400 ppm CO2 at a cathode flow rate of 1250 sccm. The cathode operated at a back pressure of 50 kPag. The battery operated at 40 mA / cm². 2 It operates at a current density. The cathode outlet is passed through a condenser to remove water and directed to a Teledyne TML20 CO2 analyzer to measure the CO2 removal rate.

[0211] The cathode outlet CO2 concentration during the 100-hour holding period is shown in Figure 20 The CO2 separation performance exhibited a low degradation rate, starting with a removal rate of 98.3% (7.0 ppm) at the beginning of the test and decreasing to 98.1% (7.7 ppm) after 100 hours. This is in contrast to Example 2 and... Figure 16A Compared to the previous results, the performance was significantly improved, with a reverse flow rate of 0.8 slpm. -1 The CO2 outlet concentration ranges from 7.0 to 7.7 ppm, while battery #3 in Example 2 requires approximately 3 slpm. -1 The reverse flow rate was adjusted to achieve the same CO2 outlet concentration. The performance improvement can be attributed to a combination of factors, including the crossflow pattern at the cathode, the thin cathode gas diffusion layer, and the reduced relative humidity.

[0212] When describing elements of the invention or preferred embodiments thereof, the articles “a / an,” “the,” and “described” are intended to indicate the presence of one or more elements. The terms “comprising,” “including,” and “having” are inclusive and mean that additional elements may be present in addition to the listed elements.

[0213] In view of the above, it will be seen that several objectives of the present invention have been achieved and other advantageous results have been obtained.

[0214] As various changes could be made in the above devices and methods without departing from the scope of the application, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

1. An electrochemical pump (ECP) for separating carbon dioxide from air, the ECP comprising: a battery including an anode, a cathode, and a membrane adjacent to and spaced apart from the anode and the cathode. The anode contains an anode electrocatalyst for oxidizing reagents to form protons or consuming hydroxide ions. The cathode contains a cathode electrocatalyst for reducing oxygen to form hydroxide ions. During the use of the ECP: The air is supplied to the cathode, and the carbon dioxide reacts with the hydroxide ions formed at the cathode to form bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions. The bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions are transported to the anode through the membrane; and The bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions react at the anode to form carbon dioxide and water; and At least one of the following: (a) The anode and the cathode are electronically connected via the membrane to form an internal current ECP (iECP), and the membrane comprises an anion exchange polymer and a conductive material or a conductive anion exchange polymer; or (b) A porous structure-ionomer interlayer separates the membrane e from the cathode; or (c) Based on platinum as the catalyst, the catalyst loading at the anode and the cathode is less than 0.4 mg catalyst / cm²; or (d) The film resistance of the ECP is between 0.5 and 20 Ohm-cm. 2 Between; or (e) The cathode further comprises a catalyst consisting of a primary amine, a secondary amine, or a tertiary amine.

2. The ECP according to claim 1, wherein the anode and the cathode are electronically connected through the membrane to form an internal current ECP (iECP), and the membrane comprises an anion exchange polymer and a conductive material or a conductive anion exchange polymer.

3. The ECP according to claim 1, wherein the porous structure-ionomer interlayer separates the membrane from the cathode.

4. The ECP according to claim 1, wherein, based on platinum as the catalyst, the catalyst loading at the anode and the cathode is less than 0.4 mg catalyst / cm².

5. The ECP according to claim 1, wherein the film resistance of the ECP is between 0.5 and 20 Ohm-cm. 2 between.

6. The ECP according to claim 1, wherein the cathode further comprises a catalyst composed of a primary amine, a secondary amine, or a tertiary amine.

7. The ECP according to any one of claims 3 to 6, wherein the membrane comprises anion exchange polymer.

8. The ECP according to claim 2 or 7, wherein the anion exchange polymer comprises a quaternary ammonium or imidazolium group and a polymer backbone without ether groups.

9. The ECP according to claim 2 or 7, wherein the anion exchange polymer comprises poly(arylpiperidinium), alkylammonium-functionalized poly(arylalkylene), substituted imidazolium-functionalized poly(arylalkylene), alkylammonium-functionalized poly(styrene), substituted imidazolium-functionalized poly(styrene), alkylammonium-functionalized poly(styrene-co-divinylbenzene), substituted imidazolium-functionalized poly(styrene-co-divinylbenzene), alkylammonium-functionalized poly(styrene-block-ethylene-co-... (butadiene-block-styrene), substituted imidazolium-functionalized poly(styrene-block-ethylene-co-butadiene-block-styrene), alkylammonium-functionalized poly(ethylene), substituted imidazolium-functionalized poly(ethylene), alkylammonium-functionalized poly(tetrafluoroethylene), substituted imidazolium-functionalized poly(tetrafluoroethylene), alkylammonium-functionalized poly(ethylene-co-tetrafluoroethylene), substituted imidazolium-functionalized poly(ethylene-co-tetrafluoroethylene), polyethyleneimine, poly(diallylammonium), or combinations thereof.

10. The ECP of claim 9, wherein the anion exchange polymer comprises poly(arylpiperidine).

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