Electrochemical devices and fuel cell systems

Abstract

Disclosed are electrochemical devices including an electrochemical pump (ECP) and fuel cell systems including a fuel cell and the ECP. Specifically, the electrochemical device can be an ECP comprising an anode, a cathode, and an anion exchange polymer separating the anode from the cathode. The ECP can 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

Technical Field

[0001] Disclosed are electrochemical devices, specifically electrochemical pumps (ECPs), and fuel cell systems comprising hydroxide exchange membrane fuel cells (HEMFCs) and ECPs. These ECPs and systems can be used to remove carbon dioxide from air and generate electricity by operating fuel cells with CO2-containing air. Background Art

[0002] Carbon dioxide (CO2) is an acidic gas that is present in the atmosphere at concentrations of approximately 400 ppm. As an acidic gas, CO2 reacts with strong bases (such as hydroxide anions) to form carbonate and bicarbonate anions.

[0003]

[0004]

[0005] Alkaline fuel cells and hydroxide exchange membrane fuel cells (HEMFC) use hydroxide conductive electrolytes and suffer significant efficiency losses when exposed to CO2. Liquid alkaline fuel cells are affected by carbonate precipitation, which blocks pores and may be fatal to the cell. HEMFC has bound cations that cannot form carbonate precipitation, but the efficiency of HEMFC is reduced by the concentration gradient of carbonate anions in the cell. When operating in a steady state in air containing CO2, the anode consumes hydroxide and accumulates bicarbonate until the local pH drops to a low enough level to decompose bicarbonate. The cell reaches a steady state in which CO2 is captured by the cathode at the same rate as it is released from the anode, and the pH gradient between the anode and cathode typically causes a loss of several hundred mV. When the cathode gas contains 400ppm CO2, the loss is typically 100-300mV.

[0006] HEMFCs have potential cost advantages over 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 non-precious metal catalysts (especially at the cathode) and cheaper bipolar plate materials possible. However, as mentioned above, achieving good HEMFC performance and efficiency requires supplying air to the cathode with a low concentration of CO2. Therefore, a compact and low-cost device for generating an air stream with a low CO2 concentration is very important for commercially viable HEMFC technology.

[0007] Existing techniques for generating an air stream with a low concentration of carbon dioxide for HEMFCs use two or more layers of regenerable polymeric amine adsorbents, as disclosed in U.S. Patent No. 9,368,819. These layers are thermally regenerated, and a minimum of two layers are required to provide continuous operation, with one layer online while the other is regenerating. This design is complex and bulky, and may not be suitable for transportation or other space-constrained HEMFC applications.

[0008] Additionally, systems for removing carbon dioxide from gas streams have many applications outside the HEMFC field. Other applications include: CO2 removal for metal-air batteries; breathing gas purification for diving, submarine, or space applications; CO2 enrichment in greenhouses to accelerate plant growth; CO2 capture from flue gases or air for subsequent use or storage; and gas separation in industrial applications.

[0009] Therefore, there is a need for a more efficient and cost-effective apparatus and method for removing carbon dioxide from a carbon dioxide-containing gas that can be used in conjunction with an additional device (eg, a fuel cell). Summary of the Invention

[0010] The present disclosure relates to fuel cell systems, electrochemical pumps, and methods of using the same to reduce carbon dioxide concentrations 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 gas containing carbon dioxide, 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; and the membrane is adjacent to and separates the anode and cathode. The gas containing carbon dioxide 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. The gas containing carbon dioxide 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] In addition, the present disclosure relates to an internal current electrochemical pump (iECP) for separating carbon dioxide from a gas containing carbon dioxide, which includes a battery, the battery including an anode, a cathode and a membrane. The anode includes an anode electrocatalyst for oxidizing a reagent to form protons or consuming hydroxide ions. The cathode includes a cathode electrocatalyst for reducing a reagent to form hydroxide ions. The membrane is adjacent to and separates the anode and the cathode. The gas containing carbon dioxide 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. The anode and the cathode are electronically connected through the membrane.

[0013] In addition, the present disclosure relates to an electrochemical pump (ECP) for separating carbon dioxide from air, which comprises a cell comprising an anode, a cathode, and a membrane, and supplies air to the cathode and hydrogen to the anode. The anode comprises an anode electrocatalyst for oxidizing hydrogen to form protons or consuming 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 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.

[0014] Additionally, the present disclosure relates to a method for separating carbon dioxide from carbon dioxide-containing gas or air, comprising supplying carbon dioxide-containing gas or air to a cathode of an electrochemical pump (ECP) of a fuel cell system described herein and supplying 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 gas containing carbon dioxide, comprising a cell comprising a membrane and two electrodes capable of acting as an anode or a cathode. The two electrodes each independently comprise a charge storage compound that reacts to form a hydroxide when acting as a cathode and to consume the hydroxide or produce protons when acting as an anode. The membrane is adjacent to and separates the two electrodes. The gas containing carbon dioxide contacts the electrode acting as the cathode, and carbon dioxide reacts with 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 acting as the anode; and the bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions react at the electrode acting as the anode to form carbon dioxide and water. The ECP also comprises a means for reversing the direction of current and simultaneously alternating the electrodes in contact with the gas containing carbon dioxide, thereby allowing each electrode to act as an anode and a cathode in turn.

[0016] The present disclosure further relates to a system comprising a metal-air battery and an electrochemical pump (ECP) as described herein, wherein the carbon dioxide-containing gas is air, and after the air is supplied to a 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.

[0017] Further disclosed is a battery system comprising a metal-air battery and an electrochemical pump (ECP) for separating carbon dioxide from a gas containing carbon dioxide, the ECP comprising a battery 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 cathode. The gas containing carbon dioxide 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. The gas containing carbon dioxide 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.

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

[0019] (a) the anode and cathode are electronically connected via a 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) a porous structure - an ionomer interlayer separates the membrane from the cathode; or

[0021] (c) a catalyst loading of less than 0.4 mg catalyst / cm2 at the anode and cathode, based on platinum as the catalyst; or

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

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

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

[0025] Figure 1 This is a schematic diagram 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 CO2 concentration 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 using hydrogen as the anode reagent in the ECP and hydrogen supplied from the purge stream of the HEMFC.

[0026] Figure 2 Schematic diagram 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. The electron current is shown as taking either an internal path (iECP) or an external path (eECP). The inset shows a stylized representation of one possible embodiment of a cathode or anode containing an electrocatalyst and ionomer within a porous structure.

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

[0028] Figure 5 is a schematic diagram of a spirally wound module showing an example of a possible battery stacking configuration.

[0029] Figure 6 Also a schematic diagram of a spirally wound module showing an example of a possible configuration comprising two cells stacked and current collectors for the stack.

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

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

[0032] Figure 9 is a schematic diagram of the iECP and describes the cell stacking of the module in detail.

[0033] Figure 10 Is a Figure 9 Schematic diagram of a spirally wound module with cell stacking details.

[0034] Figure 11 is a schematic diagram of a hollow fiber with an iECP fabricated in a housing.

[0035] Figure 12 It includes Figure 11 Schematic diagram of a module of multiple hollow fibers is shown.

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

[0037] Figure 14A The simulated anion concentration distribution through the thickness of the MEA at the position corresponding to the cathode outlet at 99.9% CO2 removal efficiency (at 20 mA / cm 2 The cell temperature was 70° C., and the gases supplied to the anode gas flow layer and the cathode gas flow layer were hydrogen containing 100,000 ppm CO 2 and air containing 0.4 ppm CO 2 , respectively, both at 2 bar.

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

[0039] Figure 15A and 15B The results are from 25cm in H2 / air mode with a range of air flow rates. 2 Graph of the cathode outlet CO2 concentration measured by ECP (cell #2). Figure 15A Shown at 10mA / cm 2 The results are given at a constant current density. Figure 15B Shown at 20mA / cm 2Results at a constant current density of 1.5 Å. The anode flow rate was 50 sccm, the relative humidity (RH) was 80%, and the outlet pressure was ambient pressure. The CO2 concentration was averaged over the last 30 minutes of the 60-minute hold.

[0040] Figure 16A and 16B The low-load cells with and without ionomer interlayer and the conventional high-load cells were tested at 70°C, 80% RH, 20 mA / cm 2 The performance of CO2 ECP is measured at 80℃, 90%RH and 5cm 2 Test high load battery under effective area. Figure 16A The CO2 concentration at the cathode outlet is shown as a function of air flow rate. 2 MEA flow rate (high load) converted to 25cm 2 Equivalent for comparison. Figure 16B The calculated average mass transfer resistance is shown as a function of the outlet CO2 concentration. Results below 1 ppm are excluded due to excessive measurement uncertainty. All measurements are averaged over the last 30 minutes of the 60-minute hold.

[0041] Figure 17 The graph shows the measured performance of iECP with hydrogen as the anode reagent and oxygen as the cathode reagent. -1 The CO2 concentration was measured at the anode and cathode outlets at an air flow rate of 100 ppm, 90% relative humidity and ambient pressure. The cathode feed gas was air containing 350 ppm CO2. The anode gas was N2 or H2 as shown (control cell output). When N2 was used as the anode gas, no significant current was generated in the cell and very 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 means that the cathode gas stream that transports CO2 has a lower CO2 concentration than the anode gas stream that transports CO2. Such transport cannot be driven by concentration gradients alone, which point in the wrong direction, and must be the result of electrochemical pumping.

[0042] Figure 18 Schematic diagram 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 diaphragm pump was connected between the anode outlet and the anode inlet to dilute the hydrogen supply with a CO2-rich anode product gas mixture to reduce the partial pressure of hydrogen.

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

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

[0045] Corresponding reference numerals indicate corresponding parts throughout the drawings. DETAILED DESCRIPTION

[0046] The present disclosure relates to an electrochemical pump (ECP) for separating carbon dioxide from a carbon dioxide-containing gas. The ECP comprises an anode, a cathode, and an anion exchange polymer membrane adjacent to and separating 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 illustrating an example of a fuel cell system. A fuel cell system can be used in methods for generating electricity.

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

[0048]

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

[0050] Many anodic and cathodic reactions may generate protons and hydroxides, respectively. Preferred anodic reactions include the hydrogen oxidation reaction (HOR),

[0051]

[0052] Ammonia oxidation reaction (AOR),

[0053]

[0054] Oxygen evolution reaction (OER),

[0055]

[0056] and nickel hydroxide oxidation reaction (NiOR),

[0057]

[0058] Preferred cathode reactions include the hydrogen evolution reaction (HER),

[0059]

[0060] Oxygen reduction reaction (ORR),

[0061]

[0062] and nickel oxyhydroxide reduction reaction (NiRR),

[0063]

[0064] Using NiOR and NiRR (Equations 7 and 10) or other charge-storing electrode reactions, a nearly pure CO2 product stream can be recovered. Continuous operation can be achieved by periodically reversing the cell current and simultaneously switching the gas connections as the electrodes become fully or nearly fully charged / discharged.

[0065] A fuel cell system is also disclosed, 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 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 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 typically air, and after the air is supplied to 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.

[0066] Figure 1 A schematic diagram of a fuel cell system is shown.

[0067] The fuel cell systems described herein can provide a carbon dioxide-containing gas supplied to the cathode of a 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, wherein these reduced levels are achieved by reaction of CO2 with hydroxide ions at the cathode of the ECP.

[0068] Additionally, the fuel cell systems described herein can enable hydrogen to be the reagent oxidized at the anode electrocatalyst of the ECP, and the hydrogen consumed by the ECP for separating carbon dioxide from air is less than about 5%, 4%, 3%, or 2% of the hydrogen consumed by the HEMFC.

[0069] For applications in generating CO2-free air for HEMFCs, the best choices for the electrode processes in the ECP are 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 can be scavenged 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.

[0070] The core component of the ECP is the MEA, which includes a membrane with electrodes on each side. Both electrodes contain an electrocatalyst and an anion exchange polymer with a porosity sufficient to allow gas transport. The electrodes are conductive for both electrons and anions. The membrane contains an anion exchange polymer and may optionally include a reinforcing polymer or an electron-conducting additive. If the membrane conducts both electrons and anions, no external electrical connection is required, and the MEA can be used in any module configuration, similar to non-electrochemical membranes. An ECP with a membrane that conducts electrons and anions is referred to herein as an internal current electrochemical pump (iECP). If the membrane only conducts anions and does not conduct 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).

[0071] The present disclosure also relates to an iECP for separating carbon dioxide from a gas containing carbon dioxide, having an anode and a cathode electronically connected by an anion exchange membrane. When a potential difference occurs across this type of cell, both ionic and electronic currents are generated 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 consuming 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 cathode. A gas containing carbon dioxide 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 the anode and cathode are electronically connected by the membrane.

[0072] Figure 2 Schematic diagrams of ECPs with either an internal current path (such as the iECP described immediately above) or an external current path (eECP) are shown.

[0073] The iECPs disclosed herein may provide membranes comprising an anion exchange polymer and a conductive material or a conductive anion exchange polymer.

[0074] iECPs allow anion exchange polymers to contain quaternary ammonium or imidazolium groups and a polymer backbone without ether groups.

[0075] Preferably, the iECP described herein may comprise an anion exchange polymer comprising poly(arylpiperidinium), alkylammonium functionalized poly(arylalkylene), substituted imidazolium functionalized poly(arylalkylene), 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-

[0045] The present invention relates to a poly(ethylene-co-tetrafluoroethylene) copolymer, wherein the poly(ethylene-co-tetrafluoroethylene) copolymer is a copolymer of a polyethyleneimine and a polyethyleneimine.

[0076] iECP can include conductive materials such as carbon, nickel, stainless steel, silver, conductive polymers, or combinations thereof. In addition, the conductive materials include nanowires or nanotubes.

[0077] These metallic conductive materials may also be alloys with other metals.

[0078] An iECP may comprise one or more cells arranged in a hollow fiber configuration.

[0079] 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 reactants will be fed into the shell side.

[0080] The module can be composed of one or more fibers encased in a cylindrical shell, the fibers being encapsulated in a sealing compound (typically epoxy resin) with a separator formed near each end. The inner cavity is in fluid communication with the end of the module outside the separator, while the outer shell space is located between the two separators and isolated from the end. The inlet and outlet for the CO2-containing gas are at both ends. The inlet and outlet for the anode reactant and the separated CO2 are located between the two separators. Countercurrent flow is advantageous but not strictly required.

[0081] exist Figure 11 and 12 One way in which this hollow fiber configuration can be arranged is shown in the schematic diagram of .

[0082] In a hollow fiber configuration, the lumen of the fiber is the cathode side, while the outer shell of the fiber is the anode side. The hollow fibers are bundled together and placed in a cylindrical shell, the ends potted in epoxy and cut open. Ports are added to the shell above and below each of the epoxy plugs to allow gas access to the lumen and outer shell sides of the fiber. Hollow fibers can be made in several configurations, as disclosed above, Figure 11 and 12 A specific example of this type of configuration is shown.

[0083] The iECP may include one or more additional cells, and these cells may contain an anode gas flow layer adjacent to one or two anodes, an anode adjacent to a membrane, a membrane adjacent to an anode and cathode, and a cathode gas flow layer adjacent to one or two cathodes, the configuration being represented as follows:

[0084] [-AG-AMC-CG-CMA-]

[0085] Where AG is the anode gas flow layer, A is the anode, M is the membrane, C is the cathode, and CG is the cathode gas flow layer.

[0086] More specifically, for iECP, both planar and spiral wound structures, as well as hollow fiber structures, are possible. There is no need to electrically connect the individual cells, which expands the possibilities. For both planar and spiral wound configurations, the cells do not require bipolar plates, but can be arranged in a pattern of CMA|AG|AMC|CG|CMA|AG|AMC|CG|…, where CMA is the MEA with the cathode on the left and the anode on the right, AMC is the MEA with the anode on the left and the cathode on the right, CG is the cathode gas flow layer, and AG is the anode gas flow layer. Spiral wound modules use one or more leaves of CMA|AG|AMC|CG and wind them in a spiral pattern so that the CG of one winding or leaf contacts the CMA of the next winding or leaf.

[0087] This configuration offers the advantage that adjacent cells can share either the cathode or anode gas flow layers. This configuration is achieved by the iECP design. Figure 10 A schematic diagram showing this configuration is shown.

[0088] The iECP described herein can also be incorporated into a fuel cell system comprising 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 reduced carbon dioxide concentration is directed from the cathode exhaust port of the iECP to the cathode inlet of the HEMFC.

[0089] Additionally, the present disclosure relates to an ECP for separating carbon dioxide from air having hydrogen directed to an anode and air directed to a cathode, and using an anion exchange polymer membrane as an electrolyte positioned between and adjacent the anode and cathode.

[0090] The ECP comprises a cell, which includes an anode, a cathode, and a membrane. The cell supplies air to the cathode and hydrogen to the anode. The anode comprises an anode electrocatalyst for oxidizing the hydrogen to form protons or consume 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 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.

[0091] Figure 2 An overall schematic diagram of the ECP is shown. Figure 3 and 4 Schematic diagrams of some planar hydrogen / air ECP configurations are shown.

[0092] The fuel cell system or ECP described herein comprising a HEMFC and an ECP can be such that the reagent oxidized by the anode electrocatalyst is hydrogen, ammonia, hydrazine, methanol, ethanol, urea, or a combination 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.

[0093] The HEMFC and ECP fuel cell systems or ECPs described herein can be such that the reagent reduced at the cathode electrocatalyst of the ECP comprises oxygen, hydrogen peroxide, or a combination thereof. Preferably, the reagent at the cathode comprises oxygen.

[0094] The fuel cell system or ECP described herein comprising a HEMFC and an ECP can include an anode electrocatalyst of the ECP comprising platinum, a platinum alloy, platinum on carbon, a platinum alloy on carbon, nickel, a nickel alloy, nickel on carbon, a nickel alloy on carbon, ruthenium, a ruthenium alloy, ruthenium on carbon, a ruthenium alloy on carbon, iridium, an iridium alloy, iridium on carbon, an iridium alloy on carbon, palladium, a palladium alloy, palladium on carbon, a palladium alloy on carbon, or a combination thereof. Preferably, the anode electrocatalyst comprises platinum on carbon.

[0095] The HEMFC and ECP fuel cell systems or ECPs described herein can include a cathode electrocatalyst for the ECP comprising silver, silver alloys, silver supported on carbon, silver alloys supported on carbon, platinum, platinum alloys, platinum supported on carbon, platinum alloys supported on carbon, palladium, palladium alloys, palladium supported on carbon, palladium alloys supported on carbon, manganese oxide, manganese oxide supported on carbon, cobalt oxide, cobalt oxide supported on carbon, heteroatom-doped carbon (XC, wherein X comprises one or more of N, C, B, P, S, Se, or O), metal-heteroatom-carbon (MXC, wherein X comprises one or more of N, C, B, P, S, Se, or O, and M comprises Fe, Ce, Cr, Cu, Co, Mo, Ni, Ru, Pd, Pt, Ir, Rh, Os, Ag, Au, Re, Ta, Ti, V, W, Mn, Zn, or Ni, or a combination thereof. n, Sn, Sb, In, Ga, Bi, Pb or Zr), perovskite (ABX3, wherein 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), carbon-supported perovskite (ABX3, wherein 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.

[0096] The HEMFC and ECP fuel cell systems or ECPs described herein may have the membrane of the ECP comprise an anion exchange polymer.

[0097] The anion exchange polymer may comprise poly(arylpiperidinium), alkylammonium functionalized poly(arylalkylene), substituted imidazolium functionalized poly(arylalkylene), 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-benzene),

[0014] The anion exchange polymer can be a substituted imidazolium functionalized poly(ethylene), a substituted imidazolium functionalized poly(styrene-block-ethylene-co-butadiene-block-styrene), an alkylammonium functionalized polyethylene, a substituted imidazolium functionalized polyethylene, an alkylammonium functionalized polytetrafluoroethylene, a substituted imidazolium functionalized polytetrafluoroethylene, an alkylammonium functionalized poly(ethylene-co-tetrafluoroethylene), a substituted imidazolium functionalized poly(ethylene-co-tetrafluoroethylene), polyethyleneimine, poly(diallylammonium), or a combination thereof. Preferably, the anion exchange polymer comprises poly(arylpiperidinium).

[0098] The ECP MEA can be combined with a gas flow layer, an optional gas diffusion layer, and an optional separator to create an ECP cell. One or more cells are packaged with a gas manifold, housing, and seals to create an ECP module. The ECP module is combined with a controller to form a complete ECP. Finally, depending on the application, the ECP can be integrated with a HEMFC stack and other balance-of-system components to form an air-fed ECP-HEMFC system. Figure 1 An example of an air-fed ECP-HEMFC system is shown.

[0099] The eECP described herein and used in a fuel cell system can have current supplied to it 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.

[0100] The fuel cell systems or ECPs described herein that include a HEMFC and an ECP may have one or more additional cells.

[0101] The ECPs described herein and the ECPs in the fuel cell systems may have one or more additional cells electrically connected in series.

[0102] For eECP, several cell and module configurations are possible. The module structure can be planar or spiral wound. Planar modules contain a stack of planar cells with manifolds incorporated into the border region outside the active area to distribute the 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 Figure 3 Shown in.

[0103] The HEMFC and ECP fuel cell systems, or ECPs, described herein may have cells electrically connected in series through electrically conductive bipolar plates.

[0104] The ECP described herein and the ECP in the fuel cell system may further comprise an anode gas flow layer and a cathode gas flow layer for each cell.

[0105] The ECPs described herein and in fuel cell systems can include an anode gas flow layer, a cathode gas flow layer, or both an anode gas flow layer and a cathode gas flow layer comprising a flow field of one or more flow channels alternating with conductive material to provide electrical connections between the anode, cathode, or both and the bipolar plates.

[0106] A typical bipolar plate is a thin sheet of stainless steel, one side of which is electrically connected to the anode and the other side to the cathode of the adjacent cell.

[0107] The bipolar plates can be integrated with one or two adjacent gas flow layers. In this case, the bipolar plates are usually stamped to form flow channels on both sides (corrugated structure).

[0108] The ECPs described herein and the ECPs in fuel cell systems can arrange two or more flow channels of a cathode gas flow layer, or two or more flow channels of an anode gas flow layer, in a substantially parallel configuration.

[0109] The ECPs described herein and the ECPs in fuel cell systems may arrange two or more flow channels of a cathode gas flow layer or two or more flow channels of an anode gas flow layer in a cross-over configuration.

[0110] The ECPs described herein and in fuel cell systems may integrate bipolar plates with adjacent anode gas flow layers or adjacent cathode gas flow layers.

[0111] The ECP described herein and the ECP in a fuel cell system may integrate a bipolar plate with an adjacent anode gas flow layer and an adjacent cathode gas flow layer.

[0112] The ECPs described herein, and ECPs in fuel cell systems, can include an electrically conductive feed separator in the anode gas flow layer, the cathode gas flow layer, or both the anode gas flow layer and the cathode gas flow layer.

[0113] The fuel cell systems or ECPs described herein comprising a HEMFC and an ECP may have a conductive feed spacer made of a mesh made of nickel, a nickel alloy, stainless steel, a conductive polymer, carbon fiber paper, or a combination thereof.

[0114] The ECPs described herein and in fuel cell systems may have the conductive feed spacer comprise a perforated metal sheet.

[0115] The ECPs described herein and in fuel cell systems may enable cells to be substantially planar and arranged in a stack.

[0116] The HEMFC and ECP fuel cell systems or ECPs described herein may have the cells in a stacked form and formed around an inner tube to form a spiral stack.

[0117] The ECP described herein and the ECP in the fuel cell system can include a cathode gas flow layer in each cell, with the cathode gas flow layer being fluidly connected to the axial ends of the spiral stack.

[0118] The ECP described herein and the ECP in the fuel cell system can include an anode gas flow layer in each cell, and the anode gas flow layer is fluidly connected to the inner surface of the tube and the outer radial surface of the spiral stack. Figure 7 and 10 As shown, air can enter and exit the axial ends of the spiral stack.

[0119] Figure 5 A spirally wound module is shown with specific cell stacking details. Figure 6 Additional configurations for battery stacking are shown, detailing a stack of two batteries and including current collectors for the stack.

[0120] Figure 7 An example of a spirally wound module with an external current path is shown, and a module axial cross section is shown. One of ordinary skill in the art will appreciate that fewer or more cells may be stacked in series prior to winding the module.

[0121] In addition, the inner tube can be divided into a hydrogen inlet and an outlet for the carbon dioxide-enriched hydrogen. For example, the HEMFC and ECP fuel cell systems or ECPs described herein can have the cell include an anode gas flow layer, and the anode gas flow layer is fluidly connected to a first manifold and a second manifold in the inner tube. In addition, the anode gas flow layer can include a flow guide element that causes the gas to flow outward from the first manifold in the inner tube through a portion of the anode gas flow layer and then inward through the second portion of the anode gas flow layer to the second manifold in the inner tube. This configuration is Figure 8 Shown in detail.

[0122] The spirally wound module configuration consists of a stack of several cells rolled into a spirally wound cylindrical module format. Each cell contains an MEA sandwiched between anode and cathode feed separators, bipolar plates made of metal foil, and gaskets that seal the edges of the cell, 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. Spirally wound modules are made by wrapping the cell stack around an inner tube and inserting it into a cylindrical housing. The anode inlet and outlet ports can be located at the inner and outer radial ends of the spiral in either order. Alternatively, both the anode inlet and outlet ports can be the inner tube with a separator in the middle separating the two ports. Flow-guiding elements can then be added to the anode feed separator to direct the gas out of the end of the blade and back inward in a U-shaped pattern. The simplest flow-guiding element would be a sealant bead or gasket applied in the line from the separator outward to almost the end of the blade, around which the gas must flow. However, there may be some stagnant areas near the outer corners of the blades, so it may be better to use multiple washers or beads of sealant to form nested U-shaped flow channels.

[0123] For iECP, the spiral wound module may have Figure 9 The battery stack shown in Figure 10 The spirally wound module can also have Figure 8 The hydrogen inlet is shown.

[0124] The HEMFC and ECP fuel cell systems or ECPs described herein can have cell pitches less than about 2 mm, less than about 1.5 mm, or less than about 1 mm.

[0125] The iECP described herein can use air as the carbon dioxide-containing gas.

[0126] The ECP described herein and the ECP in the fuel cell system can achieve a membrane area / air flow rate ratio of less than or equal to 50 cm at 1 atmosphere. 2 / Standard liters per minute (SLPM).

[0127] The ECP described herein and the ECP in the fuel cell system can achieve a cell volume / air flow rate ratio of less than or equal to 10 cm 3 / SLPM.

[0128] 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 a cathode of an ECP described herein or an ECP in a HEMFC fuel cell system and supplying a hydrogen-containing gas to an anode of the ECP.

[0129] The method may further comprise making CO2 , that is, the number of moles of CO2 entering the cathode inlet per cell per second, proportional to the current I cell Through, I cell Defined as:

[0130] I cell =nF N CO2

[0131] Where n is a number in the range of 2 to 50, and F is the Faraday constant. Operating the ECP within this range of n can achieve nearly complete removal of CO2 from an air stream while minimizing the use of hydrogen. For the methods described herein, the carbon dioxide-containing gas can be air.

[0132] Additionally, for the methods described herein, the carbon dioxide containing gas may be a flue gas.

[0133] Additionally, carbon dioxide can be collected from the ECP anode outlet stream. When carbon dioxide is collected as a mixture with hydrogen, the hydrogen:carbon dioxide ratio can be between about 1:1 and about 4:1.

[0134] A mixture of hydrogen and carbon dioxide (e.g., syngas) can be fed to a downstream reactor, with the desired ratio depending on the downstream product. For example, the hydrogen:carbon dioxide ratio can be about 4:1 for a Sabatier process (methane), about 3:1 for methanol, about 2:1 for a Fischer-Tropsch process, or about 2:1 for a Bosch reaction (for oxygen recycling on board a spacecraft (e.g., CO2 + 2H2 = C + 2H2O).

[0135] Also disclosed is an ECP for separating carbon dioxide from a carbon dioxide-containing gas, comprising a cell comprising a membrane and two electrodes, each capable of acting as an anode or a cathode; the two electrodes each independently comprising a charge storage compound that reacts to form hydroxide when acting as a cathode and reacts to consume hydroxide or produce protons when acting as an anode; the membrane is adjacent to and separates the two electrodes; wherein the carbon dioxide-containing gas is in contact with the electrode acting as the cathode, and the carbon dioxide reacts with 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 acting as the anode; the bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions react at the electrode acting as the anode to form carbon dioxide and water; wherein the ECP further comprises a means for reversing the direction of current while alternating the electrodes in contact with the carbon dioxide-containing gas, thereby allowing each electrode to serve as an anode and a cathode in turn.

[0136] The ECP may comprise one or both electrodes comprising a metal oxide, metal hydroxide, metal oxyhydroxide, or a hydrogen storage alloy. The metal oxyhydroxide may comprise nickel oxyhydroxide. The metal oxide may comprise manganese dioxide. The hydrogen storage alloy may comprise lanthanum nickel hydride.

[0137] Also disclosed is a method for separating carbon dioxide from a carbon dioxide-containing gas, comprising supplying the carbon dioxide-containing gas to a cathode of the described electrochemical pump (ECP) having one or two electrodes comprising a metal oxide, metal hydroxide, metal oxyhydroxide, or hydrogen storage alloy.

[0138] Preferably, for the process described immediately above, the carbon dioxide containing gas is flue gas.

[0139] The current in the ECP is provided by the power supply, and the power supply 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 supply.

[0140] For gas flow, four-way valves are required at the inlet and outlet. For example, the gas flow can be arranged so that in mode A, electrode 1 has an inflow of CO2-containing gas and an outflow of CO2-lean gas, while electrode 2 has an inflow of purge gas (optional) and an outflow of CO2-rich gas. In mode B, electrode 1 has an inflow of purge gas (optional) and an outflow of CO2-rich gas, while electrode 2 has an inflow of CO2-containing gas and an outflow of CO2-lean gas.

[0141] Further disclosed is a battery system comprising a metal-air battery and an electrochemical pump (ECP) for separating carbon dioxide from a gas containing carbon dioxide, the ECP comprising a battery 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 cathode. The gas containing carbon dioxide 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. The gas containing carbon dioxide 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.

[0142] When considering the following equation:

[0143] I cell =nF N CO2 ,

[0144] It is desirable to operate at low values of n to reduce energy consumption, but the capture rate of carbon dioxide decreases at low values of n. This occurs because the hydroxide: carbonate ratio in the cathode decreases (i.e., reduced hydroxide production). Hydroxide is the active agent for CO2 capture, so lower hydroxide concentrations will reduce the capture rate. As the hydroxide concentration decreases, the kinetics of CO2 capture decreases before the equilibrium partial pressure of CO2 becomes significant, which means that the same high fraction of CO2 capture is possible, but the required ECP area is larger. Using a suitable catalyst, the CO2 capture rate can be maintained at low values of n (e.g., n=2-10), thereby reducing energy (e.g., hydrogen) consumption without the need for a larger ECP.

[0145] 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 a tertiary amine is incorporated into the ionomer (physically or chemically), bicarbonate can be transferred to the ionomer and the ammonium can be rapidly neutralized by the hydroxide, making it active for capturing CO2 again. A key advantage is that the concentration of tertiary amine can be very high, even if significant carbonate accumulation has occurred, and only small amounts of hydroxide are present.

[0146] Primary and secondary amines can form bicarbonates, but mainly form ammonium carbamate -R2HNH + R2HNCOO - .

[0147] Architecturally, one approach is to incorporate branched polyethyleneimine into the cathode structure along with the ionomer. A second approach is to use ionomers with a combination of quaternary ammonium and primary-tertiary amines.

[0148] Similar to the basic principle of CO2 hydration catalysts, it is expected that performance will be improved at low n values (low current density). When carbonates accumulate at the cathode and reduce the hydroxide concentration, the CO2 capture rate decreases. For sufficiently high membrane resistance values, the ratio of carbonates to hydroxides in the cathode will be determined by the ratio of their generation rates and their electrochemical mobilities in the ionomer. In this limit, anion transport through the ionomer is dominated by migration.

[0149] However, for lower membrane resistance values, the potential gradient is smaller and diffusion plays a role. The concentration of carbonate and bicarbonate is very high near the anode, and diffusion will push hydroxide toward the anode and carbonate back to the cathode, resulting in more carbonate accumulation and reduced CO2 capture rate. Therefore, considering other competing requirements, including mechanical properties and gas permeability, it is undesirable to use a membrane with the lowest possible resistance, which is commonly used in fuel cells and electrolyzers. Instead, regardless of gas permeability or mechanical performance considerations, it is desirable to have a membrane with high resistance to reduce the back diffusion of carbonate and bicarbonate.

[0150] If the membrane resistance is too high, there will not be enough electromotive force to drive the current. Ideally, the ohmic (iR) loss should be kept between 10mV and 300mV. If the design current is 5-30mA / cm 2 , the membrane resistance can be as low as 2Ohm-cm 2 and a maximum of 10 Ohm-cm 2 More broadly, 0.5 and 20 Ohm-cm can be considered 2 These ranges are significantly higher than the membrane resistance values commonly practiced in the field of polymer electrolyte fuel cells and electrolyzers.

[0151] For the iECP described herein, there is no direct method for controlling cell current density. One possible method for controlling hydrogen consumption is to intentionally limit the hydrogen supply to the cell to produce a low average cell current through fuel starvation, although fuel starvation will provide an uneven current density distribution and poor CO2 capture performance. Even if the cell resistance is appropriately adjusted to provide the optimal current density at a certain air flow rate, the application of HEMFC fuel cell systems requires that the flow rate to the iECP be increased or decreased as the flow rate to the HEMFC is increased or decreased. If the flow rate is not increased or decreased accordingly, excessive hydrogen will be consumed at partial load.

[0152] Since the anode and cathode flow rates are the only parameters that need to be controlled in iECP, and the cathode flow rate is matched to the HEMFC load, the anode gas supply can be the target for controlling the internal current density.

[0153] In order to control the hydrogen supply rate from the anode gas flow 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, mass transfer is very fast and there is essentially no hydrogen concentration gradient between the anode gas flow layer and the anode electrocatalyst surface. This negligible hydrogen concentration gradient does not cause significant voltage loss and does not affect the cell current density.

[0154] One approach to controlling the cell current density of an iECP is to place a microporous or partially permeable barrier layer between the anode and the anode gas flow layer. Advantageously, such a barrier layer will block hydrogen transport, except for a small amount of hydrogen that can diffuse through the barrier layer (e.g., at 10 mA / cm 2 As the cell approaches this current density, the anode will be depleted 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:

[0155]

[0156] where N H2 is the flux of hydrogen, i is the limiting current density, D is the diffusion rate of hydrogen in the barrier layer, R is the gas constant, T is the temperature, and p H2 is the partial pressure of hydrogen, and L film is the thickness of the barrier layer. If we can control p H2 , then we can control i lim The partial pressure of hydrogen can be controlled by varying the total pressure, by recycling a CO2-rich, hydrogen-depleted outlet gas, or by mixing in some air or HEMFC exhaust gas (e.g., less oxygen). The latter strategy will consume some of the hydrogen through catalytic combustion but will dilute the remaining hydrogen with nitrogen.

[0157] The diffusion barrier will cause CO2 to accumulate to a higher concentration in the anode. Here, it may be advantageous to use a diffusion barrier that is selective for carbon dioxide relative to hydrogen permeation (such as an ionomer membrane). Increasing carbon dioxide permeation relative to hydrogen 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 preferred to minimize this sensitivity to achieve more predictable control of the cell current density from the hydrogen partial pressure.

[0158] The basic control approach 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. Reducing the current and hydrogen supply to a ratio greater than 1:1 can be advantageous in situations where air demand is reduced, as the required ECP performance is also lower, thus allowing for additional carbonate accumulation. This reduces parasitic hydrogen consumption when the HEMFC is operating at partial load.

[0159] For iECP cells, hydrogen recycling and hydrogen dilution strategies are expected to be applicable only to hydrogen diffusion barriers. Pulsed hydrogen flow is an alternative approach that can operate without a hydrogen diffusion barrier. This approach has the advantage that most PEMFC system implementations use pulsed purges, rather than continuous purges. The advantages of this approach may also be applicable to HEMFC systems.

[0160] If the cell is continuously 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 hydrogen is pulsed at a high flow rate, 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 cut off, the hydrogen will be consumed evenly over the entire cell from the anode gas flow layer. The current will remain at 30mA / cm 2 , until the hydrogen is exhausted, at which point 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 CO2 until the hydroxide is completely consumed. As long as the next hydrogen pulse occurs before the hydroxide concentration drops too low, adequate iECP performance will be maintained. A current pulse pumps the accumulated carbonate to the anode and replaces it with hydroxide, and the cycle begins again.

[0161] The ECP described herein can be applied to remove carbon dioxide from a gas stream containing an electrochemically reducible component and to remove carbon dioxide into a gas stream containing an electrochemically oxidizable component. Possible cathode reactions include oxygen reduction, proton reduction (i.e., hydrogen evolution). Possible anode reactions include hydrogen oxidation, water oxidation (i.e., oxygen release), and ammonia oxidation.

[0162] The ECP 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 an acid gas-containing stream. These acid gases can include sulfur dioxide and hydrogen sulfide.

[0163] The ECP described herein can be used to remove, in whole or in part, alkaline gases that dissolve, react, or dissociate in water to form cations and hydroxides from a stream containing alkaline gases. Alkaline gases can include ammonia and organic amines. In this case, the anion exchange polymer is replaced by a cation exchange polymer, 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 the cell. Oxygen reduction and proton reduction (i.e., hydrogen evolution) are a non-exhaustive list of cathode reactions compatible with the cell.

[0164] Battery electrode reactions can be used to replace the anode and cathode reactions in fuel cells. In these cases, cyclic operation is required, where 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.

[0165] definition

[0166] 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 plates.

[0167] A "bipolar plate" is a component that separates adjacent cells in a stack of series-connected cells and provides an electrical connection between the cathode of one cell and the anode of an adjacent cell while maintaining separation of the gas flow layers.

[0168] A "gas flow layer" is a layer of the cell through which gas flows and from which gas can be exchanged with the anode or cathode ("anode gas flow layer" and "cathode gas flow layer," respectively).

[0169] The “CO2 mass transfer resistance” is a performance metric for ECPs and is 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

[0170]

[0171] Where A is the total MEA area in the ECP (in m 2 ), v is the volume flow rate of CO2-containing gas to ECP (m 3 / s), and x in and x outis the CO2 mole fraction in the CO2-containing gas at the inlet and outlet of the ECP, respectively (unitless).

[0172] "sccm" corresponds to 1 cm under standard conditions of 0°C and 1 atm pressure 3 The unit of gas flow rate is / min.

[0173] "slpm" is a unit corresponding to a gas flow rate of 1 L / minute under standard conditions of 0°C and a pressure of 1 atm.

[0174] Having described the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

[0175] Examples

[0176] The following non-limiting examples are provided to further illustrate the invention.

[0177] Example 1 : Modeling of ECP for CO2 removal

[0178] The ECP mechanism of CO2 can be understood by combining a one-dimensional membrane electrode assembly (MEA) model of electrochemical transport and reactions. The conversion between CO2, bicarbonate, and carbonate is treated by assuming that the water in the ionomer behaves as a dilute aqueous electrolyte, using rate constants and activation energies from literature. The key reaction is

[0179]

[0180]

[0181] Among them, reaction

[12] is dominant in the cathode, and reaction

[11] is dominant in the anode. Carbonic acid, bicarbonate, and carbonate can be converted into each other according to two acid-base equilibria.

[0182]

[0183]

[0184] CO2 hydration i The net rate is given by:

[0185]

[0186] Among them k1k –1 k2, k –2 are the forward and reverse rate constants for the neutral (Eq. 11) and alkaline (Eq. 12) CO2 hydration mechanisms, ∈ ion is the volume fraction of ionomer in the electrode, φ Η2Ois 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 pores, c i is the concentration of ion i, and K b2 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,

[0187]

[0188] where N i is the flux, D i is the diffusion rate, z i is the charge of all ions i. Φ2 is the ionic potential, and x is the spatial coordinate. For a 20 μm low conductivity membrane (4 Ω·cm 2 ), 0.01mgPt / cm 2 Anode (5wt% Pt / C) and 1mg / cm 2 The simulated concentration curves of hydroxide, carbonate and bicarbonate in the cathode MEA are as follows: Figure 13 The 1D model was run with fixed flow channel composition as boundary conditions—in this case, 400 ppm at the cathode and 10,000 ppm at the anode. The electric field generated at low current density was sufficient to maintain a pH gradient of approximately 6 units, which creates a very large difference in the equilibrium CO2 concentrations at the anode and cathode, driving nearly irreversible CO2 pumping.

[0189] FIG14 plots the ability of a CO2 ECP to remove >99.9% of CO2 from air, showing simulation results for a cathode flow channel concentration of 0.4 ppm and an anode flow channel concentration of 100,000 ppm. Figure 14A shows the anion concentration curve, and Figure 14B Shown at open circuit, 10 and 20 mA / cm 2 The CO2 hydration / dehydration rate (i.e., capture / release, respectively) under the open circuit is 10 to 20 mA / cm 2 When the cathode is charged, CO2 is captured.

[0190] Calculations estimate that the characteristic length scale for the reaction / diffusion of CO2 into the hydroxide form of the ionomer is only 50 nm at 70°C. Within this length scale, any CO2 that diffuses through the membrane from the anode to the cathode will react with the hydroxide before reaching the cathode.

[0191] Example 2: eECP operates in air / hydrogen mode

[0192] The proof-of-concept of the ECP was demonstrated using a single air / hydrogen cell experiment to investigate the effects of operating temperature and current density on the performance of the ECP in removing CO2 from an air stream into a hydrogen stream. The cathode or anode outlet gases were monitored by a CO2 sensor (Vaisala GMP252). The first experiment was conducted at 5 cm 2 0.4 mg Pt / cm was used in both electrodes of cell (#1) 2 As 47 wt% Pt / C, and demonstrated that the 2 ) The CO2 level in the exhaust gas was less than 100 ppm. In view of this initial success and the strict cost requirements of the final application, a 25 cm 2 Battery (#2): Anode 0.013 mg Pt / cm 2 5wt.% Pt / C, cathode 0.6mg / cm 2 The second cell was studied over a wide range of flow rates, demonstrating CO removal down to the ppm level (measurements were limited by the accuracy of the CO sensor). To demonstrate room for performance improvement, cell #3 was fabricated using the same gas diffusion electrode as cell #2, but with a porous carbon-ionomer interlayer applied directly to the cathode side of the membrane. This interlayer provides a more accessible volume of ionomer for the reaction of CO with hydroxide. All experiments used PAP membranes and ionomers. PAP membranes and ionomers are described in U.S. Application No. 16 / 146,887, which is incorporated herein by reference.

[0193] When the cathode hydroxide concentration is high enough, the cathode OH - The capture of CO2 is a first-order irreversible process, and the CO2 concentration is expected to decrease exponentially 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 means that if we need 1m 2 To achieve 90% CO2 removal efficiency, we can use 2m 2 Achieve 99% removal rate and use 3m 2 A 99.9% removal rate was achieved. Experimental evidence for this advantageous characteristic has been provided.

[0194] Figure 15 describes a 25 cm 2Figure 2 CO2 removal capacity of a single air / hydrogen cell (cell #2) used as an ECP. The 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, the CO2 removal rate 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, indicating that CO2 can be pumped relative to a concentration gradient of about 3 orders of magnitude without performance loss. Except in cases where flooding is suspected, the CO2 pump exhibits first-order irreversible behavior with CO2 removal rates as high as 99%, where the limit of the sensor accuracy is reached.

[0195] FIG16 shows the CO2 removal rate and calculated CO2 mass transfer resistance for cells #2 and #3 at 70°C and for cell #1 at 80°C, both at 20 mA / cm 2 . Cell #2 had lower performance than Cell #1, which was probably due to the lower ionomer loading in the cathode, which limited the reaction with hydroxide. Cell #3 showed the best performance, with a mass transfer resistance that was half that of Cell #2. Cell #3 used a multilayer cathode structure, which combined more ionomer volume for CO2 capture without using a thick electrocatalyst layer. Thinner electrocatalyst layers would be particularly advantageous if the electrocatalyst was expensive. The mass transfer specific resistance was nearly constant with CO2 concentration (Figure 16b), indicating an ideal first-order process. Under these conditions, CO2 removal from 90 to 99.9% only required a tripling of the membrane area, making it possible to achieve the air purity specifications of the HEMFC stack.

[0196] Example 3 : iECP operates in air / hydrogen mode

[0197] In addition, the iECP concept, which aims to achieve the simplest and potentially cheapest ECP, was experimentally demonstrated by casting a PAP membrane with 30 wt% carbon nanotubes to create an internal electronic short circuit and using 0.4 mg Pt / cm2 in a Pt / C catalytic electrode. 2 It is made into MEA. Assemble 5cm 2 The battery was tested over the battery temperature range with hydrogen or nitrogen on the anode side and 350 ppm CO2-containing air on the cathode side. The results are shown in Figure 17 and with similar non-short circuit 5cm 2 The performance of the MEAs roughly matched that of the cells. Due to the smaller total cell area, the CO2 content in the air outlet did not reach ultra-low levels, but similar mass transfer coefficients were calculated compared to the cells using non-short-circuited MEAs.

[0198] Example 4: iECP operates in air / hydrogen mode with anode gas diffusion barrier and recirculation loop

[0199] Composite membranes were prepared by adding carbon nanotubes to a solution of poly(arylpiperidinium) (PAP-TP-85) (bromide counterion) in dimethyl sulfoxide solution. The weight ratio of carbon nanotubes to PAP-TP-85 polymer was 30:70. The mixture was cast onto 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 with bicarbonate counterions by repeated immersion in sodium bicarbonate solution at room temperature. The membrane thickness was 80 μm. The membrane was cut into 7.5 cm x 7.5 cm pieces.

[0200] 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 a 3.5 wt% poly(arylpiperidinium) (PAP-TP-100) polymer solution 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 a 3.5 wt% PAP-TP-100 polymer solution 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 a 3.5 wt% PAP-TP-100 polymer solution in ethanol, and 1.67 mL of isopropanol. The ink was ultrasonically mixed in an ice bath for 1 hour. After mixing, the inks were sprayed onto the composite membrane using a spray gun in the following order: First, the cathode interlayer ink was sprayed onto the cathode side of the membrane. The cathode catalyst ink was sprayed a second time onto the dried cathode interlayer. The anode catalyst ink was sprayed a third time 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 to overspray, resulting in 0.1 mg of the anode. Pt / cm 2 , 0.1 mg in cathode Pt / cm 2 and 0.5 mg in the cathode interlayer C / cm 2 of catalyst loading.

[0201] The catalyst-coated membrane was dried overnight at room temperature. A 1.6 mm thick sheet of porous ePTFE gasket material was compressed to a thickness of 0.7 mm and cut into 5.2 cm by 5.2 cm to serve as the anode gas diffusion barrier. 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 to serve as the cathode gas diffusion layer. The anode gasket was made of PTFE, 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. The cathode gasket was made of FEP, 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.

[0202] Battery configuration such as Figure 18 As shown. The single-cell iECP was assembled into a commercial 25cm 2 The fuel cell test hardware (Fuel Cell Technologies) was assembled in the following order: anode end plate, anode current collector, anode flow field (single serpentine flow pattern), anode gasket, ePTFE anode gas diffusion barrier, catalyst coated membrane, cathode gasket, cathode gas diffusion layer, cathode flow field (crossover flow pattern), cathode current collector, and cathode end plate. The cell was connected to a fuel cell test station (Scribner 850e) to control gas flow, temperature, and humidity. On the anode side, a diaphragm pump was connected between the anode outlet and anode inlet to recirculate the anode product gas to the anode inlet.

[0203] The cell was tested at 60°C with hydrogen fed to the anode at 70% relative humidity (RH) and 400 ppm CO2-containing air at 70% RH fed to the cathode. The outlet of the cathode was passed through a condenser to remove water and directed to a Teledyne TML20 CO2 analyzer to measure the CO2 removal rate. The cell was tested at various anode and cathode flow rates, with the anode circulation flow rate set to 0 or 500 mL / min. The results are shown in Figure 19 .

[0204] First, looking at the results without anode recirculation, CO2 removal is high and constant for the 50 to 200 sccm anode flow rate range, with an average residual CO2 of 5 ppm at a 1000 sccm cathode flow rate and 4 ppm at a 500 sccm cathode flow rate. However, when the anode hydrogen supply is between 7 and 25 sccm, the CO2 removal performance of the iECP is very poor because the hydrogen supply is lower than that required to support a uniform cell current density across the active area.

[0205] Due to the anode gas diffusion barrier, the cell current density can be reduced uniformly across the active area by reducing the hydrogen partial pressure. An anode recirculation flow of 500 mL / min was used to dilute the incoming hydrogen supply with a CO2-rich product gas mixture. In these cases, CO2 separation was significantly improved at hydrogen flow rates of 7 to 25 sccm compared to the results obtained without the anode recirculation flow. Even at a hydrogen supply rate of 4 sccm, CO2 removal efficiencies of 91% and 95% were observed for air flow rates of 2000 sccm and 1000 sccm, respectively. These results demonstrate that in iECPs with low hydrogen consumption, combining the anode gas diffusion barrier with a means of reducing the hydrogen partial pressure can successfully achieve high CO2 separation performance.

[0206] Example 5 : Operating the eECP in air / hydrogen mode with a cross-flow field and low cathode catalyst loading

[0207] An anode catalyst ink was prepared by mixing 13.6 mg of a 40 wt% Pt / C catalyst, 30 mg of water, 102.1 mg of a 3.5 wt% poly(arylpiperidinium) (PAP-TP-100) polymer solution in ethanol, and 1.25 mL of isopropanol. A cathode catalyst ink was prepared by mixing 13.6 mg of a 40 wt% Pt / C catalyst, 30 mg of water, 97.3 mg of a 3.5 wt% PAP-TP-100 polymer solution 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 a 3.5 wt% PAP-TP-100 polymer solution in ethanol, and 1.67 mL of isopropanol. The ink was ultrasonically mixed in an ice bath for 1 hour. After mixing, the inks were sprayed onto a poly(arylpiperidinium) membrane (PAP-TP-85, 22 μm thickness) via a spray gun in the following order. The cathode interlayer ink was sprayed onto the cathode side of the membrane first. The cathode catalyst ink was sprayed onto the dried cathode interlayer a second time. The anode catalyst ink was sprayed onto the anode (opposite) side of the membrane a third time. 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 0.1 mg of the total ink solution in the anode. Pt / cm 2 , 0.1 mg in cathode Pt / cm 2 and 0.5 mg in the cathode interlayer C / cm 2 of catalyst loading.

[0208] The catalyst-coated membrane was dried overnight at room temperature. Carbon paper gas diffusion layers without microporous layers (Toray TGP-H-030, 0.1 mm thick) were used for the anode and cathode gas diffusion layers, and 0.09 mm thick FEP gaskets were used for the anode and cathode. The single-cell eECP was assembled into a commercial 25 cm 2 The fuel cell test hardware (Fuel Cell Technology) consists of the following sequence: anode end plate, anode current collector, anode flow field (single serpentine flow pattern), anode gasket, anode gas diffusion layer, catalyst-coated membrane, cathode gasket, cathode gas diffusion layer, cathode flow field (cross-flow pattern), cathode current collector, and cathode end plate. The cell was connected to a fuel cell test station (Scribner 850e) to control gas flow, temperature, and humidity.

[0209] The cell was operated at 60°C and 70% RH for 100 hours using a hydrogen flow rate of 10 sccm at the anode and an air flow rate of 1250 sccm at the cathode containing 400 ppm of CO2. The cathode was operated at a back pressure of 50 kPag. The cell was operated at 40 mA / cm 2 The cathode outlet was passed through a condenser to remove water and directed to a Teledyne TML20 CO2 analyzer to measure the CO2 removal rate.

[0210] The cathode outlet CO2 concentration during the 100-hour holding period is shown in Figure 20 The CO2 separation performance showed a low degradation rate, starting from 98.3% removal (7.0 ppm) at the beginning of the test to 98.1% removal (7.7 ppm) after 100 hours. Figure 16A The performance was significantly improved compared to the results with a reverse flow rate of 0.8slpm. -1 and CO2 outlet concentration ranged from 7.0 to 7.7 ppm, while cell #3 of Example 2 required approximately 3 slpm -1 The improved performance can be attributed to a combination of factors, including the cross-flow pattern at the cathode, a thin cathode gas diffusion layer, and reduced relative humidity.

[0211] When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0212] In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

[0213] As various changes could be made in the above apparatus and methods without departing from the scope of the invention, 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 for separating carbon dioxide from air, the electrochemical pump comprising: A battery comprising an anode, a cathode, and a membrane adjacent to and separating the anode and cathode, The anode includes an anode electrocatalyst for oxidizing a reagent to form protons or consume hydroxide ions, The cathode includes a cathode electrocatalyst for reducing oxygen to form hydroxide ions; wherein the electrochemical pump is adapted such that, in operation: The air is supplied to the cathode, and the carbon dioxide reacts with hydroxide ions formed at the cathode to form bicarbonate ions, carbonate ions, or bicarbonate ions and carbonate ions; The bicarbonate ions, carbonate ions, or bicarbonate ions and carbonate ions are transported through the membrane to the anode; The bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions react at the anode to form carbon dioxide and water; and wherein: The anode and the cathode are electronically connected through the membrane to form an internal current electrochemical pump, and the membrane comprises an anion exchange polymer and a conductive material or a conductive anion exchange polymer.

2. The electrochemical pump of claim 1, wherein a porous structure-ionomer interlayer separates the membrane from the cathode.

3. The electrochemical pump of claim 1, wherein the membrane comprises an anion exchange polymer.

4. The electrochemical pump according to claim 3, wherein the anion exchange polymer comprises a quaternary ammonium or imidazolium group and a polymer backbone having no ether groups; or The anion exchange polymers include 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), ethylene), 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 a combination thereof; or The anion exchange polymer comprises poly(arylpiperidinium).

5. The electrochemical pump of claim 1 , wherein the conductive material comprises carbon, nickel, stainless steel, silver, a conductive polymer, or a combination thereof; or The conductive material comprises nanowires or nanotubes.

6. The electrochemical pump according to claim 1, wherein: The electrochemical pump comprises one or more cells arranged in a hollow fiber configuration; or The electrochemical pump comprises one or more additional cells, and the cells contain an anode gas flow layer adjacent to one or two anodes, the anode adjacent to the membrane, the membrane adjacent to the anode and the cathode, and a cathode gas flow layer adjacent to one or two cathodes, the configuration being as follows: [-AG-AMC-CG-CMA-] wherein AG is the anode gas flow layer, A is the anode, M is the membrane, C is the cathode, and CG is the cathode gas flow layer.

7. The electrochemical pump of claim 1 , wherein the air contains less than 20, 15, 10, 5, 4, or 2 ppm of carbon dioxide after the carbon dioxide reacts with the hydroxide ions at the cathode of the electrochemical pump.

8. The electrochemical pump of claim 1, wherein the reagent oxidized by the anode electrocatalyst comprises hydrogen, ammonia, hydrazine, water, methanol, ethanol, urea, or a combination thereof.

9. The electrochemical pump of claim 8, wherein the reagent oxidized by the anode electrocatalyst comprises hydrogen gas.

10. The electrochemical pump of claim 1 , wherein the anode electrocatalyst comprises platinum, platinum alloy, platinum on carbon, platinum alloy on carbon, nickel, nickel alloy, nickel on carbon, nickel alloy on carbon, ruthenium, ruthenium alloy, ruthenium on carbon, ruthenium alloy on carbon, iridium, iridium alloy, iridium on carbon, iridium alloy on carbon, palladium, palladium alloy, palladium on carbon, palladium alloy on carbon, or a combination thereof; or The anode electrocatalyst comprises platinum supported on carbon.

11. The electrochemical pump of claim 1 , wherein the cathode electrocatalyst comprises silver, silver alloy, carbon-supported silver, carbon-supported silver alloy, platinum, platinum alloy, carbon-supported platinum, carbon-supported platinum alloy, palladium, palladium alloy, carbon-supported palladium, carbon-supported palladium alloy, manganese oxide, carbon-supported manganese oxide, cobalt oxide, carbon-supported cobalt oxide, heteroatom-doped carbon (XC, wherein X comprises one or more of N, C, B, P, S, Se, or O), metal-heteroatom-carbon (MXC, wherein X comprises one or more of N, C, B, P, S, Se, or O, and M comprises Fe, Ce, Cr, Cu, Co, Mo, Ni, Ru, Pd, Pt, Ir, Rh, Os, Ag, Au, Re, Ta, Ti, V, W, Mn, Zn, Sn, S b, In, Ga, Bi, Pb or Zr), perovskite (ABX3, wherein 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), carbon-supported perovskite (ABX3, wherein 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; or The cathode electrocatalyst comprises silver. 12 . The electrochemical pump according to claim 1 , wherein current is supplied to the electrochemical pump by a power source or current is drawn from the electrochemical pump by a load.

13. The electrochemical pump of claim 1, wherein the electrochemical pump further comprises one or more additional batteries.

14. The electrochemical pump of claim 13, wherein the one or more additional batteries are electrically connected in series; or The cells are electrically connected in series via conductive bipolar plates.

15. The electrochemical pump of claim 14, wherein each cell further comprises an anode gas flow layer proximate the anode and a cathode gas flow layer proximate the cathode.

16. The electrochemical pump of claim 15, wherein the anode gas flow layer, the cathode gas flow layer, or the anode gas flow layer and the cathode gas flow layer comprise a flow field of one or more flow channels alternating with conductive regions to provide electrical connection between the anode, the cathode, or the anode and the cathode and the bipolar plate. 17 . The electrochemical pump of claim 16 , wherein the two or more flow channels in the cathode gas flow layer or the two or more flow channels in the anode gas flow layer are arranged in a parallel configuration or a crossed configuration.

18. The electrochemical pump of claim 14, wherein the bipolar plate is integrated with an adjacent anode gas flow layer or an adjacent cathode gas flow layer; or the bipolar plate is integrated with the adjacent anode gas flow layer and the adjacent cathode gas flow layer.

19. The electrochemical pump of claim 15, wherein the anode gas flow layer, the cathode gas flow layer, or both the anode gas flow layer and the cathode gas flow layer comprise a conductive feed separator.

20. The electrochemical pump of claim 19, wherein the conductive feed spacer comprises a mesh comprising nickel, a nickel alloy, stainless steel, a conductive polymer, carbon fiber paper, or a combination thereof; or the conductive feed spacer comprises a perforated metal sheet.

21. The electrochemical pump of claim 13, wherein the cells are arranged in a stack and are planar; or the cells are in a stack and formed around an inner tube to form a spiral stack; or Each cell comprises a cathode gas flow layer, and the cathode gas flow layer is fluidly connected to an axial end of the spiral stack; or Each cell comprises an anode gas flow layer, and the anode gas flow layer is fluidly connected to the inner surface of the spirally stacked tubes and the outer surface of the tubes; or The battery includes an anode gas flow layer, and the anode gas flow layer is fluidly connected to a first manifold and a second manifold in the inner tube, and includes a flow-guiding element that allows gas to flow outward from the first manifold in the inner tube through a portion of the anode gas flow layer and then inward through a second portion of the anode gas flow layer to the second manifold in the inner tube.

22. The electrochemical pump according to claim 1, wherein: The cell pitch of the electrochemical pump is less than 2, 1.5 or 1 mm; or The membrane area / air flow rate is less than or equal to 50 cm 2 / standard liters / minute or 10cm at 1 atmosphere and 0°C 3 / standard liters / minute at 1 atmosphere and 0°C.

23. A fuel cell system comprising a hydroxide exchange membrane fuel cell and an electrochemical pump according to any one of claims 1 to 22, wherein during use of the electrochemical pump, after the air passes through the cathode of the electrochemical pump to reduce the concentration of carbon dioxide, the air with reduced carbon dioxide concentration is guided from the cathode exhaust port of the electrochemical pump to the cathode inlet of the hydroxide exchange membrane fuel cell.

24. The fuel cell system according to claim 23, wherein the hydrogen consumed by the electrochemical pump for separating carbon dioxide from the air is less than 5% or 2% of the hydrogen consumed by the hydroxide exchange membrane fuel cell.

25. A method for separating carbon dioxide from carbon dioxide-containing gas or air, comprising supplying the carbon dioxide-containing gas or air to a cathode of an electrochemical pump according to any one of claims 1 to 22, and supplying a hydrogen-containing gas to an anode of the electrochemical pump.

26. The method according to claim 25, further comprising CO2 , that is, the number of moles of CO2 entering the cathode inlet per cell per second, proportional to the current I cell Through, I cell Defined as: I cell =nF N CO2 where n is a number in the range of 2 to 50, and F is the Faraday constant.

27. The method of claim 26, wherein: The carbon dioxide-containing gas is air.

28. The method of claim 25, wherein the carbon dioxide-containing gas is flue gas.

29. The method of claim 25, wherein the carbon dioxide is collected.

30. The method of claim 29, wherein the carbon dioxide is collected in a mixture with hydrogen and the hydrogen:carbon dioxide ratio is between 1:1 and 4:1.

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