Low-cost electrochemical cell stack for carbon dioxide gas separator

Abstract

An electrochemically-based carbon-dioxide gas separation system includes a stack of membrane electrode assemblies (MEAs), each of the MEAs including a membrane separator between a cathode and an anode. The cathode includes a charge-storage compound that reacts to form hydroxide and the anode includes a charge-storage compound that reacts to consume hydroxide or produce protons. A double-sided flow-field plate is placed between adjacent MEAs of the stack of electrochemical cells. First and last MEAs of the stack of MEAs are coupled to an end flow-field plate which is coupled to an end plate. Each of the cathodes and the anodes includes an electrical contact coupled to an electric current power supply.

Description

LOW-COST ELECTROCHEMICAL CELL STACK FOR CARBON DIOXIDE GAS SEPARATORFIELD OF THE INVENTION

[0001] The present invention relates to electrochemically based separation of carbon dioxide gas from gas mixtures, and particularly to a low-cost electrochemical cell stack for a carbon dioxide gas separator.BACKGROUND OF THE INVENTION

[0002] US Patent Application 2021 / 0036350 to Yushan Yan et al. describes an electrochemical pump (ECP) for separating carbon dioxide from a carbon dioxidecontaining gas, such as air. The ECP includes a cell, which has a membrane and two electrodes that are capable of acting as an anode or a cathode. Each of the electrodes independently comprises a charge-storage compound that reacts to form hydroxide when acting as cathode and reacts to consume hydroxide or produce protons when acting as anode. The membrane is adjacent to and separates the two electrodes. A carbon dioxide-containing gas contacts the electrode acting as 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 to the electrode serving as anode through the membrane; and the bicarbonate ions, carbonate ions, or bicarbonate and carbonate ions react at the electrode acting as anode to form carbon dioxide and water. The ECP also has means for reversing the direction of current flow and simultaneously alternating the electrode with which the carbon dioxide-containing gas is contacted, thereby allowing each electrode to act, in turn, as anode and as cathode.

[0003] The ECP of US Patent Application 2021 / 0036350 can have the cells electrically connected in series by an electrically conductive bipolar plate. The ECP thus has a flow field of one or more flow channels alternating with a conductive material to provide an electrical connection between the anode, the cathode, or the anode and cathode and the bipolar plate. One side is electrically connected to the anode, and the other side is electrically connected to the cathode of the adjacent cell. The electrochemical cells may be stacked together to increase process capacity with minimal footprint.

[0004] Reference is now made to Fig. 1, which illustrates a prior art electrochemical stack 10 of US Patent Application 2021 / 0036350. The main component of the electrochemical stack 10 is a series of membrane electrode assemblies (MEAs) 24, each of which includes a membrane separator 20 (without limitation, a solid polymer electrolyte or ion exchange membrane) disposed between two electrodes, a cathode 18 and an anode 22. The series of membrane electrode assemblies (MEAs) 24 is sandwiched at opposite ends thereof by end flow-field plates 16. Each end flow-field plate 16 is inwardly adjacent a current collector 14, which in turn is inwardly adjacent an end plate 12. Thus, at one end of the stack (the left end in the illustration), there is an end flow-field plate 16 adjacent the cathode 18 of the left-most ME A 24; the rightmost anode 22 is adjacent the end flow-field plate 16 at the other (right) end of the stack. The MEAs 24 may be separated by electrically conductive bipolar plates 26 that may have flow channels or flow pathways. The MEAs 24 are thus electrically connected in series by the bipolar plates 26. Inlet and outlet tubing connectors 28 and 29 may be provided for airflow through the stack.

[0005] Except for the inlet and outlet tubing connectors, all the other components of the stack are structured materials that have undergone processing, typically metal-based materials or graphite -based materials. These materials are used because metals and graphite-based materials conduct electrons well and possess mechanical properties adequate for cell and stack assembly. During the assembly process, the MEAs 24 are compressed between the two end plates 12, usually held together by screws or other types of connectors or fasteners. The fasteners exert compression stresses that require materials strength of at least few MPa (1-10); materials with higher strengths usually better perform (20-100 MPa). Although most metal-based and graphite -based materials are stable under such stresses with no significant deformation, they are expensive to produce at small or large scale.SUMMARY OF THE INVENTION

[0006] The present invention seeks to provide a low-cost electrochemical cell stack for a carbon dioxide gas separator, as is described more in detail hereinbelow.

[0007] There is provided in accordance with a non-limiting embodiment of the present invention an electrochemically-based carbon-dioxide gas separation system includinga stack of membrane electrode assemblies (MEAs), each of the MEAs including a membrane separator between a cathode and an anode, wherein the cathode includes a charge-storage compound that reacts to form hydroxide and the anode includes a charge-storage compound that reacts to consume hydroxide or produce protons, a double-sided flow-field plate placed between adjacent MEAs of the stack of MEAs, and wherein first and last MEAs of the stack of MEAs are coupled to an end flowfield plate which is coupled to an end plate, and wherein each of the cathodes and the anodes includes an electrical contact coupled to an electric current power supply.

[0008] In accordance with a non-limiting embodiment of the present invention the end plates, the end flow-field plates and the double-sided flow-field plates are made of a polymer.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:

[0010] Fig. 1 is a simplified illustration of a prior art electrochemically-based carbondioxide gas separation system including a stack composed of four electrochemical cells, in which EP is an end plate, CC is a current collector, ENDFF is an end flowfield plate, and BPP is a bi-polar plate.

[0011] Fig. 2 is a simplified illustration of an electrochemically-based carbon-dioxide gas separation system, in accordance with a non-limiting embodiment of the present invention, including a low-cost stack composed of four electrochemical cells (the invention is not limited to this number of cells), and in which DSFF is a double-sided flow-field, and minus and plus signs represent direct electrical contact between electrodes and a power supply.

[0012] Figs. 3A, 3B, 3C, and 3D are respectively simplified perspective, see-through perspective, planar, and cutaway illustrations of the electrochemical cell (MEA) for lower-cost production, in accordance with a non-limiting embodiment of the present invention.DETAILED DESCRIPTION OF EMBODIMENTS

[0013] Reference is now made to Fig. 2, which illustrates an electrochemically-based carbon-dioxide gas separation system 30, in accordance with a non-limiting embodiment of the present invention.

[0014] The electrochemical system 30 is a stack that includes a series of membrane electrode assemblies (MEAs) 32, each of which includes a membrane separator 34 (without limitation, a solid polymer electrolyte or ion exchange membrane) disposed between two electrodes, a cathode 33 and an anode 35. The series of membrane electrode assemblies (MEAs) 32 is sandwiched at opposite ends thereof by end flowfield plates 36. Each end flow-field plate 36 is inwardly adjacent an end plate 38. Thus, at one end of the stack (the left end in the illustration), there is an end flowfield plate 36 adjacent the cathode 33 of the left- most MEA 32; the rightmost anode 35 is adjacent the end flow-field plate 36 at the other (right) end of the stack.

[0015] Each end flow-field plate 36 includes a fluid (in this case, the fluid is typically air) supply opening and a fluid exhaust opening formed in the plate surface.

[0016] Unlike the prior art, the system 30 does not have current collectors or bipolar plates. Instead, adjacent MEAs 32 are separated from each other by a double-sided flow-field plate 40. Each side of the double-sided flow-field plate 40 has a fluid supply opening and a fluid exhaust opening formed in the plate surface. Inlet and outlet tubing connectors 42 and 43 are provided for airflow through the stack.

[0017] To lower the cost of the cell and stack hardware parts, the end plates 38, end flowfield plates 36 and double-sided flow-field plates 40 are made of low-cost polymers such as polypropylene, polyethylene, and others (e.g., polystyrene). Since most polymers do not conduct electrons well, each cathode 33 and anode 35 includes an electrical contact 53 and 55, respectively, for receiving electric current from a power supply 70. The electrical contacts 53 and 55 thus replace the current collectors of the prior art. The use of dedicated electrical contacts to each cathode and anode provides the advantage of electrical control of each cell separately in the stack.

[0018] The use of polymers can lower costs by one to two orders of magnitudes, as opposed to metals and graphite.

[0019] Reference is now made to Figs. 3A-3D, which illustrate one structure of the MEA 32, in accordance with a non-limiting embodiment of the present invention. The electrical contacts 53 and 55 of the MEA 32 may be in the form of tabs or other types of contacts. The MEA 32 may be mounted in a substrate 50 and surrounded by an elastic seal 52.

[0020] A direct electrical contact between the power source and each electrochemical cell in the multi-cell stack has several advantages over the prior art. For example, the direct electrical contact increases the modularity and flexibility of the electrochemical cell stack since each cell can be individually monitored and controlled. Another advantage is more efficient maintenance at reduced operational costs. Another advantage is that the direct electrical contact eliminates electrical issues encountered during stack assembly, such as electrical shorts, leading to more efficient assembly processes and cost reduction.

Claims

CLAIMSWhat is claimed is:

1. An electrochemically-based carbon-dioxide gas separation system comprising: a stack of membrane electrode assemblies (MEAs), each of said MEAs comprising a membrane separator between a cathode and an anode, wherein said cathode comprises a charge-storage compound that reacts to form hydroxide and said anode comprises a charge-storage compound that reacts to consume hydroxide or produce protons; a double-sided flow-field plate placed between adjacent MEAs of the stack of MEAs; and wherein first and last MEAs of the stack of electrochemical cells are coupled to an end flow-field plate which is coupled to an end plate; and wherein each of said cathodes and said anodes comprises an electrical contact coupled to an electric current power supply.

2. The electrochemically-based carbon-dioxide gas separation system according to claim 1, wherein said end plates, said end flow-field plates and said double-sided flowfield plates are made of a polymer.

3. The electrochemically-based carbon-dioxide gas separation system according to claim 1, further comprising inlet and outlet tubing connectors for airflow through said system.

4. The electrochemically-based carbon-dioxide gas separation system according to claim 1, wherein each of said MEAs is mounted in a substrate and surrounded by an elastic seal.

5. A method of electrochemically-based carbon-dioxide gas separation comprising: providing a stack of membrane electrode assemblies (MEAs), each of said MEAs comprising a membrane separator between a cathode and an anode, wherein said cathode comprises a charge-storage compound that reacts to form hydroxide and said anode comprises a charge-storage compound that reacts to consume hydroxide or produce protons; andproviding a double-sided flow-field plate placed between adjacent MEAs of the stack of MEAs, wherein first and last MEAs of the stack of electrochemical cells are coupled to an end flow-field plate which is coupled to an end plate; wherein each of said cathodes and said anodes comprises an electrical contact coupled to an electric current power supply.

6. The method according to claim 5, comprising individually monitoring and controlling said electrical contacts for each of said cathodes and said anodes.

7. The method according to claim 5, wherein the electrical contacts for each of said cathodes and said anodes increases modularity and flexibility of the stack.

8. The method according to claim 5, wherein the electrical contacts for each of said cathodes and said anodes provides more efficient maintenance at reduced operational costs.

9. The method according to claim 5, wherein the electrical contacts for each of said cathodes and said anodes eliminates electrical shorts during use of the stack.

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