Electrochemical cell stack for carbon dioxide gas separator with BI-lateral flow

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. The cathode of one of the adjacent MEAs which is on a first side of the double-sided flow-field plate faces the cathode of a next adjacent MEA on the first side, and the anode of one of the adjacent MEAs which is on a second side of the double-sided flow-field plate faces the anode of a next adjacent MEA on the second side.

Description

ELECTROCHEMICAL CELL STACK FOR CARBON DIOXIDE GAS SEPARATOR WITH BI-LATERAL FLOW FIELD OF THE INVENTION

[0001] The present invention relates to electrochemically based separation of carbon dioxide gas from gas mixtures, and particularly to an electrochemical cell stack for a carbon dioxide gas separator with bi-lateral flow.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] Fig. 1 shows a prior art electrochemical stack, which is described in PCT Patent Application PCT / IB2024 / 056511 to REPAIR-CARBON Ltd.. The stack includes a series of membrane electrode assemblies (ME As) 3, each of which includes a membrane separator (e.g., a solid polymer electrolyte or ion exchange membrane) disposed between two electrodes, 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 4 is placed between adjacent MEAs of the stack of MEAs. The first and last MEAs 3 of the stack of MEAs 3 are coupled to an end flowfield plate 5 which is coupled to an end plate 6. Each of the cathodes and the anodes includes an electrical contact coupled to an electric current power supply (not shown). The end plates, the end flow-field plates and the double-sided flow-field plates are made of a polymer, which reduces manufacturing costs significantly.

[0005] The gas mixture (typically ambient air) flows into each of the double-sided flowfield plates 4 and flows in one direction through the MEAs 4, thereby separating carbon dioxide from the gas mixture. This is called uni-lateral inlet gas flow. The separated carbon dioxide is directed from the stack in one flow (such as to a collection tank or other purpose) and the rest of the gas flow that has been depleted from carbon dioxide is directed from the stack in another flow (such as to the atmosphere or other purpose).

[0006] The design of PCT Patent Application PCT / IB 2024 / 056511 eliminates the need to strongly compress the bipolar plates. The electrical contact is achieved by direct connection of a bare extension of the conductive electrode substrate, by wiring, to its neighboring electrode (in adjacent cells). The mechanical compression needed for proper electrical contact between the electrodes and the metal flow fields (BPP - bipolar plates) is avoided. Mechanical compression is still needed to prevent leakages, but this is achieved at very low compression stresses.SUMMARY OF THE INVENTION

[0007] The present invention seeks to provide an improved electrochemical cell stack for a carbon dioxide gas separator, which has bi-lateral flow, as is described more in detail hereinbelow.

[0008] The present invention includes an innovative, low-cost, light-weight polymer- based flow field having bi-lateral flow, enabling very low pressure drop of the inlet gas mix stream across the stack (from inlet to outlet). This configuration includes novel electrical wiring, needed for maintaining multi-cell stack assemblies. This novel design optimizes the efficiency of the separation process while keeping low pressure loss of the gas stream and overall low energy consumption of the whole process (core electrochemical cells / stacks and the gas supply unit).

[0009] There is provided in accordance with a non-limiting embodiment of the present invention an electrochemically-based carbon-dioxide gas separation system including a 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 electrochemical cells are coupled to an end flow-field plate which is coupled to an end plate, and wherein the cathode of one of the adjacent MEAs which is on a first side of the double-sided flow-field plate faces the cathode of a next adjacent MEA on the first side, and the anode of one of the adjacent MEAs which is on a second side of the double-sided flow-field plate faces the anode of a next adjacent MEA on the second side.

[0010] In accordance with a non-limiting embodiment of the present invention a flowfield plate gas mixture inlet port is coupled to the double-sided flow-field plate, such that gas flows to both the first side and the second side of the double-sided flow-field plate to the adjacent MEAs which are on the first side and the second side, respectively, of the double-sided flow-field plate.

[0011] In accordance with a non-limiting embodiment of the present invention the anode an outermost MEA is electrically coupled to the cathode of an adjacent MEA which is adjacent to the outermost MEA, and the anode of the adjacent MEA is electrically coupled to the cathode of a next adjacent MEA which is adjacent to the adjacent MEA.

[0012] 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

[0013] The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:

[0014] Fig. 1 is a simplified illustration of a prior art electrochemically-based carbondioxide gas separation system with uni-lateral inlet gas flow.

[0015] 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, having bi-lateral inlet gas flow.

[0016] Fig. 3 is a simplified perspective illustration of a flow field having inlets / outlets for in-plane gas flow, in accordance with a non-limiting embodiment of the present invention. The flow field may be made of polymer. The large arrows show the nominal gas flow direction while the small arrows (up and down) show the gas flow distribution into two adjacent MEAs (MEAs are not shown in Fig. 3).

[0017] Fig. 4 is a simplified schematic illustration of electrical wiring across the bi-flow configuration of the invention.DETAILED DESCRIPTION OF EMBODIMENTS

[0018] Reference is now made to Fig. 2, which illustrates an electrochemically-based carbon-dioxide gas separation system 8, in accordance with a non-limiting embodiment of the present invention.

[0019] The electrochemical system 8 is a stack that includes a series of membrane electrode assemblies (MEAs) 10. As seen in Fig. 4, each MEA 10 includes a membrane separator 12 (without limitation, a solid polymer electrolyte or ion exchange membrane) disposed between two electrodes, a cathode 14 and an anode 16. The series of membrane electrode assemblies (MEAs) 10 is sandwiched at opposite ends thereof by end flow-field plates 18. Each end flow-field plate 18 (Figs. 2 and 4) is inwardly adjacent an end plate 20 (shown just in Fig. 2). Thus, at one end of the stack (the left end in Fig. 2 and the upper end in Fig. 4), there is an end flow-field plate 18 adjacent the outermost cathode 14 of the outermost MEA 10 (in Fig. 4, this is the uppermost MEA 10; in Fig. 2 it is the leftmost MEA 10), and the outermost anode 16 is adjacent the end flow-field plate 18 at the other end of the stack (in Fig. 4, this is the lowermost MEA 10; in Fig. 2 it is the rightmost MEA 10). It is emphasized that “upper”, “lower”, “left” and “right” are merely relative terms in the illustrations and the invention can be oriented at other orientations.

[0020] As seen in Fig. 4, each outermost cathode 14 and anode 16 includes an electrical contact coupled to an electric current power supply 22.

[0021] The end flow-field plate 18 is a one-sided (uni-lateral flow) flow-field plate. A double-sided (bi-lateral flow) flow-field plate 24 is placed between adjacent MEAs 10 of the stack of MEAs of the invention.

[0022] In the present invention, a gas mixture (typically ambient air or flue gas) flows via a gas mixture inlet manifold 26 into an end flow-field plate gas mixture inlet port (tubing connector) 27 of each end flow-field plate 18 and then flows from each of the outer end flow-field plates 18 inwards to adjacent double-sided (bi-lateral flow) flowfield plates 24. The gas mixture also flows from gas mixture inlet manifold 26 via a flow-field plate gas mixture inlet port (tubing connector) 28 into a double-sided flowfield plate 24 that is located between two other flow-field plates 24 (in this case, they are the two outer flow-field plates 24 that are adjacent the outer end flow-field plates 18).

[0023] As opposed to the prior art, in the present invention, the gas mixture flows in two directions through the MEAs 10, thereby increasing the separation of carbon dioxide from the gas mixture. This is called bi-lateral inlet gas flow. As seen in Fig. 2, the separated carbon dioxide may be directed from the stack in a carbon dioxide collector outlet manifold 30 (such as to a collection tank or other purpose) and the rest of the gas flow that has been depleted from carbon dioxide may be directed from the stack in a depleted gas manifold 32 (such as to the atmosphere or other purpose).

[0024] Reference is now made to Fig. 3, which illustrates the flow field 24 having inlets / outlets for in-plane gas flow, in accordance with a non-limiting embodiment of the present invention. The large arrows show the nominal gas flow direction (from inlet manifold 26 to outlet manifold 30) while the small arrows (23 and 25) show thegas flow distribution into two adjacent MEAs (MEAs are not shown in Fig. 3, but shown in Fig. 2).

[0025] Reference is now made again to Fig. 4. To lower the cost of the cell and stack hardware parts, the end plates 20, end flow-field plates 18 and double-sided flowfield plates 24 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 14 and anode 16 includes an electrical contact 44 and 46, respectively, for receiving electric current from power supply 22 or for connecting cathode 14 to anode 16. The electrical contacts 44 and 46 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.

[0026] The use of polymers can lower costs by one to two orders of magnitudes, as opposed to metals and graphite.

[0027] In Fig. 4, current flows from power source 22 to one of the outer cathodes 14, from that outer cathode 14 to its adjacent anode 16 of that MEA 10. The gas flows from anode 16 of that outer MEA 10 through the adjacent double-sided flow-field plate 24 to the anode 16 of the next adjacent MEA 10. The anode 16 of that outer MEA 10 is electrically coupled to the cathode 14 of the next adjacent MEA 10 (via contacts 44 and 46 seen on the right side in Fig. 4). Similarly, the anode 16 of that adjacent MEA 10 is electrically coupled to the cathode 14 of the next adjacent MEA 10 (via contacts 44 and 46 seen on the left side in Fig. 4), this next adjacent MEA 10 being the lowermost MEA in Fig. 4. The anode 16 of the lowermost MEA in Fig. 4 is connected to power supply 22.

[0028] Accordingly, the cathodes 14 of adjacent MEAs 10 face each other and the anodes

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 the cathode of one of said adjacent MEAs which is on a first side of said double-sided flow-field plate faces the cathode of a next adjacent MEA on said first side, and the anode of one of said adjacent MEAs which is on a second side of said doublesided flow-field plate faces the anode of a next adjacent MEA on said second side.

2. The electrochemically-based carbon-dioxide gas separation system according to claim 1, further comprising a flow-field plate gas mixture inlet port coupled to said double-sided flow-field plate, such that gas flows to both said first side and said second side of said double-sided flow-field plate to said adjacent MEAs which are on said first side and said second side, respectively, of said double-sided flow-field plate.

3. The electrochemically-based carbon-dioxide gas separation system according to claim 1 , wherein the anode an outermost MEA is electrically coupled to the cathode of an adjacent MEA which is adjacent to said outermost MEA, and the anode of said adjacent MEA is electrically coupled to the cathode of a next adjacent MEA which is adjacent to said adjacent MEA.

4. 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.

Images