Modular electrolyzer stack and process to convert carbon dioxide to gaseous products at elevated pressure and with high conversion rate

An electrolyzer stack (100′, 100″) to convert gaseous carbon dioxide, CO2, to at least one gas-phase product that leaves the electrolyzer stack (100′, 100″), comprising:

• a cathode-side end unit (26) with a gas inlet (21), a fluid inlet (23), a fluid outlet (24) and an electrical terminal;
• an anode-side end unit (27) with a gas outlet (22) and an electrical terminal;
• at least two electrolyzer cells (40) sandwiched between the cathode-side end unit (26) and the anode-side end unit (27), individual ones of the at least two electrolyzer cells (40) comprising:
• a cathode current collector (5;
• 5a, 5b, 5c, 5d);
• an anode current collector (10);
• a membrane electrode assembly comprising:
• an ion-exchange membrane (7) with a first side and a second side,
• a layer of cathode catalyst (6b) arranged on said first side in contact with the ion-exchange membrane (7),
• a cathode-side gas diffusion layer (6a) arranged on the layer of cathode catalyst (6b) in contact with the cathode catalyst (6b),
• a layer of anode catalyst (8b) arranged on said second side in contact with the ion-exchange membrane (7),
• an anode-side gas diffusion layer (8a) arranged on the layer of anode catalyst (8b) in contact with the anode catalyst (8b);
• a spacer element (9a, 9b) arranged between the cathode current collector (5;
• 5a, 5b, 5c,5d) and the anode current collector (10),
• wherein said spacer element (9a, 9b) is configured to fix the membrane electrode assembly between the cathode current collector (5;
• 5a, 5b, 5c, 5d) and the anode current collector (10),
• wherein
• the cathode-side gas diffusion layer (6a) is in partial contact with the cathode current collector (5;
• 5a, 5b, 5c, 5d) thereby forming a cathode-side in-plane flow structure (5″) therebetween, and
• the anode-side gas diffusion layer (8a) is in partial contact with the anode current collector (10) thereby forming an anode-side in-plane flow structure (5′) therebetween;
• a sealed continuous cell gas flow path extending between a cell gas inlet (46) and a cell gas outlet (47) within the electrolyzer cell (40) through the cathode-side flow structure (5″);
• a sealed continuous cell fluid flow path extending between a cell fluid inlet (48) and a cell fluid outlet (49) within the electrolyzer cell (40) through the anode-side flow structure (5′);
• wherein the electrical terminal of the cathode-side end unit (26), the at least two electrolyzer cells (40) and the electrical terminal of the anode-side end unit (27) are connected electrically in series;
• and
• wherein the cell gas flow paths of the at least two electrolyzer cells (40) with gas transport channels (34, 35) extending between adjacent ones of the at least two electrolyzer cells (40) through the cathode current collector (5;
• 5a, 5b, 5c, 5d), the spacer element (9a, 9b) and the anode current collector (10) form a continuous gas flow path that extends from the gas inlet (21) to the gas outlet (22) to supply CO2 to ones of the cathode-side gas diffusion layers (6a) to convert the CO2 to the gas-phase product via at least one cathodic electrolysis reaction taking place in the cathode-side flow structure (5″) of the at least two electrolyzer cells (40), and to discharge the product through said gas outlet (22), and
• wherein the cell fluid flow paths of the at least two electrolyzer cells (40) include fluid transport channels (38, 39) extending between the adjacent ones of the at least two electrolyzer cells (40) through the cathode current collector (5;
• 5a, 5b, 5c, 5d), the spacer element (9a, 9b) and the anode current collector (10) form a continuous fluid flow path that extends from the fluid inlet (23) to the fluid outlet (24) to supply a liquid-phase anolyte to each of the anode-side in-plane flow structure (5′) to complete said cathodic electrolysis reaction with at least one anodic electrolysis reaction taking place at the anode-side in-plane flow structure (5′) of the at least two electrolyzer cells (40), and to discharge the liquid-phase anolyte and reaction product(s) forming in said anodic electrolysis reaction through said fluid outlet (24).