Sunken-Serpentine Flow-Field Engineering Unlocks Ampere-Level CO ₂ Electrolysis via Local CO ₂ Enrichment and Water Management

The electrochemical CO2 reduction reaction (CO2RR) on Ag catalysts requires a balance among a high current density, high CO selectivity, and stability. Maximizing catalytic site utilization requires uniform CO2 penetration across the gas diffusion electrode (GDE) while suppressing flooding. This work elucidates the interplay between mass transport and water management in zero-gap membrane electrode assembly (MEA) electrolyzers through flow plate engineering. We demonstrate that in-plane CO2 injection enhances catalyst utilization by improving gas accessibility and facilitating water removal. Using a sunken-serpentine flow plate, we achieved a stable operation exceeding 1 A cm–2 with minimal hydrogen evolution. CO partial current densities reached 861 and 947 mA cm–2 for Ag and Ni-NC catalysts, respectively─34.5% and 18.3% higher than conventional designs. These results are supported by transport modeling and X-ray computed tomography, revealing the CO2 concentration gradients and flooding dynamics. Our findings establish a broadly applicable design strategy to overcome mass-transport limitations.