Pulsed Electrolysis Promotes CO₂ Electroreduction to Multicarbon Products by Suppressing Electrolyte Flooding

Electrochemical CO₂ reduction (CO₂RR) converts CO₂ into value-added fuels and chemicals using renewable electricity. Pulsed CO₂RR(p-CO₂RR) has been proposed to enhance the selectivity of multicarbon products (C₂₊), yet mechanistic clarity at industrially relevant rates remains limited by the complex gas-liquid-solid microenvironment of gas-diffusion electrodes (GDEs). Here, we investigate p-CO₂RR in GDE flow-cells operating at industrially-relevant current densities. Under cathodic potentials where conventional constant-potential CO₂ electrolysis yields > 70% H₂ (Faradaic efficiency, FE), pulsed operation achieves a maximum C₂₊ FE of 82.7% at current densities above 0.4 A cm^-2. Operando Raman and UV-visible spectroscopy indicates that formation of Cu_xO only weakly perturbs the coverage of *CO intermediates, suggesting that redox restructuring is not the principal driver of pulse-enhanced C₂₊ production. Instead, ex situ scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) mapping reveals a strong correlation between reduced electrolyte intrusion and improved C₂₊ selectivity, with pulsing stabilizing the gas-liquid interface, suppressing electrolyte penetration, and enhancing CO₂ mass transfer. These experimental findings are supported by numerical simulations of electrochemical capillary-pressure dynamics, which confirm that alternating cathodic and anodic potentials modulate interfacial wettability to retard flooding. These mechanistic insights contribute to the design principles for industrial p-CO₂RR systems, emphasizing hydrodynamic management over traditional catalyst engineering approaches.