Breaking the current density bottleneck in electrochemical CO2 reduction reaction via high-pressure operated Sn single-atom catalysts.

Electrochemical carbon dioxide reduction reaction (eCO2RR) in aqueous media is fundamentally constrained by the low solubility of CO2, leading to limited current densities and poor product selectivity. Herein, we have developed tin single-atom catalysts (Sn-SACs) featuring well-defined SnN4 coordination as a platform to systematically investigate the influence of CO2 pressure on reaction kinetics and selectivity. Elevating the CO2 pressure to 5 MPa markedly enhances mass transport, achieving a Faradaic efficiency for formate of 85% at -1.1 V vs. RHE with high current density, in stark contrast to 11.5% under 0.1 MPa. In situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) reveals that high pressure favors the formation of *OCHO intermediates, thereby redirecting the reaction pathway toward formate production. Complementary density functional theory (DFT) calculations corroborate that increased local CO2 concentration stabilizes the *OCHO transition state and lowers the associated energy barrier. This work has established that pressure engineering as an effective strategy to decouple mass transport, activity, and selectivity in eCO2RR, underscoring the promise of high-pressure electrochemistry for efficient CO2 conversion.