Stable, active CO2 reduction to formate via redox-modulated stabilization of active sites

Abstract Electrochemical reduction of CO 2 (CO 2 R) to formic acid upgrades waste CO 2 ; however, up to now, chemical and structural changes to the electrocatalyst have often led to the deterioration of performance over time. Here, we find that alloying p-block elements with differing electronegativities modulates the redox potential of active sites and stabilizes them throughout extended CO 2 R operation. Active Sn-Bi/SnO 2 surfaces formed in situ on homogeneously alloyed Bi 0.1 Sn crystals stabilize the CO 2 R-to-formate pathway over 2400 h (100 days) of continuous operation at a current density of 100 mA cm −2 . This performance is accompanied by a Faradaic efficiency of 95% and an overpotential of ~ −0.65 V. Operating experimental studies as well as computational investigations show that the stabilized active sites offer near-optimal binding energy to the key formate intermediate *OCHO. Using a cation-exchange membrane electrode assembly device, we demonstrate the stable production of concentrated HCOO – solution (3.4 molar, 15 wt%) over 100 h.