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

Abstract

Electrochemical reduction of CO₂ (CO₂R) to formic acid upgrades waste CO₂; 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 CO₂R operation. Active Sn-Bi/SnO₂ surfaces formed in situ on homogeneously alloyed Bi_0.1Sn crystals stabilize the CO₂R-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.

Stable electrochemical reduction to formate is still challenging. Here, the authors demonstrate a redox-modulation and active-site stabilization strategy for CO₂ to formate conversion over 100 days of continuous operation at 100 mA/cm² with a cathodic energy efficiency of 70%.