Stabilizing Oxidation State of SnO₂ for Highly Selective CO₂ Electroreduction to Formate at Large Current Densities

Abstract

Even though electrocatalytic CO2 reduction reaction (CO2RR) to formate has made significant advances, achieving a high cell energy efficiency at industrial-level current densities is still a bottleneck for the large-scale application of this technology. SnO2 is a promising electrocatalyst for formate production but is restricted by the unstable oxidation state under high reduction potentials, causing catalyst reconstruction and inactivation. Herein, we present an atomic doping strategy (by Cu, Bi, or Pt) to trigger the emergence of oxygen vacancy in the SnO2 lattice and stabilize the oxidation state of SnO2 during CO2RR. As a result, the optimal Cu-incorporated SnO2 can keep a high formate Faradic efficiency of >80% and a cell energy efficiency of about 50−60% at a wide range of current densities up to 500 mA cm−2 in a commercial flow cell, surpassing most reported works. A set of in situ spectroscopy measurements and controlled electrochemical tests suggest that the oxygen vacancy, induced by the participation of Cu/Bi/Pt single atoms, holds the key to stabilizing SnO2 as well as promoting the adsorption of formate-related *OCHO reaction intermediate. A qualitative relationship between the oxygen vacancy concentration and CO2-to-formate conversion is constructed on a series of doped SnO2 catalysts.