Ce Promotion of In₂O₃ for Electrochemical Reduction of CO₂ to Formate

Abstract

In 2 O 3 is a promising electrocatalyst for CO 2 electroreduction (CO 2 ER) to formate. In 2 O 3 nanoparticles doped with Pd, Ni, Co, Zr, and Ce promoters using flame-spray pyrolysis were characterized and evaluated in a gas diffusion electrode for the CO 2 ER. Doping results in slight shifts of the In binding energy as probed by XPS, which correlates with a change of the Faradaic efficiency to formate (FE formate ) in the order Ce-dopedHowever, the differences in CO 2 ER performance are caused mainly by the different extent of In 2 O 3 reduction. Co-doped In 2 O 3 is prone to complete reduction to a stable Co−In alloy with a low FE formate due to a high hydrogen evolution activity. The stabilizing effect of Ce on In 2 O 3 is further demonstrated by an Xray absorption spectroscopy study of a set of Ce-doped In 2 O 3 samples (10, 50, 90 at%), highlighting that reduction of In 2 O 3 is suppressed with increasing Ce content. Optimum performance in terms of FE formate is obtained at a Ce content of 10 at%, which is attributed to the stabilization of In 2 O 3 under negative bias up to −2 V. At higher Ce content, less active CeO 2 is formed. The highest FE formate of 86% observed for In 2 O 3 doped with 10 at% Ce, at a current density of 150 mA/cm 2 , compares favorably with a FE formate of 78% for In 2 O 3 .