Ce Promotion of InO for Electrochemical Reduction of CO to Formate.

InO is a promising electrocatalyst for CO electroreduction (COER) to formate. InO 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 COER. 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) in the order Ce-doped InO > Zr-doped InO > InO > Pd-doped InO > Ni-doped InO > Co-doped InO. However, the differences in COER performance are caused mainly by the different extent of InO reduction. Co-doped InO is prone to complete reduction to a stable Co-In alloy with a low FE due to a high hydrogen evolution activity. The stabilizing effect of Ce on InO is further demonstrated by an X-ray absorption spectroscopy study of a set of Ce-doped InO samples (10, 50, 90 at%), highlighting that reduction of InO is suppressed with increasing Ce content. Optimum performance in terms of FE is obtained at a Ce content of 10 at%, which is attributed to the stabilization of InO under negative bias up to -2 V. At higher Ce content, less active CeO is formed. The highest FE of 86% observed for InO doped with 10 at% Ce, at a current density of 150 mA/cm, compares favorably with a FE of 78% for InO.