The electrochemical CO 2 reduction reaction (CO 2 RR) provides an alternative protocol to producing industrial chemicals with renewable electricity sources, and the highly selective, durable, and economic catalysts should expedite CO 2 RR applications. Here, we demonstrate a composite Cu−In 2 O 3 catalyst in which a trace amount of In 2 O 3 decorated on Cu surface greatly improves the selectivity and stability for CO 2 -to-CO reduction as compared to the counterparts (Cu or In 2 O 3 ), realizing a CO faradaic efficiency (FE CO ) of 95% at −0.7 V (vs RHE) and no obvious degradation within 7 h. In situ X-ray absorption spectroscopy reveals that In 2 O 3 undergoes the redox reaction and preserves the metallic state of Cu during the CO 2 RR process. Strong electronic interaction and coupling occur at the Cu/In 2 O 3 interface which serves as the active site for selective CO 2 RR. Theoretical calculation confirms the roles of In 2 O 3 in preventing oxidation and altering the electronic structure of Cu to assist COOH* formation and demote CO* adsorption at the Cu/In 2 O 3 interface.

The electrochemical CO 2 reduction reaction (CO 2 RR) which produces high value-added products is regarded as a prospective path toward carbon cycling. However, the challenges in the electrochemical CO 2 RR are its competition to the hydrogen evolution reaction (HER) and unsatisfied product selectivity. Therefore, the design and preparation of highly effective catalysts with low overpotential, high faradaic efficiency (FE), and high selectivity are key considerations for the development of the CO 2 RR technology. In this research, binary In−Sn catalysts with In/Sn atomic ratios of 3/1 and 1/1 have been prepared. In−Sn nanoparticles (NPs) are composed of In and InSn 4 with some surface In and Sn oxides. Sn addition enhances the partial current density of formate production during the CO 2 RR. In 3 Sn/C NPs show outstanding performance with a HCOOH FE of 92.6% and excellent durability for 10 h at −1.0 V. In addition, the comparison of the binary In 3 Sn/C and physical mixture (In/C and SnO 2 /C) highlights that In 4 Sn is responsible for the high activity and stability of formate conversion. This research provides guidelines for the design of CO 2 RR catalysts with high formate conversion by optimization of compositions and structures of InSn NPs.

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