Synergistic effect of oxygen species and vacancy for enhanced electrochemical CO2 conversion to formate on indium oxide

Indium-based oxides are promising electrocatalysts for producing formate via CO2 reduction reaction, in which *OCHO is considered the key intermediate. Here, we identified that the *COOH pathway could be preferential to produce formate on In2O3 of In/In2O3 heterojunction due to the synergistic effect of oxygen species and vacancy. Specifically, *CO2 and *COOH were observed on In2O3 and related to formate production by in situ Raman spectroscopy. The theoretical calculations further demonstrated that the energy barrier of the *COOH formation on In2O3 was decreased in the presence of oxygen vacancy, similar to or lower than that of the *OCHO formation on the In surface. As a result, a formate selectivity of over 90% was obtained on prepared In/In2O3 heterojunction with 343 ± 7 mA cm–2 partial current density. Furthermore, when using a Si-based photovoltaic as an energy supplier, 10.11% solar–to–fuel energy efficiency was achieved.