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. [ABSTRACT FROM AUTHOR]