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.