Modification of In2O3 by electronic promoters to regulate electron transfer behavior of CO2/H2O adsorption and the selectivity of photocatalytic CO2 reduction

Abstract

Improving product selectivity is the most important goal for the artificial photosynthesis of CO₂ and H₂O considering that the adsorption behaviors of reactants may play an important role in the product selectivity of CO₂ conversion. In this work, a black In₂O₃ sample was modified with fluoride anions (F⁻) as electron donors or amino ions (NH₂⁺) as electron acceptors. F-modified In₂O₃ provided additional F⁻ and In²⁺ sites, which promoted H₂O to accept more electrons from the material, and exhibited a high selectivity to CH₄ of 81.95%. NH₂-modified In₂O₃ caused H₂O to donate electrons to the material by constructing a hydrophobic layer, resulting in a high combined selectivity to methanol and carbon monoxide of 87.64%. Based on the two different H₂O adsorption behaviors at In²⁺ sites adjacent to oxygen vacancy defects (V_O–In²⁺) or at In³⁺ sites, the respective formation of hydrogen ions (H⁺) or protons (*H) is key to regulating the product selectivity of CO₂ reduction. The formation of a confined-space structure of CO₂ and its capacity to accept more electrons from the material induced by a higher number of V_O–In²⁺ sites after modification both ensure the proceeding of CO₂ reduction. The findings presented in this work add to the understanding of artificial photosynthesis.