Tailoring Surface Frustrated Lewis Pairs of In₂O₃₋<i>_x</i>(OH)_y for Gas‐Phase Heterogeneous Photocatalytic Reduction of CO₂ by Isomorphous Substitution of In³⁺ with Bi³⁺

Abstract

Frustrated Lewis pairs (FLPs) created by sterically hindered Lewis acids and Lewis bases have shown their capacity for capturing and reacting with a variety of small molecules, including H₂ and CO₂, and thereby creating a new strategy for CO₂ reduction. Here, the photocatalytic CO₂ reduction behavior of defect-laden indium oxide (In₂O_3-<i>_x</i> (OH) <i>_y</i> ) is greatly enhanced through isomorphous substitution of In³⁺ with Bi³⁺, providing fundamental insights into the catalytically active surface FLPs (i.e., In-OH···In) and the experimentally observed "volcano" relationship between the CO production rate and Bi³⁺ substitution level. According to density functional theory calculations at the optimal Bi³⁺ substitution level, the 6s² electron pair of Bi³⁺ hybridizes with the oxygen in the neighboring In-OH Lewis base site, leading to mildly increased Lewis basicity without influencing the Lewis acidity of the nearby In Lewis acid site. Meanwhile, Bi³⁺ can act as an extra acid site, serving to maximize the heterolytic splitting of reactant H₂, and results in a more hydridic hydride for more efficient CO₂ reduction. This study demonstrates that isomorphous substitution can effectively optimize the reactivity of surface catalytic active sites in addition to influencing optoelectronic properties, affording a better understanding of the photocatalytic CO₂ reduction mechanism.