N-Doped Mesoporous In₂ O₃ for Photocatalytic Oxygen Evolution from the In-based Metal-Organic Frameworks

As an excellent n-type semiconductor, indium oxide (In₂ O₃ ) is also a good candidate for photocatalysis such as light-induced water splitting. However, the efficiency of the oxygen evolution reaction (OER) underperforms in view of the wide band gap (BG) and fast charge recombination in In₂ O₃ . N-doping provides a sound method to narrow the BG and to prohibit the charge recombination by forming new energy levels between the valence band (VB) and the conduction band (CB). In this work, an In-based organic framework sod-ZMOF was used as a precursor to prepare the N-doped In₂ O₃ . After calcination, sod-ZMOF is transformed into N-doped In₂ O₃ nanocrystalline, in which the ligand within sod-ZMOF serves as the nitrogen source. In addition, sod-ZMOF acts as self-template during calcination to generate abundant nanopores within the In₂ O₃ frameworks, providing large specific surface area and active sites for OER. The BG is narrowed to 2.9 from 3.7 eV of the pure In₂ O₃ on account of the N-doping. N species are doped in both the substitutional and interstitial fashion, and the interstitial doping is believed to improve the photo-induced carrier separation by the formation of oxygen vacancies. As a consequence, the overpotential for OER is effectively decreased from the pure In₂ O₃ , and the electrocatalytic experiment proves superior catalytic activity with a high current density and long-term durability compared to the In₂ O₃ nanoparticles obtained from In(OH)₃ .