Influence of indium doping on the activity of gallium oxynitride for water splitting under visible light irradiation

Visible-light-active indium-doped gallium oxynitrides with a wurtzite-like structure were synthesized from nitridation of In(OH)₃-containing Ga(OH)₃ under NH₃ flow at 625 °C and used for photocatalytic water splitting. This synthesis method yielded a homogeneous In distribution in gallium oxynitride solid solutions for Ga replacement levels of up to 1%. An appropriate amount of In substitution for Ga, approximately 0.5%, significantly enhanced the activity of gallium oxynitride in the visible-light-induced evolutions of H₂ and O₂ gases from methanol and AgNO₃ solutions, respectively. X-ray photoelectron spectroscopic analysis indicated that In doping increased the dispersion of hybridized orbitals in the valence band of gallium oxynitride. This can enhance charge mobility in gallium oxynitride and thus photocatalytic activity. A higher degree of In doping resulted in nucleation of InN-like oxynitride on the gallium oxynitride surface and degraded the photocatalytic activity. This study demonstrates that band structure engineering of gallium oxynitride powders with In doping is a facile procedure for obtaining visible-light sensitive photocatalysts with high activities.