Improved Hydrogen Production Rate of a Nickel-Doped Zinc Indium Oxysulfide Visible-Light Catalyst: Comparative Study of Stoichiometric and Nonstoichiometric Compounds

Photocatalytic hydrogen production has been considered as one of the effective methods to produce hydrogen as a green energy carrier in the future. This report systematically investigates the effect of nickel doping on the crystal structure, optical properties, and photocatalytic hydrogen production rate of the ZnInOS/In(OH)3 nanocomposite (denoted as ZI-50). It is found that nickel doping could transform the phase of ZI-50 from two phases of ZnInOS and In(OH)3 into a single phase with a ZnIn2S4 spinel structure. More importantly, all Ni-doped ZI-50 catalysts are nonstoichiometric and highly defective with a Zn(Zn,Ni,In)2(O,S)4–x spinel structure. 10% nickel precursor-doped ZI-50 as the best catalyst can achieve the highest hydrogen evolution reaction rate of 1700 μmol/g·h, which is much higher than those of Ni-free ZI-50 (340 μmol/g·h) and stoichiometric ZnIn2S4 (110 μmol/g·h). A kinetic mechanism for enhancing photocatalytic hydrogen evolution based upon the cationic antisite defects and anionic oxygen vacancy was proposed and explained.