Influence of sulfur amount in Ni-incorporated ZnIn2(O,S)4 on phase formation and the visible light photocatalytic hydrogen evolution reaction

Abstract

Hydrogen is an inevitable energy source to replace fossil fuels in the future. Herein, we report Ni-doped ZnIn₂(O,S)₄/In(OH)₃ heterojunction composites with different sulfur contents to support green hydrogen gas evolution. A simple one-step hydrothermal preparation process was carried out by simultaneously adding all chemical precursors during the synthesis of composites. The as-prepared composites were carefully characterized by XRD, FE-SEM, TEM, XPS, DRS, TPC, MS, EIS and CV techniques, which confirmed their performance in the hydrogen evolution reaction (HER) under visible-light illumination. With increasing sulfur content, XRD analysis indicated the gradual formation of Ni-doped ZnIn₂(O,S)₄ co-existing with the In(OH)₃ phase. The highest hydrogen evolution rate of 2100 μmol g⁻¹ h⁻¹ under visible-light illumination was achieved in the presence of the Ni-doped ZnIn₂(O,S)₄/In(OH)₃ composite. Its excellent photocatalytic performance is related to the good separation of photocarriers. XPS analysis suggests the formation of positively and negatively charged defects on catalyst surfaces which attract the photogenerated electrons and holes, respectively, thus leading to an extended photocarrier lifetime. Furthermore, the coupling effect with In(OH)₃ provides a more positive conduction band (CB) relative to that of the Ni-doped ZnIn₂(O,S)₄ phase for facile electron transfer. A plausible HER mechanism based on the experimental data is proposed in this work.