Engineering cation defect-mediated Z-scheme photocatalysts for a highly efficient and stable photocatalytic hydrogen production

Abstract

The construction of Z-scheme heterojunctions has been demonstrated as an effective strategy to improve photocatalytic hydrogen (H₂) production efficiency. Herein, a Zn vacancy defect-mediated direct Z-scheme CdS/ZnS (CSZS–V_Zn) heterojunction was developed to optimize the H₂ production performance, and the introduction of cation defects in ZnS could regulate the band structure of the photocatalyst by forming additional energy levels within the band gap and help to form ohmic contacts. The CSZS–V_Zn heterojunction exhibited a H₂ evolution rate of 46.63 mmol h⁻¹ g⁻¹ under visible light illumination in an aqueous Na₂S/Na₂SO₃ system, which was about 388 and 1727 times higher than those of CdS and Zn-vacancy ZnS (ZnS–V_Zn), respectively. The enhanced photocatalytic activity of CSZS–V_Zn was mainly attributed to the presence of Zn vacancy defects upon the formation of the Z-scheme heterojunction structure, by which the photogenerated electrons were trapped in the Zn vacancy defect levels of ZnS and recombined with holes in the valence bands of CdS at heterojunction interfaces through ohmic contacts. In such a way, electrons in the conduction bands of CdS were boosted to participate in H₂ evolution reactions and photocorrosion was suppressed. This work provides a viable design strategy via the engineering of cation defects in Z-scheme photocatalysts for photocatalytic H₂ evolution.