Boosting the photocatalytic H2 evolution activity of a CdS/N-doped ZnIn2S4 direct Z-scheme heterostructure using a band alignment regulation strategy

Abstract

Hexagonal ZnIn₂S₄ (ZIS) with a special layer structure has attracted great interest in visible-light-activated photocatalytic H₂ production, but rapid charge recombination restricts its practical application. In the present work, a band alignment regulation strategy converging ion doping and heterojunction construction is proposed to solve this issue. Nitrogen is first doped into ZIS nanosheets to simultaneously upshift their conduction band (CB) and valence band (VB) positions for more reductive electrons, then CdS nanoparticles are in situ grown on the surface of N-doped ZIS to form a 0D/2D CdS/N-ZIS heterostructure with a Z-scheme band alignment. Because there is a large Fermi level difference between N-ZIS and CdS, more free electrons are transferred from N-ZIS to CdS to facilitate a stronger built-in electric field at the CdS/N-ZIS interface for charge separation. Such an innovative heterojunction thus assures the accumulation of photoinduced electrons and holes on N-ZIS of more negative CB position and CdS of more positive VB position, respectively. As a result, CdS/N-ZIS exhibits a best H₂ evolution rate of 15.7 μmol h⁻¹ under visible light, which is nearly 7.4 and 2.2 times higher than those of pristine ZIS and CdS/ZIS, respectively. This investigation provides a practical strategy for designing a Z-scheme heterostructure with favorable band alignment for efficient H₂ production.