A highly active cocatalyst-free semiconductor photocatalyst for visible-light-driven hydrogen evolution: synergistic effect of surface defects and spatial bandgap engineering

Abstract

Enhancing the efficiency of semiconductor photocatalysts is still a challenging issue for photocatalytic hydrogen evolution. In this work, a synergistic strategy of surface defects and spatial bandgap engineering was realized for constructing a Zn_1−xCd_xS/SiO₂ photocatalyst. A quantum efficiency of 48.6% (at 420 nm) for hydrogen evolution was obtained without the use of a cocatalyst. The molar ratio of Cd : Zn in Zn_1−xCd_xS particles could be gradually tuned from 0.305 : 1 (inside) to 0.490 : 1 (outside). At least a 0.17 eV potential difference is present between the inside and outside of Zn_1−xCd_xS particles. Experimental and theoretical analyses showed that photogenerated electrons and holes could vectorially transfer along the spatial bandgap to reach the surface, and be trapped by the surface defects. In situ formed surface Cd species act as the active sites accelerating the surface hydrogen evolution reaction.