Periodic quantum well mediated oriented charge separation in Cd0.3Zn0.7S twin crystal towards optimized photocatalytic hydrogen evolution

Interface engineering is vital for promoting charge separation in photocatalysis. Herein, a twin crystal interface in Cd_0.3Zn_0.7S is engineered, which leads to a variation of the electric polarization along the interface and the formation of a periodic quantum well along z axis. The periodic quantum well could effectively facilitate the oriented charge separation and significantly reduce the diffusion distance simultaneously. Density functional theory (DFT) calculations confirm that Cd_0.3Zn_0.7S twin crystal possesses a relative low work function and an appropriate hydrogen adsorption Gibbs free energy (ΔG_H*), making each step of the cascaded hydrogen evolution reactions optimized. As a result, the resultant twin crystal exhibits an excellent visible light photocatalytic hydrogen evolution rate (13148.98 μmol·g⁻¹·h⁻¹), which is almost 10 and 30 times higher than those of CdS and ZnS. Importantly, it also shows a good stability because of the formation of twin crystal interface. In addition, the introduction of S vacancy defect results in narrowing the band gap and extending the photo-response to long wavelength region. Such a twin crystal interface engineering strategy provides a basic guideline for designing high-efficient photocatalysts with tunable electric polarization.