Surface defect engineering of ZnCoS in ZnCdS with twin crystal structure for visible-light-driven H2 production coupled with benzyl alcohol oxidation

Abstract

Photoredox dual reaction of organic synthesis and H₂ evolution opens up a novel pathway for collaboratively generating clean fuels and high-quality chemicals, providing a more effective approach of solar energy conversion. Herein, a surface defect-engineered ZnCoS/ZnCdS heterostructure with zinc blende (ZB)/wurtzite (WZ) phase junctions is synthesized for photocatalytic cooperative coupling of benzaldehyde (BAD) and H₂ production. This surface defect-engineered ZnCoS/ZnCdS heterostructure elaborately integrates the mixed phase junction advantage of ZnCdS semiconductor and the cocatalytic function of ZnCoS possessing Zn (V_Zn-ZnCoS/ZnCdS) or S vacancies (V_S-ZnCoS/ZnCdS). The optimum V_S-ZnCoS/ZnCdS simultaneously exhibits a superior H₂ production rate of 14.23 mmol h⁻¹ g⁻¹ accompanied with BAD formation rate of 12.29 mmol h⁻¹ g⁻¹ under visible-light irradiation, which is approximately two-fold greater than that of pristine ZnCdS. Under simulated sunlight irradiation (AM 1.5), V_S-ZnCoS/ZnCdS achieves H₂ evolution (27.43 mmol g_cat⁻¹ h⁻¹) with 0.52% of STH efficiency, accompany with 26.31 mmol g_cat⁻¹ h⁻¹ of BAD formation rate. The underlying solar-driven mechanism is elucidated by a series of in-situ characterization and control experiments, which reveals the synergistic effect of interfacial ZB/WZ phase junctions in ZnCdS and S vacancies of ZnCoS on enhancement of the photoredox dual reaction. The V_S-ZnCoS/ZnCdS follows a predominant oxygen-centered radical integrating with carbon-centered radical pathways for BAD formation and a simultaneous electron-driven proton reduction for H₂ production. Interestingly, the nature of surface vacancies not only facilitates the separation of photoinduced charge carriers but also able to selectively adjust the mechanism pathway for BAD production via tuning the oxygen-centered radical and carbon-centered radical formation.