S vacancy in n-n type heterojunction accelerate electron transfer, improve the photocatalytic activity of CO₂RR and H₂ evolution

The introduction of anionic vacancies is a promising strategy to improve the photocatalytic activity of catalysts, however, the introduction of sulfur vacancy defects at the interface of heterojunction is a challenging task. Therefore, in this work, a secondary hydrothermal method was used to generate sulfur vacancy defects (Vs) at the interface of CdS/MoS₂ heterojunction (Vs-CdS/MoS₂), which was applied to photocatalytic reduction of CO₂ and hydrogen evolution. The CO yield of the prepared CM-7 sample was 3.1 times higher than that of pristine CdS, and the H₂ yield was 10.2 times higher. Experimental analysis showed that sulfur vacancies were detected on the (002) crystal surface of CdS in the heterojunction, providing active sites, redistributing the local charge, lowering the charge transport resistance and carrier complexation rate, and increasing the carrier migration rate, which led to the improvement of the photocatalytic activity. This work provides a novel strategy for designing heterojunctions with defect engineering applied to photocatalytic reduction of CO₂ and hydrogen evolution.