Synergistic effect of the rearranged sulfur vacancies and sulfur interstitials for 13-fold enhanced photocatalytic H2 production over defective Zn2In2S5 nanosheets

Intrinsic defect engineered semiconductor photocatalysts have been widely investigated for reaching visible light active photocatalytic H2 production. However, these defects are usually not stably present, thus requires external elements for stabilization. In this paper, we demonstrate a new strategy for significantly enhancing the photocatalytic H2 conversion efficiency. The strategy is based on synergistic effect of the properly rearranged sulfur interstitials and sulfur vacancies without introducing any external dopants. Toward this, the defective Zn2In2S5 nanosheets are successfully synthesized by a simple hydrothermal method. The synergetic contribution of the rearranged sulfur vacancies and sulfur interstitials within the material is strongly supported by that the photo-generated charge-carrier separation efficiency is obviously (∼2-fold) enhanced, and the activity for H2 production at the end of the fourth cycle test is 13-fold more than that of the beginning of the first cycle test. The rearranged positively charged sulfur vacancies and negatively charged sulfur vacancies in-situ form defect associates, which possess electric filed. We propose that the electric filed could effectively separate the photo-generated charge-carriers, and the positively charged sulfur vacancies act as trapping centers for splitting H2O via capturing O atoms into vacancy sites. The trapped O atoms can be subsequently removed by Na2S sacrificial reagent to reactivate the sulfur vacancies. Internally consistent reaction mechanism is proposed that describe the synergistic contribution of the rearranged sulfur vacancies and sulfur interstitials to the dramatically enhanced activity for photocatalytic H2 production. This inspires new design of defective semiconductor materials.