Visible-light-driven water splitting by yolk-shelled ZnIn2S4-based heterostructure without noble-metal co-catalyst and sacrificial agent

The exploitation of low-cost, high-performance and visible-light-activated photocatalysts is of great significance for hydrogen economy. Herein, we report the rational design of a ZnIn2S4-based noble-metal-free photocatalyst for direct splitting of water into H2 and O2. Semi-metallic NiCo2S4 with low reduction barrier is selected as H2 evolving co-catalyst under the guidance of density functional theory (DFT) computation. Controllable preparation of hierarchical heterostructure is achieved by fine-tuning NiCo2S4 yolk-shell hollow spheres from metal-organic framework (MOF) precursors, followed by tight growth of ZnIn2S4 nanosheets on its outer surface and decoration of O2 evolving co-catalyst, Co3O4 nanoparticles, on the outermost layers. Locating reduction and oxidation sites on interior and exterior surfaces of ZnIn2S4 effectively harness the charge recombination as well as undesired back reaction. As a result of directional charge separation, ZnIn2S4 modified with separated dual co-catalysts exhibits promising photocatalytic activity, which is superior to most of analogous sulfide-based photocatalysts.