Hierarchical 3D ZnIn2S4/graphene nano-heterostructures: their in situ fabrication with dual functionality in solar hydrogen production and as anodes for lithium ion batteriesElectronic supplementary information (ESI) available: FTIR spectra of GO samples and all the ZnIn2S4/Gr heterostructures, and data related to recycling and reuse of catalysts. See DOI: 10.1039/c5cp05546f

Hierarchical 3D ZnIn 2 S 4 /graphene (ZnIn 2 S 4 /Gr) nano-heterostructures were successfully synthesized using an in-situ hydrothermal method. The dual functionality of these nano-heterostructures i.e. for solar hydrogen production and lithium ion batteries has been demonstrated for the first time. The ZnIn 2 S 4 /Gr nano-heterostructures were optimized by varying the concentrations of graphene for utmost hydrogen production. An inspection of the structure shows the existence of layered hexagonal ZnIn 2 S 4 wrapped in graphene. The reduction of graphene oxide (GO) to graphene was confirmed by Raman and XPS analyses. The morphological analysis demonstrated that ultrathin ZnIn 2 S 4 nanopetals are dispersed on graphene sheets. The optical study reveals the extended absorption edge to the visible region due to the presence of graphene and hence is used as a photocatalyst to transform H 2 S into eco-friendly hydrogen using solar light. The ZnIn 2 S 4 /Gr nano-heterostructure that is comprised of graphene and ZnIn 2 S 4 in a weight ratio of 1 : 99 exhibits enhanced photocatalytically stable hydrogen production i.e. ∼6365 μmole h −1 under visible light irradiation using just 0.2 g of nano-heterostructure, which is much higher as compared to bare hierarchical 3D ZnIn 2 S 4 . The heightened photocatalytic activity is attributed to the enhanced charge carrier separation due to graphene which acts as an excellent electron collector and transporter. Furthermore, the usage of nano-heterostructures and pristine ZnIn 2 S 4 as anodes in lithium ion batteries confers the charge capacities of 590 and 320 mA h g −1 after 220 cycles as compared to their initial reversible capacities of 645 and 523 mA h g −1 , respectively. These nano-heterostructures show high reversible capacity, excellent cycling stability, and high-rate capability indicating their potential as promising anode materials for LIBs. The excellent performance is due to the nanostructuring of ZnIn 2 S 4 and the presence of a graphene layer, which works as a channel for the supply of electrons during the charge-discharge process. More significantly, their dual functionality in energy generation and storage is quite unique and commendable. In-situ hydrothermal synthesis of hierarchical 3D ZnIn 2 S 4 /graphene (ZnIn 2 S 4 /Gr) nano-heterostructures for energy generation & storage (LIB).