Promising visible-light driven hydrogen production from water on a highly efficient CuCo2S4 nanosheet photocatalystElectronic supplementary information (ESI) available: Calculations of donor concentration, number of H2 molecules produced, apparent quantum yield, turnover frequency, ECSA, additional TEM/SEM images, EDX, solution phase optical absorption spectra, GC data, variation of catalysts and SR solution data. See DOI: 10.1039/c9ta00391f

Here we report the development of CuCo 2 S 4 nanosheets (NSs) as a promising semiconductor photocatalyst for the first time for water splitting reactions under visible light ( λ ≥ 420 nm) conditions, without the support of any noble metal co-catalyst. These NSs were produced via a simple hydrothermal route and have desirable properties with a band gap of 2.24 eV, and are photo-catalytically active under visible light with an apparent quantum yield (AQY) of 2.48%. Under visible light, CuCo 2 S 4 NSs exhibit excellent weight-normalized photoactivity that generates ∼25 900 μmol h −1 H 2 for 1 g of material with sulphide + sulphite as the sacrificial agent under 7.68 mW cm −2 illumination, which is the best evolution reported for any chalcogenide semiconductor material without any co-catalyst to date with unprecedented long-term operational stability (up to 12 h study time). The rate and number of hydrogen gas molecules produced are 8.2855 × 10 15 s −1 cm −2 which remained constant for three catalytic cycles with a turnover frequency (TOF) value of 0.017 s −1 . The effect of Cu substitution on photoactivity was also investigated for comparative studies and it was found that CuCo 2 S 4 NSs show superior activity to Cu 0.5 Co 2.5 S 4 and Co 3 S 4. These CuCo 2 S 4 NSs absorb the entire visible range of the spectrum from 420 to 800 nm, and have a highly populated density of states at the Fermi level and a high donor concentration of 7.22 × 10 18 cm −3 which have been evaluated by Mott-Schottky analysis and favourable adsorption of H + on S-sites and conversion to H 2 corroborate their efficient photocatalytic activity. CuCo 2 S 4 nanosheets have been developed which work as an excellent water splitting photocatalyst with H 2 evolution activity under visible light.