Promising visible-light driven hydrogen production from water on a highly efficient CuCo2S4 nanosheet photocatalyst

Abstract

Here we report the development of CuCo₂S₄ 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, CuCo₂S₄ NSs exhibit excellent weight-normalized photoactivity that generates ∼25 900 μmol h⁻¹ H₂ 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 × 10¹⁵ 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 CuCo₂S₄ NSs show superior activity to Cu_0.5Co_2.5S₄ and Co₃S_4. These CuCo₂S₄ 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 × 10¹⁸ cm⁻³ which have been evaluated by Mott–Schottky analysis and favourable adsorption of H⁺ on S-sites and conversion to H₂ corroborate their efficient photocatalytic activity.