Achieving long-lived photogenerated holes in ZnIn2S4 loaded with CoOx clusters for enhanced photocatalytic pure water splitting

Abstract

The photocatalytic pure water splitting performance of photocatalysts is still restricted by the low utilization efficiency of photogenerated holes. Recent studies suggest that metal oxide clusters can efficiently abstract holes from a bulk photocatalyst via discrete energy bands. However, the decay dynamics of excited states in such a heterostructure have not been explored. Herein, ultra-small CoO_x clusters decorated on ZnIn₂S₄ (ZIS) are prepared for pure water splitting. Experimental characterization studies confirm that CoO_x clusters efficiently capture holes from ZnIn₂S₄, thus inhibiting charge recombination. Femtosecond transient absorption spectroscopy (fs-TAS) reveals that the lifetime of holes trapped by CoO_x clusters is prolonged to 911.6 ps, enabling more opportunities to participate in the surface reaction. Moreover, density functional theory calculation suggests that the CoO_x cluster is the preferential adsorption site for H₂O to boost surface water oxidation. Benefiting from the above factors, the optimized CoO_x/ZIS shows improved H₂ and H₂O₂ evolution rates of 404.1 μmol g⁻¹ h⁻¹ and 371.9 μmol g⁻¹ h⁻¹ under visible light irradiation, respectively, which are about ten times higher than that of pure ZIS. The study highlights the significance of efficient hole extraction for improving photocatalytic pure water splitting performance.