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 bulk photocatalyst via discrete energy bands. However, the decay dynamics of excited states in such heterostructure have not been explored. Herein, ultra-small CoOx clusters decorated on ZnIn2S4 (ZIS) is prepared for pure water splitting. Experimental characterizations confirm that CoOx clusters efficiently capture holes from ZnIn2S4, thus inhibiting charge recombination. Femtosecond transient absorption spectroscopy (fs-TAS) reveals that the lifetime of trapped holes by CoOx clusters is prolonged to 911.6 ps, enabling more opportunities to participate in surface reaction. Moreover, density functional theory calculation suggests that CoOx cluster is the preferential adsorption site for H2O to boost surface water oxidation. Benefited from above factors, the optimized CoOx/ZIS shows an 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 is 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.