In Situ Photodeposition of Cobalt Phosphate (CoH_xPO_y) on CdIn₂S₄ Photocatalyst for Accelerated Hole Extraction and Improved Hydrogen Evolution

The ternary metal sulfide CdIn₂S₄ (CIS) has great application potential in solar-to-hydrogen conversion due to its suitable band gap, good stability and low cost. However, the photocatalytic hydrogen (H₂) evolution performance of CIS is severely limited by the rapid electron–hole recombination originating from the slow photogenerated hole transfer kinetics. Herein, by simply depositing cobalt phosphate (CoH_xPO_y, noted as Co-Pi), a non-precious co-catalyst, an efficient pathway for accelerating the hole transfer process and subsequently promoting the H₂ evolution reaction (HER) activity of CIS nanosheets is developed. X-ray photoelectron spectroscopy (XPS) reveals that the Co atoms of Co-Pi preferentially combine with the unsaturated S atoms of CIS to form Co-S bonds, which act as channels for fast hole extraction from CIS to Co-Pi. Electron paramagnetic resonance (EPR) and time-resolved photoluminescence (TRPL) showed that the introduction of Co-Pi on ultrathin CIS surface not only increases the probability of photogenerated holes arriving the catalyst surface, but also prolongs the charge carrier’s lifetime by reducing the recombination of electrons and holes. Therefore, Co-Pi/CIS exhibits a satisfactory photocatalytic H₂ evolution rate of 7.28 mmol g⁻¹ h⁻¹ under visible light, which is superior to the pristine CIS (2.62 mmol g⁻¹ h⁻¹) and Pt modified CIS (3.73 mmol g⁻¹ h⁻¹).