Black Ultrathin Single-Crystalline Flakes of CuVP₂S₆ and CuCrP₂S₆ for Near-Infrared-Driven Photocatalytic Hydrogen Evolution

The development of new near-infrared-responsive photocatalysts is a fascinating and challenging approach to acquire high photocatalytic hydrogen evolution (PHE) performance. Herein, near-infrared-responsive black CuVP₂S₆ and CuCrP₂S₆ flakes, as well as CuInP₂S₆ flakes, are designed and constructed for PHE. Atom-resolved scanning transmission electron microscopy images and X-ray absorption fine structure evidence the formation of ultrathin single-crystalline sheet-like structure of CuVP₂S₆ and CuCrP₂S₆. The synthetic CuVP₂S₆ and CuCrP₂S₆, with a narrow bandgap of ≈1.0 eV, shows the high light-absorption edge exceeding 1100 nm. Moreover, through the femtosecond-resolved transient absorption spectroscopy, CuCrP₂S₆ displays the efficient charge transfer and long charge lifetime (18318.1 ps), which is nearly 3 and 29 times longer than that of CuVP₂S₆ and CuInP₂S₆, respectively. In addition, CuCrP₂S₆, with the appropriate d-band and p-band, is thermodynamically favorable for the H⁺ adsorption and H₂ desorption by contrast with CuVP₂S₆ and CuInP₂S₆. As a result, CuCrP₂S₆ exhibits high PHE rates of 9.12 and 0.66 mmol h⁻¹ g⁻¹ under simulated sunlight and near-infrared light irradiation, respectively, far exceeding other layered metal phospho–sulfides. This work offers a distinctive perspective for the development of new near-infrared-responsive photocatalysts.