Phase change of core-shell CuO@Cu7S4 cubic photocatalysts with enhanced and stable H2 production activity

Background

Forming heterostructures of CuO with other semiconductors can hinder the electron-hole recombination and enhance photocatalytic activity. CuO@Cu₇S₄ nanomaterials have not been used for the photocatalytic H₂ generation application.

Methods

The cubic cuprous oxide was synthesized, and then sulfidation by an ion exchange method using sodium sulfide to prepare CuO@Cu₇S₄ core-shell photocatalyst.

Significant findings

During the sulfidation process with increasing concentrations of Na₂S, a series of phase transitions occur, sequentially forming the photocatalysts Cu₂O, Cu₂O@Cu₇S₄, Cu₂O/CuO@Cu₇S₄, and CuO@Cu₇S₄. The surface morphology also changes as the Cu₇S₄ shell forms after sulfidation. Tauc plot analysis, ultraviolet photoelectron spectroscopy (UPS), and electron paramagnetic resonance (EPR) measurements indicate that the CuO@Cu₇S₄ photocatalyst possesses an S-scheme band structure. The CuO@Cu₇S₄ composite photocatalyst demonstrates strong light absorption, low charge transfer resistance, efficient electron-hole separation, and enhanced hydrogen (H₂) production activity. The improved photocatalytic performance of the CuO@Cu₇S₄ heterojunction is attributed to the in-situ growth of Cu₇S₄ via sulfidation, which facilitates intimate interfacial contact between CuO and Cu₇S₄. The H₂ production activity of optimized CuO@Cu₇S₄ photocatalyst (COCS3) reaches 11,934 μmol g^-1h^-1. 90.4 % of hydrogen production activity was retained after three repeated cycles.