Engineering sulfur vacancies and photothermal effects in a CoAl2O4/MnCdS S-scheme heterojunction for broad-spectrum photocatalytic hydrogen production

Abstract

Constructing a band-matched S-scheme heterojunction is an effective approach to mitigate the high recombination rate of photogenerated carriers. In this work, sulfur vacancy-engineered and photothermally mediated CoAl₂O₄/MCS-Vs S-scheme heterostructures were constructed by coupling MCS-Vs nanorods onto porous CoAl₂O₄ nanoflowers via an ultrasound-assisted method, enabling efficient broad-spectrum photocatalytic hydrogen production. Remarkably, the 10CMCS-Vs composite demonstrated a remarkable hydrogen evolution rate of 26.43 mmol g⁻¹ h⁻¹ under visible light, representing a 6.74-fold enhancement over pristine MCS-Vs, with an apparent quantum efficiency (AQE) of 26.53% at 420 nm and a maximum solar-to-hydrogen (STH) efficiency of 5.01%. This can be attributed to the strong synergistic effect between sulfur vacancies and the photothermal effect. Dielectric function analysis demonstrates that defect-induced modifications in local electronic states effectively broaden the light absorption spectrum while creating intermediate energy levels to facilitate charge separation in the S-scheme junction. Meanwhile, the photothermal effect synergistically enhances the photocatalytic hydrogen evolution performance of 10CMCS-Vs by elevating local temperature to accelerate carrier mobility and reduce reaction activation energy. This work provides fundamental insights into the defect-mediated and photothermal synergistic interface engineering strategies for developing high-performance S-scheme photocatalysts.