Integrating noble-metal-free metallic vanadium carbide cocatalyst with CdS for efficient visible-light-driven photocatalytic H2 evolution

Abstract

Developing highly active and stable cocatalysts at lower costs is greatly crucial for high-performance semiconductor-based photocatalytic H2 evolution from water splitting. Herein, we report that noble-metal-free metallic vanadium carbide (VC) can function as a superior cocatalyst when integrated with CdS for efficient photocatalytic H2 evolution under visible light irradiation (≥420 nm). The most efficient CdS/VC (15 wt.%) composite photocatalyst exhibits an exceptionally high photocatalytic H2 evolution rate of 14.2 mmol h−1 g−1, up to 12 times higher than that of pristine CdS. The apparent quantum efficiency (AQE) of H2 evolution reaches up to 8.7% at 420 nm. Moreover, the CdS/VC (15 wt.%) shows good stability for H2 evolution after eight consecutive cycles of continuous light irradiation of 40 h. Most notably, the H2 evolution activity of CdS/VC is even higher than or comparable to that of platinized CdS (CdS/Pt) prepared by photoreduction or chemical reduction at the same cocatalyst loading (1 wt.%). Furthermore, VC can also serve as an efficient H2 evolution cocatalyst on various semiconductor photocatalysts (TiO2 and g-C3N4) and in a dye-sensitized photocatalytic system. Electrochemical and photoelectrochemical measurements reveal that VC can function as an efficient electrocatalyst not only to reduce the overpotential of H+/H2O reduction to H2 but also to effectively capture the photogenerated electrons of CdS for enhancing the separation efficiency of photogenerated carriers thanks to its outstanding metallic conduction, thus substantially improving the photocatalytic H2 evolution activity of CdS/VC photocatalyst. This work demonstrates that noble-metal-free VC is a promising alternative to Pt as an efficient H2 evolution catalyst for electrocatalytic and photocatalytic energy conversion.