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

Developing highly active and stable cocatalysts at lower costs is greatly crucial for high-performance semiconductor-based photocatalytic H-2 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 H-2 evolution under visible light irradiation ( >= 420 nm). The most efficient CdS/VC (15 wt.%) composite photocatalyst exhibits an exceptionally high photocatalytic H-2 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 H-2 evolution reaches up to 8.7% at 420 nm. Moreover, the CdS/VC (15 wt.%) shows good stability for H-2 evolution after eight consecutive cycles of continuous light irradiation of 40 h. Most notably, the H-2 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 H-2 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 H-2 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 H-2 evolution activity of CdS/VC photocatalyst. This work demonstrates that noble-metal-free VC is a promising alternative to Pt as an efficient H-2 evolution catalyst for electrocatalytic and photocatalytic energy conversion.