Developing an efficient NiCo₂S₄ cocatalyst for improving the visible light H₂ evolution performance of CdS nanoparticles

Abstract

Developing efficient alternatives to the widely used Pt cocatalyst in photocatalytic H₂O splitting is of great importance in view of large-scale production of clear H₂ energy. Herein, we report the facile synthesis of NiCo₂S₄ and its first use as a highly active and cost-affordable cocatalyst to boost visible light H₂ generation with the CdS semiconductor. The synthesized NiCo₂S₄/CdS composite materials are fully characterized by various techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), UV-Vis diffusion reflectance spectroscopy (DRS), and N₂ adsorption measurements. With the optimized NiCo₂S₄/CdS composite sample, a high H₂ generation rate of 137 μmol h^-1 is obtained under visible light irradiation, which is more than 17 times higher than that of bare CdS material. The results of photoluminescence (PL) spectroscopy, transient photocurrent response and electrochemical impedance spectroscopy demonstrate the remarkably promoted migration and separation of photogenerated charge carriers over the heterostructured NiCo₂S₄/CdS material, thus leading to obviously enhanced photocatalytic performance. Moreover, a possible mechanism for the photocatalytic H₂ evolution reaction is also proposed based on the observed results of activity evaluation and photoelectrochemical measurements.