Two-dimensional nickel hydroxide/sulfides nanosheet as an efficient cocatalyst for photocatalytic H evolution over CdS nanospheres.

The intriguing features of two-dimensional (2D) materials such as better charge carrier separation and abundant surface reaction sites endow them with potential applications as cocatalysts in photocatalysis. In this paper, a ternary 2D nickel hydroxide/sulfides nanosheet composed of Ni(OH), NiS and NiS was loaded on CdS nanospheres by a simple chemical deposition route. The composition of nickel hydroxide/sulfides was determined clearly through an overall analysis using X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Mott-Schottky, electrochemical impedance, steady-state and time-resolved photoluminescence spectroscopy were used to investigate the charge transfer process in CdS and Ni(OH)/NiS/NiS-CdS. The results confirm that a synergistic effect of Ni(OH)/NiS/NiS on CdS has occurred under light irradiation, where the Ni(OH) and nickel sulfides act as hole storage and surface reaction sites, respectively, to promote the charge transfer on CdS. The improved charge transfer and separation efficiency as well as the increased surface reaction sites in Ni(OH)/NiS/NiS-CdS finally result in a dramatically improved photocatalytic performance. The photocatalytic H evolution rate of Ni(OH)/NiS/NiS-CdS is ca. 46 times higher than that of CdS, and the photocatalytic stability of CdS is also improved substantially under visible light irradiation.