Electron-enriched regulation of sulfur-active site for accelerating atomic hydrogen desorption of S-rich MoWS2+ cocatalyst toward efficient photocatalytic H2 evolution of TiO2

Abstract

• An electron-rich regulation idea was developed to weaken the strong S-H ads bonds. • The active-sulfur number and efficiency of MoWS 2+ x was simultaneously optimized. • The S-rich MoWS 2+ x was prepared by one-step photoinduced electron-reduction method. • H 2 -evolution rate of TiO 2 can be significantly improved by S-rich MoWS 2+ x . Metal chalcogenides (MS x ) as H 2 -evolution cocatalysts generally suffer from unfavorable H desorption property because of the strong interfacial interaction between the adsorbed H and intensely electronegative S sites (S-H ads , 363 KJ mol −1 ), which seriously hampers the H ads from desorbing to generate free H 2 . Herein, a universal strategy of electron-enriched regulation of sulfur-active site is developed to weaken the strong S-H ads bonds by introducing W heteroatoms into MoS 2+ x to form sulfur-rich MoWS 2+ x bimetal cocatalyst (expressed as MoWS 2+ x ). In this case, the S-enriched MoWS 2+ x is skillfully produced and simultaneously anchored with the TiO 2 by a facile photoinduced electron-reduction method, involving the aforehand formation of homogeneous W(MoS 4 ) x and their subsequent in-situ photoinduced deposition procedure. Photoactivity experiments exhibit that the MoWS 2+ x /TiO 2 (2:1) sample obtains the highest H 2 -evolution rate of 4620.8 μmol h −1 g −1 (AQE = 22.2 %) with a great promotion of 3.6 folds compared to the MoS 2+ x /TiO 2 sample. In situ/ex situ XPS characterizations and density functional theory (DFT) calculations reveal that the integration of W heteroatom into MoS 2+ x can regulate its electron density to form electron-enriched S (2+δ)− sites, thus availably weakening the S-H ads bonds to optimize atomic H desorption and accordingly enhancing the hydrogen-evolution activity of TiO 2 . This study provides a unique idea to optimize the electron densities of activity sites, which is vital for the development of efficient catalytic materials.