Sulfur Substitution and Defect Engineering in an Unfavored MnMoO₄ Catalyst for Efficient Hydrogen Evolution under Visible Light

Abstract

A novel and nonstoichiometric Mn1–x Mo(S,O)4–y oxysulfide catalyst with oxygen vacancies and a partial Mo6+-to-Mo4+ transition after the substitution of sulfur was synthesized for an efficient photocatalytic hydrogen evolution reaction (PHER). With appropriate sulfur substitution, a MnMoO4 semiconductor with a wide band gap was converted to Mn1–x Mo(S,O)4–y with a narrow gap and a suitable band position for PHER. MnMo oxysulfide of 50 mg achieved a high PHER rate of 415.8 μmol/h under visible light, an apparent quantum efficiency (AQE) of 4.31% at 420 nm, and a solar-to-hydrogen (STH) conversion efficiency of 1.28%. Oxygen vacancies (VO) surrounded by low coordination metal atoms act as active reaction sites, which strengthen water adsorption and activation. Here, we demonstrate that sulfur substitution of MnMoO4 for lowering its wide band gap can not only disturb the strict periodicity of the lattice but also the valence states of Mn and Mo for enhancing PHER via material design.

Oxygen-doped Sn17Sb6S29 bimetal oxysulfide catalysts for efficient reduction of organic pollutants and hexavalent chromium in the dark

“…It can be seen that SnSbOS-3 has the characteristics of mesoporous materials with a type IV isotherm and a hysteresis loop. 45 The total pore volume, specific surface area, and average pore diameter of the SnSbOS-3 sample are 26.5 m 2 g −1 , 0.050 m 3 g −1 , and 30.6 nm, respectively, with the pore size distribution shown in Fig. 3k.…”

Photocatalytic fixation of nitrogen to ammonia with a Ce/S co-doped TiO2 catalyst: synergistic tuning of heterovalent metal states and oxygen vacancy defects

“…2c. According to the equation of Φ = hv − ( E C − E F ), 54 where E F for the Fermi energy level is 0.43 eV and E C for the secondary electron cutoff is 17.71 eV. The Φ of TiCeOS-3 is 4.96 eV.…”

“…16,23 Step III: within TiCeOS-3, the Vo always emerges near Ce 3+ . 54,70,71 This linkage promotes electron transfer between Ce 3+ and Ce 4+ , effectively extends electron lifetimes, and activates O–H bonds and NN. 72 Step IV: adsorbed N 2 molecules on the surface of TiCeOS accept electrons and protons, which are photo-excited, resulting in NH 3 production, followed by NH 3 release and Vo formation.…”

Sulfur-doped cobalt molybdenum oxide with a hydrangea-like structure for bi-functionally efficient overall water splitting

“…40,41 Additionally, the appearance of two new peaks located at 231.4 eV and 228.3 eV indicates the generation of new Mo 4+ species, providing further evidence for the successful introduction of S. 42 The presence of Mo 4+ and the formation of oxygen vacancies (O V ) may be attributed to the capture of electrons by Mo 6+ from the nearby lattice oxygen (O Lat ). 43 Specific reactions may be O Lat − 2e − → 1/2O 2 + O V 2+ and Mo 6+ + 2e − → Mo 4+ . The S 2p spectrum (Fig.…”