H2 Evolution with Silicotungstic Acid Electron Mediator over V-Doped MoS2 Electrocatalysts

Metal-doped molybdenum sulfide (MoS₂) shows promise for achieving platinum-like catalytic activity in the hydrogen evolution reaction (HER) of electrocatalysis, though the proton and electron transfer kinetics remain poorly understood. In this study, we investigated the HER kinetics and mechanism on both pristine and vanadium(V)-doped MoS₂ catalysts using silicotungstic acids as electron mediators. V-doped MoS₂ exhibits an HER rate approximately 5 times that of MoS₂ (696.4 vs 140.7 mmol_H2 g^–1 min^–1). This enhancement is attributed to accelerated proton adsorption and transfer kinetics, driven by an increased number of active sites and favorable proton transfer in the Volmer step. Moreover, silicotungstic acids mediate electron transfer through an inner-sphere mechanism, showing identical reaction orders on both pristine and V-doped MoS₂. Electrochemical Tafel slopes reveal that H₂ evolution follows a Volmer–Heyrovsky mechanism, regardless of V doping. This work highlights the significance of proton adsorption and transfer kinetics in enhancing HER rates.