Electrochemical reconstruction- and electronegativity-induced electron redistribution for activating sulfur atoms of MoOxSy-based materials toward efficient hydrogen evolution

Abstract

Amorphous MoOxSy compounds have attracted considerable attention in the field of hydrogen evolution reaction (HER) due to their unique structural advantages, which include the retention of high electrical conductivity of the O-doped MoS2 (O-MoS2), and abundant potential active sites of amorphous MoSx such as molybdenum and sulfur atoms. Nevertheless, the controllable preparation of MoOxSy compounds, precise regulation of the localized electron surroundings of the active sites, and elucidation of possible electrocatalytic mechanism persist in the significant challenges within the field of HER. Herein, we have proposed a novel and eco-friendly strategy for electrochemical reconstruction- and electronegativity-induced electron redistribution for activating sulfur atoms of the MoOxSy compounds toward efficient HER. The anodic oxidation/cathodic reduction in-situ reconstruction strategy has been employed to successfully transform crystalline O-MoS2 into amorphous MoOₓSy. A thorough investigation reveals that the number of oxygen atoms in MoOxSy is effectively modulated by extending the oxidation time. Our results demonstrate that the electrochemical reconstruction induces the electron redistribution among Mo, O and S atoms. Furthermore, the typical sample (Mo3O2S6/CC) might establish the electron transfer pathways along the S1-Mo-S3-Mo-O route, where oxygen-mediated charge modulation activates inert sulfur atoms through optimizing hydrogen adsorption free energy change (ΔGH*). Consequently, Mo3O2S6/CC achieves exceptional HER activity with a low overpotential of about 237.8 mV at a current density of 200 mA cm-2, surpassing most previously-reported MoOxSy-based catalysts. Additionally, the chronoamperometric test at 100 mA cm-2 reveals that the corresponding overpotential remains almost constant during a 24.0 h operating period, with only a marginal increase from - 0.40 to - 0.45 V. This signifies the excellent stability. Third, the electrode pair consisting of Mo3O2S6/CC and RuO2, at 200 mA cm-2, exhibits satisfactory overall water splitting performance of about 1.72 V at 75 °C. This work opens up a novel concept for the design of the MoOxSy-based electrocatalysts toward achieving efficient HER.