Beneficial surface defect engineering of MoS2 electrocatalyst for efficient hydrogen evolution reaction

Hydrogen evolution reaction (HER) is considered the most efficient method for hydrogen production using an effective electrocatalyst. Molybdenum disulfide (MoS₂), with its unique 2D layered structure, is the most promising electrocatalyst. This is attributed to its flexibility, which facilitates the exploration of various MoS₂ phases and properties, closely mirroring those of platinum, particularly its Gibbs energy (ΔG_{H* ̃} 0.08 eV), which makes MoS₂ an excellent electrocatalyst. However, its low electrical conductivity and inert basal planes limit its effectiveness for HER. This study utilized a facile hot-gun approach to successfully introduce sulfur vacancies, simultaneously incorporating oxygen from the air, which partially occupied these vacancies. This process resulted in the formation of an intermediate MoO_xS_y interlayer, yielding a highly effective electrocatalyst. Exposure to the hot gun for a short duration led to several changes, notably expanding the interlayer spacing and altering the atomic S:O ratio from approximately 75 % to 57 %, primarily affecting the MoS₂ structure. The optimal duration for hot-gun treatment was determined to be 30 s, enhancing electrochemical activity for HER, with an overpotential of 486 mV vs. RHE (briefly marked as V_RHE) at a current density of 10 mA·cm⁻² and Tafel slope of 224 mV·dec^-1. The improvement in basal active sites, attributable to the formation of defects from sulfur vacancies and partial passivation by oxygen at these sites, was identified as the key factor for this enhanced performance.