Controllable desulfurization in single layer MoS₂ by cationic current treatment in hydrogen evolution reaction

The sulfur vacancy (Sv) generation in the MoS₂ basal plane is an efficient strategy for improving the hydrogen evolution reaction (HER). By using cationic current treatment, the Sv density can be controlled by modifying the setting voltage ranges and treatment time. The Sv generation mechanism was clearly defined using Raman mapping. From the Raman mapping characterizations, for the first time, we experimentally found that Sv tends to be generated next to existing Sv by appearing around cracked/damaged areas or group formations. The S: Mo atomic ratio reduced from 2.02:1 to 1.86:1 after treatment. As a result, the current density at −0.3 V vs RHE sharply increases up to 27-fold in comparison to that with untreated MoS₂, and the overpotential of treated MoS₂ reaches 222 mV at 10 mA/cm² with a Tafel slope of 96 mV/decade. Hence, the controllable Sv generation in monolayer MoS2 using a cationic current method can be considered as a fast, simple, and effective process to improve HER performance in large-scale production.