Continuously tuning the hydrogen evolution activity of MoS2 through sodium ions insertion

Abstract Though enormous attention has been paid to MoS2 in the field of electrocatalytic hydrogen evolution reaction (HER), the conventional 2H MoS2 is hardly regarded as an alternative to noble Pt due to the limited number of active sites and semiconducting character. Herein, sodium ions were intentionally introduced into the MoS2 to regulate its structure and thus HER activity. We found that the HER activity of MoS2 would gradually increase at the intercalation stage and further increase at the early stage of conversion reaction. Based on various characterization techniques, the possible structure-performance relationship was established. The first increase in activity was ascribed to interlayer expansion and phase transformation, and the second increase in activity was mainly ascribed to increase of active sites due to the fragmentation of MoS2 after triggering conversion reaction. Even though deep discharging MoS2 to 0.01 V (vs. Na+/Na) would slightly impair HER activity, such an activity was still much better than that of pristine MoS2, which might be originated from the doping of S into molybdenum oxide according to the DFT calculation.