Enhancing the hydrogen evolution reaction on MoS2 flakes by cold plasma treatment

The edge sites of molybdenum disulfide (MoS2) have high catalytic activity for the hydrogen evolution reaction (HER). However, the ratio of edge sites to those on the surface of MoS2 is generally low, which limits the catalytic activity. Thus, efficient and rapid creation of catalytically active sites on the inert MoS2 basal plane is important. Cold plasma treatment can achieve such a result. Here we report the use of a cold plasma method to introduce defects and local phase transformation of the inert 2H phase of MoS2. After cold plasma treatment with argon or oxygen, the previously inert MoS2 basal plane shows outstanding performance. The overpotential, at a high current density of 300 mA cm(-2), was reduced by 30% (18%) from 373 mV to 261 mV (307 mV) after argon (oxygen) cold plasma treatment. Our results clearly show that argon and oxygen cold plasma treatments have the effect of activating the inert 2H phase of MoS2. This is a promising method for the creation of active sites on two-dimensional materials.