Phase‐Engineering of 1T/2H Molybdenum Disulfide by Using Ionic Liquid for Enhanced Electrocatalytic Hydrogen Evolution

Abstract Two‐dimensional (2D) molybdenum disulfide (MoS 2 ) has been regarded as an attractive non‐precious‐metal electrocatalyst for the hydrogen evolution reaction (HER). Engineering the crystal phase of MoS 2 to activate the basal planes/edges and simultaneously improve the electronic conductivity is currently an effective strategy for enhancing its HER activity. Herein, we report a facile and efficient hydrothermal route to prepare 1T/2H‐MoS 2 catalysts using ionic liquid (N‐butyl pyridinium bromide, [BPy]Br) as a structure‐directing agent, where the large steric hindrance of [BPy]Br and the mutual π‐stacking interaction induce the phase transition of MoS 2 from 2H to the 1T phase. By adding a suitable amount of [BPy]Br in the reaction system, the portion of the 1T phase in 1T/2H‐MoS 2 was increased, which can expose more active sites on its basal planes/edges as well as facilitate charge transfer for the HER. Consequently, 1T/2H‐MoS 2 with the 1T portion of 91.9 % exhibits a significantly enhanced HER activity compared to that of the MoS 2 synthesized without the aid of [BPy]Br, in terms of a lower Tafel slope of 59 mV dec −1 . This synthesis strategy provides valuable guidance for designing the phase structure of MoS 2 ‐based electrocatalysts to achieve high HER efficiency.