Two-Dimensional Lamellar Mo2C for Electrochemical Hydrogen Production: Insights into the Origin of Hydrogen Evolution Reaction Activity in Acidic and Alkaline Electrolytes.

Developing high surface area Mo2C with certain crystal plane exposed is an efficient strategy but is an urgent challenge to optimize the hydrogen evolution reaction (HER) catalytic performances. In addition, the effects of certain crystal faces on catalytic performance have been limitedly understood. Toward this end, the (1 0 0) plane oriented two-dimensional lamellar Mo2C transformed from carbon fibers is synthesized successfully in a molten salt system. Subsequently, the electrocatalytic properties toward HER show that (1 0 0) plane oriented Mo2C functions well in both acidic and basic media. The density functional theory calculations show that the most stable Mo/C termination of the (1 0 0) plane contains multiple catalytically active centers. These close-to-zero Δ GH* values verify its better HER performance. Besides, the correlation between hydrogen adsorption behavior and the water dissociation process as well as their corresponding roles in the overall acid and alkaline HER rates have been discussed in depth. A simple mechanistic analysis is put forward to explain the favorable HER performance of the lamellar structure β-Mo2C in alkaline other than acid electrolytes. The molten salt method may provide a new way for developing electrocatalysts with oriented crystal faces.