Thermodynamics guided ultrafast and continuous preparation of Mo2C nanocrystals for hydrogen evolution electrocatalysis

Existing nano-Mo 2 C preparation methods suffer from expensive raw materials, subtle operation demands and complex synthesis steps. Herein, both theoretical and experimental studies were performed to develop a more efficient and economical method for nano-Mo 2 C preparation. Reaction thermodynamics of gas-vapor system of CH 4 -MoO 3 -N 2 indicates that high-proportion inert gas significantly increases the required carbonization potential (CO/CO 2 ) for Mo 2 C formation, but surplus carbon produced from methane decomposition can trigger water gas producing reaction and Boudouard reaction to help meet the requirement. Nano-Mo 2 C was then synthesized by mixing N 2 -carried MoO 3 vapor with CH 4 under varying conditions including temperature, gas flowrate and vapor concentration. It is found that MoO 3 vapor experienced conversions to monoclinic MoO 2 to cubic Mo to hexagonal Mo 2 C, and all these stages could be finished in as short as about 6 s at 1100 °C with initial molar ratio of CH 4 to MoO 3 over 3.5. The final products were present as porous plate-like single crystals or chain-like polycrystals, which are determined by initial vapor concentration and gas flowrate. Furtherly, electrocatalytic properties of Mo 2 C nanocrystals for hydrogen evolution reaction were measured, and the sample with the largest specific surface area and cleaner surface showed competitive performance over reported nano-Mo 2 C.