Active facet regulation of highly aligned molybdenum carbide porous octahedrons via crystal engineering for hydrogen evolution reaction

Active crystal facet regulation and crystal structure design of electrocatalysts are of vital importance for hydrogen evolution reaction (HER) from water splitting. Herein, a porous and highly aligned molybdenum carbide nano-octahedron (PHA-Mo2C) is synthesized by using CdMoO4 octahedron precursor. The presence of cadmium and prereduction process play a crucial role in the formation of porous and highly aligned structure and the regulation of active crystal facet to enhance the HER activity. The effects of Cd on the crystal structure transition, regulation of active crystal facet and inhibition of carbon deposition are detailly characterized and theoretically calculated. The obtained PHA-Mo2C as electrocatalysts exhibit efficient HER activity with a low onset potential of -25 mV vs. RHE and an overpotential of 93 mV at the current density of -10 mA/cm(2), as well as ultra-high long-term catalytic stability in acidic electrolyte. The calculated ratio value of (200)/(121) crystal facets, defined as active face index (AFI), is proposed to evaluate the HER activity of Mo2C. This work provides a new strategy for cadmium engineering synthesis of efficient molybdenum carbide electrocatalysts with active crystal facet regulation and high electrochemical active area.