β-Mo₂C Nanoparticles Produced by Carburization of Molybdenum Oxides with Carbon Black under Microwave Irradiation for Electrocatalytic Hydrogen Evolution Reaction

The synthesis of electrochemically active -Mo 2 C nanoparticles for hydrogen production was achieved by a fast and energy-efficient microwave-assisted carburization process from molybdenum oxides and carbon black. With the use of microwavebased production methods, we aim to reduce the long-time high-temperature treatments and the use of hazardous gases often seen in traditional molybdenum carbide synthesis processes. In our process, carbon black not only serves as a carbon source but also as a susceptor (microwave absorber) and conductive substrate. The irradiation power, reaction time, and Mo:C ratio were optimized to achieve the highest electrocatalytic performance toward hydrogen production in an acidic electrolyte. A complete transformation of MoO 3 to -Mo 2 C nanoparticles and an additional graphitization of the carbon black matrix were achieved at 1000 W, 600 s, and Mo:C ratio above 1:7.5. Under these conditions, the optimized composite exhibited an excellent HER performance ( 10 = 156 mV, Tafel slope of 53 mVdec -1 ) and large turnover frequency per active site (3.09 H 2 s -1 at an overpotential of 200 mV), making it among the most efficient non-noble-metal catalysts. The excellent activity was achieved thanks to the abundance of -Mo 2 C nanoparticles, the intimate nanoparticle-substrate interface, and enhanced electron transport toward the carbon black matrix. We also investigated the flexibility of the synthesis method by adding additional Fe or V as secondary transition metals, as well as the effect of the substrate.