Threshold carbonization exceptionally upgrading intrinsic activity of molybdenum carbide for alkaline hydrogen...

Developing high-activity non-noble metal catalyst to replace high-cost Pt-based catalyst to catalyze hydrogen evolution reaction (HER) is desirable but challenging for industry-level hydrogen production from water splitting. Molybdenum carbide (Mo₂C) possesses Pt-like d-band structure, however, its HER performance is far away from that of Pt-based catalyst. In this work, a threshold carbonization strategy is developed to substantially upgrade the intrinsic activity of Mo₂C catalyst for electrochemical HER. The prepared Mo₂C-700 catalyst exhibits overpotential of as low as 90 mV for achieving current density of 10 mA/cm² in alkaline electrolyte and excellent catalytic durability, being close to Pt-based catalyst and outperforming most reported Mo₂C-based catalysts. Mechanism studies demonstrate that threshold carbonization reaction of MoO₃ with H₂/CH₄ at 700 °C substantially inhibits the formation of carbon deposits and leads to more exposed Mo sites and hydroxyl groups on the surface of Mo₂C-700 catalyst, thus endowing the Mo₂C-700 catalyst with superhydrophilic and superaerophobic surface to facilitate water adsorption and H₂ bubbles release. Density functional theory calculations reveal that the less carbon deposits on Mo₂C catalyst surface upgrades the Mo d-band center toward Fermi level, substantially enhances the capacity of water adsorption, decreases the energy barrier of water dissociation reaction, and furthermore, results in near-zero hydrogen adsorption Gibbs free energies on Mo₂C catalyst, thus endowing Mo₂C-700 exceptional activity for alkaline HER.