Self-activated oxophilic surface of porous molybdenum carbide nanosheets promotes hydrogen evolution activity in alkaline environment

Molybdenum carbides are promising alternatives to Pt-based catalysts for the hydrogen evolution reaction (HER) due to their similar d-band electronic configuration. Notably, Mo_xC exhibits superior HER kinetics in alkaline media compared to acidic conditions, contrasting with Pt-based catalysts. Herein, we present 3D porous β-Mo₂C nanosheets, achieving an overpotential of 111 mV at 10 mA cm^-2 in 1 M KOH, significantly lower than in acidic environments. Simulations on pristine Mo₂C surface reveal that water dissociation poses a higher energy barrier in alkaline media, suggesting that crystal structure alone does not dictate kinetics. Operando attenuated total reflection surface-enhanced infrared absorption spectroscopy shows that Mo₂C activates interfacial water, generating liquid-like and free water, and facilitates hydroxyl species adsorption, reducing activation energy to below 38.43 ± 0.19 kJ/mol. Our findings on the self-activation effect offer insights into the HER mechanism of Mo-based electrocatalysts and guide the design of highly active HER catalysts.