Organic-Inorganic-Hybrid-Derived Molybdenum Carbide Nanoladders: Impacts of Surface Oxidation for Hydrogen Evolution Reaction

Molybdenum carbides are widely adopted as efficient noble-metal-free electrocatalysts for hydrogen evolution reaction (HER). Their surface oxidation is inevitable under air but is often ignored, which can be detrimental for the accurate understanding and precise design of stable carbide catalysts. Herein, molybdenum carbide nanoladders are derived via pyrolyzing MoOx/amine hybrid precursors, and two types of impact of surface oxidation on their HER performance are obvious: (1) the downshift of d-band center in Mo, and (2) the introduced steric hindrance from surface oxygen. Consequently, the negative hydrogen-binding free energy (Delta G(H*), -0.52 eV) of pristine MoC gradually increases to positive values with surface oxidation, indicating the effectively weakened strength of Mo-H. With moderate surface oxygen incorporation, a Delta G(H*) of almost 0 eV is in accordance with the efficiently promoted HER performance via a good balance of Volmer and Heyrovsky/Tafel steps in kinetics. The optimal catalyst supported on a Ti plate (1 cm(2)) gives a high hydrogen production rate of 0.35 mL min(-1) at 300 mV with high stability over the self-made water-splitting configuration. This work does not only make us reacquaint the surface oxidation of carbides on electrocatalysis but also paves the way for developing efficient and stable catalysts via surface engineering.