Metal-organic framework-guided growth of Mo₂C embedded in mesoporous carbon as a high-performance and stable electrocatalyst for the hydrogen evolution reaction

Large-scale production of H₂ by electrochemical water splitting is discerned as one of the most economical and viable approaches and designing Pt-less electrocatalysts remains at the forefront of this technology development. Herein, in situ transformation of metal-organic frameworks (MOF), impregnated with a molybdenum precursor, into a porous and rigid carbon support and molybdenum carbide (Mo₂C) was demonstrated to fabricate highly active and stable β-Mo₂C/C heterostructure for electrocatalytic H₂ evolution. The two-step synthesis approach involved the impregnation of molybdenum source into frameworks of MOF (namely MIL-53(Al)) followed by nucleation and growth of Mo₂C nanocrystals into confined porous texture through carburization. Characterization revealed the formation of mesoporous carbon embodied with crystalline nanoparticles of β-Mo₂C (between 5 and 10 nm). A probable mechanism for the formation of Mo₂C/C nanocomposite is proposed. The propensity of the catalyst was tested towards the electrocatalytic H₂ evolution reaction (HER) under alkaline aqueous media (1 M KOH). The electrocatalyst showed a remarkable HER activity as compared to the benchmark electrocatalyst Pt/C and Mo₂C/XC72 black catalysts at 10 mA cm^-2 and stability for 20 h at the same current density. Electrochemical impedance spectroscopy results of Mo₂C/C were construed by two time constants, porosity and charge transfer, and the HER reaction followed the Volmer-Heyrovsky mechanism.