The natural nitrogenase is still the most efficient catalyst on earth to reduce the ambient N2 into ammonia. The central part of the molecular machine is powered by a metallic core, usually a molybdenum atom, whose co-ordination valence state remains an enigma for us to unveil and mimic. Unlike the flexible bio-enzyme, inorganic heterogeneous catalysts are usually rigid in the coordination structure, making their valence states invariable, except some localized defects. In this study, we successfully synthesized a two-dimensional MoS2/Mo2C elec-trocatalyst, which contains a heterostructured interface with efficient charge and magnetism separation, exhibiting a gradual and broad valence state transition from Mo4+ to Mo2+. Density functional theory (DFT) calculations reveal that Mo3+ sites at the interface have a strong N2 adsorption energy of -0.75 eV with the side -on configuration, and an activated hydrogenation of *NH2 species. This bionic electrocatalyst displays a splendid performance in nitrogen reduction reaction with a Faradic efficiency of 42 % at-0.1 V vs RHE.