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[Display omitted] • Both ion-sharing interface and directional doping are employed to construct a heterostructured HER electro-catalyst. • Electronic structure and coordination chemistry of Mo and Co centers are tailored to optimize adsorption/desorption of H ads and OH– intermediates for lowering the energy barriers. • Mo center with more coordination vacancies are main active sites responsible for rate-limiting step in the Volmer-Heyrovsky regime. • This catalyst presents an extremely low overpotential of 37 mV at 10 mA cm−2 in alkaline media, and excellent performance for overall water splitting. Interfacing and doping can effectively harmonize the electronic and coordination states of active centers in the electrocatalysts. Herein, we prepare heterostructured N-MoS 2 /Se-CoS 2 electrocatalyst with ion-sharing interfaces and directional doping to activate inert basal phases for hydrogen evolution reaction (HER). Based on experimental and theoretical results, their synergistic effects on electron redistribution, electronic structure and coordination chemistry are investigated; furthermore, roles of each component and bridged Mo-S-Co sites at the phase interfaces as active sites in optimizing the adsorption/desorption of essential reaction intermediates H* and OH–, as well as the free energies of unit reaction steps in the HER, are elucidated in depth. The N-MoS 2 /Se-CoS 2 catalyst needs only 37 mV to give current density of 10 mA cm−2 with a low Tafel slope of 49.4 mV dec−1; more importantly, the catalyst delivers a long-term durability for HER in alkaline condition and comparable performance with commercial RuO 2|| Pt/C system in a two-electrode assembled electrolyzer. This work provides more insights into the design and preparation of high-performance heterostructured electrocatalysts. [ABSTRACT FROM AUTHOR]