Regulating d-orbital electronic character and HER free energy of VN electrocatalyst by anchoring single atom

Too strong or too weak orbital electron-coupling with active adsorbents basically results in unsatisfied free energies, and consequently limiting the HER kinetics and activity. Herein, Co-VN catalyst is fabricated to highlight that atomically implanted Co into VN can regulate its d orbital electronic character and corresponding free energy for further improving its alkaline HER performances. Experimental results and density functional theory calculations reveal that atomically implanted Co into VN could induce local charge redispersion to further downshift the d band center position of V-3d in Co-VN. The lowered d band center of the V-3d could not only decrease the d orbital electron-coupling between V site and O atom of OH intermediate to boost desorption of OH species and H2O dissociation kinetics, but also simultaneously balance the hydrogen adsorption free energy to facilitate the desorption of as-formed H2, both of which synergistically increase the Volmer and Heyrovsky kinetics and overall HER activity of Co-VN. Moreover, the structural stability of Co-VN after long-term HER is also investigated by transmission electron microscopy and X-ray photoelectron spectroscopy to uncover its activity-stability trade-off riddle. As a result, Co-VN catalyst expectantly displays a low overpotential of 59 mV at −10 mA cm−2, a small Tafel slope of 46.3 mV dec−1, and a favorable long-term stability. The proposed regulation strategy of orbital electronic structure and free energy could be extended to design other high-performance catalysts.