Thedesign of active and low-cost electrocatalyst for hydrogenevolution reaction (HER) is the key to achieving a clean hydrogenenergy infrastructure. The most successful design principle of hydrogenelectrocatalyst is the activity volcano plot, which is based on Sabatierprinciple and has been used to understand the exceptional activityof noble metal and design of metal alloy catalysts. However, thisapplication of volcano plot in designing single-atom electrocatalysts(SAEs) on nitrogen doped graphene (TM/N4C catalysts) forHER has been less successful due to the nonmetallic nature of thesingle metal atom site. Herein, by performing ab initio moleculardynamics simulations and free energy calculations on a series of SAEssystems (TM/N4C with TM = 3d, 4d, or 5d metals), we findthat the strong charge-dipole interaction between the negativelycharged *H intermediate and the interfacial H2O moleculescould alter the transition path of the acidic Volmer reaction anddramatically raise its kinetic barrier, despite its favorable adsorptionfree energy. Such kinetic hindrance is also experimentally confirmedby electrochemical measurements. By combining the hydrogen adsorptionfree energy and the physics of competing interfacial interactions,we propose a unifying design principle for engineering the SAEs usedfor hydrogen energy conversion, which incorporates both thermodynamicand kinetic considerations and allows going beyond the activity volcanomodel.
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