▎ 摘　　要

The electrochemical hydrogen evolution reaction (HER) is regarded as a practical means for the production of high-purity hydrogen from abundant water. Understanding the HER mechanism is therefore crucial to the design of high performance HER catalysts. Although approaches based on activity descriptors for the acidic HER have proven to be successful in revealing the origin of activity, and in directing the synthesis of electrocatalysts, the alkaline HER mechanisms and the activity descriptors remain largely unexplained. This impedes the overall design of electrocatalysts. Here, we systematically investigate the HER mechanism and the underlying origin of catalytic activity for the HER using Pt and Ru dimer structures as model catalysts. For the acidic HER, we found that PtRu dimer on nitrogen-doped graphene displayed a hydrogen adsorption free energy of -0.07 eV with higher atomic utilization. For the alkaline HER, we propose the dissociative chemisorption energy of water (Delta E-diss) as a singular activity descriptor following the analysis of several potential activity descriptors. Delta E-diss is proposed both because it has the capacity to identify the smallest theoretical thermodynamic overpotential and because it scales linearly with the kinetic barrier. We present new insight into the mechanism route from the electronic structure (d-band center) via Delta E-diss to alkaline HER activity. We conclude that this work will be of immediate benefit to guide rational development of electrocatalysts via electronic structural engineering to regulate Delta E-diss for the alkaline HER.