We attempted to measure hydrogen binding energies (HBEs) of the catalysts by determining the potentials for underpotential hydrogen deposition (Hupd) through cyclic voltammetry (CV). The characteristic Hupd peak of Pt/pN-C was negatively shifted to a lower potential, indicating a weaker HBEapp (i.e., weaker HBE or stronger water adsorption) than Pt/C. However, the Hupd peak was absent in Ru/pN-C samples, probably it overlapped with the Ru oxidation (Supplementary Figure ). We then applied H2 chemisorption to probe the HBEs of the catalysts (Supplementary Figure ). The H2 volumetric isotherms were fitted using a dual-Langmuir model, assuming that the adsorption consists of a strong adsorption (chemisorption) and a weak adsorption (physisorption) (See Methods). The fitting results are listed in Supplementary Table . Fig. summarized the adsorption constant of chemisorption k1 values of the four samples. Ru/C has the highest k1, consistent with previous reports that Ru has an overly strong HBE which leads to non-optimized HOR/HER activity . Ru/pN-C has a much lower k1 than Ru/C, and hence a much lower HBE. This result can be understood by the charge transfer from Ru to pN-C, which lowered the d band center of Ru and decreased the binding energies of adsorbates. Both Pt/C and Pt/pN-C have modest k1, consistent with the lack of charge transfer between Pt and pN-C according to XPS analysis. .