The X-ray photoelectron spectroscopy (XPS) spectra indicate the presence of both metallic and surface oxide species in all sampled (Fig. and). In the Ru 3p3/2 spectra, the metallic Ru and Ru (δ + ) peaks were observed at around 461.5 eV and 463.1 eV, respectively (Fig. ) . The Ru(δ + ) peaks might originate from either RuOx, or Ru-SAs, or both. The differentiation of RuOx, and Ru-SAs is difficult due to small quantity of Ru-SAs that are present (Fig. ). The binding energy of metallic Ru in Ru/pN-C is increased by 0.3 eV from that in Ru/C, indicating a charge transfer from Ru to pN-C. In the Pt 4f7/2 spectra, metallic Pt and surface PtOx were identified in Pt/C (Fig. ). For Pt/pN-C, additional peaks attributed to Pt SAs were necessary to fit the XPS spectra (Fig. ). On the other hand, comparison of the Pt 4f7/2 spectra of Pt/C and Pt/pN-C indicates that there is no apparent charge transfer between Pt and pN-C. X-ray adsorption near-edge structure (XANES) spectra of Ru K-edge showed an increased edge energy from Ru/C to Ru/pN-C (Fig. ), consistent with the XPS data that indicated the charge transfer from Ru to pN-C. The whiteline energy of Pt L-edge increased slightly from Pt/C to Pt/pN-C, which can be attributed to the existence of Pt-SA in Pt/pN-C (Fig. ). All samples have higher oxidation states compared to their foil counterparts due to the surface oxidation layers, which are expected to be removed under HOR-relevant potentials. The existence of the oxide layers was also revealed by the Fourier transforms (FTs) of the extended X-ray adsorption fine structure (EXAFS) spectra of Ru/C and Pt/C, where their first shell corresponds to Ru-O path and Pt-O path, respectively. Similarly, the first shell for Ru/pN-C and Pt/pN-C can be ascribed to Ru-O/N, and Pt-O/N path, respectively (Fig. , F, Supplementary Figure and Supplementary Table , 3).