Fig. 1: Structural characterization of the RhRu₃O_x.

a Schematic diagram of MRu₃O_x synthesis process. b XRD patterns of RhRu₃O_x, Hom-RuO₂ and Com-RuO₂ (from up to bottom). c, d HAADF-STEM images of RhRu₃O_x. The inserted histogram in (c) is the particle size distribution statistics of the corresponding RhRu₃O_x NPs. e The fast Fourier transform pattern corresponds to the (d). f HAADF image and corresponding EDS elemental mapping images of RhRu₃O_x. g, h Operando X-ray absorption near edge structure (XANES) (g) and extended X-ray absorption fine structure (EXAFS) (h) spectra of RhRu₃O_x at the Ru K-edge. The black rectangle inserted in (g) shows the magnified operando spectrum. i Ru oxidation states as a function of the Q₁ edge positions. The Q₁ edge position is defined as the energy at normalized absorption of 0.5. j Energy shift of the Q₁ edge positions and Ru oxidation states shift in RhRu₃O_x and Hom-RuO₂ at different potentials compared with the corresponding sample at 1.24 V_RHE.