Nanocrystalline electrocatalytically active materials of chemical composition Ru 1-x Zn x O 2 (0< x < 0.3) were synthesized by freeze-drying technique. The diffraction patterns of the prepared samples corresponded to single-phase rutile type oxides. Local structure of the Ru 1-x Zn x O 2 based on refinement of Ru K and Zn K edge EXAFS functions shows clustering of the Zn ions in the blocks with ilmenite structure intergrowing with Ru-rich rutile blocks. Ru 1-x Zn x O 2 oxides are selective catalysts for anodic oxygen evolution. The selectivity toward oxygen evolution in the presence of chlorides is affected by the actual Zn content and can be ascribed to structural hindrance of the formation of the surface peroxo group based active sites for chlorine evolution. The selectivity toward oxygen evolution in presence of chlorides is accompanied by the drop of the total activity, which gets more pronounced with increasing Zn content.

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Chemical composition, crystal structure, as well as short-range atomic arrangement of nanocrystalline Ru1−x Ni x O2−δ oxides with x ranging between 0 and 0.3 were studied using energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS). The prepared materials form single-phase nanocrystals with rutile structure. Regardless of the chemical composition, the surface of Ru1−x Ni x O2−δ oxides is Ni-enriched with respect to overall chemical composition. According to both XPS and XANES, the oxidation state of Ru remains +4 in the studied materials. Ni ions are present in both divalent and trivalent states with the fraction of trivalent ions decreasing with increasing Ni content. The refinement of local structure using EXAFS data based on Ru−K and Ni−K edge absorption spectra shows that Ru preserves local arrangement characteristic for ruthenium dioxide. The incorporated Ni shows a tendency to form clusters within a rutile structure for low Ni concentration. At high Ni content, the architecture of the Ni-rich defects resembles architecture of shear planes in oxygen-deficient rutile. These Ni-rich regions likely manifest themselves on the surface as line or plane defects, which are the most likely structural features active in the electrocatalytic processes.

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