Characterization of Bulk and Surface Composition of CoxNi1-xOy Mixed Oxides for Electrocatalysis

Films of general composition CoxNi1-xOy with x = 0, 11.1, 22.2, 33.3, 44.4, 55.6, 66.7, 77.8, 88.9, and 100 mol %, prepared by thermal decomposition of 2-propanol solutions of Ni and Co nitrates on Ni supports, have been characterized by X-ray diffraction (XRD), infrared spectroscopy (IRS), and X-ray photoelectron spectroscopy (XPS). These techniques have provided the surface chemical composition, the crystalline structure, and the oxidation state of Co and Ni in the bulk as well as on the surface. The results have revealed, in addition to previous work where NiO and NixCo2-xO4 solid solutions were found to be the predominant crystalline phases, that Ni and Co hydroxides interact in the surface layer of nanosized crystallites of the oxide phase. The interaction in the hydroxylated surface has a redox character and results in two oxidation states (+2 and +3) for both Ni and Co ions. This work has shown that Co hydroxide fragments are localized in the periphery of Ni hydroxide domains. The redox interaction between the hydroxides prevents Ni ions from being oxidized to higher valency states in anodic electrocatalytic processes, which results in improved anodic corrosion stability of Ni + Co mixed oxides.