The physicochemical/electrochemical properties of binary Ni-Co oxides

The voltammetric behavior of Ni-Co oxides fabricated by thermal decomposition as well as their activities for the oxygen evolution reaction (OER) are examined by cyclic voltammetry (CV) and log i-E curves (Tafel study) in alkaline media. The reversibility of Co(IV)/Co (III) and Tafel slope of the OER are found to depend on the crystalline structure and composition/surface morphology of these binary oxides performed by X-ray diffraction, energy-dispersive spectrometry and scanning electron microscopy, respectively. A combination of the electrochemical and textural investigations reveals that NiO, NiCo2O4 and Co3O4 predominate the electrochemical behavior of Ni-Co oxides with Ni composition (i) above 80 m/o, (ii) between 60/70 and 20 m/o and (iii) below 20 m/o, respectively. The intimate mixing of NiO and NiCo2O4 with ca. 50 m/o Ni, rendering an increase in the nonstoichiometric sites, exerts a synergistic effect for the OER.