Bimetallic nickel-cobalt oxides: A comprehensive insight into Ni/Co ratio, intrinsic structure and electrochemical behaviors

Abstract

As a widely explored batty-type electrode materials, bimetallic nickel-cobalt oxides with different Ni/Co ratios were synthesized. The influence of Ni/Co ratios on the as-synthesized products is emphasized and systemically studied from the aspect of morphology and microstructure, phase and composition, electrochemical performance, activity as well as energy storage mechanism. The results demonstrated the dependence of phase and composition, morphology and microstructure on Ni/Co ratios. When nickel and cobalt nitrate coexist in the reactant, the as-prepared samples are composed of multiphases instead of a single-phase material. Ni/Co ratio of the reactant is not necessarily related to the proportion of nickel and cobalt of the product. Therefore, it is recommended that the author should clearly state the nickel/cobalt ratio in the product rather than in the reactant. Additionally, the capacity of all samples is mainly originated from pseudo-capacitive capacity, demonstrating a more capacitive behavior in nickel-cobalt oxides. Moreover, theoretical calculation verified that nickel/cobalt substitution could lower OH− adsorption energy and facilitate the electrochemical activity on the active site. This paper conducts a comprehensive understanding of the influence of component and microstructure on electrochemical energy storage behaviors of nickel-cobalt-based oxides, which has a certain value for the follow-up study of nickel-cobalt-based compounds.