Role of Oxygen Vacancy in Copper-Cobalt Spinel Nanostructures for Electrochemical Energy-Storage

Abstract

The incorporation of oxygen vacancies in metal oxides has been reported to remarkably increase their electrochemical performance in water splitting, photoluminescence, and electrochemical energy-storage. The oxygen vacancies are originated by removal of neutral oxygen atoms from the metal oxides, leaving excess electrons in the vacancies. The excess electrons offer high electrical conductivity, huge number of electroactive sites at or within the surface of metal oxides that could facilitate a adsorption/intercalation of anions (e.g., OH-) at or within the electrode surface and diffusion of ions and electrons within the electrode/electrolyte interface for efficient energy-storage. It has been reported that the spinels with the proper oxygen vacancies could exhibit higher capacitance values compared with that for perfect-crystal. The agglomerated nanostructures of the spinels, Cu2Co2O4 are often prepared by conventional solid-phase or solvothermal/hydrothermal methods, which require non-conductive binders (e.g., Nafion and polyvinylidene fluoride (PVDF)) to achieve strong and stable adhesion onto a substrate. In addition, the conventional synthetic method usually requires high-temperature sintering with complicated procedures, which creates morphological deformation and severe aggregation, decreasing the content of electroactive oxygen vacancies. Therefore, the development of a synthetic procedure is one of the most important tasks needed to get effective nanostructures of Cu2Co2O4 with controllable surface morphology, oxygen vacancies/electroactive sites, and electrical conductivity for the application in capacitors as effective electrode materials. In the present report, we directly grew a series of CuxCo3 - xO4 nanostructures with controllable surface morphology, oxygen vacancies/electroactive sites and electrical conductivity on a stainless steel substrate by a simple and straightforward electrochemical deposition process and applied them as electrodes for electrochemical charge-storage.