Spiny Co₃O₄@Hollow Carbon Spheres─Polyacrylonitrile/Carbon Black Fiber-Based Bifunctional Air Electrodes

In the realm of zinc-air batteries, high bifunctional catalytic efficacy is intimately tied to the evaluation of catalysts. Consequently, the pursuit of proficient bifunctional catalysts that can efficiently catalyze both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remains a paramount objective in this research area. In this study, the spiny cobalt tetroxide (Co₃O₄) encapsulated hollow carbon spheres (HCSs) are constructed by anchoring Co₃O₄ onto HCS via hydrothermal or annealing treatment. The strategic interface design of the HCS encourages an abundance of sites while simultaneously facilitating the proliferation of spiny Co₃O₄, offering an expansive surface area and abundant active sites. The surface active Co³⁺ ions and the induction of surface oxygen vacancies in spiny Co₃O₄ encapsulated HCS endow it with outstanding bifunctional catalytic activity and stability. After spray-coating and subsequent annealing of the spiny Co₃O₄ encapsulated HCS catalyst on the flexible carbon-based polyacrylonitrile (PAN) nanofiber support, the spiny Co₃O₄ encapsulated HCS-PAN/carbon black (C) 800 air electrode is successfully integrated. Moreover, the optimized spiny Co₃O₄ encapsulated HCS-PAN/C 800 air electrode displays a decreased potential difference (ΔE) of 0.77 V for catalyzing the ORR and OER performance. This work introduces a promising candidate approach for exploring innovative bifunctional oxygen electrocatalysts, targeting enhanced efficiency in portable energy storage applications.