Hydrogel-Derived Co₃ZnC/Co Nanoparticles with Heterojunctions Supported on N-Doped Porous Carbon and Carbon Nanotubes for the Highly Efficient Oxygen Reduction Reaction in Zn–Air Batteries

It is crucial for metal–air batteries and fuel cells to design non-precious-metal catalysts instead of platinum-based materials to boost the sluggish oxygen reduction reaction (ORR). Herein, Co3ZnC/Co nanoparticles with heterojunctions supported on N-doped porous carbon and carbon nanotubes (CNTs) are fabricated by pyrolyzing the hydrogel prepared from melamine and citric acid chelated with Co2+/Zn2+ ions. This hybrid shows strong ORR catalytic activity as its half-wave potential reaches 0.88 V (vs reversible hydrogen electrode (RHE)) in 0.1 M KOH and Zn–air batteries with the catalyst have higher discharge plateaus and capacity than those employing Pt/C. The hybrid mixed with RuO2 can also be used as an efficient bifunctional catalyst for rechargeable Zn–air batteries. The excellent performance is primarily derived from the Co3ZnC/Co heterojunctions, the electron transfer of which boosts the ORR catalysis. Moreover, the suitable ratio of Co/Zn in precursors results in the epitaxial growth of hollow CNTs and abundant mesopores, hence promoting the adsorption of oxygen and the transport of ORR-related species.