Controllable Solid-Phase Fabrication of an Fe₂O₃/Fe₅C₂/Fe-N-C Electrocatalyst toward Optimizing the Oxygen Reduction Reaction in Zinc-Air Batteries

Preparing advanced electrocatalysts via solid-phase reactions encounters the challenge of low controllability for multiconstituent hybridization and microstructure modulation. Herein, a hydrothermal-mimicking solid-phase system is established to fabricate novel Fe₂O₃/Fe₅C₂/Fe-N-C composites consisting of Fe₂O₃/Fe₅C₂ nanoparticles and Fe,N-doped carbon species with varying morphologies. The evolution mechanism featuring a competitive growth of different carbon sources in a closed hypoxic space is elucidated for a series of Fe₂O₃/Fe₅C₂/Fe-N-C composites. The size and dispersity of Fe₂O₃/Fe₅C₂ nanoparticles, the graphitization degree of the carbonaceous matrix, and their diverse hybridization states lead to disparate electrocatalytic behaviors for the oxygen reduction reaction (ORR). Among them, microspherical Fe₂O₃/Fe₅C₂/Fe-N-C-3 exhibits an optimal ORR performance and the as-assembled zinc-air battery shows all-round superiority to the Pt/C counterpart. This work presents a mild solid-phase fabrication technique for obtaining a variety of nanocomposites with effective control over composition hybridization and microstructural modulation, which is significantly important for the design and optimization of advanced electrocatalysts.