Cubic imidazolate frameworks-derived CoFe alloy nanoparticles-embedded N-doped graphitic carbon for discharging reaction of Zn-air battery

Abstract

The construction of transition metal-based catalysts with high activity and stability has been widely regarded as a promising method to replace the precious metal Pt for oxygen reduction reaction (ORR). Herein, we synthesized CoFe alloy nanoparticle-embedded N-doped graphitic carbon (CoFe/NC) nanostructures as ORR electrocatalysts. The ZIF-67 (zeolitic imidazolate framework, ZIF) nanocubes were first synthesized, followed by an introduction of Fe2+ ions to form CoFe-ZIF precursors via a simple ion-exchange route. Subsequently, the CoFe/NC composites were synthesized through a facile pyrolysis strategy. The ORR activity and the contents of cobalt and iron could be effectively adjusted by controlling the solution concentration of Fe2+ ions used for the ion exchange and the pyrolysis temperature. The CoFe/NC-0.2-900 composite (synthesized with 0.2 mmol of FeSO4·7H2O at a pyrolysis temperature of 900°C) exhibited ORR activity that was superior to the other samples owing to a synergistic effect of the bimetal, especially considering the extremely high limiting current density of 6.4 mA cm−2 compared with that of Pt/C (5.1 mA cm−2). Rechargeable Zn-air batteries were assembled employing CoFe/NC-0.2-900 and NiFeP/NF (NiFeP supported on nickel foam (NF)) as the catalysts for the discharging and charging processes, respectively, The above materials achieved reduced discharging and charging platforms, high power density, and prolonged cycling stability compared with conventional Pt/C+RuO2/C catalysts.