Ferrocene-based porous organic polymer derived N-doped porous carbon/Fe3C nanocrystal hybrids towards high-efficiency ORR for Zn–air batteries

Exploring low-cost and high-powered nonprecious metal oxygen reduction catalysts (ORR) in fuel cells and metal–air batteries is critical for the commercialization of these sustainable energy devices. In this study, novel iron-based catalysts consisting of Fe3C nanoparticles encapsulated in a micro/mesoporous Fe–N-doped graphitic carbon matrix was prepared via a cost-effective method using cheap and easily available ferrocene-based porous organic polymers (POPs) as the sole precursors. The POP precursors with tertiary methyl-linkage, namely Fc-Car (spherical) and Fc-Py (rod-like), were facilely prepared via the polycondensation of 1,1-ferrocenedicarboxaldehyde (Fc) with carbazole (Car) or pyrrole (Py), respectively. The optimal catalyst (FC-950) obtained via the carbonization of Fc-Car at 950 °C presents outstanding ORR activity and stability in both alkaline and neutral media. It displays a half-wave potential (E1/2) of 0.841 V (vs. RHE) and limiting current density (5.29 mA cm−2) closely comparable to the state-of-the-art Pt/C (0.825 V, 5.62 mA cm−2) in alkaline media. A self-assembled Zn–air battery validates FC-950 also features great application potential for real devices with an open-circuit of 1.452 V and a relative high power density of 176.8 mW cm−2.