Engineering atomic Fe–N–C with adjacent FeP nanoparticles in N,P-doped carbon for synergetic oxygen reduction and zinc–air battery

Abstract

Herein, a carbon-based catalyst co-doped with transition metals (FeP and Fe–N–C) and heteroatoms (N, P), i.e., FeP-900, was facilely synthesized via the direct pyrolysis of a novel conjugated microporous polymer (CMP), denoted as FeP-CMP, constituted by Fe–phthalocyanine and cyclotriphosphazene. FeP-CMP was obtained via the self-polymerization of hexa-(3,4-dicyanophenoxy)cyclotriphosphazene (DPCP) in the presence of FeCl₃. Strikingly, the inherently porous and rigid skeleton structure of CMP confined the growth of FeP effectively, ensuring the formation of ultrafine and high crystalline nanoparticles, which were well wrapped in the N,P-rich carbon matrix. Owing to the synergistic effect of Fe–N–C and FeP, FeP-900 with simultaneous high specific surface areas and hierarchical pore structure, exhibited excellent ORR performance, with superior long-term running stability and methanol immunity both in the alkaline and neutral media. For example, it showed an ORR performance comparable to that of commercial Pt/C (20%) with an onset potential (E_onset) of 1.03 V, a half-wave potential (E_1/2) of 0.823 V, and a limiting current density of 5.51 mA cm⁻², which could function as a substitute to Pt/C, benefitting from the richness and cheapness of FeP-900. Furthermore, the home-made zinc–air battery employing FeP-900 as the cathode catalyst presented a high specific capacity and energy density as well as long cycle sustainability, outperforming the battery catalyzed by 20% Pt/C. This study provides a new insight into the controlled synthesis of low-cost catalysts as alternatives for Pt/C in renewable energy-generation systems.