An Interpenetrating Porous Organic Polymer as a Precursor for FeP/Fe₂ P-Embedded Porous Carbon toward a pH-Universal ORR Catalyst

Interpenetrating porous organic polymers (PNFc-POP) inspired by the structure of DNA were synthesized through a two-stage polymerization method under catalyst-free conditions. A ferrocene-rich hyper-crosslinked polymer (Fc-melamine) was interwoven with cyclotriphosphazene-based conjugated porous polymer (PN-CMP) to obtain an interconnected polymer network (PNFc-POP). The sequential interpenetrating polymer network contained a diverse range of heteroatoms (P, N, O and Fe) and exhibited a large BET surface area. Simple pyrolysis of the dual polymer interweaved skeletons at 900 °C afforded nanocrystalline FeP/Fe₂ P-embedded N and P codoped porous carbon composites. The optimal catalyst obtained by the pyrolysis of PNFc-POP at 900 °C (PNFc-900) exhibited hierarchical porosity and large BET surface areas. It also exhibited excellent oxygen reduction reaction catalytic activities over the entire pH range. The onset potential (E_onset =1.01 V) and half-wave potential (E_1/2 =0.86 V) of PNFc-900 exceeded those of commercial Pt/C (E_onset =0.99 V and E_1/2 =0.84 V) in alkaline conditions. The obtained catalysts with a four-electron transfer pathway for the reduction of oxygen also displayed excellent long-term stability and methanol tolerance.