Hollow-structured conjugated porous polymer derived Iron/Nitrogen-codoped hierarchical porous carbons as highly efficient electrocatalysts

Iron and nitrogen (Fe/N) co-doped porous carbons have already shown great potential as electrocatalysts for oxygen reduction reaction in alkaline media. However, it still remains a great challenge to finely integrate a hierarchical porous structure and Fe/N co-doping effect into one material at the same time. In this work, a rational design toward Fe/N-codoped hierarchical porous carbon spheres was developed by the formation of an iron-porphyrin-containing conjugated microporous polymer sphere with hollow structure (HCMP) through a silica sphere template directed condensation of pyrrole and 1,4-phthalaldehyde, then etched with NaOH, and treated with FeCl₂. The resulting HCMP-Fe polymer was readily converted to a series of Fe/N co-doped hierarchical porous carbons (HPC-Fe/N-X, X = 700–900) upon pyrolysis at different temperatures and etching treatment. These porous carbons exhibit the high specific surface areas up to 518 m² g⁻¹ and the contents of N and Fe up to 3.28 at.% and 0.85 wt.%, respectively. Benefiting from the high surface area, Fe/N co-doping character, HPC-Fe/N-700 exhibited excellent electrochemical catalytic performance for oxygen reduction reaction under alkaline condition (0.1 M KOH) with a low half-wave potential (0.84 V), a dominant four-electron transfer mechanism (n = 3.89 at 0.65 V), as well as a high diffusion limiting current density (J_L = 5.19 mA cm⁻²), comparable to those porous carbon-based ORR catalysts with excellent electrochemical performance.