Efficient oxygen reduction reaction electrocatalysts synthesized from an iron-coordinated aromatic polymer framework

Abstract

Aromatic polymers with abundant nitrogen-coordinated iron (Fe–N_x) species provide a big opportunity to prepare iron–nitrogen co-doped carbon (Fe–N_x/C) catalysts with highly efficient oxygen reduction reaction (ORR) activity; however, such types of materials have not been reported so far. Herein, we synthesized a metal-coordinated aromatic polymer, Fe_(III)–poly(o-phenylene-diamine) (Fe–PPDA), with dense Fe–N_x species by a facile route. Fe–PPDA was obtained by polymerization of the o-phenylenediamine/ferric–ion complex in the presence of sodium bicarbonate, which was essential in retaining abundant Fe–N_x species and increasing the surface area of the polymer. Fe–PPDA polymer derived Fe–N_x/C catalysts demonstrated activity in ORRs, with onset and half-wave potentials (E_1/2) of 1.11V_RHE and 0.92V_RHE, respectively, which were superior to the values obtained for commercial Pt/C (E_1/2, 0.85V_RHE) and are the best values yet reported for the Fe–N_x/C family in alkaline medium. It also demonstrated comparable ORR activity to that of the commercial Pt/C catalyst in acidic medium (E_1/2, 0.76V_RHEvs. 0.78V_RHE). The excellent ORR activity was ascribed to the abundant Fe–N_x modulated carbon nanostructure and the high surface area.