Defects engineered hierarchical porous iron-nitrogen-enriched carbon derived from pyridyl conjugated microporous polytriphenylamine networks for efficient oxygen reduction reaction

Abstract

Iron-nitrogen-carbon catalysts are promising non-precious metal-based electrocatalysts for oxygen reduction reaction (ORR) used in fuel cells. However, the rational design and fabrication of iron–nitrogen-carbon catalysts with tunable ORR activity remain challenging. Herein, iron–nitrogen-enriched carbon materials (FeNCs) were produced using the precursor of pyridyl conjugated microporous polytriphenylamine with the impregnation of FeCl3via two cycles of high-temperature pyrolysis with acid leaching in-between. The Fe doping content and pyrolysis temperature were varied to manipulate the state of active sites, the degree of graphitization and electrocatalytic performance. The optimized FeNCs exhibit enhanced stability, methanol tolerance and superior ORR activity in alkaline media with a higher onset potential (0.990 V vs RHE), half-wave potential (0.878 V vs RHE) and diffusion current density JL (5.95 mA cm−2) compared to commercial Pt/C catalyst (0.974 V, 0.860 V, 5.10 mA cm−2). The excellent electrocatalytic performance is ascribed to the co-existing highly active sites of Fe4N and Fe3C, the hierarchical porous structures for full action of active sites and a high surface area (1397 m2 g−1) with defect engineered graphitic and amorphous carbon for efficient electron conduction of ORR. Accordingly, the high-performance FeNCs can become an alternative low-cost catalyst to precious Pt/C catalyst for fuel cells.