Crumpled and Multi-Scale Porous Fe−N−C Catalyst with Enhanced Site Accessibility and Mass Transport in Oxygen Reduction
The sluggish kinetics of the oxygen reduction reaction (ORR) necessitates platinum-based catalysts, but their high cost and scarcity drive the search for platinum-group metal-free (PGM-free) alternatives. Fe−N−C catalysts with atomically dispersed Fe−N4 sites are promising, yet their practical performance is limited by buried active sites and poor mass transport. Here, a crumpled, multi-scale porous Fe−N−C catalyst (Fe−N−PCG) is synthesized via spray pyrolysis coupled with high-temperature metal etching. The crumpled morphology, formed by capillary compression during rapid solvent evaporation, and in-plane mesopores from Fe nanoparticle etching, synergistically enhance site accessibility and mass transport. Fe−N−PCG achieves a site density (SD) of 2.74×10^19 sites g−1 and Fe utilization (UFe) of 51.7%. As a gas diffusion electrode, it delivers a mass transport overpotential (ηmt) of 67 mV at 800 mA cm−2. In zinc-air batteries, Fe−N−PCG exhibits a peak power density of 296.1 mW cm−2 at 500 mA cm−2, outperforming Pt/C (241 mW cm−2 at 438 mA cm−2). At 50 mA cm−2, it delivers a discharge voltage of 1.19 V and a specific capacity of 815 mAh g−1, surpassing Pt/C (1.13 V, 715 mAh g−1). These results demonstrate that morphology and porosity engineering can concurrently optimize intrinsic activity, site utilization, and mass transport, offering a rational design strategy for high-performance PGM-free catalysts.