Hierarchically Porous Carbons with Highly Curved Surfaces for Hosting Single Metal FeN 4 Sites as Outstanding Oxygen Reduction Catalysts.

Fe-N-C materials have emerged as a promising alternative to platinum-group-metals for catalyzing the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. However, their low intrinsic activity and stability have been major impediments. Herein, we report a Fe-N-C electrocatalyst with dense FeN4 sites on hierarchically porous carbons with highly curved surfaces (denoted as FeN4-hcC). The FeN4-hcC catalyst displayed exceptional ORR activity in acidic media, with a high half-wave potential of 0.85 V (versus reversible hydrogen electrode) in 0.5 M H2SO4. When integrated into a membrane electrode assembly, the corresponding cathode displayed a high maximum peak power density of 0.592 W cm-2 and demonstrated operating durability over 30000 voltage cycles under harsh H2/air conditions, outperforming previously reported Fe-N-C electrocatalysts. Our experimental and theoretical studies suggested that the curved carbon support fine-tuned the local coordination environment, lowered the energies of the Fe d-band centers, and inhibited the adsorption of oxygenated species, which could enhance the ORR activity and stability. This work provides new insight into the carbon nanostructure-activity correlation for ORR catalysis. It also offers a new approach to designing advanced single-metal site catalysts for energy conversion applications. This article is protected by copyright. All rights reserved.