Among existed oxygen reduction electrocatalysts, iron-based catalysts have shown great advantages oflow cost and extraordinary reactivity, which are even comparable to commercialized platinum basedcatalysts. However, the propensity of iron catalysts to aggregate and passivate has emerged as afundamental barrier to high-power fuel cell applications. In this study, biomass egg yolk derived carbonnanotubes were designed as an armor to host iron complexes, offering multiple active sites such as FeNx, Fe3C, Fe2P for efficient oxygen reduction reaction (ORR). Although the true active sites of ironbased catalysts on the enhanced ORR activities is still under debates, a consensus on the contributionsof Fe-Nx active center has been reached via a smart material design in this work, which enables ORRonset potential at 0.9 V vs. RHE with excellent four-electron selectivity in alkaline media. Meanwhile,the state-of-the-art carbon shells promote the performance stability remarkably (retaining above 96% ofits activity after 27 hours)..
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