Simultaneously Crafting Single-Atomic Fe Sites and Graphitic Layer-Wrapped Fe₃C Nanoparticles Encapsulated within Mesoporous Carbon Tubes for Oxygen Reduction

The rational design and facile synthesis of 1D hollow tubular carbon-based materials with highly efficient oxygen reduction reaction (ORR) performance remains a challenge. Herein, a simple yet robust route is employed to simultaneously craft single-atomic Fe sites and graphitic layer-wrapped Fe₃C nanoparticles (Fe₃C@GL NPs) encapsulated within 1D N-doped hollow mesoporous carbon tubes (denoted Fe-N-HMCTs). The successional compositional and structural crafting of the hydrothermally self-templated polyimide tubes (PITs), enabled by Fe species incorporation and acid leaching treatment, respectively, yields Fe-N-HMCTs that are subsequently exploited as the ORR electrocatalyst. Remarkably, an alkaline electrolyte capitalizing on Fe-N-HMCTs achieves excellent ORR activity (onset potential, 0.992 V; half-wave potential, 0.872 V), favorable long-term stability, and strong methanol tolerance, outperforming the state-of-the-art Pt/C catalyst. Such impressive ORR performances of the Fe-N-HMCTs originate from the favorable configuration of active sites (i.e., atomically dispersed Fe-N_x sites and homogeneously incorporated Fe₃C@GL NPs) in conjunction with the advantageous 1D hollow tubular architecture containing adequate mesoporous surface. This work offers a new view to fabricate earth-abundant 1D Fe-N-C electrocatalysts with well-designed architecture and outstanding performance for electrochemical energy conversion and storage.