Seeded growth of branched iron-nitrogen-doped carbon nanotubes as a high performance and durable non-precious fuel cell cathode

摘要

Achieving a high-density Fe-N-x moieties in a highly graphitic and porous carbon matrix is critical for developing iron/nitrogen-doped carbon (Fe-N/C) electrocatalysts with both high activity and high stability on oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). Herein, we report the growth of Fe/N-doped carbon nanotubes (CNTs) by pyrolysis of Fe-doped zeolitic imidazolate framework-8 (Fe-ZIF-8) precursors on a primary Fe/N-doped CNT seed. Such seeded growth enabled the successful conversion of the Fe-ZIF-8 precursor, with inherent Fe-N-x complex, into a large number of secondary CNTs doped with high-density Fe-N-x sites while keeping a high degree of graphitization. The resulted catalyst possesses high-density Fe-N-x active sites, porous network, enhanced electron conductivity and improved anti-corrosion capability which lead to both improved performance and durability in PEMFCs compared to the pyrolyzed Fe-ZIF-8 catalyst (Fe-ZIF'). In addition, the highly graphitic structure combined with the hierarchically branched CNT network enables a high hydrophobicity for efficient water removal and thus much slower performance decay than the benchmark Fe-ZIF' catalyst during accelerated stress tests. The successful introduction of active Fe-N-x sites into highly graphitic and branched CNTs provides a new way for the development of durably active noble-metal-free ORR electrocatalysts. (c) 2020 Published by Elsevier Ltd.