Heteroatom-doped carbon interpenetrating networks: a signpost to achieve the best performance of non-PGM catalysts for fuel cells

Abstract

Non-platinum group metal (non-PGM) catalysts, constructed from cheap and abundant carbon, nitrogen and 3d transition metals as bricks, have been regarded as the most promising candidates for the oxygen reduction reaction (ORR) in fuel cells and metal–air batteries. In this work, well-defined carbon interpenetrating networks have been fabricated by controllable pyrolysis carbonization of polyaniline (PANI) nanotubes epitaxially grown using a dodecahedral zeolitic imidazolate framework (ZIF-8) with FeCl₃ at 900 °C. The interpenetrating networks feature a stable free-standing three-dimensional structure, composed of carbon nanotubes (CNTs) derived from PANI and carbon nanoparticles (CNPs) from ZIF-8. In KOH solution, the synthesized catalyst with an interpenetrating network structure shows a superior ORR activity with a half-wave potential of 0.95 V (vs. RHE) and a mass activity of 0.046 A mg_cat⁻¹ at 0.9 V (vs. RHE), which are much better than those of most Fe–N–C reported and commercial Pt/C (0.84 V vs. RHE, 0.044 A mg_pt⁻¹). Moreover, it also displays superior performance and long-term durability in a Zn–air full battery, outperforming recently reported carbon-based catalysts. It was determined from DFT calculation results that there exist remarkably increased at-edge Fe–N_x moieties at the boundaries and interfaces in the chemically connected CNT/CNP composites. These edge moieties are the main active sites that should be responsible for the substantially improved performances. Therefore, the design of carbon/carbon composites with a smart nanophase structure is an effective strategy for developing next-generation non-PGM catalysts.