Metal-nitrogen-carbon catalysts loaded on fluorinated carbon nanotubes for efficient oxygen reduction reaction

In recent years, transition metal-nitrogen-carbon (M–N-C) composites are expected to be an alternative to platinum group metal (PGM) among various non-precious metal catalysts investigated. However, the major challenge comes from insufficient electrocatalytic performance and durability for oxygen reduction reaction (ORR). In addition to the selection of suitable central metal active sites, the electrocatalytic activity and stability of the M–N-C catalysts can be enhanced by adjusting the electronic structure of the catalysts. In this work, M–N-C/F composites were synthesized by loading transition metal phthalocyanine complexes onto pre-fluorinated carbon nanotubes through a simple pyrolysis method. Pyrroline-N (PN) and graphite-N (GN) formed after thermal treatment can act as electron acceptors to modulate their charge distribution on the M-N4 sites, and the use of pre-fluorinated nanotubes also allows for a more controlled introduction of fluoride ions that are well coordinated to transition metals, both of which can modulate and modify the electronic structure of M–N-C catalysts. The obtained manganese phthalocyanine/fluorinated carbon nanotubes at 800 °C (MnPc/FCNT800) exhibit a competitive electrocatalytic ORR performance with the half-wave potential (E1/2) of 0.9 V and only 12.1% decay after 20-h long-term chronoamperometry (CA) test in 1.0 M KOH electrolyte, outperforming the commercial Pt/C. Overall, this work paves the way of the electronic structure modification and design of such M–N-C composites for sustainable energy applications.