A Citric Acid-Assisted Method for Constructing Multi-dimensional Acid-Resistant Fe/N/C Catalysts for Oxygen Reduction Reactions.

Iron–nitrogen co-doped carbon (Fe/N/C) catalysts derived from zinc-based zeolite imidazole frameworks (ZIF-8) have been ideal alternatives to platinum group metals (PGM) and shown great potential to catalyze oxygen reduction reaction (ORR). Unfortunately, the ORR performance is seriously suppressed by the insufficient density and accessibility of the electrochemical active Fe–N sites. The precise regulation of ZIF-8 to the formation of Fe/N/C catalysts with the desired Fe–N sites for ORR is a critical challenge. Herein, a citric acid assisted reconstitution strategy is proposed to design Fe doped ZIF-8 frameworks and construct multi-dimensional Fe/N/C catalysts composed of inner concave and entangled carbon nanotubes outer moieties for efficient acid-resistant ORR reaction. The introduction of citric acid imparts Fe/N/C catalysts with dense accessible active sites and highly opened multi-dimensional mass transfer pathways. Therefore, the optimized Fe/N/C catalysts dominant half-wave potential of 0.785 V and great acid stability were obtained in 0.5 M H2SO4 with a high number of transferred electrons and a low yield of H2O2 ( n ¯ = 3.97 and average yield = 4%). This work provides a novel and feasible approach to design and tailoring of Fe/N/C catalysts with improved distribution density and accessibility of the Fe–N active sites. [ABSTRACT FROM AUTHOR]