Transition metal-nitrogen-carbon catalysts for oxygen reduction reaction in neutral electrolyte

- Systematic kinetics study on PGM-free catalysts in neutral media.
- Mn-, Fe-, Co-, Ni- AAPyr were used as PGM-free catalysts.
- Fe-AAPyr had higher current densities and an apparent 4e− transfer mechanism.
- Mn-, Co-, Ni- AAPyr seems to follow a 2 × 2e− mechanism.
- Fe-AAPyr was cycled 10,000 times with minimal degradation.

Platinum group metal-free (PGM-free) catalysts based on M-N-C types of materials with M as Mn, Fe, Co and Ni and aminoantipyrine (AAPyr) as N-C precursors were synthesized using sacrificial support method. Catalysts kinetics of oxygen reduction reaction (ORR) was studied using rotating ring disk electrode (RRDE) in neutral pH. Results showed that performances were distributed among the catalysts as: Fe-AAPyr > Co-AAPyr > Mn-AAPyr > Ni-AAPyr. Fe-AAPyr had the highest onset potential and half-wave potential. All the materials showed similar limiting current. Fe-AAPyr had an electron transfer involving 4e− with peroxide formed lower than 5%. Considering H2O2 produced, it seems that Co-AAPyr, Mn-AAPyr and Ni-AAPyr follow a 2 × 2e− mechanism with peroxide formed during the intermediate step. Durability test was done on Fe-AAPyr for 10,000 cycles. Decrease of activity was observed only after 10,000 cycles.

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