High electrocatalytic performance of NH ₃-activated iron-adsorbed polyaniline for oxygen reduction reactions

We demonstrate how a highly active non-precious metal-based catalyst for oxygen reduction reactions (ORRs) can be prepared using commercially available polyaniline (PANI) as both nitrogen source and carbon precursor. To do this, PANI-derived catalysts are prepared by pyrolyzing PANI and Fe-impregnated PANI (Fe-PANI) in either N ₂ or NH ₃ atmospheres. When the catalyst precursor is pyrolyzed under an NH ₃ stream, the resultant catalysts (PANI-A and Fe-PANI-A; A denotes treatment with ammonia) have higher microporosities and pyridinic nitrogen contents than those of N ₂-pyrolyzed catalysts (PANI-N and Fe-PANI-N; N denotes treatment with nitrogen). Microporosity produced by pyrolysis and pyridinic nitrogen contents are important factors for ORR activity, which is borne out by the better ORR performance of NH ₃-pyrolyzed catalysts compared to N ₂-pyrolyzed samples. In addition, Fe species coordinated with nitrogen serve as a highly active site to facilitate ORR, leading to Fe-PANI-A delivering the best ORR performance among the PANI-derived catalysts. The onset and half-wave potentials of Fe-PANI-A for ORR were measured as 0.916 and 0.787 mV, respectively, better than for commercial Pd/ C. Although some degradation in ORR activity of Fe- PANI-A is observed after a durability test, the loss in the half-wave potential is only 52 mV, indicating a relatively stable ORR activity for Fe-PANI-A.