Molecular architectures of iron complexes for oxygen reduction catalysis-Activity enhancement by hydroxide ions...

Developing cost-effective and high-performance electrocatalysts for oxygen reduction reaction (ORR) is critical for clean energy generation. Here, we propose an approach to the synthesis of iron phthalocyanine nanotubes (FePc NTs) as a highly active and selective electrocatalyst for ORR. The performance is significantly superior to FePc in randomly aggregated and molecularly dispersed states, as well as the commercial Pt/C catalyst. When FePc NTs are anchored on graphene, the resulting architecture shifts the ORR potentials above the redox potentials of Fe^2+/3+ sites. This does not obey the redox-mediated mechanism operative on conventional FePc with a Fe²⁺-N moiety serving as the active sites. Pourbaix analysis shows that the redox of Fe^2+/3+ sites couples with HO^- ions transfer, forming a HO-Fe³⁺-N moiety serving as the ORR active sites under the turnover condition. The chemisorption of ORR intermediates is appropriately weakened on the HO-Fe³⁺-N moiety compared to the Fe²⁺-N state and thus is intrinsically more ORR active.