Biomimicking Vitamin B₁₂: A Co Phthalocyanine Pyridine Axial Ligand Coordinated Catalyst for the Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is of extreme importance in energy converting systems since oxygen is cheap and abundant electron (e) acceptor. The complete reduction of O₂ to water is a multistep reaction, which involves splitting of the O-O bond and transfer of 4e. The ORR complexity hampers the development of synthetic cost-efficient electrocatalysts and the massive commercialization of PEM fuel cells. Co complexes involving the Co phthalocyanine (CoPc) have been extensively studied as ORR electrocatalysts. Among these complexes, vitamin B₁₂ (a naturally occurring molecule) has attracted attention because, instead of catalysing the 2e reduction of O₂ to H₂O₂ as CoPc, it promotes the 4e reduction to H₂O. In this work, we study a CoPc axially coordinated to pyridine, which is anchored to a metallic carbon nanotube (CoPc-Py-CNT), biomimicking the vitamin B₁₂ active site. Density functional theory calculations are used to characterize the O₂ adsorption and dissociation on the metal center of CoPc-Py-CNT, whereas the synthetized catalyst was characterized by EPR and XPS spectroscopy, revealing insights into the mechanism of action of Co penta-coordinated complexes.