Cobalt Phenanthroline-Indole Macrocycles as Highly Active Electrocatalysts for Oxygen Reduction

The replacement of scarce and expensive platinum species poses a challenge in fuel-cell development. The design and synthesis of a novel type of Co-II-N-4 macrocyclic complex, [CoN4], based on the phenanthroline-indole macrocyclic ligand (PIM) is reported. This unique ligand allows the formation of mono- and dinuclear complexes with defined active sites that facilitate the direct four-electron reduction of oxygen. Electrochemical measurements revealed that the [CoN4]/C (20wt%) catalysts have a high activity and long-term stability for the oxygen-reduction reaction (ORR) under alkaline conditions, similar to the Pt/C catalyst. These structurally well-defined complexes represent a nonprecious alternative to platinum species for future fuel-cell applications.