Combining scaling relationships overcomes rate versus overpotential trade-offs in O2 molecular electrocatalysis.

The development of advanced chemical-to-electrical energy conversions requires fast and efficient electrocatalysis of multielectron/multiproton reactions, such as the oxygen reduction reaction (ORR). Using molecular catalysts, correlations between the reaction rate and energy efficiency have recently been identified. Improved catalysis requires circumventing the rate versus overpotential trade-offs implied by such "scaling relationships." Described here is an ORR system-using a soluble iron porphyrin and weak acids-with the best reported combination of rate and efficiency for a soluble ORR catalyst. This advance is achieved not by "breaking" scaling relationships but rather by combining two of them. Key to this behavior is a polycationic ligand, which enhances anionic ligand binding and changes the catalyst E 1/2. These results show how combining scaling relationships is a powerful way toward improved electrocatalysis.