Promoted O 2 Activation at a Co III Center for Significantly Improved Electrocatalytic Oxygen Reduction Reaction

Electrocatalytic oxygen reduction reaction (ORR) near its thermodynamic equilibrium potential is vital for efficient energy conversion. However, low-valent metal ions generated at high cathodic potentials are typically required to achieve effective O2 activation. Herein we report O2 activation promoted by a Sc3+-hung CoIII corrole, which realizes markedly boosted ORR electrocatalysis. CoIII corrole 1 with an appended crown ether substituent was synthesized. By grabbing a Sc3+ ion, the ORR overpotential with Sc3+-hung 1 decreased by 1.0 V in acetonitrile and 170 mV in 0.5 M H2SO4 solutions. Importantly, Sc3+-hung 1 achieved an ORR half-wave potential of 0.78 V vs RHE in 0.5 M H2SO4 solutions with a transferred electron number of 3.87. Our results suggest that the hanging Sc3+ promotes O2 binding and activation at the CoIII ion of 1 to generate a CoIII–superoxo–Sc3+ corrole cation radical and assists subsequent O–O bond cleavage by accepting the leaving hydroxide.