Options
2021
Journal Article
Titel
Controlling Oxygen Reduction Selectivity through Steric Effects: Electrocatalytic Two-Electron and Four-Electron Oxygen Reduction with Cobalt Porphyrin Atropisomers
Abstract
Achieving a selective 2 e− or 4 e− oxygen reduction reaction (ORR) is critical but challenging. Herein, we report controlling ORR selectivity of Co porphyrins by tuning only steric effects. We designed Co porphyrin 1 with meso-phenyls each bearing a bulky ortho-amido group. Due to the resulted steric hinderance, 1 has four atropisomers with similar electronic structures but dissimilar steric effects. Isomers avav and aaaa catalyze ORR with n=2.10 and 3.75 (n is the electron number transferred per O2), respectively, but aavv and aaav show poor selectivity with n=2.89-3.10. Isomer avav catalyzes 2 e− ORR by preventing a bimolecular O2 activation path, while aaaa improves 4 e− ORR selectivity by improving O2 binding at its pocket, a feature confirmed by spectroscopy methods, including O K-edge near-edge X-ray absorption fine structure. This work represents an unparalleled example to improve 2 e− and 4 e− ORR by tuning only steric effects without changing molecular and electronic structures.
Author(s)