Controlling Oxygen Reduction Selectivity through Steric Effects: Electrocatalytic Two‐Electron and Four‐Electron Oxygen Reduction with Cobalt Porphyrin Atropisomers
Bin Lv, Xialiang Li, Kai Guo, Jun Ma, Yanzhi Wang, Haitao Lei, Fang Wang, Xiaotong Jin, Qingxin Zhang, Wei Zhang, Ran Long, Yujie Xiong, Ulf‐Peter Apfel, Rui Cao
Abstract
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 αβαβ and αααα catalyze ORR with n =2.10 and 3.75 ( n is the electron number transferred per O 2 ), respectively, but ααββ and αααβ show poor selectivity with n =2.89–3.10. Isomer αβαβ catalyzes 2 e − ORR by preventing a bimolecular O 2 activation path, while αααα improves 4 e − ORR selectivity by improving O 2 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.