Enhanced Four‐Electron Oxygen Reduction Selectivity of Clamp‐Shaped Cobalt(II) Porphyrin(2.1.2.1) Complexes
Songlin Xue, W. Ryan Osterloh, Xiaojuan Lv, Ningchao Liu, Yimei Gao, Haitao Lei, Yuanyuan Fang, Zhongti Sun, Peifeng Mei, Daiki Kuzuhara, Naoki Aratani, Hiroko Yamada, Rui Cao, Karl M. Kadish, Fengxian Qiu
Abstract
Abstract The molecular structure, electrochemistry, spectroelectrochemistry and electrocatalytic oxygen reduction reaction (ORR) features of two Co II porphyrin(2.1.2.1) complexes bearing Ph or F 5 Ph groups at the two meso ‐positions of the macrocycle are examined. Single crystal X‐ray analysis reveal a highly bent, nonplanar macrocyclic conformation of the complex resulting in clamp‐shaped molecular structures. Cyclic voltammetry paired with UV/Vis spectroelectrochemistry in PhCN/0.1 M TBAP suggest that the first electron addition corresponds to a macrocyclic‐centered reduction while spectral changes observed during the first oxidation are consistent with a metal‐centered Co II /Co III process. The activity of the clamp‐shaped complexes towards heterogeneous ORR in 0.1 M KOH show selectivity towards the 4e − ORR pathway giving H 2 O. DFT first‐principle calculations on the porphyrin catalyst indicates a lower overpotential for 4e − ORR as compared to the 2e − pathway, consistent with experimental data.