Issue 1, 2020

Significantly improved electrocatalytic oxygen reduction by an asymmetrical Pacman dinuclear cobalt(ii) porphyrin–porphyrin dyad

Abstract

Pacman dinuclear CoII triphenylporphyrin-tri(pentafluorophenyl)porphyrin 1 and dinuclear CoII bis-tri(pentafluorophenyl)porphyrin 2, anchored at the two meso-positions of a benzene linker, are synthesized and examined as electrocatalysts for the oxygen reduction reaction (ORR). Both dinuclear Co bisporphyrins are more efficient and selective than corresponding mononuclear CoII tetra(pentafluorophenyl)porphyrin 3 and CoII tetraphenylporphyrin 4 for the four-electron electrocatalytic reduction of O2 to water. Significantly, although the ORR selectivities of the two dinuclear Co bisporphyrins are similar to each other, 1 outperforms 2, in terms of larger catalytic ORR currents and lower overpotentials. Electrochemical studies showed different redox behaviors of the two Co sites of 1: the CoIII/CoII reduction of the Co-TPP (TPP = triphenylporphyrin) site is well-behind that of the Co-TPFP (TPFP = tri(pentafluorophenyl)porphyrin) site by 440 mV. This difference indicated their different roles in the ORR: CoII-TPFP is likely the O2 binding and reduction site, while CoIII-TPP, which is generated by the oxidation of CoII-TPP on electrodes, may function as a Lewis acid to assist the O2 binding and activation. The positively charged CoIII-TPP will have through-space charge interactions with the negatively charged O2-adduct unit, which will reduce the activation energy barrier for the ORR. This effect of Co-TPP closely resembles that of the CuB site of metalloenzyme cytochrome c oxidase (CcO), which catalyzes the biological reduction of O2. This work represents a rare example of asymmetrical dinuclear metal catalysts, which can catalyze the 4e reduction of O2 with high selectivity and significantly improved activity.

Graphical abstract: Significantly improved electrocatalytic oxygen reduction by an asymmetrical Pacman dinuclear cobalt(ii) porphyrin–porphyrin dyad

Supplementary files

Article information

Article type
Edge Article
Submitted
07 10 2019
Accepted
03 11 2019
First published
04 11 2019
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2020,11, 87-96

Significantly improved electrocatalytic oxygen reduction by an asymmetrical Pacman dinuclear cobalt(II) porphyrin–porphyrin dyad

Y. Liu, G. Zhou, Z. Zhang, H. Lei, Z. Yao, J. Li, J. Lin and R. Cao, Chem. Sci., 2020, 11, 87 DOI: 10.1039/C9SC05041H

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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