Electroreduction of CO2 Catalyzed by a Heterogenized Zn-Porphyrin Complex with a Redox-Innocent Metal Center

Yueshen Wu; Jianbing Jiang; Zhe Weng; Maoyu Wang; Daniël L J Broere; Yiren Zhong; Gary W Brudvig; Zhenxing Feng; Hailiang Wang

doi:10.1021/acscentsci.7b00160

Electroreduction of CO₂ Catalyzed by a Heterogenized Zn-Porphyrin Complex with a Redox-Innocent Metal Center

ACS Cent Sci. 2017 Aug 23;3(8):847-852. doi: 10.1021/acscentsci.7b00160. Epub 2017 Jul 26.

Authors

Yueshen Wu^{1

2}, Jianbing Jiang^{1

2}, Zhe Weng^{1

2}, Maoyu Wang³, Daniël L J Broere¹, Yiren Zhong^{1

2}, Gary W Brudvig^{1

2}, Zhenxing Feng³, Hailiang Wang^{1

2}

Affiliations

¹ Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States.
² Energy Sciences Institute, Yale University, West Haven, Connecticut 06516, United States.
³ School of Chemical, Biological, and Environmental Engineering, Oregon State University, Corvallis, Oregon 97331, United States.

Abstract

Transition-metal-based molecular complexes are a class of catalyst materials for electrochemical CO₂ reduction to CO that can be rationally designed to deliver high catalytic performance. One common mechanistic feature of these electrocatalysts developed thus far is an electrogenerated reduced metal center associated with catalytic CO₂ reduction. Here we report a heterogenized zinc-porphyrin complex (zinc(II) 5,10,15,20-tetramesitylporphyrin) as an electrocatalyst that delivers a turnover frequency as high as 14.4 site^-1 s^-1 and a Faradaic efficiency as high as 95% for CO₂ electroreduction to CO at -1.7 V vs the standard hydrogen electrode in an organic/water mixed electrolyte. While the Zn center is critical to the observed catalysis, in situ and operando X-ray absorption spectroscopic studies reveal that it is redox-innocent throughout the potential range. Cyclic voltammetry indicates that the porphyrin ligand may act as a redox mediator. Chemical reduction of the zinc-porphyrin complex further confirms that the reduction is ligand-based and the reduced species can react with CO₂. This represents the first example of a transition-metal complex for CO₂ electroreduction catalysis with its metal center being redox-innocent under working conditions.