Homogeneous Electrocatalytic Reduction of CO2 by a CrN3O Complex: Electronic Coupling with Redox-Active Terpyridine Fragment Favors Selectivity for CO

20 April 2022, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Electrocatalyst design and optimization strategies continue to be an active area of research interest for the applied use of renewable energy resources. The electrocatalytic conversion of CO2 is an attractive approach in this context, because of the added potential benefit of addressing its rising atmospheric concentrations. In previous experimental and computational studies, we have described the mechanism of the first molecular Cr complex capable of electrocatalytically reducing CO2 to CO in the presence of an added proton donor, which contained a redox-active 2,2'-bipyridine (bpy) fragment, CrN2O2. The high selectivity for CO in the bpy-based system was dependent on a delocalized Cr(II)(bpy•−) active state. Subsequently, we became interested in exploring how expanding the polypyridyl ligand core would impact selectivity and activity during electrocatalytic CO2 reduction. Here, we report a new CrN3O catalyst, Cr(tpytbupho)Cl2 1, where 2-([2,2':6',2''-terpyridin]-6-yl)-4,6-di-tert-butylphenolate = [tpytbupho]–, which reduces CO2 to CO with almost quantitative selectivity via a different mechanism than our previously reported Cr(tbudhbpy)Cl(H2O) catalyst. Computational analyses indicate that although the stoichiometry of both reactions is identical, changes in the observed rate law are the combined result of a decrease in intrinsic ligand charge (L3X vs L2X2) and an increase in ligand redox activity, which result in increased electronic coupling between the doubly reduced tpy fragment of the ligand and the Cr(II) center. The strong electronic coupling enhances the rate of protonation and subsequent C–OH bond cleavage, resulting in CO2 binding becoming the rate-determining step, which is an uncommon mechanism during protic CO2 reduction.

Keywords

chromium
electrocatalysis
CO2
homogeneous
molecular
DFT

Supplementary materials

Title
Description
Actions
Title
Supporting Information
Description
Experimental details, computational details, additional CV plots, additional computational plots
Actions

Comments

Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.