Issue 33, 2021

Electrochemical reduction of CO2 to CO and HCOO using metal–cyclam complex catalysts: predicting selectivity and limiting potential from DFT

Abstract

Sustainable fuel production from CO2 through electrocatalytic reduction is promising but challenging due to high overpotential and poor product selectivity. Herein, we computed the reaction free energies of electrocatalytic reduction of CO2 to CO and HCOO using the density functional theory method and screened transition metal(M)–cyclam(L) complexes as molecular catalysts for CO2 reduction. Our results showed that pKa of the proton adduct formed by the protonation of the reduced metal center can be used as a descriptor to select the operating pH of the solution to steer the reaction toward either the CO or hydride cycle. Among the complexes, [LNi]2+ and [LPd]2+ catalyze the reactions by following the CO cycle and are the CO selective catalysts in the pH ranges 1.81–7.31 and 6.10 and higher, respectively. Among the complexes that catalyze the reactions by following the hydride cycle, [LMo]2+ and [LW]3+ are HCOO selective catalysts and have low limiting potentials of −1.33 V and −1.54 V, respectively. Other complexes, including [LRh]2+, [LIr]2+, [LW]2+, [LCo]2+, and [LTc]2+ catalyze the reactions resulting in either HCOO from CO2 reduction or H2 from proton reduction; however, HCOO formation is always thermodynamically more favorable. Notably, [LMo]2+, [LW]3+, [LW]2+ and [LCo]2+ have limiting potentials less negative than −1.6 V and are based on Earth-abundant elements, making them attractive for practical application.

Graphical abstract: Electrochemical reduction of CO2 to CO and HCOO− using metal–cyclam complex catalysts: predicting selectivity and limiting potential from DFT

Supplementary files

Article information

Article type
Paper
Submitted
29 Jun 2021
Accepted
10 Jul 2021
First published
14 Jul 2021

Dalton Trans., 2021,50, 11446-11457

Author version available

Electrochemical reduction of CO2 to CO and HCOO using metal–cyclam complex catalysts: predicting selectivity and limiting potential from DFT

Z. Masood and Q. Ge, Dalton Trans., 2021, 50, 11446 DOI: 10.1039/D1DT02159A

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