Redox-Active Ligand Assisted Multielectron Catalysis: A Case of Electrocatalyzed CO₂-to-CO Conversion

The selective reductionof carbon dioxide remains a significantchallenge due to the complex multielectron/proton transfer process,which results in a high kinetic barrier and the production of diverseproducts. Inspired by the electrostatic and H-bonding interactionsobserved in the second sphere of the [NiFe]-CODH enzyme, researchershave extensively explored these interactions to regulate proton transfer,stabilize intermediates, and ultimately improve the performance ofcatalytic CO2 reduction. In this work, a series of cobalt(II)tetraphenylporphyrins with varying numbers of redox-active nitro groupswere synthesized and evaluated as CO2 reduction electrocatalysts.Analyses of the redox properties of these complexes revealed a consistentrelationship between the number of nitro groups and the correspondingaccepted electron number of the ligand at -1.59 V vs. Fc(+/0). Among the catalysts tested, TNPPCo with four nitro groupsexhibited the most efficient catalytic activity with a turnover frequencyof 4.9 x 10(4) s(-1) and a catalyticonset potential 820 mV more positive than that of the parent TPPCo.Furthermore, the turnover frequencies of the catalysts increased witha higher number of nitro groups. These results demonstrate the promisingdesign strategy of incorporating multielectron redox-active ligandsinto CO2 reduction catalysts to enhance catalytic performance.