First principles studies of mononuclear and dinuclear Pacman complexes for electrocatalytic reduction of CO2

Abstract

The electrochemical reduction of carbon dioxide (CO₂) generating value-added chemicals or fuels using renewable energy resources represents a promising approach to mitigate the greenhouse gases present in the atmosphere. However, a critical challenge to this approach is to develop highly efficient catalysts with minimum energy input and maximum conversion efficiency. Stable and strong electrocatalysts, which can promote the electroreduction of CO₂ beyond the two-electron process to produce various useful products, are highly desirable. Herein, we studied mononuclear and dinuclear complexes of Cr, Mn, Fe, Co and Ni with macrocyclic Schiff-base calixpyrrole ligands, often referred to as Pacman ligands, for their activity towards catalysing the reduction of CO₂ to methane (CH₄) or methanol (CH₃OH). In the case of mononuclear complexes, only one N₄ cavity is occupied by the transition metal. In contrast, in the case of dinuclear complexes, the transition metal is placed in each of the two N₄ cavities of the macrocyclic ligand. Our DFT calculations have shown that the iron-containing mononuclear complex displayed the highest activity and selectivity for the transformation of CO₂ to CH₄ with a very low negative value of limiting potential of −0.24 V. However, in the case of dinuclear complexes, the lowest negative limiting potential was found to be −0.45 V. This work offers a technique for developing electrocatalysts that have great potential for CO₂ reduction reactions.