High current density microkinetic and electronic structure analysis of CO2 reduction using Co and Fe complexes on gas diffusion electrode

Abstract

Reaction mechanisms of electrocatalytic CO 2 reduction into CO over Co or Fe complexes were examined using gas diffusion electrodes to meet the requirement of high current densities for industrial deployment. Our experimental and theoretical calculation results consistently revealed that the Fe-based molecular catalysts exhibited more positive redox potentials relevant to CO 2 electrocatalysis but disfavored the desorption of generated CO, especially at high overpotentials, failing to achieve appreciable reaction rates. Distinctively, the heterogenized Co-based molecular complexes were found to be tolerant to the high coverage of CO at steady state on the active site and achieved rates exceeding 100 mA cm −2 toward exclusive CO evolution. Density-functional theory calculations not only disclosed the redox non-innocent tetraphenylporphyrins and phthalocyanines during electrocatalytic CO 2 reduction but also corroborated the energetics, especially for CO 2 and CO adsorption, accounting for distinctive reaction pathways between Co and Fe complexes. • Microkinetic analysis was performed at high current densities • The redox non-innocent TPP and Pc were disclosed by electronic structure analysis • The distinctive performance between Co and Fe complexes was interpreted Molecular catalysts can electrocatalytically convert CO 2 reduction into CO at nearly 100% selectivity. However, the associated electrokinetic data and reaction mechanisms remain debatable, especially under higher current densities, hindering the establishment of design guidelines for effective catalysis. Herein, the reaction mechanism using Co and Fe complexes was examined using a gas diffusion electrode to meet the requirement of high current densities. The distinctive performance between Co and Fe complexes was detailed using microkinetic analysis and theoretical calculations. This work not only provides conclusive representation related to electronic structure and reaction mechanism of molecular complexes but also sheds light on the further development of immobilized molecular electrocatalysts at an industrial scale. The reactivity and energetics at each elementary step of immobilized Co and Fe complexes on gas diffusion electrode for the electrocatalytic CO 2 reduction reaction were examined through a combination of microkinetic assessment and theoretical DFT calculations. The experimental and theoretical calculation results disclosed distinctive performance between Co and Fe complexes resulting from their electronic structure and CO or CO 2 adsorption free energies on the metal center.