Potential Dependence and Substituent Effect in CO₂ Electroreduction on a Cobalt Phthalocyanine Catalyst

Abstract

Cobalt phthalocyanine molecules combined with carbon materials (CoPc@NC) have been reported to exhibit prominent electrocatalytic performance toward the CO 2 reduction reaction (CO 2 RR). However, the molecular-scale insights into the mechanisms regarding its high activity or Faraday efficiency remain limited due to the great challenge in modeling the electrochemical interface. Herein, an explicit computational model with the inclusion of solvation and electrode potential was employed to explore the mechanistic nature of the CO 2 RR at the graphene-supported CoPc electrochemical interface. It is suggested that the reaction mechanisms of the CO 2 RR on the molecular CoPc catalyst can be remarkably affected by solvation and electrode potential. The DFT-based constrained ab initio molecular dynamics simulations with the thermodynamic integration method support the notion that the frontier molecular orbitals of the molecular CoPc catalyst can be easily modulated by the electrode potentials and thus influence the redox performance during the CO 2 RR. The CO 2 adsorption step involving partial charge transfer from the molecular catalyst is strongly potential-dependent. Once the CO 2 is absorbed, subsequent protonation, as the rate-determining step, is not significantly affected by the electrode potential. Moreover, the overall catalytic activity of the CO 2 RR can be remarkably enhanced by introducing an electron-donating substituent such as a cyano group (−CN), which is attributed to the charge redistribution between the carbon substrate and the molecular CoPc catalyst. Our work not only provides deep insights into the electronic structure of the CoPc@NC system but also illustrates the critical role of the carbon substrate and substituents on the CoPc catalyst, paving a promising way for advancing efficient CO 2 transformation.

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