Stimulating the Pre-Catalyst Redox Reaction and the Proton–Electron Transfer Process of Cobalt Phthalocyanine for CO₂ Electroreduction

The mechanism for electrochemical carbon dioxide reduction reaction (CO 2 RR) to carbon monoxide on cobalt phthalocyanine (CoPc) in aqueous electrolytes remains debatable, impeding the design of high-performance catalysts. By using a quasi-empirical protocol with density functional theory calculations, we identify the mechanisms of two important steps for CO 2 RR on CoPc: the reduction of Co II Pc to form catalytically active [Co II Pc] 2– for CO 2 adsorption and the proton–electron transfer to the key intermediate [CoPc-COO] 2– to form [CoPc-COOH] 2– . According to the charge states and pK a analysis, the formation of the adsorbed carboxyl (*COOH) takes place via the concerted proton–electron transfer process at low potentials, and the sequential proton–electron transfer process becomes thermodynamically favored at more reductive potentials, which successfully elucidates the potential-dependent reaction kinetics of CO 2 RR on CoPc catalysts. Electron-withdrawing substituents of CoPc would enhance the reduction of CoPc but hinder the protonation of *CO 2, which accounts for previous conflicting results. Our findings not only deepen the understanding of CoPc-catalyzed CO 2 RR but also provide a guideline for molecular engineering of CoPc-based catalysts.