Proton-Coupled Electron Transfer Mechanisms for CO2 Reduction to Methanol Catalyzed by Surface-Immobilized Cobalt Phthalocyanine

Phillips Hutchison; Logan E Smith; Conor L Rooney; Hailiang Wang; Sharon Hammes-Schiffer

doi:10.1021/jacs.4c05444

Proton-Coupled Electron Transfer Mechanisms for CO₂ Reduction to Methanol Catalyzed by Surface-Immobilized Cobalt Phthalocyanine

J Am Chem Soc. 2024 Jul 24;146(29):20230-20240. doi: 10.1021/jacs.4c05444. Epub 2024 Jul 10.

Authors

Phillips Hutchison¹, Logan E Smith^{1

2}, Conor L Rooney^{1

3}, Hailiang Wang^{1

3}, Sharon Hammes-Schiffer^{1

2}

Affiliations

¹ Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States.
² Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States.
³ Energy Sciences Institute, Yale University, West Haven, Connecticut 06516, United States.

PMID: 38984971
DOI: 10.1021/jacs.4c05444

Abstract

Immobilized cobalt phthalocyanine (CoPc) is a highly promising architecture for the six-proton, six-electron reduction of CO₂ to methanol. This electroreduction process relies on proton-coupled electron transfer (PCET) reactions that can occur by sequential or concerted mechanisms. Immobilization on a conductive support such as carbon nanotubes or graphitic flakes can fundamentally alter the PCET mechanisms. We use density functional theory (DFT) calculations of CoPc adsorbed on an explicit graphitic surface model to investigate intermediates in the electroreduction of CO₂ to methanol. Our calculations show that the alignment of the CoPc and graphitic electronic states influences the reductive chemistry. These calculations also distinguish between charging the graphitic surface and reducing the CoPc and adsorbed intermediates as electrons are added to the system. This analysis allows us to identify the chemical transformations that are likely to be concerted PCET, defined for these systems as the mechanism in which protonation of a CO₂ reduction intermediate is accompanied by electron abstraction from the graphitic surface to the adsorbate without thermodynamically stable intermediates. This work establishes a mechanistic pathway for methanol production that is consistent with experimental observations and provides fundamental insight into how immobilization of the CoPc impacts its CO₂ reduction chemistry.