The encapsulation of cobalt phthalocyanine (CoPc) catalysts within the coordinating polymer poly-(4-vinyl pyridine) (P4VP) drastically increases the activity and selectivity of the resulting catalyst-polymer composite CoPc-P4VP for the CO2 reduction reaction (CO2RR). Within the polymer, pyridyl moieties on the P4VP coordinate to the Co metal center forming a 5-coordinate complex. The axial coordination of these pyridyl groups to the Co center is hypothesized to increase the Co dz2 orbital energy, increasing the metal center's nucleophilicity and facilitating the CO2 binding compared to the parent four-coordinate CoPc complex. To test this hypothesis, we evaluated a series of five-coordinate CoPc(L) complexes with varying magnitudes of the σ-donor ability of the ligand (L) for CO2RR activity using a combination of electrochemical measurements and density functional theory calculations. The combined computational and experimental studies demonstrated that increasing the σ-donor ability of the axial ligand increases the Co dz2 orbital energy, resulting in the increase CO2RR activity. These studies illustrate the influence of axial coordination on electronic structure and electrocatalytic activity for the CO2RR for this class of catalysts and provides important design considerations for future macrocyclic MN4-based electrocatalytic systems.

Combined experimental and computational approach to increase the CO2 reduction activity of cobalt phthalocyanine

ACS Spring Meeting 2021

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