Polymer Coordination Promotes Selective CO2 Reduction by Cobalt Phthalocyanine

Polymer Coordination Promotes Selective CO2 Reduction by Cobalt Phthalocyanine

Wesley W Kramer and Charles McCrory

Chem. Sci., 2016, Accepted Manuscript
DOI: 10.1039/C5SC04015A
Received 22 Oct 2015, Accepted 01 Feb 2016

Cobalt phthalocyanine (CoPc) is a known electrocatalyst for the carbon dioxide reduction reaction (CO2RR) that, when adsorbed onto edge-plane graphite (EPG) electrodes, shows modest activity and selectivity for CO production along with co-generation of H2. In contrast, electrodes modified with CoPc immobilized in a poly-4-vinylpridine (P4VP) film show dramatically enhanced activity and selectivity compared to those modified CoPc alone. CoPc-P4VP films display a Faradaic efficiency of ~90% for CO production, with a turnover frequency of 4.8 s-1 at just -0.75 V vs RHE. Two properties of P4VP contribute to enhancing the activity of CoPc; (1) the ability of individual pyridine residues to coordinate to CoPc and (2) the high concentration of uncoordinated pyridine residues throughout the film which may enhance the catalytic activity of CoPc through secondary and other outer coordination sphere effects. Electrodes modified with polymer-free, five-coordinate CoPc(py) films (py = pyridine) and with CoPc catalysts immobilized in non-coordinating poly-2-vinylpyridine films were prepared to independently investigate the role that each property plays in enhancing CO2RR performance of CoPc-P4VP. These studies show that a synergistic relationship between the primary and outer coordination sphere effects is responsible for the enhanced catalytic activity of CoPc when embedded in the P4VP membrane.

Polyannulated Bis(N-heterocyclic carbene)palladium Pincer Complexes for Electrocatalytic CO2 Reduction

Polyannulated Bis(N-heterocyclic carbene)palladium Pincer Complexes for Electrocatalytic CO2 Reduction

Jeffrey A. Therrien, Michael O. Wolf,* and Brian O. Patrick

Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada

Inorg. Chem. DOI: 10.1021/acs.inorgchem.5b01698

Abstract:

Phenanthro- and pyreno-annulated N-heterocyclic carbenes (NHCs) have been incorporated into lutidine-linked bisNHC Pd pincer complexes to investigate the effect of these polyannulated NHCs on the ability of the complexes to electrochemically reduce CO2 to CO in the presence of 2,2,2-trifluoroacetic acid and 2,2,2-trifluoroethanol as proton sources. These complexes are screened for their ability to reduce CO2 and modeled using density functional theory calculations, where the annulated phenanthrene and pyrene moieties are shown to be additional sites for redox activity in the pincer ligand, enabling increased electron donation. Electrochemical and computational studies are used to gain an understanding of the chemical significance of redox events for complexes of this type, highlighting the importance of anion binding and dissociation.

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