Enhancements to electrocatalyic reduction of CO_2 by cobalt phthalocyanine upon immobization in polyvinylpyridine membrane

Abstract

The factors governing the electrocatalytic CO_2 redn. reaction (CO_2RR) by cobalt phthalocyanine (CoPc) modified edge-plane graphite electrodes have been studied by a no. of electrochem. techniques. Electrodes modified with CoPc immobilized in poly-4-vinylpridine (PVP) show dramatic enhanced activity and selectivity compared to electrodes modified with CoPc alone. CoPc-PVP films reduce CO_2 to CO with Faradaic efficiencies of 98% while displaying large TON and TOF. Two properties of PVP contribute to enhancing the activity of CoPc; (1) the ability of individual pyridine residues to coordinate to CoPc and (2) the high concn. of uncoordinated pyridine residues throughout the film. Electrodes modified with polymer-free, five-coordinate CoPc(L) films (L = pyridine and 4-dimethylaminopyridine) and with CoPc catalysts immobilized in the noncoordinating poly-2-vinylpyridine were prepd. to independently investigate the role of each property plays in enhancing CO_2RR activity of CoPc-PVP. These studies showed that a synergistic relationship between axial coordination and the PVP chem. environment is responsible for the enhanced catalytic activity of CoPc when embedded in the polymer membrane. Kinetic anal. of the electrocatalytic activity of each catalyst obtained at rotating-disk electrodes will be presented, as will the results of controlled-potential electrolysis studies.