Utilization of Electropolymerized Films of Cobalt Porphyrin for the Reduction of Carbon Dioxide in Aqueous Media

• Published in: ChemCatChem Vol. 8; no. 22; pp. 3536 - 3545
• Main Authors: Pander III, James E., Fogg, Alex, Bocarsly, Andrew B.
• Format: Journal Article
• Language: English
• Published: Weinheim Blackwell Publishing Ltd 22.11.2016; Wiley Subscription Services, Inc
• Subjects: cobalt; electrochemistry; macrocycles; polymers; reduction
• ISSN: 1867-3880; 1867-3899
• DOI: 10.1002/cctc.201600875

A facile electropolymerization process was utilized to prepare electrodes modified with thin films of cobalt protoporphyrin IX. These thin films exhibited a high Faradaic efficiency (84±2 %) for the reduction of CO2 to CO in aqueous solutions near neutral pH with 450 mV of overpotential and a turnover frequency at zero overpotential (log(TOF0)) of −5.9. The production of CO was stable over several hours at these modest potentials. The use of a 13CO2 reactant led exclusively to 13CO as the product. Polymeric films of the unmetalated porphyrin did not demonstrate catalysis for CO2 reduction. UV/Vis spectroelectrochemical experiments indicate that the parent CoII complex is reduced to CoI at the electrode surface before interaction with CO2. It is proposed that the rate‐determining step in the reduction of CO2 is the initial reduction of the CoII moiety to CoI, which binds CO2 and then undergoes a proton‐coupled electron transfer and a loss of water to form CO. Additionally, a new metric for the evaluation of electrocatalysts, the catalytic efficiency, is proposed. The catalytic efficiency is the ratio of the power stored to power consumed for a given electrochemical reaction and can be used to describe both the kinetics and overpotential considerations of a given system. The reduction of carbon dioxide: A facile electropolymerization process is utilized to prepare electrodes modified with thin films of cobalt protoporphyrin IX. These thin films exhibit a high Faradaic efficiency (84±2 %) for the reduction of CO2 to CO in aqueous solutions near neutral pH with 450 mV of overpotential and a turnover frequency at zero overpotential of −5.9. A new metric for the evaluation of electrocatalysts, the catalytic efficiency, is proposed.