Synthesis and electropolymerization of phthalocyanine derivatives for electrochemical reduction of carbon dioxide

Abstract

This research describes synthesis and electrochemical polymerization of novel bithiophenyl-substituted phthalocyanines in order to get polymeric films that have electrocatalytic activities towards reduction of carbon dioxide (CO2). The target phthalocyanine monomers are synthesized by a two-step procedure including Suzuki reaction and cyclization of the resulting phthalonitrile. After that, electropolymerization of the target monomers on an indium tin oxide-coated glasses or carbon papers is performed by a cyclic voltammetry technique. The resulting polymer films are characterized by various spectroscopic methods. Catalytic performance towards the electrochemical reduction of CO2 of these polymers is investigated by the cyclic voltammetry and controlled potential electrolysis measurements. The results show that the polymer film of the cobalt(II) phthalocyanine derivative on the carbon papers exhibits remarkable electrocatalytic performance among all polymers by giving carbon monoxide (CO) with faradaic efficiency (FE) 94% as a major product by applying potential of –1.30 V vs. Ag/AgCl (3M KCl) and a 0.5 M KHCO3 aqueous solution in a three-electrode two-compartment cell after 2-h electrolysis. Upon 20-h electrolysis under the same condition by using online gas chromatography monitoring, this polymer film is found to be stable throughout the experiment and afforded CO at constant current density and FE of 72%, corresponding to accumulated turnover number and average turnover frequency of 12,359 and 0.17 s–1, respectively.