High-performance CoII-phthalocyanine-based polymer for practical heterogeneous electrochemical reduction of carbon dioxide

Abstract

A new bithiophenyl-substituted CoII-phthalocyanine is synthesized and electropolymerized to obtain corresponding polymer films on an indium tin oxide-coated glass and a carbon paper. Formation of the target polymer on substrates is confirmed by Ultraviolet–visible spectrophotometry, Raman spectroscopy and attenuated total reflection-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy analysis, scanning electron microscopy and energy dispersive X-ray spectroscopy. Heterogeneous electrochemical reduction of carbon dioxide (CO2) in a 0.5 M KHCO3 aqueous solution under catalysis of the target polymer coated on the carbon paper gives carbon monoxide (CO) as a major product. Controlled potential electrolysis at a constant potential of –0.66 V vs. reversible hydrogen electrode, corresponding an overpotential of –0.54 V from thermodynamic potential for CO production, for 2 h leads to optimum yield of CO with Faradaic efficiency (FE), turnover number (TON) and turnover frequency (TOF) of 94%, 2.10 × 103 and 0.29 s–1, respectively. Upon 20-h electrolysis with quantitative product monitoring, the target polymer appears to be stable throughout the process and continuously produces CO with the FE, TON and TOF of 72%, 1.24 × 104 and 0.17 s–1, respectively. Spectroelectrochemical study suggests metal-centered mechanism via formation of active reduced species having significant interaction of CoI with CO2. This research demonstrates the use of the synthetically practical CoII-phthalocyanine-based polymeric material as an efficient and stable electrocatalyst for the CO2 reduction.