Preparation of Highly Conductive Phthalocyaninato-Cobalt Iodide at the Interface between Aqueous KI Solution and Organic Solvent and Catalytic Properties for Electrochemical Reduction of CO2

Abstract

Abstract For the industrial practical use of cobalt phthalocyanine (CoPc) as a catalyst for CO2 reduction, the effect of improving conductivity of CoPc crystal on the catalytic activity was investigated. Focusing on (phthalocyaninato) cobalt iodide (CoPcI), which is a highly conductive charge-transfer complex, a simple method for synthesizing CoPcI by simply mixing at an interface between aqueous KI solution and CH2Cl2 solution containing CF3COOH and CoPc was developed by applying the CoPc crystal phase transformation method. The X-ray diffraction pattern of the obtained powder at the interface of CoPc organic and potassium iodide aqueous solutions revealed that the powder is composed of one-dimensional columns of CoPc and a linear array of triiodide ions (I3−). UV-vis absorption spectra showed that iodide ions (I−) change to triiodide ions (I3−) at the interface between aqueous KI solution and organic solvent under acidic conditions. The catalytic property of CoPcI was investigated by polarization measurement and electrochemical impedance spectroscopy using a gas diffusion carbon electrode. CoPcI showed high catalytic activity for CO2 reduction with high CO production selectivity.