Electrodeposition of Carbon from CO2 in Room-Temperature Ionic Liquid Triethylpentylphosphonium Bis(trifluoromethanesulfonyl)imide

Abstract

The conversion of CO2 to solid carbon by the electrochemical method is an attractive process as a CO2 recycling technology, but the electrolyte has been limited to high-temperature molten salts. In this study, the electrodeposition of solid carbon from CO2 on an Ag substrate in triethylpentylphosphonium bis(trifluoromethanesulfonyl)imide at room temperature and 1 atm CO2 atmosphere was investigated. Cyclic voltammetry with multiple cycles revealed that the three potential steps causing reduction, oxidation, and reduction current are important for the carbon electrodeposition from CO2. Based on the cyclic voltammogram, potentiostatic electrolysis was performed in the three potential steps. Consequently, the Ag substrate was covered with a black film because of the electrodeposited solid carbon. Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy revealed that the deposits were composed of the electrodeposited solid carbon and nanometer-size silver particles coming from the Ag substrate. From the experimental results, we propose a model of the electrochemical formation mechanism of solid carbon from CO2 on the Ag substrate. This study shows that the electrochemical method has the potential to convert CO2 into valuable carbonaceous materials with optimized electrochemical parameters, even at room temperature, and that this technique will contribute to developing a carbon-circulation society.