Electrochemical reduction of CO2 into CO in tetrabutylammonium perchlorate/propylene carbonate: Water effects and mechanism

Electrochemical reduction of carbon dioxide (CO2) into carbon monoxide (CO) is of interesting because this method has a promising prospect in the chemical industry. Since CO2 is a non-polar molecule, and has high solubility in organic solvent, it would be beneficial to conduct CO2 reduction in organic electrolyte. However, because the electrochemical reduction of CO2 into CO naturally produces H2O, this reaction actually proceeds under the influence of H2O. In present work, we have investigated a variety of commonly used organic electrolytes with the aim to look for an organic electrolyte which is suitable for industrial application. By comparison, we have selected tetrabutylammonium perchlorate (Bu4NClO4)/propylene carbonate (PC) as the desirable one. It has been found that the presence of H2O in Bu4NClO4/PC plays a crucial role in improving the performance of Bu4NClO4/PC, such as increasing conductivity, decreasing viscosity, promoting CO2 solubility. In addition, owing to the hydrophobic nature of PC, H2O can separate from Bu4NClO4/PC when its content exceeds 6.8 wt %. This advantage is crucial for industrial application. We have conducted CO2 reduction in Bu4NClO4/PC containing 6.8 wt % H2O at Au electrode for 4 h. The Faradaic efficiency for CO formation and the cathodic current density have been stabilized at 84.3% and 6.3 mA/cm2 after 30 minuet of electrolysis, no degradation has been observed on the performance of Bu4NClO4/PC, indicating NBu4NClO4/PC has a promising perspective in the chemical industry.