Coupled CO2 reduction and Alcohol Oxidation for Fuel Synthesis and CO2 Utilization

Abstract

Electro-conversion CO2 to fuels like formic acid, methanol, and ethanol is an attractive method to recycle CO2 and close the carbon cycle associated with these fuels, which could benefit the environment, national energy security Many CO2 electrolyzers oxidize water or hydroxyl ions as a counter reaction which releases oxygen. However, this can lead to a large cell potential due to oxygen’s large, positive reduction potential. Further, oxygen is a relatively low-value product. These systems also use an ion exchange membrane to prevent crossover of CO2 reduction products to the anode while conducting ions between the electrodes.Instead of oxygen evolution, the partial oxidation of alcohols could serve as the anodic counter reaction to synthesize oxygenated fuel additives. Partial alcohol oxidation could be coupled with CO2 reduction which could regenerate the alcohol. Coupling the anodic and cathodic reactions in this way could preclude the need for an ion exchange membrane, and lower required energy input by decreasing the thermodynamic cell voltage. Our system is also capable of high-pressure operation, which could allow higher concentrations of CO2 in the electrolyte. This study examines the use of alcohol/water mixtures as a working fluid for a CO2 electrolyzer, and the effect of pressure and catalyst composition on the current density and product selectivity. Linear sweep voltammetry and chronoamperometry will be used to evaluate the current densities and cell voltages for different catalysts at pressures up to 90 bar. Gas and liquid products will be analyzed following chronoamperometry studies to determine the faradaic efficiencies. Noble and transition metal catalysts will be used at the cathode and anode based on their purported ability to drive CO2 reduction to alcohol and partial oxidation of alcohols.