Formic acid generated from CO2 has been proposed both as a key intermediate renewable chemical feedstock as well as a potential energy storage chemical media for hydrogen. In this paper, we describe a novel three compartment electrochemical cell configuration with the capability of directly producing a pure formic acid product in the concentration range of 5 – 20 wt% at high current densities and Faradaic yields. The electrochemical cell employs a Dioxide Materials Sustainion™ anion membrane, allowing for the improved CO2 electrochemical reduction performance. Stable electrochemical cell performance for more than 500 hours has been experimentally demonstrated.

Figure 1 shows the current produced as a function of the cell voltage in a cell with a tin cathode, and IrO2 anode, and deionized water in the middle compartment with no electrolyte added to the water. Notice that one can obtain up to 200 mA/cm² at reasonable cell voltages.

Figure 2 shows how the exit concentration and Faradaic efficiency varies with flowrate. Experimentally, as the Faradaic efficiency decreases as the formic acid concentration rises. Physically, the some of the formic acid is transported to the anode, where it is oxidized leading to formic acid loss. The use of thicker and/or higher MW PSA cation membranes significantly reduces these formate losses.

Figure 3 shows a steady state run. In this case, we are able to maintain an output concentration of 15% formic acid for 500 hours, with no significant change in cell voltage.