High Pressure Electrochemical Reduction of CO(2) to Formic Acid/Formate: A Comparison between Bipolar Membranes and Cation Exchange Membranes

[Image: see text] A high pressure semicontinuous batch electrolyzer is used to convert CO(2) to formic acid/formate on a tin-based cathode using bipolar membranes (BPMs) and cation exchange membranes (CEMs). The effects of CO(2) pressure up to 50 bar, electrolyte concentration, flow rate, cell potential, and the two types of membranes on the current density (CD) and Faraday efficiency (FE) for formic acid/formate are investigated. Increasing the CO(2) pressure yields a high FE up to 90% at a cell potential of 3.5 V and a CD of ∼30 mA/cm(2). The FE decreases significantly at higher cell potentials and current densities, and lower pressures. Up to 2 wt % formate was produced at a cell potential of 4 V, a CD of ∼100 mA/cm(2), and a FE of 65%. The advantages and disadvantages of using BPMs and CEMs in electrochemical cells for CO(2) conversion to formic acid/formate are discussed.