To produce formic acid from CO2 Renew CO2 is working on the development of a commercially viable, aqueous triple compartment electrolyzer, a chemical reactor using an electrical potential to drive the conversion of CO2. On the cathode, the side of the reactor where the negative potential is applied, CO2 is reduced to form, or deprotonated formic acid. On the opposite side, the anode, the reactor is producing protons for acidification of the mixture.
A gas diffusion electrode (GDE), referring to an electrode that, in opposite to simple metal sheets, consists of tin nanoparticles dispersed on a porous carbon mesh serves as the cathode, whereas a second GDE using iridium as catalyst acts as a anode. The use of GDEs dramatically improves reactor performance as the CO2 can be pumped through the pores in the electrodes, overcoming inherent solubility problems a traditional reactor would face when trying to dissolve CO2 in water.
The anode and cathode are separated by an anionic exchange membrane, composed of a porous polymer structure functionalized with positively charged side groups, next to the cathode and a cationic exchange membrane, bearing negatively charged groups, close to the anode. The charged groups of the membranes only allow ions of the opposite charge to travel through them. These membranes, as depicted in the figure below divide the electrolyzer into its three compartments and are necessary to prevent (1) oxidation of the formate back to CO2 on the anode, (2) protons from poisoning the tin catalyst and (3) a too acidic pH in the cathode compartment leading to efficiency losses due to hydrogen evolution. Formic acid is then produced in the middle compartment by acidification of formate and flushed out of the electrolyzer.