In recent decades, CO₂ capture and utilization (CCU) strategy has been actively promoted because of the potential of CO₂ to be used as a feedstock for producing useful organic and inorganic substances such as methanol, formic acid, and carbonates through biological, thermal, photochemical and electrochemical methods.

In this study, we report a development of compact continuous-flow electrochemical cells for an energy-efficient electrochemical splitting of brine (aqueous NaCl) to produce alkali (NaOH) and hydrochloric acid (HCl) that would be used to convert carbon dioxide into carbonate minerals at a subsequent stage. Cell structures and types of polymer electrolyte membranes (PEMs) have been explored for constructing energy efficient electrochemical cells in terms of reaction rates and caustic (Faradaic) efficiencies (CE). Two types of cell designs representing a first version (design 1, namely one-membrane cell) and an advanced version (design 2, namely two-membranes cell) are investigated.

The one-membrane cell consisted of a membrane sandwiched between an anode and a cathode. A feedstock comprised of a NaCl solution and H₂ gas was supplied to the anode side while pure water was supplied to the cathode side. Upon applying a voltage of 1.5V between the two electrodes, the electrolytic reactions proceeded to produce HCl at the anode and NaOH and H₂ at the cathode. In the case of two-membrane cells, two-membranes were used and a separator plate was placed between the two membranes and the NaCl solution was fed to the separator plate while H₂ gas was fed to the anode.

The one-membrane cells show initial reaction rates as high as 400 mA/cm² at an applied voltage of 1.5V. The reaction rate, however, drops rapidly due to the degradation of the anode catalyst by hydrochloric acid that is produced at the anode side during the reaction. On the other hand, the two-membranes cells show very stable performance over 200 hours though their reaction rates are kept below 80mA/cm² at an applied voltage of 1.5V. In addition, we have tested various types of fluorine-based and hydrocarbon-based polymer electrolyte membranes. While two-membranes cells display definitely higher CEs than their counter parts, some membranes show comparable CEs even in a one-membrane cell. Therefore, development of PEMs suitable for this electrolytic cells is crucial in improving the cell performance. Optimization of the operating conditions, cell structures and types of membranes have been further carried out to enhance the reaction rates while maintaining the CEs high.

In conclusion, the two-membranes cells are estimated superior to the one-membrane cells because of their stability over long run though their reaction rates are somewhat lower than the latter.