Simulation of a Passive Osmosis-Integrated Electrolyzer for Seawater Electrolysis
Abstract
Efforts to develop direct seawater electrolysis technology have been ongoing due to the need for pure water in electrolysis and the abundance of seawater. However, progress has been hampered by several issues, including competition with the chlorine evolution reaction, higher membrane resistance, corrosion of electrodes, and scaling from multivalent cations [1]. To avoid these issues, our project has proposed a new reactor that integrates passive osmosis (extracting fresh water from seawater) with electrolysis. In this thesis, we will discuss the operation of the osmosis-integrated electrolyzer and show theoretical predictions of the osmotic pressure differential and water flux/velocity profiles under different conditions. The numerical model that will be presented was applied to two generations of cell design. The first-generation cell consists of three different configurations that have been physically developed. The first configuration consists of two anion exchange membranes (AEMs) with two side chambers containing Potassium hydroxide (KOH) and a middle chamber containing Sodium Chloride (NaCl). The second configuration has KOH in one outer compartment and Sulfuric acid (H2SO4) in the other. The central compartment containing NaCl is separated from the KOH compartment by an AEM and the H2SO4 compartment by a cation exchange membrane (CEM). The third configuration eliminates the central compartment and allows osmosis to occur outside of the cell. On the other hand, the second-generation cell consists of four compartments in which seawater is fed to outer compartments, and the middle compartments are initially filled with KOH with different concentrations. In addition, those compartments are separated into two AEMs. The simulation results for both generations show that by increasing the concentration of KOH and H2SO4 in the side chambers for all three models, the amount of water transferred from the middle chamber, containing NaCl to the side chambers increases. The simulation results were validated by experiments. In addition, the model can quantify the transport of ions in the system, including chloride ions through the AEM. Lastly, the mass transfer model is integrated with an electrochemical model where an anode and cathode are added to the second-generation system to consume the water that is transported through the membranes.