Study on Separator for Alkaline Water Electrolysis

The performance of separators of ion-exchange membrane (IEM) and diaphragm types in the zero-gap system of alkaline water electrolysis (AWE) was examined using different sizes of cells (i.e., 20, 100 and 1600 cm 2 ).The optimum KOH concentrations for AWE were found to be ca.15 and 25-30 wt% for IEM and diaphragm, respectively, which are different from the KOH concentration (ca.35 wt% at 80 • C) at which the maximum conductivity is obtained.It was confirmed that only anode side feeding operation is available without any serious mixing of both anolyte and catholyte using 1600 cm 2 pilot-cell under ca 2.94 kPa differential pressure, typically, the cell voltage of 1600 cm 2 pilot-cell was 1.81 V at 0.4 A/cm 2 and 82 • C with hydrogen purity of 99.96%.The flow rate of electrolyte does not dominate the purity of hydrogen gas produced.The fluctuation of cell voltage in the diaphragm-based AWE process is very large, suggesting that the quality and/or pretreatment of diaphragm dominate the performance of AWE.It was also confirmed that the diffusion amounts through the diaphragm as gas and dissolved species are on the same level.