Alkaline water electrolysis is one of the most efficient ways to produce hydrogen in a large scale with mature technique. It employs porous separators to provide the ionic conductivity of alkaline electrolyte between the electrodes, while separating the evolved gases. Zirconia nanoparticles and polysulfone composite separator exhibits satisfactory performance of high bubble point (2.5 bar) and low area resistance (~0.3 Ωcm²). However, the alkaline water electrolysis shows the efficiency loss in the lower partial load mainly due to the gas crossover through the separator. Therefore, detailed characterization and its effects on bubble point, resistance, and gas crossover are investigated.

In this study, we synthesized a porous ZrO₂/polysulfone composite separator varying the amount of ZrO₂ (70-85 wt.%) via film casting method. Scanning electron microscopy and thermogravimetric analysis show that the increased amount of ZrO2 reduces the bubble point and area resistance and increases the gas crossover, mainly due to the instability of the composite separator. 80wt.% ZrO₂/20wt.% polysulfone composite separator shows a bubble point of 2.1 bar, low area resistance (~0.2 Ωcm²) and reduced hydrogen permeability (<2 E-11 mol cm^-1 bar^-1 sec^-1) compared to the Zirfon PERL^® separator. The enhanced performance is attributed to large portion of small size pore (< 100 nm from Hg porosimetry) and increased concentration of ZrO2 nanoparticles on the skin surface (XPS analysis), resulting in the high wettability. This experimental study suggests the various characterization methods that determine the performance of the composite separator for alkaline water electrolysis coupled with the renewable energy sources.