The rapid expansion of renewable energy sources present a great challenge to balance the electric grid due to their intermittent and volatile nature. Alkaline water electrolysis can be operated in a dynamic mode using renewable energy sources on a large scale. The commercial porous separator Zirfon PERL exhibits a satisfactory performance. However it suffers from limited dynamic range of the electrolyzer. Therefore, it is necessary to develop a porous separator with reduced gas crossover. In this study, we synthesize a porous ZrO2/polysulfone composite separator via the film casting method. The synthesized composite separator shows a high bubble point, a low ionic resistance, and are reduced hydrogen permeability compared to that of Zirfon PERL separator. The enhanced performance of this separator is attributed to the reduced average pore size high surface wettability. This result will help an alkaline electrolyzer systems be operated as more controllable loads.