Porous separators have been widely used in classical alkaline electrolysers. The development of an advanced separator with low ohmic resistance and hydrogen permeability is essential for operating a high-rate alkaline electrolyser in a dynamic mode. In this study, we report the synthesis of a Zirfon-type separator with a reduced ohmic resistance of 0.10 Ω cm2 and hydrogen permeability of 0.2 × 10−12 mol cm−1 bar−1 sec−1 measured in 30 wt% KOH electrolyte solution at ambient conditions while exploring the effects of coagulation temperature, poly(vinylpyrrolidone) addition, and separator thickness. This separator was employed in the single cell of a lab-scale water electrolyser with non-noble metal catalysts demonstrating a stable cell voltage of 1.83 V at a current density of 1000 mA cm−2, temperature of 80 °C, and 30 wt% KOH concentration in the electrolyte solution during 300 h of operation. The anodic hydrogen content at a low current density of 50 mA cm−2, differential pressure of 0.3 bar, and temperature of 80 °C was only 1.2%, while the corresponding value obtained for a Zirfon PERL separator exceeded 2%. These results are comparable with the cell parameters previously achieved using anion exchange membranes combined with noble metal-based catalysts.