Alkaline water electrolyzer (AWE) can be an economical choice to achieve large-scale hydrogen production due to its high maturity and low material cost. Pressurized electrolyzers combined with renewable energy sources are essential for power to gas applications. However, the use of porous separators in AWE limits high-pressure operation due to gas crossover, which is far less than that of PEM electrolysis. Here, we propose a modified polyphenylene sulfide (mPPS)-incorporated separator with gas cross-resistance and high ionic conductivity. The mPPS showed improved tensile strength and the formation of hydrogen bonds with polymer binders, leading to the denser morphology. Electrolytic cells with advanced electrodes achieve 85% efficiency (1.74V) at a high current density of 1A cm–2 over 300 hours of operation. The anode hydrogen content is only 0.1% at a differential pressure of 0.3 bar, while that of the Zirfon separator is above 2%. The mPPS-containing separator allows pressurized AWE to operate more safely and dynamically over a wider load range.