High-current-density experimental operation and dynamic response of a zero-gap alkaline water electrolysis stack at system level

The present paper explores the experimental performance of a zero-gap 500 kW, 30 barg alkaline water electrolysis (AWE) stack and associated electrolyzer balance-of-plant designed for high current-density operation (up to 1.2 A cm −2 ). This paper reports a complete experimental characterization of the system, including performance, efficiency, dynamics, and safety-relevant gas cross contamination. Tests covered 0.2–1.2 A cm −2 , 15–31 barg, and variable production rates (10–110%) under steady and renewable-representative dynamic profiles. Gas purity remained within safety limits at all set points; hydrogen contamination in oxygen stayed below 1.6% vol even at ∼13% production rate. Identified operating conditions to keep system-level specific energy consumption below 50 kWh kg −1 H 2 . Dynamic tests showed fast, repeatable transients (∼10 s for 10–100% load steps; ∼20 s from 0 to 100%, limited by the power unit). Start-up required inertization/cleaning and pressurization, with duration scaling with target pressure and operating current. Energy breakdown indicates auxiliary loads dominate below ∼30% production rate, highlighting a key lever for part-load optimization and grid-flexible operation.