Experimental Validation of ENDURE Testing Protocols Using a Zero-Gap 10-kW Alkaline Stack with a Unique Three-Dimensional Electrode Architecture

This work presents the validation of stack-level testing protocols on a 10-kW zero-gap alkaline water electrolysis stack equipped with Ni-foam electrodes with a unique three-dimensional electrode architecture. The experimental methodology comprises a first fingerprint test to define the operating window, a 400-h long-term test, and a second fingerprint to assess performance evolution, supported by electrochemical impedance spectroscopy (EIS). The stack is characterised over 0.3–0.7 A/cm 2 , 5–20 barg, and 0.12–0.37 mL/min/cm 2 . During the 400-h operation, a voltage decrease of 53–67 mV per cell is observed, indicating performance improvement rather than degradation, likely linked to a break-in effect. Crossover also decreased over time. 2nd fingerprint measurements confirm a persistent voltage reduction of 80–121 mV across operating conditions. EIS analysis at stack level further provides unique insight into the evolution of cell resistances and reaction kinetics. Overall, the results demonstrate the validity of the proposed testing protocol.