Voltage Stability Challenges in a 1 kW-Class PEMFC Stack for Air-Independent Propulsion Applications

This study investigates the operational behavior and voltage stability of a 1 kW-class AIP PEMFC stack under high-pressure H2 and O2 conditions. AIP PEMFCs, unlike conventional air-based systems, operate in enclosed environments using stored O2, requiring designs that minimize parasitic power losses while ensuring stable operation. To establish a performance baseline, single cell tests were conducted to isolate the effects of in-plane components, including the MEA, GDL, and flow field geometry. Results indicated that temperature and pressure significantly influenced performance, whereas humidity and flow rate had minimal effects under the tested conditions. A 27-cell stack was then assembled and evaluated under various current densities, flow rates, and humidity levels. Time-resolved voltage measurements revealed that low flow rates (stoichiometry ≤ 1.5) led to voltage instability, particularly at high humidity and current density. Instability was more pronounced in cells positioned farthest from the inlet and outlet ports. These findings underscore the importance of optimizing operational parameters and stack architecture to achieve stable AIP PEMFC performance under reduced flow conditions. The results provide key insights for developing compact, efficient, and durable AIP fuel cell systems for use in enclosed or submerged environments such as submarines or unmanned underwater vehicles, while highlighting key challenges associated with AIP-targeted applications.