A comprehensive investigation on the effect of hydrogen concentration on the consistency of high-power multi-cell stacks

Nitrogen accumulation at the anode of proton exchange membrane fuel cell (PEMFC) systems necessitates periodic purging. However, excessive purging reduces system efficiency, while insufficient purging leads to hydrogen dilution and voltage inconsistency, particularly in high-power multi-cell stacks. This study investigates the influence of anode hydrogen concentration on stack performance and voltage uniformity under various operating conditions. Results reveal a two-stage voltage degradation behavior, with a clear turning point at 85 % hydrogen concentration under 231 A, beyond which the voltage decay rate accelerates sharply, reaching 15.6 % at 77 %. Cells near the hydrogen inlet exhibit the most pronounced decline. Moderate temperature elevation improves membrane hydration and gas diffusivity, enhancing voltage consistency, while overheating induces dehydration and performance loss. Adjusting blower speed and pressure differentials alleviates local hydrogen starvation but cannot fully address distribution imbalances. At 330 A, cell 209 shows an exponential increase in voltage decay as hydrogen concentration drops from 84 % to 80 %, indicating a heightened starvation risk. A compensatory relationship between hydrogen concentration and inlet stoichiometric ratio is established, enabling the definition of a boundary curve for purge control. This work provides a quantitative basis for optimizing hydrogen concentration thresholds and anode recirculation strategies, contributing to improved hydrogen utilization efficiency and supporting the broader goals of efficient, low-emission energy systems.