PEMFC cathode humidification: Can direct water injection compete with membrane humifiers? A direct comparison study

Proton exchange membrane fuel cells (PEMFCs) require effective water management for optimal performance. To achieve this, the majority of current PEMFC systems for mobility applications employ a membrane humidifier. Membrane humidifiers are effective but costly, cumbersome, and fragile. Direct water injection in the airflow feeding the cathode represents a promising alternative. However, it remains relatively under-explored in the literature, as flooding issues encountered in early studies were considered a drawback compared to membrane humidifiers. To our knowledge, no previous study directly compared the performance of both direct water injection and membrane humidifiers for the same fuel cell stack and operating conditions. The present study addresses this gap. We present experimental results obtained with a recent 2 kW short-stack that confirm the effectiveness of direct water injection, but show a 5 % decrease in cell voltage compared to the membrane humidifier method under nominal operating conditions. We argue that this voltage decrease is due to poorer membrane hydration, despite a sufficient amount of water entering the cathode, and identify opportunities for optimization of direct water injection performance. • Direct water injection and membrane humidifier for PEMFC humidification are compared. • Cell voltage at 1 A/cm 2 was 40 mV lower with direct water injection than with a membrane humidifier. • Presented the effect of water flow rate and cell temperature on direct water injection performance. • Lower performance of the direct water injection was due to incomplete evaporation of liquid water.