Optimization of Fuel Cell Self-Humidifying System Design and SUSD Control Strategies

Abstract

Fuel cells are widely used in vehicles and are characterized by frequent start-up/shut-down (SUSD) and dynamic load changes. These characteristics often lead to inadequate gas humidification and rapid catalyst and carbon support degradation, which can accelerate fuel cell performance deterioration. In this study, a fuel cell self-humidifying system is designed and the SUSD control strategies are optimized to address the insufficient gas humidification and rapid catalyst and carbon support degradation problems. To avoid insufficient air humidification, cooling water is allowed to flow into the wet side of the humidifier to increase the air humidity, which in turn improves the performance output of the fuel cell. The water generated by the fuel cell system is condensed and recycled into the cooling system. The adequacy of the amount of condensing water depends on the power output requirements of the system and the condensing temperature settings. Experimental results show that a condensing temperature setting of 40 °C is optimal as it satisfies the humidification water requirements for different system outputs and minimizes the power consumption of the condensing fan. The results also demonstrated a 10.4% improvement in fuel cell performance at an output power of 2.97 kW. The SUSD control strategies were optimized by changing the operating voltage, reactant concentration, and reaction time. The effect of carbon corrosion on cell performance was reduced via voltage control, vacuum pumping, and gas evacuation. After 3000 SUSD tests, the results showed a 3.6% degradation rate at the main operating power (500 mA/cm²)—a significant improvement compared with the 17.6% degradation rate of the conventional non-optimized SUSD strategy. Besides the theoretical and experimental analyses, the results of this study were integrated into a fuel cell scooter to demonstrate its feasibility. Additionally, a standard dynamic load test based on the Chinese National Standards (CNS 3105) was performed. The findings of this study could be applied to any vehicle type to enhance the performance and durability of fuel cell systems.