Development of an Accelerated Stress Test for Fuel Cell Freeze Start Durability Validation Using Real-World Driving Data of Light-Duty FCEVs

The reliability and durability of vehicles are crucial for the acceptance of new technologies by customers. Realistic test methods are necessary to validate or ensure the lifespan of vehicles and their components, particularly regarding specific conditions such as freeze start. This article provides an overview of the current state of research on the effects of freeze starts on the degradation of fuel cells. With this knowledge, relevant operating and boundary conditions for potential damage of the fuel cell are identified (e.g. start temperature, duration in subzero operation, dehydration). The field data from the BMW demonstrator fleet of iX5 Hydrogen Next were analyzed to gain insights into realistic freeze start related stress to the fuel cells. The dynamics of heating rates and the influence of the operating strategy are best represented on a Fuel Cell System (FCS). An experimental setup for a stack centered test on a FCS was developed including a climatic chamber and a subzero coolant supply in this study. The identified automotive conditions could be implemented similarly and reproducibly for the stack. In total of 140 freeze starts with the start stack temperatures between - 7 °C and - 18 °C were performed. These test results and the vehicle data were compared, and the limitations of this accelerated stress test are stated. The advantage of this method is the feasibility to validate the lifetime regarding freeze starts within a period of 1-2 month in 24/7 operation. The occurred problems during test development and their solutions are also described, and suggestions for improvement for less damaging freeze starts process are given.