Experimental Study of PEMFC Stack Performance Degradation Considering the Shutdown and Rest Processes

The improvement of durability is one of the most critical factors for expanding the commercialization of proton exchange membrane fuel cells (PEMFCs). Many experimental studies of continuous operation cycles have been carried out to gain an understanding of fuel cell durability, ignoring the shutdown and rest process. This paper performed durability tests over 1000 h in total, including the shutdown and rest processes, to investigate the impact of voltage recovery on cell degradation in real applications. Each durability test was operated only 8-10 h per day, and then the stack entered a shutdown and rest process. The results show that the voltage recovery after the shutdown and rest processes makes the fuel cells maintain the performance in the long term. The performance can be higher than the previous stage, which differs from the constant performance degradation observed in continuous tests. This paper specifically investigates the influence of operating conditions on durability, the characteristics of voltage degradation, and the underlying reasons for those phenomena during dynamic cycles that include shutdown and rest processes. The decrease in voltage uniformity is analyzed. The results indicate that imprecise control of the operating conditions could lead to a reduction in the fuel cell durability. During the processes of voltage degradation and recovery, marked improvements in performance are observed. Following the initial rapid decline in performance, the fuel cell degradation exhibited a strong correlation with the variations in voltage uniformity. Notably, the excessive degradation observed in a certain cell was the primary factor contributing to the reduction in voltage uniformity rather than the overall cell's nonuniform voltage. The shutdown and rest processes are crucial components of the dynamic cycles, and the mechanism of voltage recovery after the shutdown and rest processes should be focused on to improve the fuel cell life.