Fuel cell system degradation analysis of a Chinese plug-in hybrid fuel cell city bus

•A two-stage flowchart is proposed for performance degradation analysis of fuel cell vehicles.•A detailed on-road fuel cell stack performance degradation analysis is presented.•The voltage declines of different degradation mechanisms are compared.•The performance degradation otherness in five regions of a fuel cell stack is analyzed.

Fuel cell hybrid electric vehicles are attracting increasing attention and research. However, the durability of fuel cell systems (FCS) is the main bottleneck in commercial application. A plug-in fuel cell city bus was developed by our group, and it completed several months of demonstration operation. A two-stage flowchart was proposed to clarify the FCS degradation analysis. The average cell voltage decline rate is approximately 346 μV/h at a current density of 120 A, under which the initial voltage is about 0.7 V. The estimated lifetime in the third stage reaches the design target. The final electrochemically active surface areas are approximately 80% of the initial value. A detailed degradation analysis of fuel cell voltage uniformity is presented, and a five-region degradation otherness analysis is proposed for performance uniformity analysis. The difference of equivalent resistance has been verified to be the main factor in degradation otherness of the regions and in system performance degradation.