Cold Start Degradation of Proton Exchange Membrane Fuel Cell: Dynamic and Mechanism

Improving cold start durability is essential for the commercialization of proton exchange membrane fuel cells (PEMFCs). This paper focuses on degradation mechanism of cold start. By applying segmented print circuit board technology and local characterizations, the degradation behavior of cold start is analyzed in combination with the dynamic response during cold start for the first time, and the degradation mechanism is built from macroscopic to microscopic. The results show that cell performance and uniformity of the current density distribution are severely degraded after 30 cold start failures. Local current density tests show that during failed cold start, the current is first generated downstream of the cathode, and most of the current is generated there before the cold start fails, suggesting that the in-plane distribution of ice in the catalyst layer is not uniform. Local electrochemical and physical characterizations on the downstream, middle and upstream regions demonstrate that the degradation of the downstream region is the most severe, while the middle and upstream regions is slight, which further illustrates the non-uniformity of the degradation distribution during failed cold start. Meanwhile, local physical characterizations indicate that freezing induced crack formation, Pt particle growth, and ionomer agglomeration in the catalyst layer are the root cause of the freezing damage. Through comprehensive characterizations in the research, the degradation mechanism of cold start is investigated in a more profound way, which is conductive to understand the cold start process.