Degradation Analysis of Aged Fuel Cell Stack via Polarization Change Curve

A 20-cell self-humidifying fuel cell stack containing two types of MEAs was assembled and aged by a 1000-hour durability test. To rapidly and effectively analyze the primary degradation, the polarization change curve is introduced. As the different failure modes have a unique spectrum in the polarization change curve, it can be regarded as the fingerprint of a special degradation mode for repaid analysis. By means of this method, the main failure mode of two-type MEAs was clearly distinguished: one was attributed to the pinhole formation at the hydrogen outlet, and another was caused by catalyst degradation only, as verified by infrared imaging. The two distinct degradation phases were also classified: (i)conditioning phase, featuring with high decay rate, caused by repaid ECSA change from particle size growth of catalyst. (ii) performance phase with minor voltage loss at long test duration, but with RH cycling behind, as in MEA1. Then, an effective H₂-pumping recovery is conducted, and MEA performance rejuvenated to the level of phase transition time (218h). It indicated the voltage loss at the performance phase is reversible, while the conditioning phase is not as expected. Therefore, there are few perquisites for the durability test, including proper selection of current density point as a baseline, test duration beyond the conditioning time, and effective recovery procedure; otherwise, the lifetime of the stack would be extremely underestimated. As massive voltage loss is from catalyst degradation in the conditioning phase for all MEAs and featuring irreversible, more understanding about catalyst degradation at the conditioning phase is suggested for further durability improvement.