Modelling of mechanical microstructure changes in the catalyst layer of a polymer electrolyte membrane fuel cell

Microstructure changes in catalyst layers limit durability which is essential for the commercialization of polymer electrolyte membrane fuel cells. In this study, a mathematical model is developed for the mechanical changes in the microstructure of catalyst layers resulting from variations in clamping force, temperature and relative humidity. Finite element method is adopted and cohesive zone model is used to simulate the microstructure behavior, including the occurrence of delamination between different structures and phases as well as within the ionomer due to its breakdown (crack initiation). It is shown that subject to a startup and shutdown cycle, the interface between the ionomer and catalyst agglomerate can start to delaminate near the end of the shutdown process, and the change in the relative humidity is the dominant factor that influences the delamination process, because the ionomer in the catalyst layer structure expands and shrinks with its water content. The delamination between the ionomer and catalyst agglomerate is found to propagate or increase with the number of the startup and shutdown cycles, and nearly 90% of the interface delaminates after 100 cycles. The plastic strain inside the ionomer, which is not fully recoverable, accumulates (increases) with the cycling, although it is smaller than the breakdown strain of the ionomer after 100 cycles, it may lead to the internal crack initiation if the cycling continues. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.