A comprehensive mathematical model for chemical membrane degradation of proton exchange membrane fuel cell with considering precipitated Pt formation

Abstract

Chemical membrane degradation under open-circuit/idling condition results in membrane thinning and gas separation deterioration, which subsequently reduces the durability and lifetime of proton exchange membrane fuel cells (PEMFCs). Traditional membrane degradation models do not consider the existence of precipitated Pt in the membrane. This is the reason why the simulated membrane degradation adjacent to the anode catalyst layer (CL) is more severe than that adjacent to the cathode CL, which is not consistent with the experiment results. To address such an inconsistency, a comprehensive membrane degradation model was developed with consideration of precipitated Pt. In this model, the processes of precipitated Pt formation, H₂O₂ formation and decomposition, and attack of free radicals on membrane are included. This makes the simulated spatial nonuniformity of membrane degradation notably consistent with the experimental results, which subverts the traditional membrane degradation models. The concentration distributions of O₂, H₂, H₂O₂, Fe²⁺/Fe³⁺, as well as local potential and ionomer species in the membrane were obtained. Moreover, membrane degradation under various temperatures and relative humidity values was explored. It was found that an increasing temperature weakens the nonuniformity of membrane degradation and that a lowering humidity can inhibit membrane degradation. Finally, the membrane degradation process can be separated into the finite dissociation and fragmented stages, which are dominated by the scission and unzipping of ionomer chains and falling off of short-chain fragments, respectively. This model enables comprehensive understanding of the membrane degradation process and facilitates the development of corresponding mitigation strategies.