Cation Contamination in Polymer Electrolyte Fuel Cells: Impacts, Mechanisms, and Mitigation

Polymer electrolyte fuel cells (PEFCs), a promising source of clean energy in automotive application, still require durability improvement before commercialization. Cationic contaminants originated from either the ambient air (e.g. roadside contaminants) or from the corrosion of stack and balance of plant components can significantly decrease the performance and life time of PEFCs. This work is focused on the experimental and theoretical study of the effects of cationic contaminants on the performance of PEFCs. Specifically, this work assesses the impact of a foreign cation on the durability of PEFCs, clarify the mechanisms responsible for the performance degradation, devise performance recovery strategies after exposure to a foreign cation, and complete an analytical model. In the cation contamination model, a catalyst agglomerate model was utilized and for the first time, a decrease in oxygen concentration in the catalyst layer was found due to cation contamination. During experimental studies, it was found that ingress of cation into the membrane increased high frequency resistance (HFR) more than 50% in the individual membrane layer and water management was significantly affected by cation contamination which may result in salt precipitation causing serious mass transport losses, and salt was preferentially deposited at the outlet of the cell at our operating conditions. It was also found that gas diffusion layer (GDL) played an important role in the transport of cations in as well as out of the membrane electrode assembly (MEA), and hydrophobic nature of the GDL can act as a barrier to the transport of cation solution. Based on experimental and computational model, mitigation methodologies for cation contamination were designed depending on the presence of contaminants in various parts of the fuel cell. Cation contaminants from the membrane can be completely removed by re-protonating the membrane using acidic solution. For removing salt deposit from GDL and flow field, an ex-situ acid flush technique was utilized and salt deposit on flow field was completely removed, whereas some white patches of salt deposit still was observed on the GDL. Ex-situ mitigation process using acidic solution worked well, but additional factors need to be identified that hinder the full recovery process.