Proton Exchange Membrane Fuel Cell Chemical and Mechanical Durability Study of Heteropoly Acid Functionalized Perfluorinated Sulfonic Acid with Expanded Polyteterafluoroethylene Support

Abstract

The application of proton exchange membrane fuel cells to heavy-duty vehicles has been a new trend for fuel cell society due to high efficiency, power density, faster refueling, and ability to remove auxiliary power units. However, the critical bottleneck for the commercialization and technology transfer from already-commercialized light-duty fuel cell vehicles is the chemical and mechanical durability of the proton exchange membranes. Chemical degradation is initiated by H2O2 which forms ▪OH radicals during the fuel cell operation. The radicals that are formed during the fuel cell operation can be suppressed by adding a radical decomposing catalyst such as cerium, cerium oxide, manganese, manganese oxide, and heteropoly acids. However, those metal oxides and heteropoly acids lack immobilization. We have previously reported the chemical immobilization of silicotungstic acid (HPA), a heteropoly acid with radical decomposing functionality, using dehydrofluorination. This has resulted in improvements in both the chemical durability and proton conductivity, wherein the HPA serves as a proton conductor.In this study, we applied the chemical anchoring synthesis method to multiple polymers with different binding monomer group ratios and supported with expanded-polyterafluorethylene (e-PTFE) support. We investigated the optimized HPA ratio to the perfluorinated sulfonic acid membrane and studied the chemical and mechanical durability of the composite membrane. The structure-property relationship of composite membranes was studied using scanning electron microscopy (SEM), small angle x-ray scattering, and dynamic mechanical analysis (DMA). The chemical degradation was tested with open-circuit voltage (OCV) and fluoride release rate (FRR) under the accelerated standard condition (AST).