Development of Polymer Composite Membranes with Hydrophilic TiO<sub>2</sub> Nanoparticles and Perfluorosulfonic Acid-Based Electrolyte for Polymer Electrolyte Fuel Cells Operating over a Wide Temperature Range
R Ohno, Kazuki Shudo, Tetsuro Tano, Katsuyoshi Kakinuma
Abstract
High Resolution Image Download MS PowerPoint Slide Commercial perfluorosulfonic acid-based electrolyte membranes (PFSA, e.g., Nafion) are essential components in polymer electrolyte fuel cells (PEFCs) operated in the normal temperature range from 60 to 80 °C. Toward the widespread use of heavy-duty vehicles (HDVs) equipped with PEFCs, it will be necessary to approach higher temperature operation, up to approximately 120 °C, in addition to the normal temperature range, leading to the concept of so-called wide temperature range operation. We here propose a composite PFSA membrane with a hydrophilic filler of Ta-doped TiO 2 (Ta-TiO 2 ) for wide temperature range operation. A composite PFSA membrane (9 cm × 9 cm × 25 μm t ) prepared by die coating was flexible, without pores or cracks. The hydrophilic Ta-TiO 2 filler with a unique fused-aggregate network microstructure was well-dispersed in the composite membrane. The proton conductivity of the composite membrane was found to be 1.3 times higher than that of a commercial Nafion membrane at 80 °C over a wide humidity range, from 20% RH to 80% RH. Small-angle X-ray scattering (SAXS) profiles indicated a morphological change of the composite membrane compared with a commercial Nafion membrane and the preservation of a constant water cluster size over a wide range of humidity. The proton conductivity also increased, without an increase in water uptake, most likely due to enhanced hopping between the clusters. The mechanical strength of the composite membrane was similar to that of the commercial membrane. The current–voltage performance of a single cell using the composite membrane was higher than that for a cell using a commercial Nafion membrane at 120 °C, 20% RH, and was equivalent to that of a cell using Nafion at 80 °C, 100% RH. Thus, the newly developed composite membrane can be considered as an effective candidate to be applied in PEFCs operating over a wide temperature range.