We developed polymer electrolyte membranes (PEMs) utilizing charge-transfer (CT) interactions for polymer electrolyte fuel cells (PEFCs). CT complex formation was applied to control the position of proton conductive groups in the membranes. To understand the effect of CT complex formation on PEM performance, heat treatment was performed to enhance the extent of CT complex formation in the membrane. In this work, sulfonated polyimide (SPI) was used as the electron-accepting polymer, while polyether-containing electron-rich dialkoxy­naphthalene (Poly-DAN) was used as the electron-donating polymer. After heat treatment at 150 °C for 50 h, the concentration of CT complex in the membrane was significantly enhanced by about 13 times. Heat-treated SPI/Poly-DAN membranes showed higher mechanical strength (50.8 MPa) than Nafion 212 (15.5 MPa) and highly chemical durability compared to the untreated membrane by the synergetic effect of enhanced CT complex formation and chemical cross-linking. Heat-treated SPI/Poly-DAN membranes also showed reasonable proton conductivity (32.3 mS cm–1, 80 °C, and 90% RH), although some cross-linking occurred between sulfonic acid units due to the heat treatment process. In single cell tests, heat-treated SPI/Poly-DAN membranes had maximum power densities of 255 mW cm–2 at 80 °C and 95% RH and 59.0 mW cm–2 at 110 °C and 31% RH, indicating that these heat-treated CT complex membranes could be used for fuel cell applications.

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− Recently, there are many efforts focused on development of more economical non-fluorinated membranes for PEMFCs (Proton Exchange Membrane Fuel Cells). In this study, to test the durability of sPEEK MEA (Membrane and Electrode Assembly), ADT (Accelerated Degradation Test) of MEA degradation was done at the condition that membrane and electrode were degraded simultaneously. Before and after degradation, I-V polarization curve, hydrogen crossover, electrochemical surface area, membrane resistance and charge transfer resistance were measured. Although the permeability of hydrogen through sPEEK membrane was low, sPEEK membrane was weaker to radical evolved at low humidity and OCV condition than fluorinated membrane such as Nafion. Performance after MEA degradation for 144 hours and 271 hours were reduced by 15% and 65%, respectively. It was showed that the main cause of rapid decrease of performance after 144 hours was shorting due to Pt/C particles in the pinholes.

Polymer electrolyte membranes are developed from blends of chemically durable silicone‐containing epoxy (Si‐Epoxy) and proton conducting sulfonic polyimide (SPI). A charge‐transfer (CT) complex is formed between electron‐donating dihydroxynaphthalene units in Si‐Epoxy, and electron‐accepting naphthalenediimide units in SPI, as confirmed via X‐ray diffraction and visible spectroscopy. The blend membranes show comparable mechanical strength to Nafion 211, but the elongation to break is much lower, indicating better resistance to deformation under strain stress, attributed to CT complex formation. The chemical durability of the blend membranes was much higher than pure SPI according to Fenton's test, also attributed to CT complex formation. Meanwhile, the proton conductivity is dependent on the sulfonic acid content of the SPI, which in turn affects the fuel cell performance. The maximum proton conductivity was measured to be 23.1 mS cm−1 at 80°C and 90 %RH for a 1:1 blend, and the membranes were successfully incorporated into PEFCs.