OH⁻ Conductive Properties and Water Uptake of Anion Exchange Thin Films

Abstract

Several investigations have indicated that proton conduction and hydration properties of acidic ionomers differ from those of membranes. However, relations between the OH− conductivity and water uptake in thin film forms of anion exchange membranes have not been reported yet. For this study, new in situ measurements were established to elucidate the OH− conductivity and water uptake without allowing any influence of CO2 from the air. Poly[(9,9‐bis(6′‐(N,N,N‐trimethylammonium)‐hexyl)‐9H‐fluorene)‐alt‐(1,4‐benzene)], denoted as PFB+, was synthesized as a model ionomer. The highest OH− conductivity of 273 nm‐thick PFB+ film was 5.3×10−2 S cm−1 at 25 °C under 95 % relative humidity (RH), which is comparable to the reported OH− conductivity of PFB+ membrane. Reduced OH− conductivity was found in the thinner film at 95 % RH. The decreased OH− conductivity is explainable by the reduced number of water molecules contained in the thinner film. The OH− conductivity was reduced only slightly under the same water uptake.

Hydration and OH–/Br– Conduction Properties of Fluorene–Thiophene-Based Anion Exchange Thin Films Tethered with Different Cations

“…Conductivities decrease in the order of PFT6-TMA-OH (1.8 × 10 –2 S cm –1 ) > PFT6-Pip-OH (6.8 × 10 –3 S cm –1 ) > PFT6-TMA-Br (4.3 × 10 –3 S cm –1 ) > PFT6-Pip-Br (1.5 × 10 –3 S cm –1 ). A higher OH – conductivity than the Br – conductivity was observed within the whole RH region, which is consistent with the results of our earlier work . The energy-dispersive X-ray spectroscopy (EDX) spectra obtained before and after ion exchange were used to confirm ion exchange processes (Figures S10 and S11).…”

“…A higher OH − conductivity than the Br − conductivity was observed within the whole RH region, which is consistent with the results of our earlier work. 7 The energy-dispersive X-ray spectroscopy (EDX) spectra obtained before and after ion exchange were used to confirm ion exchange processes (Figures S10 and S11).…”

“…Our earlier work found that the 273 nm thick poly[(9,9-bis(6′-(N,N,N-trimethylammonium)-hexyl)-9H-fluorene)-alt-(1,4benzene)] (PFB + ) film showed a superior OH − conductivity value (5.3 × 10 −2 S cm −1 at 25 °C under 95% RH) compared to the Br − conductivity. 7 Nevertheless, some challenges remain for the systematic study of OH − conduction and hydration of anion exchange thin films, especially the temperature-dependent OH − conductivity of anion exchange thin films. To overcome this obstacle, new anion conductive polymers were synthesized and investigated as thin film forms.…”

Conductivity and Stability Properties of Anion Exchange Membranes: Cation Effect and Backbone Effect

“…[36,37] Water is the medium for transporting OH À , and the values of both IC and chemical stability are correlated with AEMs WU. [38,39] Besides, the cathodic oxygen reduction reaction in AEMFCs requires the participation of water, and WU of AEMs plays an important role in affecting the performance of AEMFCs. [40,41] Therefore, to eliminate the influence of IEC on SD and WU, the AEMs with similar IEC values are prepared.…”

Relationship between the Proton Conductive Performance and Water Uptake Ratio on a Filler-Filled Polymer Electrolyte Membrane

“…Therefore, we expect that, under the same relative humidity, if we use material with higher water uptake for the matrix resin, the water content in the membrane should be higher, resulting in greater proton conductivity across the membrane. 31 In this paper, we selected materials for the binder resin based on several criteria: variation in water uptake rates, the ability to use fabrication methods consistent with our previous experiments, general purpose, durability against redox reactions, and insolubility in hot water, as a result of the general operating environment of polymer electrolyte fuel cells (PEFCs) 32−36 having temperatures over 50 °C under wet conditions. Three binder resins, poly(methyl methacrylate) (PMMA), PC, and PS, were selected on the basis of these criteria and used to fabricate each membrane (CNC@PVPA-b-PS/PMMA, CNC@PVPA-b-PS/PC, and CNC@PVPA-b-PS/ PS).…”