A Combined Theoretical and Experimental Investigation of the Transport Properties of Water in a Perfluorosulfonic Acid Proton Exchange Membrane Doped with the Heteropoly Acids, H3PW12<

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• 作者：Yuan Liu ; Somisetti V. Sambasivarao ; James L. Horan ; Yuan Yang ; C. Mark Maupin ; Andrew M. Herring
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：January 16, 2014
• 年：2014
• 卷：118
• 期：2
• 页码：854-863
• 全文大小：500K
• ISSN：1932-7455

文摘

The 3M 825EW perfluorosulfonic acid (PFSA) ionomer was doped with the heteropoly acids (HPAs), H₃PW₁₂O₄₀ (HPW) and H₄SiW₁₂O₄₀ (HSiW). Dynamic vapor sorption measurements at 95% RH showed a decrease in water content as a result of HPA doping from 位 = 8.05 for the undoped 825EW 3M ionmer to 位 = 4.40 for a 5% HSiW doped film. FTIR measurement revealed strong interactions between the HPAs, ionomer, and H₂O. Irrespective of hydration level, it was found that the PFSA films showed tortuous proton diffusion behavior. At maximum hydration and 25 掳C, the self-diffusion coefficient of water was found to decrease upon addition of HPA from 4.97 to 2.19 (脳10^鈥? cm²/s) for the undoped 825EW 3M ionomer and 1% HPW, respectively, in excellent agreement with computation. The model at low HPA loadings revealed the decreased diffusion coefficient was due to the water preferentially residing near the HPA as opposed to the SO₃^{鈥?/sup> groups. The addition of HPA generally improved overall conductivity due to additional formation of hydrogen-bonding networks between the HPA particles. At high RH, it was observed that the proton conductivity increased while the water diffusion coefficient decreased as HPA was incorporated. In addition, a mismatch between the conductivity values and those calculated from the Nernst鈥揈instein equation using the self-diffusion coefficient of water in the system indicated an enhancement in Grotthuss hopping mechanism upon addition of HPA.}