A Combined Theoretical and Experimental Investigation of the Transport Properties of Water in a Perfluorosulfonic Acid Proton Exchange Membrane Doped with the Heteropoly Acids, H₃PW₁₂O₄₀ or H₄SiW₁₂O₄₀

Abstract

The 3M 825EW perfluorosulfonic acid (PFSA) ionomer was doped with the heteropoly acids (HPAs), H 3 PW 12 O 40 (HPW) and H 4 SiW 12 O 40 (HSiW). Dynamic vapor sorption measurements at 95% RH showed a decrease in water content as a result of HPA doping from λ = 8.05 for the undoped 825EW 3M ionmer to λ = 4.40 for a 5% HSiW doped film. FTIR measurement revealed strong interactions between the HPAs, ionomer, and H 2 O. Irrespective of hydration level, it was found that the PFSA films showed tortuous proton diffusion behavior. At maximum hydration and 25 °C, the self-diffusion coefficient of water was found to decrease upon addition of HPA from 4.97 to 2.19 (×10 −6 cm 2 / 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 SO 3 − 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−Einstein equation using the self-diffusion coefficient of water in the system indicated an enhancement in Grotthuss hopping mechanism upon addition of HPA.

Molecular dynamics simulation of Keggin HPA doped Nafion® 117 as a polymer electrolyte membrane

“…56 and 57)), it can be concluded that these particles improve proton conductivity through proton hopping or that the hydrophilic particles can cause slower vehicular transport by decreasing the water diffusion coefficient. Liu et al 33 argued that proton transport in HPA doped 3M ionomer membranes is faster than in the undoped one and that adding HPA may improve the proton hopping. When the hydronium diffusion rate was the same as that of water molecules, they observed a higher proton conductivity for doped 3M ionomer membrane with SiW 4À in comparison with a PW 3À /3M ionomer composite.…”

Electrostatic assembled of Keggin-type polyoxometalates onto poly(4-vinylpyridine)-grafted poly(vinylidene fluoride) membranes

“…the P-O band at 1074 cm À1 , the W]O band at 975 cm À1 , the W-O-W corner (the corner-sharing WO 6 octahedra) at 873 cm À1 , and the W-O-W edge (the edge-sharing WO 6 octahedra) band at 813 cm À1 , indicating that the primary Keggin-type HPW is present on the PVDF-g-P4VP membrane surfaces. 41 On the other hand, the W-O-W edge band of [PW 12 O 40 ] 3À on the PVDF-g-QP4VP/HPW membrane exhibits slightly red shied positions (804 cm À1 ) as compared to PVDF-g-P4VP/HPW, indicating the presence of an electrostatic interaction between the HPW anions and pyridinium groups of PVDF-g-QP4VP membrane.…”

Nanostructure/Swelling Relationships of Bulk and Thin‐Film PFSA Ionomers

“…Thus, PFSA ionomers with lower equivalent weights (EWs) (or higher ion‐exchange capacities (IECs)) and shorter side‐chain chemistries are being developed to overcome such transport limitations (e.g., the 3M PFSA ionomer shown in Figure ). It is well documented that ion conductivity rises and crystallinity falls, with increasing PFSA‐ionomer IEC. To date, however, structure/function relationships of non‐Nafion PFSA ionomers have been investigated only as bulk membranes and only in limited studies, and 3M PFSAs being studied only more recently (see refs.…”