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Microstructure Characterization of Nafion®g HP JP as a Proton Exchange Membrane for Fuel Cell: Positron Annihilation Study

100%
Mohamed H., Abdel-Hady E., Abdel-Hamed M., Said M.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1543-1547
EN
Free volume size V_{f} and proton conductivity σ of a novel polymer electrolyte membrane were investigated as a function of temperature and relative humidity up to 140°C and 80%, respectively. The free volume size V_{f} for Nafion® HP JP reflect the α-transition temperature at about 98°C. In addition the free volume size V_{f} for Nafion® HP JP is smaller than that for Nafion® NRE212 membrane which leads to lower methanol permeability of the former membrane. The proton conductivity σ for Nafion® HP JP decreases with increase of temperature up to transition temperature due to free and bound water loss, then it starts to increase due to dynamic segmental motion. It increases for Nafion® HP JP with the increase of the relative humidity. A good correlation between V_{f} and σ was successfully established for both membranes which indicates that σ is governed by the free volume. In conclusion, Nafion® HP JP is a suitable membrane for a proton exchange membrane fuel cell application.
2
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Proton Conductivity and Free Volume Properties in Per-Fluorinated Sulfonic acid/PTFE Copolymer for Fuel Cell

100%
Mohamed H., Abdel-Hady E., Abdel-Hamed M.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1509-1514
EN
The proton conductivity mechanism in per-fluorinated sulfonic acid/PTFE copolymer Fumapem® membranes for polymer electrolyte membranes has been investigated. Three samples of Fumapem® F-950, F-1050 and F-14100 membranes with different ion exchange capacity 1.05, 0.95, and 0.71 meq/g, respectively, were used in this study after drying. The o-Ps hole volume size (V_{FV,Ps}) was quantified using the positron annihilation lifetime technique while the proton conductivities (σ ) were measured using LCR Bridge as function of temperature. It was found that as the ion exchange capacity increases, the proton conductivity increases and the free volume expands. Temperature dependences of proton conductivity and the o-Ps hole volume size (V_{FV,Ps}) reflect the glass transition temperature of the membrane. A good linear correlation between the reciprocal of the o-Ps hole volume size (1/V_{FV,Ps}) and log(σ)+Δ E_a/2.303k_{B}T, (where ΔE_a is the activation energy, T is the absolute temperature and k_{B} is the Boltzmann constant) at different temperatures indicate that the ionic motion in dry Fumapem® is governed by the free volume. A linear relationship between the critical hole size γ V*_{i} and the ion exchange capacity was also achieved.
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Free Volume of PVA/SSA Proton Exchange Membrane Studied by Positron Annihilation Lifetime Spectroscopy

76%
Gomaa M., Hugenschmidt C., Dickmann M., Abdel-Hamed M., Abdel-Hady E., Mohamed H.
Acta Physica Polonica A
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2017
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vol. 132
|
issue 5
1519-1522
EN
Humidity control and water management in polymer electrolyte membranes for fuel cells are still of high importance to improve the fuel cells' efficiencies. In this study, poly (vinyl alcohol) (PVA)was crosslinked using 15 wt% sulfosuccinic acid (SSA) by a solution casting method and additionally thermally crosslinked at 100°C. Positron annihilation lifetime spectroscopy was used to study the mean free volume size and the distribution at different humidity. A slight decrease in the free volume was found up to a relative humidity of 30% whereas it increases strongly for a relative humidity of more than 30%. The volume of the voids duplicates from 0.036 to 0.078 nm³ by changing the relative humidity from 30 to 80%. Thermogravimetric analyzer was used to determine the thermal stability of the membrane. From thermogravimetric analyzer data, it was found that the PVA with 15 wt% SSA membrane are chemically stable up to 200°C.
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