الفهرس 
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Abstract
In this study, a novel proton-conducting polymer electrolyte membrane based on a mixture of polyvinyl alcohol (PVA)/polyvinyl pyrrolidone (PVP) (1:1) mixed with different ratios of graphene oxide (GO) and plasma-treated was successfully synthesized. The prepared samples were treated with dielectric barrier dielectric (DBD) plasma at fixed power input (2 kV, 50 kHz) and different dosage rates (2, 4, 6, 7, 8, and 9 min). The treated samples were soaked in a solution of styrene and tetrahydrofuran (70:30 wt%) with 5x10-3 g of benzoyl peroxide as an initiator in an oven at 60 oC for 12h and then sulfonated to create protonic membranes.
The impacts of GO on the physical, chemical, and electrochemical properties of plasma-treated PVA/PVP-g-PSSA: x wt. % GO membranes (x = 0, 0.1, 0.2, and 0.3) have been investigated using different techniques. SEM results showed a better dispersion of nanocomposite-prepared membranes; whereas the AFM results showed an increase in total roughness with increasing the content of GO. To verify their occurrence, FTIR spectra offer further details regarding the structural change resulting from the grafting and sulfonation processes. The X-ray diffraction pattern showed that the PVA/PVP-g-PSSA: x wt% GO composite is semi-crystalline. As the level of GO mixing rises, the crystallinity of the mixes decreases. The thermal stability of the prepared membranes was assessed using the TGA technique. Thermal stability was found to improve as GO concentration increased. According to the TGA curve, the PVA/PVP-g-PSSA: x wt% GO membranes are chemically stable up to 180 oC which is suitable for proton exchange membrane fuel cells (PEMFCs). Water uptake (WU) was also measured and found to decrease from 87.6 to 63.3% at equilibrium with increasing GO content. Ion exchange capacity (IEC) was calculated using the titration method, and the maximum IEC value was 1.91 meq/g for the PVA/PVP-g-PSSA: 0.3 wt% GO composite membrane.
Transport properties, including proton conductivity and methanol permeability, were studied under different operating conditions similar to cell conditions. The maximum proton conductivity was 98.9 and 144mS/cm for PVA/PVP-g-PSSA:0.3 wt% GO membrane at room temperature and 80oC, respectively. In addition, the same sample recorded a methanol permeability of 1.03x10-7 cm2/s, which is much less than that of Nafion NR-212 (1.63x10-6 cm2/s).
Proton conductivity, dielectric constant ε’, and loss ε’’ for the prepared PVA/PVP-g-PSSA: x wt% GO membranes were measured as a function of frequency at various temperatures. It was noticed that the dielectric constant and loss increased with increasing GO concentration and decreased with frequency. The values of the s-parameter were smaller than unity and dropped with temperature; according to that, the correlated barrier hopping model (CBHM) is the conduction mechanism. For the membranes under study, the values of the frequency exponent s for the associated barrier hopping and the binding energy of the charge transporters Wm decrease with increasing temperature while rising with GO concentration.
At room temperature, PALS measurements showed that the o-Ps lifetime τ3 and its intensity I3 decreased with an increase in doping concentration in the blend composite. Therefore, in the current case, the observed difference of τ3 and I3 cannot be understood based on the free volume model and may be related to chemical quenching, oxidation, or inhibition.
Finally, the obtained results of the various characterization and measurements imply potential applications for modified polyelectrolytic membranes in fuel cell technology.