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Article Citation - WoS: 11Citation - Scopus: 13Characterization and Fuel Cell Performance of Divinylbenzene Crosslinked Phosphoric Acid Doped Membranes Based on 4-Vinylpyridine Grafting Onto Poly(ethylene-Co Films(Pergamon-elsevier Science Ltd, 2018) Guler, Enver; Sadeghi, Sahl; Gursel, Selmiye AlkanThe effect of divinylbenzene (DVB) as crosslinker on the graft polymerization of 4-vinylpyridine (4VP) from poly(ethylene-co-tetrafluoroethylene) (ETFE) films was studied. The resulted films were doped with phosphoric acid (PA) and characterized for mechanical, surface, thermal properties, and fuel cell performance. The crosslinked membrane obtained from grafting a mixture of 4VP with 1% DVB improved the polymerization kinetics and resulted in about 50% graft level depending on graft conditions. The crosslinked membranes were also found to have better mechanical properties compared to its non-crosslinked counterpart. The resulted membrane exhibited proton conductivity as high as 75 mS/cm under 50% relative humidity (RH) at 120 degrees C, besides almost doubling the power output of fuel cell compared to a non-crosslinked membrane. To the best of our knowledge, DVB crosslinked 4VP based ETFE membranes were, for the first time, tested in practical fuel cell test station correlating their performance to operating temperature. Furthermore, surface properties of produced membranes were additionally correlated to the degree of crosslinking. Humidity dependence is less pronounced in the produced membranes resulting in strong potential for testing at intermediate temperature (80-120 degrees C) polymer electrolyte membrane fuel cells. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Article Citation - WoS: 6Citation - Scopus: 6Salinity Gradient Energy Conversion by Custom-Made Interpolymer Ion Exchange Membranes Utilized in Reverse Electrodialysis System(Elsevier Sci Ltd, 2023) Altiok, Esra; Kaya, Tugce Zeynep; Smolinska-Kempisty, Katarzyna; Guler, Enver; Kabay, Nalan; Tomaszewska, Barbara; Bryjak, MarekReverse electrodialysis (RED) is one of methods to extract salinity gradient energy between two aqueous solu-tions with different salt concentrations. In this work, custom-made interpolymer ion exchange membranes were employed in the RED stack. The effects of divalent (Mg2+, Ca2+ , SO42-) and monovalent (Li+, K+ and Cl-) ions in the feed solutions prepared from NaCl salt as a function of such process parameters as number of membrane pairs, flow rate , salinity ratio on power generation by the RED method were studied. It was shown that the maximum power density of 0.561 W/m2 was reached by using three membrane pairs using 1:45 of salt ratio with a feed flow rate of 120 mL/min using only NaCl salt in the feed solutions. The maximum power density was 0.398 W/m2 at 120 mL/min of the flow rate of the feed solutions composed of 90 wt% NaCl and 10 wt% KCl by using a salt ratio of 1:30 while the lowest power density of 0.246 W/m2 was obtained with a feed flow rate of 30 mL/min in the presence of SO42-ions with a similar salt ratio. Consequently, it was seen that while the presence of divalent ions in NaCl solutions had negative impact on power generation by RED system, the addition of monovalent ions having smaller hydrated radius than that of the Na+ ions contributed positively to the power generation.Article Citation - WoS: 24Citation - Scopus: 28Enhancing Proton Conductivity Via Sub-Micron Structures in Proton Conducting Membranes Originating From Sulfonated Pvdf Powder by Radiation-Induced Grafting(Elsevier Science Bv, 2018) Sadeghi, Sahl; Sanli, Lale Isikel; Guler, Enver; Gursel, Selmiye AlkanWe report here submicron-structured proton conducting poly(vinylidene fluoride)-graft-poly(styrene sulfonic acid) (PVDF-g-PSSA) membranes for polymer electrolyte membrane fuel cells (PEMFC). Highly conductive proton exchange membranes were obtained by single-step radiation grafting of sodium styrene sulfonate (SSS) to powder-form PVDF, followed by casting and subsequent solvent evaporation. The obtained submicron structure of membrane through solvent evaporation led to the arrangement of ionic channels proving increasing proton conductivity with the increase in graft level. In addition, a temperature above melting point of PVDF was used for solvent evaporation to allow melted PVDF to fill the formed pores, providing denser structure resulting in improved mechanical properties of the membranes. SSS grafting to PVDF powder was verified by NMR spectroscopy, and resultant membranes were characterized for proton conductivity, water up-take, morphology, mechanical and thermal properties, and fuel cell performance. According to preliminary tests, proton conductivities which were observed to increase with graft level were found to be around 70 mS cm(2) at 35% graft level. Thus, this led to a promising power density of 250 mW/cm(2) at 650 mA/cm(2).Article Citation - WoS: 18Citation - Scopus: 20Investigations on the Effects of Operational Parameters in Reverse Electrodialysis System for Salinity Gradient Power Generation Using Central Composite Design (ccd)(Elsevier, 2022) Altiok, Esra; Kaya, Tugce Zeynep; Othman, Nur Hidayati; Kinali, Orhan; Kitada, Soma; Guler, Enver; Kabay, NalanReverse electrodialysis (RED) can be utilized for the production of renewable energy from salinity gradients. However, there are many key parameters that could influence the performance of RED. This study investigates the use RSM for development of a predictive power density (PD) and open-circuit voltage (OCV) model for the RED system. A three-factor central composite design (CCD) was used to quantify the effects of flow velocity (X-1), salinity ratio (X-2), and number of cell pairs (X-3) towards PD and OCV. A total of 17 experimental data were fitted and ANOVA was used to validate the accuracy of the models. 3D and surface plots were created to foresee the optimal levels of each variable. It was found that flow velocity and salinity ratio have the most dominant influences on the RED performances as compared to number of cell pairs. The predicted PD and OCV values were found to be reasonably fit with the experimental data, validating the predictability of applied models. Therefore, this study suggests that CCD can be considered an effective tool for evaluating and optimizing the RED system using a minimum number of experiments.Article The Impact of Quaternization Degree in Polyepichlorohydrin-Based Anion Exchange Membranes on Salinity Gradient Energy Generation by Reverse Electrodialysis(Elsevier, 2025) Cihanoglu, Aydin; Guler, Enver; Kabay, NalanAnion exchange membranes with tailored fixed-charge densities can improve monovalent ion selectivity and performance in reverse electrodialysis for salinity gradient power generation. In this study, poly(epichlorohydrin) was blended with polyacrylonitrile and quaternized with 1,4-diazabicyclo[2.2.2]octane at three different molar ratios to produce AEMs with systematically varied quaternization degrees via a one-step amination/ crosslinking procedure. The resulting membranes were characterized for their physicochemical, electrochemical, and RED performance using ATR-FTIR, XPS, SEM, AFM, water uptake, swelling degree, contact angle, surface zeta potential, ion exchange capacity, fixed charge density, and electrical resistance. Higher quaternization increased the IEC, reduced resistance, and shifted surface charge, leading to improved stack power output in model NaCl solutions. In the presence of Na2SO4, power loss was reduced for more highly quaternized membranes, indicating enhanced exclusion of divalent anions (SO42-) and reduced uphill transport. Fouling tests with humic acid/fulvic acid mixtures showed greater stability for quaternized membranes compared to a commercial benchmark. Moreover, stability tests conducted on fouled membranes revealed that the tailor-made membrane exhibits superior durability and lower fouling-induced power loss than commercial Fujifilm Type II AEMs. Overall, these results demonstrate that tuning the degree of quaternization is an effective strategy to balance conductivity and ion selectivity in AEMs for RED applications.Article Citation - Scopus: 1Effect of Asymmetric Feed Flow Rate and Temperature on Reverse Electrodialysis: A Response Surface Methodology Approach(Elsevier, 2025) Gul, Taha Furkan; Gonlugur, Miray Emreol; Guler, Enver; Cihanoglu, Aydin; Kabay, NalanReverse electrodialysis (RED) has the potential to generate sustainable energy by utilizing the salinity gradient potential between natural water sources with different salinities, such as river water and seawater. It is essential to comprehend the RED process's characteristics and optimize operational parameters to enhance its commercial viability. This study investigated the effects of varying inlet feed flow rates and temperatures on RED performance using Response Surface Methodology. Unlike conventional approaches, where inlet flow rates of seawater and river water solutions are typically kept equal, this research explores their diverse combinations. Key performance metrics of RED, including power density and open circuit voltage, were evaluated. Moreover, the impacts of different feed flow rates and temperatures on ohmic and non-ohmic resistances were thoroughly examined. The findings underscore significant interactions between feed flow rates, temperature, and RED performance outputs, providing insights essential for optimizing RED operations and enhancing its practical application in sustainable energy solutions.
