Development and characterization of composite proton exchange membranes for fuel cell applications

Akay, Ramiz Gültekin
Intensive research on development of alternative low cost, high temperature membranes for proton exchange membrane (PEM) fuel cells is going on because of the well-known limitations of industry standard perfluoro-sulfonic acid (PFSA) membranes. To overcome these limitations such as the decrease in performance at high temperatures (>80 0C) and high cost, non-fluorinated aromatic hydrocarbon based polymers are attractive. The objective of this study is to develop alternative membranes that possess comparable properties with PFSA membranes at a lower cost. For this purpose post-sulfonation studies of commercially available engineering thermoplastics, polyether-ether ketone (PEEK) and polyether-sulfone (PES), were performed by using suitable sulfonating agents and conditions. Post sulfonated polymers were characterized with proton nuclear magnetic resonance spectroscopy (H+-NMR), sulfur elemental analysis and titration to calculate the degree of sulfonation (DS) values and with TGA and DSC for thermal stability and glass transition temperature (Tg). Chemical stabilities were evaluated by hydrogen peroxide tests. Proton conductivities of sulfonated PEEK (SPEEK) measured by electrochemical impedance spectroscopy (EIS) were observed to increase linearly with degree of sulfonation (DS). However, above a certain DS SPEEK loses its mechanical stability significantly with excessive swelling which leads to deteriorations in mechanical stability. Therefore, DS of 50-70% were used for the fabrication of composite membranes. To improve mechanical stability, SPEEK polymers were blended with more stable polymers, polyether-sulfone (PES) or in its sulfonated form (SPES) or with polybenzimidazole (PBI). In addition, the composite approach, which involves the incorporation of various inorganic fillers such as zeolite beta, TiO2, montmorrilonite (MMT), heteropolyacids (HPA), was used for further improvement of proton conductivity. Among the composite membranes 20% TPA/SPEEK (DS=68) composites conductivity value exceeded that of Nafion‘s at room temperature. Effects of various parameters during the fabrication process such as the filler type and loading, DS of sulfonated polymer, casting solvents, and thermal and chemical treatment were also investigated and optimized. Various blend/composite membranes were fabricated with solvent casting method, and characterized for their proton conductivity, chemical/thermal stability and for evaluating their voltage/current performance at various temperatures in a single cell setup. Chemically and thermo-hydrolytically stable composite/blend membranes such as 25% tungstophosphoric acid (TPA)/PBI(5%)/SPEEK (DS=68) with good single cell performances at 800C were developed (~450 mA/cm2 at 0.5 V). The performance of the hydrolytically stable composite/blend membrane prepared with SPEEK (DS=59); 5% PBI; and 10% TiO2 increased appreciably when the temperature was raised from 80 0C to 90 0C while the performance of Nafion decreases sharply after 80 0C. Methanol permeability studies were also performed for investigating the potential of fabricated blend/composite membranes for direct methanol fuel cell (DMFC) use. Selectivities (conductivity/methanol permeability) vi greater than Nafion 112 (S=7.3x107) for DMFC were observed for composite/blend membranes such as 10% TiO2/10% PES blend with SPEEK (DS=68) with a selectivity of 9.3x107. The factors that affect proton conductivity measurements were investigated and equivalent circuit analysis was performed with results obtained by electrochemical impedance spectroscopy (EIS). The choice of the conductivity cell (electrodes, cell geometry) and the method (2-probe vs 4-probe) were shown to affect the conductivity analysis. A systematic development and characterization route was established and it was shown that by optimizing proton conductivity and thermal/chemical stability with blending/composite approaches it is possible to produce novel high performance proton exchange membranes for fuel cell applications.


Improvement of PEMFC performance with Nafion/inorganic nanocomposite membrane electrode assembly prepared by ultrasonic coating technique
Devrim, Yilser; Erkan, Serdar; BAÇ, NURCAN; Eroğlu, İnci (2012-11-01)
electrode assemblies with Nafion/nanosize titanium silicon dioxide (TiSiO4) composite membranes were manufactured with a novel ultrasonic-spray technique and tested in proton exchange membrane fuel cell (PEMFC). Nafion/TiO2 and Nafion/SiO2 nanocomposite membranes were also fabricated by the same technique and their characteristics and performances in PEMFC were compared with Nafion/TiSiO4 mixed oxide membrane. The composite membranes have been characterized by thermogravimetric analysis, scanning electron m...
Development of self-humidifying nano-composite membrane for polymer electrolyte membrane fuel cell
Çaçan, Umut Baki; Özkan, Necati; Devrim, Yılser; Department of Polymer Science and Technology (2015)
Low humidity self-humidifying nano-composite membrane electrode assemblies (MEA) were developed for Polymer Electrolyte Membrane Fuel Cell (PEMFC) working at elevated temperatures. The nano-composite membranes were prepared by adding nano-sized silica particles (SiO2) or inorganic fillers with a size of approximately 20 nm to a polymeric material which is commercially named as Nafion (Perfluoro Sulfonic Acid/PFSA). The particle content of the nano-composite membranes were between 2.5 – 10 wt. %. In this man...
Nafion/titanium silicon oxide nanocomposite membranes for PEM fuel cells
DEVRİM, YILSER; Erkan, Serdar; BAÇ, NURCAN; Eroğlu, İnci (2013-04-01)
In the present study, Nafion/Titanium Silicon Oxide (TiSiO4) nanocomposite membranes were prepared by recasting method for proton exchange membrane fuel cells. The composite membrane containing 10wt% TiSiO4 had a membrane thickness of 80 mu m. The membrane was characterized by thermogravimetric analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). SEM and XRD results have proven the uniform and homogeneous distribution of TiSiO4 in Nafion, and consequently, the crystalline character of ...
Cross-linked polybenzimidazole membranes for high temperature PEM fuel cells
Özdemir, Yağmur; Özkan, Necati; Devrim, Yılser; Department of Polymer Science and Technology (2018)
Literature studies have shown that it is desirable to increase operation temperature of Proton Exchange Membrane Fuel Cells (PEMFCs) due to the reasons like reduced fuel impurity sensitivity, fast electrode kinetics, simple thermal and water management. However, during fuel cell operation at high temperatures, the PEM suffers from inevitable leaching out of the doped acid, which can have deteriorating effect on the membrane performance. Thus, there is always a need to minimize this problem by making ways so...
Experimental investigation of CO tolerance in high temperature PEM fuel cells
DEVRİM, YILSER; Albostan, Ayhan; Devrim, Huseyin (Elsevier BV, 2018-10-04)
In the present work, the effect of operating a high temperature proton exchange membrane fuel cell (HT-PEMFC) with different reactant gases has been investigated throughout performance tests. Also, the effects of temperature on the performance of a HT-PEMFC were analyzed at varying temperatures, ranging from 140 degrees C to 200 degrees C. Increasing the operating temperature of the cell increases the performance of the HT-PEMFC. The optimum operating temperature was determined to be 160 degrees C due to th...
Citation Formats
R. G. Akay, “Development and characterization of composite proton exchange membranes for fuel cell applications,” Ph.D. - Doctoral Program, Middle East Technical University, 2008.