Surface Modification of Sulfonated Polystyrene Ethylene Butylene Polystyrene Membranes by Layer-by-layer Assembly of Polysulfone for Application in Direct Methanol Fuel Cell

Methanol permeability is a major drawback for application of sulfonated polystyrene ethylene butylenes polystyrene block copolymers (SPSEBS) in direct methanol fuel cells (DMFC). Modification of SPSEBS by layer-by-layer (LBL) assembly of aminated (APSU) and sulfonated polysulfone (SPSU) was attempted to reduce its methanol permeability. The LBL deposition of APSU and SPSU on SBSEBS was carried out by dipping in their solutions alternatively for 10 min. The LBL assembly was confirmed by SEM analysis. The methanol permeability was lower than SPSEBS and Nafion 117. The proton conductivity, ion exchange capacity, and water absorption were lower than SBSEBS but higher than Nafion 117. Its selectivity ratio (0.70 × 10⁵) was higher than both SBSEBS (0.54 × 10⁵) and Nafion 117 (0.06 × 10⁵). The maximum power density of LBL (62 mW/cm²) was about five times higher than SBSEBS. These features of LBL confirm the LBL assembly method as a very simple procedure to modify SBSEBS for application in DMFC.     

Novel membranes based on poly(5‐(methacrylamido)tetrazole) and sulfonated polysulfone for proton exchange membrane fuel cells

Proton‐exchange membrane fuel cells (PEMFC)s are increasingly regarded as promising environmentally benign power sources. Heterocyclic molecules are commonly used in the proton conducting membranes as dopant or polymer side group due to their high proton transfer ability. In this study, 5‐(methacrylamido)tetrazole monomer, prepared by the reaction of methacryloyl chloride with 5‐aminotetrazole, was polymerized via conventional free radical mechanism to achieve poly(5‐(methacrylamido)tetrazole) homopolymer. Novel composite membranes, SPSU‐PMTetX, were successfully produced by incorporating sulfonated polysulfone (SPSU) into poly(5‐(methacrylamido)tetrazole) (PMTet). The sulfonation of polysulfone was performed with trimethylsilyl chlorosulfonate and high degree of sulfonation (140%) was obtained. The homopolymers and composite membranes have been characterized by NMR, FTIR, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). ¹H‐NMR and FTIR confirmed the sulfonation of PSU and the ionic interaction between sulfonic acid and poly(5‐(methacrylamido)tetrazole) units. TGA showed that the polymer electrolyte membranes are thermally stable up to ～190°C. Scanning electron microscopy analysis indicated the homogeneity of the membranes. This result was also supported by the appearance of a single T_g in the DSC curves of the blends. Water uptake and proton conductivity measurements were, as well, carried out. Methanol permeability measurements showed that the composite membranes have similar methanol permeability values with Nafion 112. The maximum proton conductivity of anhydrous SPSU‐PMTet0.5 at 150°C was determined as 2.2 × 10^?6 S cm^?1 while in humidified conditions at 20°C a value of 6 × 10^?3 S cm^?1 was found for SPSU‐PMTet2. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40107.     

Properties and performance of composite electrolyte membranes based on sulfonated poly(arylenethioethersulfone) and sulfonated polybenzimidazole

A novel composite membranes comprising a sulfonated polyarylenethioethersulfone homopolymer (SPTES-100) and a sulfonated poly(p-phenylene benzobisimidazole) (SPBI), was described in this article. The composite membrane was obtained via a solution cast process in a mixture solvent of N, N-Dimethylacetamide (DMAc) and methanol (MeOH). The proton conductivity of the composite membranes was found to increase with the SPTES-100 content increased. The higher proton conductivity was ∼110 mS/cm at 85 °C and 85% relative humidity for the SPTES/SPBI 70/30 (wt) composite membrane which was considerably less than that of the 300 mS/cm of the SPTES-100 membrane. The mechanical properties indicated that the swelling of the composite membranes was reduced, which is relative to the SPTES-100 polymers, due to the reduced water uptake of the composite membrane by introducing the SPBI into the SPTES polymer matrix. The morphology of the SPTES/SPBI composite membranes was examined by a combination of techniques such as scanning electron microscopy (SEM) and elemental mapping to confirm the dispersion of the SPBI and study the micro-structure of the composite. The membrane electrode assembly (MEA) performance of the composite membranes was preliminary studied for H₂/Air fuel cells applications.     

Sulfonated polysulfone as promising membranes for polymer electrolyte fuel cells

A new, milder sulfonation process was used to produce ion‐exchange polymers from a commercial polysulfone (PSU). Membranes obtained from the sulfonated polysulfone are potential substitutes for perfluorosulfonic acid membranes used now in polymer electrolyte fuel cells. Sulfonation levels from 20 to 50% were easily achieved by varying the content of the sulfonating agent and the reaction time. Ion‐exchange capacities from 0.5 to 1.2 mmol SO₃H/g polymer were found via elemental analysis and titration. Proton conductivities between 10⁻⁶ and 10⁻² S cm⁻¹ were measured at room temperature. An increase in intrinsic viscosity with increasing sulfonation degree confirms that the sulfonation process helps to preserve the polymer chain from degradation. Thermal analysis of the sulfonated polysulfone (SPSU) samples reveals higher glass transition temperatures and lower decomposition temperatures with respect to the unsulfonated sample (PSU). Amorphous structures for both PSU and SPSU membranes were detected by X‐ray diffraction analysis and differential scanning calorimetry. Preliminary tests in fuel cells have shown encouraging results in terms of cell performance. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1250–1257, 2000     

Effects of membrane electrode assembly preparation on the polymer electrolyte membrane fuel cell performance

This paper presents results of recent investigations to develop an optimized in-house membrane electrode assembly (MEA) preparation technique combining catalyst ink spraying and assembly hot pressing. Only easy steps were chosen in this preparation technique in order to simplify the method, aiming at cost reduction. The influence of MEA fabrication parameters like electrode pressing or annealing on the performance of hydrogen fuel cells was studied by single cell measurements with H₂/O₂ operation. Toray paper and carbon cloth as gas diffusion layer (GDL) materials were compared and the composition of electrode inks was optimized with regard to most favorable fuel cell performance. Commercial E-TEK catalyst was used on the anode and cathode with Pt loadings of 0.4 and 0.6 mg/cm², respectively. The MEA with best performance delivered approximately 0.58 W/cm², at 65 °C cell temperature, 80 °C anode humidification, dry cathode and ambient pressure on both electrodes. The results show, that changing electrode compositions or the use of different materials with same functionality (e.g. different GDLs), have a larger effect on fuel cell performance than changing preparation parameters like hot pressing or spraying conditions, studied in previous work.     

Gas Diffusion Layers for Proton Exchange Membrane Fuel Cells Using In situ Modified Carbon Papers with Multi‐walled Carbon Nanotubes Nanoforest

Gas diffusion layers (GDLs) in the proton exchange membrane fuel cells (PEMFCs) enable the distribution of reactant gases to the reaction zone in the catalyst layers by controlling the water in the pore channels apart from providing electrical and mechanical support to the membrane electrode assembly (MEA). In the present work, we report the in situ growth of carbon nanotubes nanoforest (CNN) directly onto macro‐porous carbon paper substrates. The surface property as analysed by a Goniometer showed that the CNN/carbon paper surface is highly hydrophobic. CNN/carbon paper was employed as a GDL in an MEA using Nafion‐212 membrane as an electrolyte and evaluated in single cell PEMFCs. While the GDLs prepared by wire‐rod coating process have major performance losses at lower humidities, the in situ CNN/carbon paper, developed in this work, shows very stable performance at all humidity conditions demonstrating a significant improvement for fuel cell performance. The CNN/carbon‐based MEAs showed very stable performance with power density values of ∼1,100 and 550 mW cm^–2, respectively, both using O₂ and air as oxidants at ambient pressure.     

Sulfonated graphene oxide‐doped proton conductive membranes based on polymer blends of highly sulfonated poly(ether ether ketone) and sulfonated polybenzimidazole

Simultaneously improving the proton conductivity and mechanical properties of a polymer electrolyte membrane is a considerable challenge in commercializing proton exchange membrane fuel cells. In response, we prepared a new series of miscible polymer blends and thus the corresponding crosslinked membranes based on highly sulfonated poly(ether ether ketone) and sulfonated polybenzimidazole. The blended membranes showed more compact structures, due to the acid‐base interactions between the two constituents, and improved mechanical and morphological properties. Further efforts by doping sulfonated graphene oxide (s‐GO) forming composite membranes led to not only significantly elevated proton conductivity and electrochemical performance, but also better mechanical properties. Notably, the composite membrane with the filler content of 15 wt % exhibited a proton conductivity of 0.217 S cm^?1 at 80 °C, and its maximum power density tested by the H₂/air single PEMFC cell at room temperature reached 171 mW cm^?2, almost two and half folds compared with that of the native membrane. As a result, these polymeric membranes provided new options as proton exchange membranes for fuel‐cell applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46547.     

Nanostructured membranes based on sulfonated poly(aryl ether sulfone) and silica for fuel‐cell applications

Nanostructured sulfonated poly(aryl ether sulfone) (SPSU) membranes were made from SPSU/silica composites through the addition of amorphous, precipitated, and micronized silica particles (Tixosil 333) and short or segmented linear structures. Linear and branched segments of silica were obtained from the in situ reaction of tetraethoxysilane (TEOS) in an SPSU solution through a sol–gel acid‐catalyzed process. Different amounts of silica in the SPSU composites were prepared to evaluate their influence on the ionic conductivity, the water and alcohol solution sorption capacities, and the stability in an ethanol medium. The effect of silica (Tixosil) on the conductivity was higher than that of the silica made from TEOS in SPSU composites. The conductivities of the membranes containing 10% Tixosil and 6.6% silica prepared from TEOS were measured at 80°C; their values were 60 and 33 mS/cm, respectively. Furthermore, a membrane made of a silica blend (5% Tixosil and 3% TEOS) in SPSU attained a value of 92 mS/cm, whereas the commercial membrane Nafion 117, used as a reference, had a conductivity of 54 mS/cm measured under the same conditions. All those composites membranes could be used as components in hydrogen fuel cell. However, only the SPSU/2% Tixosil composite could be used in both hydrogen and ethanol direct fuel cells. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nanostructured membrane electrode assemblies from layer‐by‐layer composite/catalyst containing membranes and their fuel cell performances

In this study, two approaches are compared to develop nanostructured membrane electrode assemblies (MEA) using layer‐by‐layer (lbl) technique. The first is based on the direct deposition of polyallylamine hydrochloride (PAH) and sulfonated polyaniline (sPAni) on Nafion support to prepare lbl composite membrane. In the second approach, sPAni is coated on the support in the presence of platinum (Pt) salt, Nafion solution and Vulcan for obtaining catalyst containing membranes (CCMs). SEM and UV–vis analysis show that the multilayers are deposited on both sides of Nafion successfully. Although H₂/O₂ single cell performances of acid doped lbl composite membrane based MEA are found to be at the range of 126 and 160 mW cm^?2 depending on the number of deposited layers, the cell performance of MEA obtained from catalyst containing lbl self‐assembled thin membrane (PAH/sPAni‐H⁺)_10‐Pt is found to be 360 mW cm^?2 with a Pt utilization of 720 mW mgPt^?1. This performance is 82% higher as compared to original Nafion^®117 based MEA (198 mW cm^?2). From the cell performance evaluations for different structured MEAs, it is mainly found out that the use of lbl CCMs instead of composite membranes and fabrication of thinner electrolytes result in a higher H₂/O₂ cell activity due to significant reduction in ohmic resistivity. Also, it is observed that the use of sPAni slightly improves the cell performance due to an increased probability of the triple phase contact and it can lead to superior physicochemical properties such as conductivity and thermal stability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40314.     

Heteropolyacid in glass electrolytes for the development of H2/O2 fuel cells

The scope of the present work was to investigate and evaluate the electrochemical activity of H₂/O₂ fuel cells based on the influence of a heteropolyacid glass membrane with a Pt/C electrode at low temperature. A new trend of sol-gel derived PMA (H₃PMo₁₂O₄₀) heteropolyacid-containing glass membranes inherent of a high proton conductivity and mechanical stability, was heat treated at 600 °C and implemented to H₂/O₂ fuel cell activities through electrochemical characterization. Significant research has been focused on the development of H₂/O₂ fuel cells using optimization of heteropolyacid glasses as electrolytes with Pt/C electrodes at 30 °C. A maximum power density of 23.9 mW/cm² was attained for operation with hydrogen and oxygen, respectively, at 30 °C and 30% humidity with the PMA glass membranes (4-92-4 mol%). Impedance spectroscopy measurements were performed on a total ohmic cell resistance of a membrane-electrode-assembly (MEA) at the end of the experiment.     

Recent developments in fuel‐processing and proton‐exchange membranes for fuel cells

In recent years, great progress has been made in the development of proton‐exchange membrane fuel cells (PEMFCs) for both mobile and stationary applications. This review covers two types of new membranes: (1) carbon dioxide‐selective membranes for hydrogen purification and (2) proton‐exchange membranes; both of these are crucial to the widespread application of PEMFCs. On hydrogen purification for fuel cells, the new facilitated transport membranes synthesized from incorporating amino groups in polymer networks have shown high CO₂ permeability and selectivity versus H₂. The membranes can be used in fuel processing to produce high‐purity hydrogen (with less than 10 ppm CO and 10 ppb H₂S) for fuel cells. On proton‐exchange membranes, the new sulfonated polybenzimidazole copolymer‐based membranes can outperform Nafion^® under various conditions, particularly at high temperatures and low relative humidities. Copyright © 2010 Society of Chemical Industry     

Synthesis and Characterization of a New Fluorine‐Containing Polybenzimidazole (PBI) for Proton‐Conducting Membranes in Fuel Cells

A new type of fluorine‐containing polybenzimidazole, namely poly(2,2′‐(2,2′‐bis(trifluoromethyl)‐4,4′‐biphenylene)‐5,5′‐bibenzimidazole) (BTBP‐PBI), was developed as a candidate for proton‐conducting membranes in fuel cells. Polymerization conditions were experimentally investigated to achieve high molecular weight polymers with an inherent viscosity (IV) up to 1.60 dl g^–1. The introduction of the highly twisted 2,2′‐disubstituted biphenyl moiety into the polymer backbone suppressed the polymer chain packing efficiency and improved polymer solubility in certain polar organic solvents. The polymer also exhibited excellent thermal and oxidative stability. Phosphoric acid (PA)‐doped BTBP‐PBI membranes were prepared by the conventional acid imbibing procedure and their corresponding properties such as mechanical properties and proton conductivity were carefully studied. The maximum membrane proton conductivity was approximately 0.02 S cm^–1 at 180 °C with a PA doping level of 7.08 PA/RU. The fuel cell performance of BTBP‐PBI membranes was also evaluated in membrane electrode assemblies (MEA) in single cells at elevated temperatures. The testing results showed reliable performance at 180 °C and confirmed the material as a candidate for high‐temperature polymer electrolyte membrane fuel cell (PEMFC) applications.     

Polyethersulfone Membranes: The Effect of Sulfonation on the Properties

Polyethersulfone (PES) was sulfonated using chlorosulfonic acid in order to improve proton conductivity. Incorporation of ?SO₃H groups into polymer main chain through sulfonation was confirmed using FTIR and ¹H NMR. Ion exchange capacity of sulfonated membranes was determined via titration. Morphological studies (AFM, SEM) revealed the presence of hydrophilic proton transfer channels, which became continuous at higher degrees of sulfonation. Thermal stability was observed from thermogravimetric analysis (TGA). Storage modulus and tan δ also exhibited an increase with degree of sulfonation as determined from DMA. Conductivity measurements and fuel cell performance showed that sulfonated samples possessed higher conductivity than virgin PES.     

Enhanced Fuel Cell Performance of Decalin Treated Nafion® Membranes

The interaction of Nafion^® 212 membrane with a carbocyclic fuel, decalin was studied. Membrane electrode assemblies (MEA) fabricated with decalin treated membranes exhibited significant increase in power density in a H₂/Air fuel cell at 60% relative humidity. Small angle X‐ray scattering experiments were used to understand the morphological changes in the membrane due to decalin treatment.     

Preparing a catalyst layer in magnetic field to improve the performance of proton exchange membrane fuel cells

Electro catalyst Pt–Co/multi-walled C nanotubes were synthesized by using the modified polyol method with glycol as reducer. The magnetic-field-assisted fabrication of membrane electrode assemblies (MEAs) for proton exchange membrane fuel cells (PEMFCs) was proposed, to orient catalyst layers and increase the efficiency of catalyst utilization. PEMFCs with the magnetic-field-treated MEA (M-MEA) exhibited significant performance improvement over common MEA (C-MEA) without magnetic-field treatment. Under the same operating conditions, the maximum power density of MEA increased from 149.6 to 223.8 mW cm^?2 when C-MEA was replaced by M-MEA. Scanning electron microscope images showed that catalysts exhibited a “cluster-like structure” in M-MEA opposed to a chaotic arrangement in C-MEA. Electrochemical impedance spectroscopy measurements revealed that M-MEA reaction resistance was lower than that of C-MEA. Cyclic voltammetry data showed an increment of almost 29.6 % in electrochemical surface area as a result of the magnetic-field treatment.     

Lithium sulfonate promoted compatibilization in single ion conducting solid polymer electrolytes based on lithium salt of sulfonated polysulfone and polyether epoxy

Polymeric lithium salts of sulfonated polysulfone (SPSU(X)Li) were synthesized via post sulfonation route followed by ion exchange. A novel single ion conducting solid polymer electrolyte (SPE) was prepared by curing poly(ethylene glycol)diglycidyl ether (PEGDGE) with 4,4′ diaminodiphenyl sulfone (DDS) in SPSU(X)Li matrix. The ionic conductivity, thermal stability and tensile properties were investigated as a function of degree of sulfonation and PEGDGE concentration. The introduction of lithium sulfonate groups in polysulfone promoted compatibility of SPSU(X)Li and PEGDGE in SPE. AFM analysis demonstrated heterogeneous phase morphology and reduction in size of dispersed PEGDGE phase with increasing degree of sulfonation. The interactions between lithium sulfonate and polyether epoxy improved thermal stability of the epoxy network. The enhanced compatibility also caused improvement in elongation at break compared to neat SPSU(X)Li. The higher Li⁺ ion concentration and the segmental mobility of the polymer chains above T_g contributed to the high ionic conductivity at high temperature in the single ion conducting SPE.     

Novel KOH-free anion-exchange membrane fuel cell: Performance comparison of alternative anion-exchange ionomers in catalyst ink

Alkaline membrane electrode assemblies (MEAs) were fabricated and tested in 5 cm² single cell configuration. The fuel cell tests were preformed in the absence of any liquid electrolyte, such as KOH. This study shows fuel cell polarization curves for alkaline membrane fuel cell (AMFC) systems that were fabricated with novel anion-exchange ionomers. A comparison of two novel anion-exchange ionomers incorporated into the catalyst ink was achieved by comparing the performance under H₂/O₂ and H₂/air operating conditions. The results presented here indicate that the chemical and physical properties of the recast anion-exchange ionomer that is utilized in AMFC catalyst layers directly influence the obtainable fuel cell performance. It is shown that ionomer materials that are less prone to swelling from hydration and tend to pack closely together in the solid state will result in stronger catalyst-ionomer interfacial interactions. The O₂ transport properties in alkaline MEA cathodes are influenced by the resulting void volume of the electrode as defined by the structure and packing arrangement of the recast ionomer molecules.     

Novel polysulfone/sulfonated polyaniline/niobium pentoxide polymer blend nanocomposite membranes for fuel cell applications

New series of polymer nanocomposite membranes were prepared from polysulfone (PSU), sulfonated polyaniline (SPANI) and niobium pentoxide (Nb₂O₅) by solution casting technique. In order to assess the suitability of the polymer electrolytes in fuel cell applications, the membranes were characterized with respect to their physicochemical properties. Scanning electron microscope, X-ray diffraction, and X-ray photoelectron spectroscopy data confirmed the successful incorporation of nanofillers into the polymer matrix. The membrane loaded with 10 wt% of niobium pentoxide into PSU/SPANI exhibited a proton conductivity of 0.0674 S cm⁻¹, whereas the control membrane showed 0.0110 S cm⁻¹. The incorporation of niobium pentoxide into pristine polymer not only improved the ionic conductivity but also enhanced the thermal and oxidative stabilities. The substantial results achieved with the organic–inorganic polymer composites derived from PSU-SPANI and Nb₂O₅ have been established and can be viable materials for electrolyte in fuel cell applications.     

Structure-property-performance relationships of sulfonated poly(arylene ether sulfone)s as a polymer electrolyte for fuel cell applications

This article focuses on structure-property-performance relationships of directly copolymerized sulfonated polysulfone polymer electrolyte membranes. The chemical structure of the bisphenol-based disulfonated polysulfones was systematically alternated by introducing fluorine moieties or other polar functional groups such as benzonitrile or phenyl phosphine oxide in the copolymer backbone. Ac impedance measurements of the polymer electrolyte membranes indicated that fluorine incorporation increased proton conductivity, while polar functional group incorporation decreased conductivity. Likewise, other properties such as water uptake and ion exchange capacity are impacted by the incorporation of fluorine moiety or polar groups. These properties are critically tied with H₂/air and direct methanol fuel cell performance. We have rationalized fuel cell performance of these selected copolymers in light of structure-property relationships, which gives useful insight for the development and application of next generation polymer electrolytes.     

Cost effective cation exchange membranes: A review

This paper will look at developments of new polymer electrolyte membranes to replace high cost ion exchange membranes such as Nafion^®, Flemion^® and Aciplex^®. These perfluorinated polymer electrolytes are currently the most commercially utilized electrolyte membranes for polymer electrolyte fuel cells, with high chemical stability, proton conductivity and strong mechanical properties. While perfluorinated polymer electrolytes have satisfactory properties for fuel cell applications, they limit commercial use due to significant high costs as well as reduced performance at high temperatures and low humidity. A promising alternative to obtain high performance proton-conducting polymer electrolyte membranes is through the use of hydrocarbon polymers. The need for inexpensive and efficient materials with high thermal and chemical stability, high ionic conductivity, miscibility with other polymers, and good mechanical strength is reviewed in this paper. Though it is difficult to evaluate the true cost of a product based on preliminary research, this paper will examine several of the more promising materials available as low cost alternatives to ion exchange membranes. These alternative membranes represent a new generation of cost effective electrolytes that can be used in various ion exchange systems. This review will cover recent and significant patents regarding low cost polymer electrolytes suitable for ion exchange membrane applications. Promising candidates for commercial applications will be discussed and the future prospects of cost effective membranes will be presented.