Sulfonic Acid Membranes Research Articles

Perfluorinated Sulfonic Acid Membrane and Membrane Electrode Assembly Degradation Correlating Accelerated Stress Testing and Lifetime Testing

An important step in achieving fundamental understanding of fuel cell failure mechanisms and development of technology to mitigate these failures is accomplished by analysis of directed lifetime and failure test results. Several lifetime, accelerated stress, and drive cycle test protocols have been developed and carried out. The two major ASTs that have been developed to evaluate membrane degradation are 1) Open circuit voltage tests, which are designed to accelerate chemical degradation, and 2) Relative humidity cycling tests, which are designed to accelerate mechanical degradation. The results from these tests have been compared to field tests. The ultimate goal is to use the laboratory tests to predict data in the field. An overall predictive decay model is being developed through a combination of specific modeling and tests.

Modeling of processes in fuel cells based on sulfonic acid membranes and platinum clusters

The density functional theory with account for gradient correction (DFT/PBE) and periodical boundary conditions was used to model the main stages of processes occurring in hydrogen low-temperature fuel cells. Modeling was carried out at the example of calculation of catalytic anodic and cathodic processes occurring on the surface of the Pt19 catalyst supported on a SnO2 and water adsorption processes on the surface of a membrane represented by a crystal of metisylene sulfonic acid dihydrate [(CH3)3C6H2SO 3 − · H5O 2 + ]. It was shown that the most energy-efficient process in the membrane is formation of crystals, in which two stoichiometric water molecules correspond to a single SO3H group. Superstoichiometric water is adsorbed on the crystal surface with the adsorption energy of 0.3–0.6 eV; its transition inside the crystal is energy-consuming (2 eV). Barriers of surface proton conductivity are 0.2–0.3 eV.

Long-term durability of radiation-grafted PFA-g-PSSA membranes for direct methanol fuel cells

Poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether)-graft-poly(styrene sulfonic acid) (PFA-g-PSSA) membranes were prepared by γ-ray radiation-induced grafting of styrene onto 50μm PFA films and a subsequent sulfonation. The properties of the PFA-g-PSSA membranes such as ion exchange capacity, water uptake, proton conductivity, and methanol permeability were evaluated and compared with commercial Nafion 115 membrane. The characteristic properties and direct methanol fuel cell (DMFC) performances with PFA-g-PSSA membrane were better than that with the Nafion 115 membrane. The power density of the single cell with PFA-PSSA30, PFA-PSSA50, PFA-PSSA80 membranes having different degree of grafting (DOG), and Nafion 115 membranes was 113, 123, 118, and 111mWcm−2 at 0.4V, respectively. To study the long-term durability of the prepared membrane electrode assembly (MEA) with a PFA-PSSA50 membrane, the single cell was tested for 2066h in a galvanostatic mode under a constant load 150mAcm−2 and at a temperature of 60°C. The performance loss of the MEA after 2066h operation was about 26.8%. Before and after the long-term performance test, the degradation of MEA with PFA-g-PSSA membrane was investigated by polarization curve technique, electrochemical impedance spectroscopy, TEM, X-ray diffraction, and ion exchange capacity.

Atomic force microscopy studies of conductive nanostructures in solid polymer electrolytes

The conductivity of three different sulfonated polymer electrolyte membranes (PEM), two perfluorinated membranes, Nafion® and Aquivion®, and JST, a non-perfluorinated aromatic block copolymer, were compared using advanced material-sensitive and conductive atomic force microscopy (AFM). All of the membranes required activation by a current flow to reach significant conductivity for the AFM analysis, indicating the existence of a highly resistive surface skin layer. The two perfluorinated sulfonic acid membranes, a membrane with long side-chains (Nafion®) and a membrane with short side-chains (Aquivion®), exhibited similar properties. A lamellar surface structure, with polymer bundles or micelles in a parallel orientation, was also found for the Aquivion® membrane. AFM high-resolution current images, performed under a continuous current flow, were used to distinguish between the conducting network and the subsurface phase distribution at the membrane surface. The connected subnets of the JST membrane were approximately 100–200nm in size, whereas those for the perfluorinated membrane surfaces were 200–300nm in size. The conductive areas of the Aquivion® and JST membranes exhibited larger homogeneous conducting areas, corresponding to the smaller correlation lengths of ionic phase separation. Membrane cross sections were analyzed to elucidate the structure of the bulk ionic network of the Nafion® membrane, before and after operation. The existence of extended water layers in the bulk, even before operation, was confirmed.

Sensors based on zirconia-modified perfluorinated sulfonic acid membranes sensitive to organic anions in multiionic aqueous solutions

The effect of modification of perfluorinated sulfonic acid membranes with zirconia on their conducting properties and electrode-active properties for potentiometric sensors whose analytical signal is the Donnan potential (DP) has been studied. It has been found that the incorporation of ZrO2 particles into the membrane matrix results in an increase in the ionic conductivity, as compared with unmodified membranes, and the proton diffusion coefficient changes nonmonotonically. Membranes with a gradient dopant distribution along the sample length provide for a partial decrease in the cation-exchange function of DP sensors because of a decrease in the concentration of fixed cation-exchange groups and due to the sorption of coions. This results in an increase in the sensor sensitivity to organic and sulfur-containing anions in multiionic aqueous solutions. Multivariate calibration methods with a nonorthogonal experimental design were used to evaluate the effects of the concentrations and nature of counterions and coions and pH in the test solutions on the characteristics of DP sensors.

Fuel Cell Perfluorinated Sulfonic Acid Membrane Degradation Correlating Accelerated Stress Testing and Lifetime

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTFuel Cell Perfluorinated Sulfonic Acid Membrane Degradation Correlating Accelerated Stress Testing and LifetimeMarianne P. Rodgers*, Leonard J. Bonville, H. Russell Kunz, Darlene K. Slattery, and James M. FentonView Author Information Florida Solar Energy Center, University of Central Florida, 1679 Clearlake Road, Cocoa, Florida 32922-5703, United States*E-mail: [email protected]Cite this: Chem. Rev. 2012, 112, 11, 6075–6103Publication Date (Web):October 12, 2012Publication History Received8 November 2011Published online12 October 2012Published inissue 14 November 2012https://doi.org/10.1021/cr200424dCopyright © 2012 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views4702Altmetric-Citations229LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (6 MB) Get e-AlertsSUBJECTS:Degradation,Electrodes,Fuel cells,Membranes,Platinum Get e-Alerts

Role of Mechanical Factors in Controlling the Structure–Function Relationship of PFSA Ionomers

Ion-conducting polymers are ideal solid electrolytes for most energy storage and conversion devices where ion transport is a critical functionality. The system performance and stability are related to the transport and mechanical properties of the ionomers, which are correlated through physiochemical interactions and morphology. Thus, there exists a balance between the chemical and mechanical energies which controls the structure–function relationship of the ionomer. In this paper, it is reported how and why thermal treatments result in different water uptakes and nanostructures for a perfluorinated sulfonic acid (PFSA) membrane. The nanostructure of the PFSA membrane is characterized using small- and wide-angle X-ray scattering experiments. These changes are correlated with water content and mechanical properties and result in fundamental relationships to characterize the membrane with different thermal histories. Moreover, quasi-equilibrium water uptake and domain spacing both decrease with predrying or preconstraining the membrane, thereby suggesting that similar mechanical energies govern the structural changes via internal and external constraints, respectively. The findings suggest that heat treatments alter the balance between the chemical–mechanical energies where the interplay of the morphology and mechanical properties controls the structure–function relationship of the membrane. Finally, a model is developed using an energy-balance approach with inputs of the mechanical and structural properties; the dependence of water uptake on pretreatment is successfully predicted.

ChemInform Abstract: Organic—Inorganic Nanocomposite Polymer Electrolyte Membranes for Fuel Cell Applications

AbstractReview: 371 refs.

Investigation of Water-Molecule Network in Hydrated Polymer Electrolyte Membranes by Raman Spectroscopy: Effect of Polymer Structure and Cation Impregnation

We examined Raman spectra in both perfluorinated sulfonic acid (PFSA) and hydrocarbon (HC) membranes under different RH conditions to investigate water-molecule network. Raman spectra showed variation with relative humidity among these membranes and was affected by polymer structure. The PFSA membrane showed broad peak in Raman spectra while the HC membrane showed narrow peak even in low RH condition. These observations suggest that water-molecule network is intensively established in the PFSA membrane. We also confirmed that the K-form and the Na-form membrane showed less formation of water-molecule network than the H-form, while Na-form membrane showed less water-molecule network than the K-form. These results indicated that dissociation and ionic radius of cations affected formation of water-molecule network in these membranes.

Sulfonic and Phosphonic Acid and Bifunctional Organic-Inorganic Hybrid Membranes and Their Proton Conduction Properties

Hybrid organic-inorganic approaches are used for the synthesis of bifunctional proton exchange membrane fuel cell (PEMFC) membranes owing to their ability to combine the properties of a functionalized inorganic network and an organic thermostable polymer. We report the synthesis of both sulfonic and phosphonic acid functionalized mesostructured silica networks into a poly(vinylidenefluoride-co-hexafluoropropylene) (poly(VDF-co-HFP) copolymer. These membranes, containing different amounts of phosphonic acid and sulfonic acid groups, have been characterized using FTIR and NMR spectroscopy, SA-XRD, SAXS, and electrochemical techniques. The proton conductivity of the bifunctional hybrid membranes depends strongly on hydration, increasing by two orders of magnitude over the relative humidity (RH) range of 20 to 100%, up to a maximum of 0.031 S cm(-1) at 60 °C and 100% RH. This value is interesting as only half of the membrane conducts protons. This approach allows the synthesis of a porous SiO(2) network with two different functions, having -SO(3)H and -PO(3)H(2) embedded in a thermostable polymer matrix.

Studies on PEM fuel cell noble metal catalyst dissolution

A combination of electrochemical, spectroscopic and gravimetric methods was carried out on Proton Exchange Membrane (PEM) fuel cell electrodes with the focus on platinum and ruthenium catalysts dissolution, and the membrane degradation. In cyclic voltammetry (CV) experiments, the noble metals were found to dissolve in 1 M sulfuric acid solution and the dissolution increased exponentially with the upper potential limit (UPL) between 0.6 and 1.6 vs. RHE. 2–20% of the Pt (depending on the catalyst type) was found to be dissolved during the experiments. Under the same conditions, 30–100% of the Ru (depending on the catalyst type) was found to be dissolved. The faster dissolution of ruthenium compared to platinum in the alloy type catalysts was also confirmed by X-ray diffraction measurements. The dissolution of the carbon supported catalyst was found one order of magnitude higher than the unsupported catalyst. Other factors like medium acidity, chloride content and oxygen partial pressure all turned out to influence the noble metal dissolution. The degradation of the polyfluorinated sulfonic acid membrane electrolyte was also found to be an important source of increased acidity in the Three-Phase-Boundary (TPB), and consequently the dissolution of the noble metal catalysts.

Radiation grafted poly(vinylidene fluoride)-graft-polystyrene sulfonic acid membranes for fuel cells: Structure-property relationships

Structure-property relationships for poly(vinylidene fluoride)-graft-polystyrene sulfonic acid (PVDF-g-PSSA) fuel cell membranes prepared by a single step method involving radiation-induced grafting of sodium styrene sulfonate (SSS) onto electron beam (EB) irradiated poly(vinylidene fluoride) (PVDF) films were established. The physico-chemical properties of the membranes such as ion exchange capacity, water swelling and proton conductivity were correlated with the degree of grafting (G, %) and the structural changes taking place in the membrane matrix during the preparation procedure. The variation in the crystallinity and the thermal stability of membranes was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The membranes were found to undergo substantial structural changes in forms of ionic sites increase, hydrophilicity enhancement, hydrophobicity reduction and crystallinity decrease with the variation in G (%) and the preparation method. The structural and thermal properties of the obtained membranes were also compared with their counterparts prepared by a conventional two-steps method i.e. radiation induced grafting of styrene onto EB irradiated PVDF films followed by sulfonation. The PVDF-g-PSSA membranes obtained by a single-step method were found to have superior properties compared to those obtained by the conventional two-steps method.

Effects of contaminant on thermal properties in perfluorinated sulfonic acid membranes

The influence of controlled cationic contaminant on the thermal behaviour of proton conducting perfluorosulfonic acid membrane (PFSA) was studied. A series of Ni 2+-exchanged membrane was prepared by varying the ratio between positive charges resulting from the contaminant to the negative charges originating from the sulfonate groups. A large change in properties was evidenced at a ratio close to 0.2. Above this threshold, the PFSA exhibited significantly higher main relaxation and degradation temperatures. The set of experimental data could be described with the help of a phenomenological microstructural model essentially based on ionic interactions. The impurity model could then be employed to understand changes in protonic conductivity from the literature.

Electric mass transport through homogeneous and surface-modified heterogeneous ion-exchange membranes at a rotating membrane disk

Polarization characteristics of the homogeneous MF-4SK perfluorinated sulfonated cation-exchange membrane and the heterogeneous MK-40 sulfonic acid membrane with its surface modified by a homogeneous film of Nafion are studied at a rotating membrane disk in 0.1 and 0.001 M sodium chloride solutions. Partial current-voltage curves (CVC) are obtained for sodium and hydrogen ions, and limiting current densities in the electromembrane systems (EMS) under study are calculated as a function of the rotation rate of the membrane disk. Contribution from different mechanisms (electrodiffusion, electroconvection, dissociation of water, and the effect of the limiting-current exaltation) to the total ion flow is estimated experimentally and theoretically under conditions that the diffusion layer in the EMS has stabilized in thickness. It is established that surface modification of the heterogeneous MK-40 membrane with a 7 µm layer of a modifying agent almost completely eliminates the dissociation of water molecules, and the properties of the heterogeneous MK-40 membrane approximate those of the homogeneous Nafion membrane. From IR spectra and potentiometric titration curves of the MK-40 and MF-4SK membranes, it is shown that the acidity of the sulfonate groups in these membranes is nearly identical, but a difference in the dissociation rate of water at these membranes is determined by a different character of charge-density distribution and potential near the membrane-solution interphase boundary. By means of the theory of the overlimiting state in EMS, the internal parameters of the systems under investigation are calculated: distribution of space-charge density and electric-field potential in the diffusion layer and in the membrane. Partial CVC are calculated for H+ ions for the space-charge region in the phase of the MF-4SK and MK-40/Nafion ion-exchange membranes. Partial CVC with similar characteristics are compared for the heterogeneous monopolar MK-40 and the bipolar MB-2 membranes, which contain sulfonate groups. It is concluded that the membrane surface layer, where the space charge is localized, plays a dominant role in speeding up the dissociation of water in EMS.

Conductivity and Thermal Behaviour of Sulfonated ABS Membranes for Fuel Cell Applications

In the present work, proton conductive membranes based on poly(acrylonitrile-co-butadiene-co-styrene) (ABS) were obtained by sulfonation. The sulfonic acid ABS (ABS-SO3H) membranes exhibited thermal stability near 370 oC, similarly to the ABS original polymer. DSC curves of the sulfonic acid membranes showed two glass transition temperatures, associated with thermal processes taking place at the polymer main chain and at the hydrophilic domains. These hydrated regions are formed by water molecules and dissociated sulfonic acid groups [-SO3-(H2O)nH+], as pointed out in other works. Electrochemical impedance spectroscopy evidenced the conductive-capacitive behaviour of ABS-SO3H membranes, which exhibited an Ahrrenius-like conductivity dependence with temperature, from 7.6×10-6 Ω-1cm-1 at 20 oC and 1.4×10-5 Ω-1cm-1 at 80 oC (ABS-SO3H 2:1).

Accelerated Degradation of Perfluorinated Sulfonic Acid Membranes

The degradation of PFSA membranes in fuel cells is a critical factor for fuel cell life time. Ex situ methods for determining the degradation processes have been used extensively, mainly radically initiated from gas or liquid phase. Gas phase degradation has proven to cause cleavage of the main polymer chain causing the degradation speed to increase. In this study decomposition products washed out in the water form both gas and liquid phase degradation experiments have been analyzed. Decomposition products were pre-concentrated using solid phase extraction (SPE) and analyzed with HPLC-MS. The distribution of decomposition products is significantly different for gas phase and liquid phase degradation. The same analysis procedure is applied on water condensed during fuel cell operation. The HPLC-MS chromatogram showed that the condition inside a fuel cell operating at optimal conditions, most probably is less harsh than those in both liquid and gas phase ex situ degradation experiments.

Accelerated Degradation of Perfluorinated Sulfonic Acid Membranes

not Available.

Preparation of PVdF/PSSA composite membranes using supercritical carbon dioxide for direct methanol fuel cells

Composite membranes were prepared using supercritical carbon dioxide (scCO2) impregnation and polymerization procedures and were optimized as electrolytes by controlling the amount of divinylbenzene (DVB) for polymerization. These poly(vinylidene fluoride)/polystyrene sulfonic acid (PVdF/PSSA) membranes were characterized by various methods. The cross-sectional superficial morphology and structure of the PVdF/PSSA membranes were analyzed by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), FT-IR and small-angel X-ray scattering (SAXS). The ion exchange capacity (IEC), ion conductivity, methanol permeability and cell performance of PVdF/PSSA membranes were measured and compared with Nafion 115. As the concentration of added DVB increased, the ion conductivity and methanol permeability of the PVdF/PSSA membranes decreased. The PVdF/PSSA membrane containing 7.5 wt% DVB achieved 94% of the current density with Nafion 115.

Electrospun Nafion Nanofiber for Proton Exchange Membrane Fuel Cell Application

Proton exchange membrane fuel cells (PEMFCs) are attractive power plants for use in many applications, including portable power sources, electric vehicles, and on-site combined power/heat plants, due to the inherently high efficiency and low emission. The membrane electrode assembly (MEA) is the key component of a PEMFC. A standard five layer MEA consists of a proton exchange membrane, two catalyst layers, and two gas diffusion layers. The most commonly used electrolyte material is proton conductive perfluorinated sulfonic acid membrane, such as Nafion. Hydrogen is oxidized at the anode/electrolyte interface, the so-called triple-phase-boundary (TPB) active sites. TPB region must be a good electron conductor, a good ion conductor, and a porous structure for fuel/air diffusion. Typical PEMFC TPB is a porous structure made with Nafion and catalyst particle mixture. In this paper, electrospinning is used to synthesize polymer/Nafion nanofibers. Electrospinning is a straightforward method that has been successfully used to prepare fibers or fiber mats from a broad range of organic polymers. In the electrospinning process, a polymer solution held by its surface tension at the end of a capillary tube is subjected to an electric field, and as the electric field strength increases, a solid fiber is generated as the electrified jet is continuously stretched because of the electrostatic repulsions between the surface charges and the evaporation of solvent. Uniform one-dimensional Nafion nanofibers have been fabricated using Nafion solution and solutions containing polyvinyl pyrrolidone, polyethylene oxide, and polyvinyl alcohol. The morphologies of polymer/Nafion nanofibers, fabricated under different electrospinning conditions and different polymer compositions, are presented.

Modeling and Simulation of the Degradation of Perfluorinated Ion-Exchange Membranes in PEM Fuel Cells

A polymer electrolyte membrane (PEM) fuel cell model that incorporates chemical degradation in perfluorinated sulfonic acid membranes is developed. The model is based on conservation principles and includes a detailed description of the transport phenomena. A degradation submodel describes the formation of hydrogen peroxide via distinct mechanisms in the cathode and anode, together with the subsequent formation of radicals via Fenton reactions involving metal-ion impurities. The radicals participate in the decomposition of reactive end groups to form carboxylic acid, hydrogen fluoride, and . Degradation proceeds through unzipping of the polymer backbone and cleavage of the side chains. Simulations are presented, and the numerical code is shown to be extremely time-efficient. Known trends with respect to operating conditions are qualitatively captured, and the exhibited behavior is shown to be robust to changes in the rate constants. The feasibility of a chemical degradation mechanism based on peroxide and radical formation is discussed.