Ozlem Sel

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.

Determination of the diffusion coefficient of protons in Nafion thin films by ac-electrogravimetry.

This letter deals with an adaptation of the ac-electrogravimetry technique to extract separately the dynamic properties of H(+) and water in Nafion nanometric thin films (average thickness of 400 nm). An original theoretical approach was developed to extract the representative parameters from ac-electrogravimetry data. The concentration change of the exchanged species and the diffusion coefficient of the protons in a Nafion nanometric thin film (D = 0.5 × 10(-6) cm(2) s(-1) at 0.3 V vs SCE) were estimated for the first time according to the applied potential. The conductivity value of Nafion thin films was calculated from the Nernst-Einstein equation using diffusion coefficients and concentration values extracted from ac-electrogravimetry data. The calculated conductivity results agree well with the experimental proton conductivity values of Nafion thin films.

Proton Insertion Properties in a Hybrid Membrane/Conducting Polymer Bilayer Investigated by AC Electrogravimetry

In this paper, original hybrid organic/inorganic membranes based on a poly(vinylidenefluoride-co-hexafluoropropylene) polymer associated with mesostructured modified silica and made through sol-gel techniques were characterized by using cyclic electrogravimetry and ac electrogravimetry. To perform these experiments, a polypyrrole-heteropolyanion doped mediator film was generated between the working electrode of the microbalance and the hybrid membrane (HM). This mixed conductor mediator film is necessary to provide proton transfer between the different interfaces and, therefore, proton transport inside the HM, which is only an ion conductor. These coupled techniques, due to their extraordinary sensitivity and precision, constitute an indirect way of understanding the H + insertion (at the interfaces)/diffusion (through the HMs) behavior of the HMs, where the H + transport is complex. Complementary to the ionic conductivity values, the characterization of the HMs with these novel techniques can explain the modest proton conduction and can determine if the limiting mechanism is the proton insertion or diffusion. Therefore, it represents a useful tool for studying the proton conduction mechanisms and, consequently, for designing HMs with low ohmic losses. These techniques can be extended to other proton exchange membrane fuel cell membranes and can constitute a general tool for characterizing the materials where the insertion of H + induces charge transfer.

Proton Diffusion Coefficient in Electrospun Hybrid Membranes by Electrochemical Impedance Spectroscopy

Electrochemical Impedance Spectroscopy (EIS) was, for the first time, used to estimate the global transverse proton diffusion coefficient, D(H+)(EHM), in electrospun hybrid conducting membranes (EHMs). In contrast to conventional impedance spectroscopy, EIS measurements were performed at room temperature with a liquid interface. In this configuration, the measure of the bulk proton transport is influenced by the kinetics of the transfer of proton at the solid/liquid interface. We demonstrated that the use of additives in the process of the membrane impacts the organization of the hydrophilic domains and also the proton transport. The D(H+)(EHM) is close to 1.10(-7) cm(2) s(-1) (± 0.1.10(-7) cm(2) s(-1)) for the EHMs without additive, whereas it is 4.10(-6) cm(2) s(-1) (± 0.4.10(-6) cm(2) s(-1)) for EHMs with additives.

The role of NH 4 + cations on the electrochemistry of Prussian Blue studied by electrochemical, mass, and color impedance spectroscopy

The role of the ammonium cation on the reversible electrochemistry of Prussian Blue thin films was analyzed through in situ combination of three different impedance techniques. Electrochemical impedance spectroscopy provides information on the electron transfer. Mass impedance spectroscopy allows the exchange of free water, ammonium, and proton ions to be elucidated. Color impedance spectroscopy provides the kinetics of electrochromic changes of Prussian Blue structure (main backbone structure, ferrocyanide vacancies, and trapped structures). The simultaneous measurement of the three impedances gives detailed information on the mechanism of the whole process, specifically one faster and two slower, which have been identified during the electrochemical reactions of Prussian Blue films in NH4Cl acidic solutions.

Design and Development of High-Performance Hybrid Inorganic-Organic Fuel Cell Membranes

Performance Hybrid InorganicOrganic Fuel Cell Membranes Christel LABERTY-ROBERT, Ozlem SEL, Karine VALLE, Franck PERREIRA, Clement SANCHEZ UPMC, Univ. Paris 06, UMR 7574, Laboratoire de Chimie de la Matiere Condensee de Paris, F-75005 Paris, France CNRS, UMR 7574, Laboratoire de Chimie de la Matiere Condensee de Paris, F-75005 Paris, France CEA, Laboratoire « Sol-Gel » et Simulation au Departement Materiaux du CEA-Le Ripault, BP 16, 37260 Monts, France