Christiane Poinsignon

Proton conducting sulfon:sulfonamide functionalized materials based on inorganic-organic matrices

A new class of inorganic‐organic protonic polymer electrolyte was developed recently by grafting sulfonic and sulfonamide groups to the inorganic network by the sol‐gel route. It associates the mechanical and thermal resistance of the silica backbone to the chemical reactivity induced by the organic chains grafted to the silica network. The organic chains are slightly acidic proton conductors bearing sulfonic and sulfonamide groups. The polycondensation of alkoxysilanes provides the inorganic silica backbone whereas the organic network is formed from reactive functional groups R% of alkoxysilanes of the type R%Si(OR)3, or by copolymerization of reactive organic monomers with functionalized alkoxysilanes. The synthesis of the resins is completed by organic crosslinking reactions (thermal or UV-curing). The transport of the protons through the solid could be described as a mechanism in which the proton was transferred from a donor (sulfonic group) to a suitable placed acceptor (e.g. sulfonamide group) in the case of a dry material. The conductivity was also studied as a function of relative humidity (r.h.) (wet proton conductors). Here, the proton transport could be described as a vehicular mechanism where the proton rides on a carrier molecule (H3O). Furthermore the conductivity dependence on temperature follows a VTF behavior. By increasing the water content of the membranes up to 16 mass%, the conductivity increases from 10 4 to 6 10 2 Sc m 1 at 70°C. These materials will be developed for thin film batteries. Their mechanical properties, thermal stability and glass transition temperature are discussed in connection with the conductivity results.

Organic—inorganic protonic polymer electrolytes as membrane for low-temperature fuel cell

Abstract An organic—inorganic protonic polymer electrolyte (ormolyte—organically modified silane electrolyte) to be used as membrane in direct methanol fuel cells is presented. The synthesis, prepared by the sol—gel method, is based on several organically modified alkoxy silanes, chosen according to the particular properties needed in the final product. The membrane thus prepared exhibits a protonic conductivity of about 10 −2 Ω −1 at room temperature.

Cation ordering in Li2Mn3MO8 spinels: structural and vibration spectroscopy studies

Abstract Lithium-manganese oxide spinels with 1/4 manganese replaced by Mg, Ti, Co, Ni, Cu, Zn and Ga, yielding formula LiMn1.5M0.5O4 (or Li2Mn3MO8) have been prepared. Cationic ordering was known previously for M=Mg and Zn, resulting in a superstructure with primitive cubic symmetry. Given the poor chemical contrast of X-ray diffraction between Mn and Ti, Co, Ni, Cu or Ga, neutron diffraction studies were carried out. Evidence of cation ordering is found for M=Ni and Cu, but not for Ti, Co or Ga. These results are confirmed by FTIR and Raman spectroscopies. Doubly-substituted samples (Li0.5M0.5)[Mn1.5M0.5]O4 (overall formula LiMn3M2O8) were also prepared for M=Mg and Zn. These do not form the primitive superstructure, a result ascribed to the lower manganese valence with respect to LiMn1.5M0.5O4. Zn-containing spinels give rise to an extensive Li/Zn cation inversion, which also shows up as additional high-frequency bands in IR and Raman spectroscopies. This investigation shows that the cell volume is determined by the average octahedral-site cation radius, and that the main driving force for octahedral cation ordering is the charge difference between Mn and M atoms.

Structural–chemical disorder of manganese dioxides: 1. Influence on surface properties at the solid–electrolyte interface

Relationships between lattice parameters of manganese dioxides and their surface properties at the solid-aqueous solution interface were investigated. The studied series ranged from ramsdellite to pyrolusite and encompassed disordered MD samples. The structural model used takes into account structural defects: Pr (rate of pyrolusite intergrowth) and Tw (rate of microtwinning). Water adsorption isotherms showed that the cross sectional area of water molecules adsorbed in the first monolayer is positively correlated to Pr. Titration of the surface charge of the MD series evidenced a positive linear relationship between the PZC and Pr (Pr=0, Tw=0, PZC=1 for ramsdellite; Pr=1, Tw=0, PZC=7.3 for pyrolusite; gamma-MD with intermediate values of Pr (0.2 to 0.45) have increasing PZC values). The rate of microtwinning appeared as a secondary factor for the increase of the PZC. The above correlations are explained by the chemical defects at the origin of the structural disorder, respectively Mn(3+)/Mn4+ substitution for Pr and Mn vacancies for Tw, which result in proton affinity and thus in increased PZC. The experimental results are compared with data collected in the literature for manganese dioxides as well as for dioxides of transition elements with tetragonal structure.

Structural–chemical disorder of manganese dioxides

Relationships between lattice parameters of manganese dioxides and their surface properties at the solid-aqueous solution interface were investigated. The studied series ranged from ramsdellite to pyrolusite and encompassed disordered MD samples. The structural model used takes into account structural defects: Pr (rate of pyrolusite intergrowth) and Tw (rate of microtwinning). Water adsorption isotherms showed that the cross sectional area of water molecules adsorbed in the first monolayer is positively correlated to Pr. Titration of the surface charge of the MD series evidenced a positive linear relationship between the PZC and Pr (Pr=0, Tw=0, PZC=1 for ramsdellite; Pr=1, Tw=0, PZC=7.3 for pyrolusite; gamma-MD with intermediate values of Pr (0.2 to 0.45) have increasing PZC values). The rate of microtwinning appeared as a secondary factor for the increase of the PZC. The above correlations are explained by the chemical defects at the origin of the structural disorder, respectively Mn(3+)/Mn4+ substitution for Pr and Mn vacancies for Tw, which result in proton affinity and thus in increased PZC. The experimental results are compared with data collected in the literature for manganese dioxides as well as for dioxides of transition elements with tetragonal structure.

Structural–chemical disorder of manganese dioxides: II. Influence on textural properties

Relationships between structural parameters of MnO2 and their surface properties at the solid-gas interface were investigated. The studied series ranged from ramsdellite to pyrolusite and encompassed disordered gamma-MnO2 samples. The structural model used takes into account structural defects: Pr (rate of pyrolusite intergrowth in the ramsdellite network) and Tw (rate of microtwinning). Analysis of the N2 adsorption isotherm evidenced positive correlations between specific surface area and Tw for gamma-MnO2 only and between the energetic constant C and (1-Pr). No microporosity is evidenced. Water adsorption isotherms evidenced the dependence of the H2O monolayer volume on Tw and showed a positive correlation between the cross-section area of water molecules adsorbed in the first monolayer and Pr, ranging from 13.5 A2 for Pr=1 to 6.3 A2 for Pr=0.2 (12 sites/nm2). Energetic heterogeneity is quantified from Ar and N2 low-pressure adsorption isotherms with the DIS procedure and correlated with H2O adsorption. High-energy adsorption domains are quantified and assigned to the different crystal faces: (110) faces with a common 1 x 1 octahedra layer of pyrolusite and ramsdellite and the (001) face of ramsdellite with 2 x 2 octahedra on which channels and plateaus are differentiated. The specific surface area ratio of ramsdellite high-energy sites to total ramsdellite content is shown to depend on Tw. The dependence on microtwinning of low cross-sectional area of N2 and much lower cross-sectional of residual H2O molecules leads us to assume that their adsorption sites on grain boundaries are represented by the twin planes between the structured nanocrystals generated by oxygen evolution during MD synthesis.

Proton conducting inorganic–organic matrices based on sulfonyl- and styrene derivatives functionalized polycondensates via sol–gel processing

Proton conducting inorganic-organic hybrid polymer electrolytes were developed in the last decade based on sulfonated, methacryl and epoxy functionalized alkoxysilanes for thin film cells [Electrochim. Acta 45 (2000) 137]. To improve the electrochemical stability of the materials for applications like polymer electrolyte membranes for direct methanol fuel cells, the less stable methacryl and epoxy alkoxysilanes of the former test system [Electrochim. Acta 45 (2000) 137] were replaced by styrene derivative functionalized alkoxysilanes. These alkoxysilanes were synthesized with a new modified Grignard reaction. The sol-gel materials were prepared in a two-step reaction: first, an alkoxysilane containing a sulfonated group and an alkoxysilane containing at least a nitrogen heterocycle, an amine group or a sulfonamide group were separately hydrolyzed and co-condensed each with one half of the amount of a styrene derivative functionalized alkoxysilane. Then, these two co-condensates were mixed. After evaporation of the solvent, the resin was cast in Teflon® moulds or applied on a substrate as a film and finally organically crosslinked via UV and/or thermal curing. The influence of the sample composition on the conductivity and the mechanical properties was studied. Conductivities of 3 x 10 -3 S cm -1 at room temperature were obtained for membranes free of water, whose precursor composition consists of 60% sulfonated alkoxysilane, finally mixed with 2 mol imidazole per mol -SO 3 H. If the imidazole is exchanged by water (max. 15 mass% absorption within membrane), the membranes show conductivities up to 8 x 10 -3 S cm -1 at room temperature. A thermal stability of the inorganic- organic matrix of up to 180 °C ( < 5% weight loss) was measured by thermo-gravimetric (TG) analysis.

Manganese Dioxides Surface Properties Studied by XPS and Gas Adsorption

Structurally well defined γ-MnO 2 in terms of Pr and Tw were studied using X-ray photoelectron spectroscopy (XPS) to complete surface investigations performed by high-resolution gas adsorption, water adsorption, and acid-base surface titration. The O Is s and Mn 2p spectra were deconvoluted into three components Mn-OH + 2 , Mn-OH, and Mn-O - . Analysis of the O Is spectra in energy shift and relative intensity shows that 70 to 80% of the surface groups stay as neutral OH, 5% as Mn-OH 2 and 20 to 30% as Mn-OH: their relative amount varies with Pr as well as PZC, water cross-sectional area and energetic constant C. Mn 2p spectra are far less sensitive than O is to the charge variation. Nevertheless a correlation is shown between the relative amount of surface species, the binding energy of Mn = O and O = Mn species and Tw.

Proton-vacancy-conducting polymers based on anion-grafted ormosils synthesized via sol-gel process

A novel basic proton conducting polymer (so-called proton-vacancy conducting polymer) has been synthesized. It is based on the copolymerization via the sol-gel process of sulfonamide- containing groups, partially deprotonated, and an internal plasticizer (POE segments). All the organic groups are attached to trialkoxysilanes which, through the hydrolysis-condensation process, lead to a silica-based backbone. The flexible films obtained are homogeneous and transparent. Maximum conductivities are observed with approximately equals 15% of the sulfonamide groups deprotonated by the organic base and approximately equals 10% of 2000 Mw POE plasticizer. The conductivity values are 2 10-7Ω-1-cm-1 at 30 degree(s)C and 10-5 Ω -1cm-1 at about 84 degree(s)C. The polymers are thermically stable up to 220 degree(s)C and their electrochemical stability range is close to 2 V.

Low Cost Filled Thermostable Ionomer Membrane for P.E.M.F.C.

A filled ionomeric membrane was achieved by dispersing phosphatoantimonic acid H 3 Sb 3 P 2 0 14 , ×H 2 0 (H3) in a Sulfonated PolySulfone (SPS) solution [1]. Water up-take is higher for filled than unfilled membrane as well as Protonic conductivity which is larger than that expected from the overall calculated concentration in charge carriers : a conductivity value of 0.135 S.cm −1 was gained at 50°C under 1003% Relative Humidity (HR) for a 1.6 meq.g −1 cationic exchange capacity (cec) SPS filled with 8% in H3 against 0.06S.cm −1 for an unfilled one. Mechanical measurements on the wet membrane shows the plasticizing effect of sulfonation, water and of the filler content which simultanously reinforced the cohesion of the membrane.