Membranes for direct methanol fuel cell based on modified heteropolyacids

Organic–inorganic membranes for direct methanol fuel cell (DMFC) application were prepared from sulfonated polyether ether ketone (SPEEK), containing heteropolyacids and an oxide phase either generated by hydrolysis ofamino-modified silanes or by dispersion of a surface-modified fumed silica. The heteropolyacid was based on lacunary divacant [γ-SiW10O36]8– and contained epoxy groups which reacted with the amino-groups in the oxide phase. The reaction provides a covalent bond between the heteropolyacid to the insoluble oxide phase, resulting in its fixation in the membrane. The organic–inorganic composites prepared in this way were more stable than the plain membrane, had lower methanol crossover and proton-conductivity in the same order of magnitude.

Organic–inorganic membranes for direct methanol fuel cell (DMFC) application prepared from polymer solutions of sulfonated polyether ether ketone (SPEEK), containing an oxide phase, either generated by the hydrolysis of aminomodified silanes, or by dispersion of a surfacemodified fumed silica, and the acidic form of organosilyl derivatives of the divacant tungstosilicate [γ-SiW10O36]8–, were investigated. The ring opening reaction between the epoxy group, contained in the anion structure of the heteropolyacid and the amino group attached to the insoluble oxide phase was successful to fix the heteropolyacid in the membrane, without consuming protons of the heteropolyanion structure and therefore without affecting their acidity. That was reflected in the conductivity of these organic– inorganic materials, which is in the same order of magnitude of that of the plain polymer when the surface-modified fumed silica was used as oxide phase. The stability in alcohol solution was considerably higher for the organic–inorganic membranes with heteropolyacid bonded to oxides than that of the plain membrane. The methanol permeability of the organic–inorganic membranes was considerably lower than that of the plain membrane, especially when the alkoxysilane was used to generate the oxide phase. Acknowledgments We thank the DFG for the fellowship of M.L. Ponce and specially Prof. Stimming, TU München for stimulating this work as part of the network “Neue Schichtstrukturen für Brennstoffzellen”. We thank Dr. S. Vetter for sulfonating the poly (ether ether ketone). The work of Vasco Silva was supported by FCT (Grant SFRH/BD/6818/2001).