FUEL-CELLS WITH H3PW12O40-CENTER-DOT-29H(2)O AS SOLID-ELECTROLYTE

Electrochemical activity tests have been performed on a fuel cell fed with H-2/O-2 at room temperature utilizing phosphotungstic acid (PWA) as solid electrolyte. Two different procedures were followed to prepar e the electrolyte layers. One consisted of mixing the precursor of a s ilicon polymer with the crystalline powder of the PWA in an agate mort ar and spreading the paste on a glass surface or on the surface of an electrode; the polymerization occurred with the layer already formed. A composite elastic material which held the acid entrapped in the pore s of the polymer was obtained, The other procedure consisted of impreg nating an inert porous material with a concentrate solution of PWA, fo r a longer time, to obtain a flat layer after successive drying. A sti ff and undeformable material reinforced by the porous matrix was obtai ned by this method. Poor fuel cell electrochemical performances were o btained with the composite electrolyte layer principally due to the hi gh protonic internal resistance. Moreover, the polymeric skeleton was unstable under the working conditions of the cell. Maximum power densi ty of 0.075 W/cm(2) was obtained at 0.2 A/cm(2) with the electrolyte l ayer formed by 70 wt% of PWA and 30 wt% of silicone polymer. Better el ectrochemical fuel cell performance was obtained with the reinforced e lectrolyte layer containing glass microfibers prepared by the second m ethod. This can be summarized in current density of 0.45 and 2.0 A/cm( 2) at cell potential of 0.6 and 0.33 V, respectively, power density of 0.738 W/cm(2) at 1.8 A/cm(2) and a Tafel slope of 0.058 V/decade. (C) 1997 International Association for Hydrogen Energy.