SOFC anodes based on infiltration of tungsten bronzes

Several tungsten bronzes were investigated for use in solid oxide fuel cell (SOFC) anodes. Composite anodes were prepared by infiltration of the precursor salts into a porous yttria-stabilized zirconia (YSZ) scaffold to produce 40-wt% composites with bronze compositions of Na0.8NbyW1−yO3−δ (y = 0, 0.3, 0.7, and 1), K0.5WO3−δ, Cs0.2WO3−δ, and Rb0.2WO3−δ. XRD data showed that the bronze structures were formed following reduction in humidified H2 at 873 K but that the bronzes were partially reduced to metallic W above 1073 K. Composite conductivities as high as 130 S/cm were observed at 973 K for the Na0.8WO3−δ-YSZ composite but substitution of Nb significantly decreased the conductivity without increasing the temperature at which tungsten was reduced. The impedance of Na0.8WO3−δ-YSZ anodes in humidified H2 at 973 K was greater than 1.0 Ω cm2 but this decreased to approximately 0.3 Ω cm2 upon the addition of 1-wt% Pd for catalytic purposes. The possible use of anodes based on tungsten bronzes is discussed.