Mixed ionic electronic conducting powder bed for grid level energy storage and release: A study of tungsten oxide reduction kinetics

The reduction kinetics of tungsten trioxide (WO3) powder using hydrogen gas was studied with titanium dioxide (TiO2) or 8 mol% yttria-stabilized zirconia (8YSZ) mixed into the powder bed. TiO2 was selected as an inert volume filler, and 8YSZ was selected to increase the ionic conductivity of the powder bed. The reduction sequence of tungsten trioxide in hydrogen is known to take place in the following steps: WO3 → WO2.9 → WO2.72 → WO2 → W. When the electronic and ionic conductivities of the mixed powder bed were both sufficiently high, reduction rates were found to increase. Specifically, reaction kinetics improved with the addition of 8YSZ to the WO3 when compared to experiments in which TiO2 was added to the WO3 powder bed. Chemical reaction rates were determined by first recording changes in mass as a function of time during reduction using thermogravimetry, and then reaction rates were calculated using relevant kinetic theory.