Novel highly titania doped YSZ anodes for SOFCs

In the ternary system ZrO2-Y2O3-TiO2 compositions with titania concentrations of 18 mol-% can be dissolved in the cubic fluorite structure. The electrical properties of these compositions close to the high titania, low yttria limit were found to have a predominant ionic conductivity of about 0.01 Scm(-1). Substantial electronic conductivity of about 0.2 Scm(-1) at 930 degrees C is introduced into the system at oxygen pressures below 10(-13) atm. For applications in the SOFC, I-V polarisation studies were performed on anode compositions, screen printed on YSZ electrolytes, using a gold mesh current collector. A low effective contact area of about 20% of the geometrical area suggested that these materials need to be supplemented by a current collecting component. With increasing polarisation of the electrode, the effective contact area decreased due to oxidation of the electrode. However currents, related to the effective contact area were reasonable. By impedance studies the polarisation losses were associated with the electrode and electrolyte resistances, diffusion and charge transfer losses were not very large, perhaps indicating the benefit of an ionically conducting electrode.