Effect of intergranular glass films on the electrical conductivity of 3Y-TZP

The electrical conductivity of 3Y-TZP ceramics containing SiO2 and Al2O3 has been investigated by complex impedance spectroscopy between 500 and 1270 K. At low temperatures, the total electrical conductivity is suppressed by the grain boundary glass films. The equilibrium thickness of intergranular films is 1-2 nm, as derived using the "brick-layer” model and measured by HRTEM. A change in the slope of the conductivity Arrhenius plots occurs at the characteristic temperature Tb at which the macroscopic grain boundary resistivity has the same value as the resistivity of the grains. The temperature dependence of the conductivity is discussed in terms of a series combination of RC element

Performance and aging of microtubular YSZ-based solid oxide regenerative fuel cells

Fuel electrode supported microtubular solid oxide fuel cells (SOFC) fabricated at ICMA have been characterised in both solid oxide steam electrolyser (SOEC) and fuel cell modes. The cells consists of a fuel electrode supporting tube of Ni/YSZ with 40% porosity, ∼400 μm thickness, 2.4 mm diameter and 100–150 mm length, a 15 μm thick YSZ electrolyte and a 50 vol% LSM/YSZ composite air electrode of 20 μm thickness and LSM/YSZ (80/20 vol%) up to 2 cm2 area as current collector in the air side. Platinum paste and wires were used as interconnectors in the air chamber and Ni felt in the fuel side. SOFC and SOEC experiments were performed at temperatures between 750 and 950 °C using synthetic air in the oxygen electrode and different partial pressures of steam in the fuel side. Analysis of the polarisation contributions to the j–V curve in FC operation mode was performed using theoretical models, as discussed in the text. The effect of the steam concentration and temperature on the electrolysis and fuel cell experiments is presented and discussed. The cells are reversible in both modes of operation at low fuel conversion rates. According with previous observations, when cells are operated at high steam conversion rates the cell voltage tends to saturate. Irreversible damage was observed by SEM at the YSZ–oxygen electrode interface after operation, probably due to the electrolyte reduction produced at high voltages.We would like to thank UKERC (NERC-TSEC programme grant number: NE/C516169/1), and grants MAT2009-14324-C02-01, GA-LC-009/2009 and CIT-120000-2007-50 financed by the Spanish Government, DGA-Caixa and Feder program of the European Community for funding the project.Peer Reviewe