Solid oxide fuel cells (SOFC) are environmentally friendly energy conversion systems to produce electrical energy with minimal environmental impact. They have several additional advantages over conventional power generation systems such as high power density, high energy-conversion efficiency, low emissions of CO2, CO, NOX, SO2, fuel flexibility, modularity, ability to utilize high temperature exhaust for cogeneration or hybrid applications (with an efficiency up to approximately 70% in this case).(Fergus et al. 2009; Singhal & Kendall, 2001; Taroco et al., 2009). The single cell is composed of two electrodes (anode and cathode), an electrolyte, interconnects and sealing materials. The electrodes are porous, they exhibit an electronic conductivity and preferably also an ionic conductivity at the SOFC operating temperature. The electrolyte must be dense with good ion conducting characteristics (Badwal, 2001).

The conventional SOFC’s operate at high temperature (800-1000 oC). Currently, there is an increasing interest in the development of SOFC’s operating at intermediate temperatures (IT_SOFC: 600–800 C)(Badwal, 2001; Charpentier et al., 2000; Wincewicz & Cooper, 2005). The main difficulty with SOFCs operating at intermediate temperatures is the significant decline in performance mainly due to lower ion conduction of the electrolyte, and to a strong cathode polarisation. Solutions to improve the cell performance include the use of alternative electrolyte and electrode materials, besides a decrease in the electrolyte thickness (Charpentier et al., 2000; Singhal & Kendall, 2001; Sun et al., 2007, 2009). On the anode (fuel electrode) side the gaseous fuel is oxidized according to equation (in the case of a hydrogen fuel): 2H2 (g) O+ 4e-. The electrons flow through the external electrical circuit. On the cathode (air electrode) side, oxygen reacts with incoming electrons and ions O2-are formed: O2 (g)+ 2O2-→ 2H2+ 4e-→ 2O2-. The oxygen ions migrate through the electrolyte and combine with hydrogen on the anode side as schematized by the first equation (Fig. 1). Most of the electrochemical reactions occur at three-phase boundaries (TPB), which are defined as the sites where the ionic, electronic conductor and the gas phase are in contact ie where the electrode, the electrolyte and the gas phase are in contact. TPB characteristics have a large influence on the electrochemical performance of cell. The ideal voltage (E◦) of a single cell under open circuit (OCV) conditions is close to 1.01 V at 800 oC as calculated from the Nernst equation with pure hydrogen at the anode and air at the cathode (Acres, G., 2001). Under operation, the useful voltage output (V), is given by: