ABSTRACT
Recently, the interest in nano-technology has provided inspiration in the search for highlyperforming and stable electrodes for solid oxide fuel cells (SOFCs). Positively to say, the decrease in the size of the electro-catalysts has greatly enhanced the cell performance due to the increase in three phase boundary (TPB) sites and the improved catalytic activities of nano-particles. The promotion has been reported in a number of combinations including perovskite/yttria stabilized zirconia (YSZ) cathodes (Chen et al., 2008; Huang et al., 2005), perovskite/doped ceria cathodes (Chen et al., 2007; Jiang and Leng et al., 2006; Wang, 2005; Wang et al., 2012; Xu et al., 2006; Zhang et al., 2008) and Ni/electrolytes anodes (Ding et al., 2008a,b; Jiang et al., 2002; 2005; Liu et al., 2011; Wang et al., 2006; Zhu et al., 2006). The unique structure with nano-particles seems also to be beneficial to cell stability, although this remains controversial. Taking a cathode derived by the impregnation method as an example: it is prepared by depositing the nano-catalysts into porous pre-sintered backbones, which are co-fired with the dense electrolyte layer at a high temperature. The backbones are strongly bondedwith the electrolyte forming a robust incorporate body for tough operational conditions (Zhao, 2008a). The nano-sized catalysts are formed from the decomposition of the nitrate solutions at relatively low temperatures, under which the possible deleterious reaction between the catalysts and the electrolyte has been effectively suppressed, thus enlarging the selection alternatives for cathode materials. In the case of nano-anodes, derived by the impregnation technique, the nickel catalysts are free to suffer the support strength, and a little amount of nickel is introduced to reach the percolation limit for electron transfer (Suzuki et al., 2005; Uchida et al., 2003). Thus, the mechanical properties of the anode have been inevitably enhanced by having little influence from the micro-structure change of the nickel during the thermal or redox operation. However, with regard to thermodynamics, the nano-sized particles tend to grow up to release the free energy spontaneously by reducing the surface area. Grain coarsening could be observed in the nano-structured electrodes after a long isothermal test, especially at high temperatures, which was responsible for the performance degradation (Jiang et al., 2009a,b,c; Suzuki et al., 2009). Therefore, the use of the nano-structured electrode for practical application still needs to be carefully considered unless it definitely has a long-time stability with a reasonable degradation rate or a predictable performance as a function of operating time. This chapter focuses on the nano-structured effects on electrode durability, i.e. cell durability.
Fundamental aging mechanisms of the electrode components are also summarized. Long-time performances of the nano-structured electrodes are introduced to reveal the nano-size effects on electrode durability. Furthermore, models ever reported for the prediction of durability are included for better understanding the influence from the nano-size scale.
