**1.6 Research directions**

In recent years, research has been aimed at further reducing the operating temperature of the cell, leading to the development of a new class of planar SOFC, the intermediate temperature (IT-SOFC). This configuration provides an even greater reduction in operation temperature, allowing a large-scale use of metal interconnects. However, the ionic conductivity of the electrolyte is greatly affected by reducing the temperature. In this context, there are two ways to develop electrolytes for IT-SOFC: by changing the electrolyte to a material that has a high conductivity; or by reducing of the electrolyte thickness. In IT-SOFC cells, the electrolyte thickness should be as thin as possible (less than 10 µm has been suggested). In this case, the cell can operate at temperatures between 600 °C and 800 °C (Cooper et al., 2008).

In recent years, research has been aimed at further reducing the operating temperature of the cell, leading to the development of a new class of planar SOFC, the intermediate temperature (IT-SOFC). This configuration provides an even greater reduction in operation temperature, allowing a large-scale use of metal interconnects. However, the ionic conductivity of the electrolyte is greatly affected by reducing the temperature. In this context, there are two ways to develop electrolytes for IT-SOFC: by changing the electrolyte to a material that has a high conductivity; or by reducing the electrolyte thickness. In IT-SOFC cells, the electrolyte thickness should be as thin as possible (less than 10 µm has been suggested). In this case, the cell can operate at temperatures between 600 °C and 800 °C.

For the case of electrolyte change, materials with better ionic conductivity than YSZ have been studied to replace it. LSGM has been successful when applied with a metallic Ni anode, presenting ionic conductivity in temperatures around 400 °C (Sasaki et al., 2008; Tuker, 2010). The problem with such material is its low chemical stability. Another exhaustly studied material for SOFC electrolyte is gadolinium-doped ceria (CGO). This material has better ionic conductivity than YSZ and can be used in lower temperatures. However, at 600 °C the Ce reduction occurs. This reduction confers electric conduction to the material and the cell can suffer a short circuit (Tuker, 2010; Yuan et al., 2010).

The greatest challenge nowadays is to reach fuel cells operating around 700 °C without efficiency losses. The operation temperature can be lowered when the electrolyte thickness is reduced and the densification optimized. Several researches aim the obtaining of thin and dense electrolytes (Gaudon et al., 2006).

In the present study, some results about the elaboration of the YSZ thin film by spray pyrolysis process will be presented.
