Use of Rare Earth Oxides as Potential Cathode for IT-SOFC

Intermediate temperature solid oxide fuel cell (IT-SOFC) is known for its clean power generation as it produces extremely low emission which hazards the environment. IT-SOFC efficiency crucially depends on cathode performance. Rare-earth oxides with K2NiF4 - structure have gained much attention towards its use as cathode because of its many encouraging properties. This study objects at synthesis of rare earth (electron) and alkaline earth metal (hole) doped cathode materials using combustion route. Examine effect of impurity addition on structural, electrical and electrochemical performance of cathode. Optimization of dopant concentration on the basis of maximum conductivity and minimum (area specific resistance) ASR followed by estimating the effect of oxygen partial pressure on electrical and electrochemical properties of doped cathode. Experimentally, the Nd2-xSrxFeO4+ (x = 0.1 - 0.4 ) single phase rare earth oxide is prepared using combustion synthesis. The SEM photographs depict agglomeration of the submicron sized crystallites resulted into formation of porous electrode layer. The dc conductivity showed maximum for x = 0.2 , coinciding with minimum activation energy. The comparative low dc conductivity with literature reports is due to high porosity as obtained from agglomerated submicron crystallites. Sr-dependent conductivity in Nd2-xSrxFeO4+ is explained from defect chemistry. The Nd1.8Sr0.2FeO4+ cathode exhibits lowest ASR ( = 1.92 0.015 Ohm- cm2 ) at is obtained from complex impedance measurements. Analyzing ASR in reduced partial pressure atmosphere indicated that charge transfer at electrode-electrolyte interface is the rate limiting step.