Microwave irradiation synthesis to obtain La0.7-xPrxCa0.3MnO3 perovskites : electrical and electrochemical performance

Abstract

La0.7-xPrxCa0.3MnO3 (LPCM) perovskites previously synthesized by the microwave-assisted method at 4 min and with different stoichiometry (x = 0.35, 0.52 and 0.63) were evaluated through thermogravimetric analysis (TGA), electrical conductivity, thermal expansion coefficient (TEC), scanning electron microscopy (SEM), Brunauer- Emmet- Teller (BET) analysis and electrochemical impedance spectroscopy (EIS) using yttria stabilized zirconia (YSZ) as an electrolyte. The results are discussed in terms of the potential as cathode material to be applied in solid oxide fuel cells (SOFCs) applications at temperatures from 600 to 800 °C. Results derived from TGA showed that Pr promotes the uncoupling oxygen and oxygen vacancies favoring the fuel combusting. Also, TEC analysis revealed adequate stability between the YSZ electrolyte and the La0.7-xPrxCa0.3MnO3 to avoid cracking or failing, especially with high amount of Pr. The transition in morphology from irregular to regular shapes improves the BET and Barret- Joyner- Halenda (BJH) surfaces and promotes the triple phase boundary (TPB) connectivity. The electrical conductivity correlated to the availability in oxygen vacancies showed maximum conductivities in the order of 10−2 S cm−1. Activation energy (Ea) was found to be reduced with a minimum quantity of Pr (0.071 eV). EIS results indicate that the oxygen vacancies in the LPCM/YSZ system were better promoted with the highest amount of Pr = 0.63 (η = 0.9 V, 800 °C and 0.06 V of amplitude) in comparison with the minimum, Pr = 0.35 (η = 1.2 V, 800 °C and 0.06 V of amplitude).