Impedance spectroscopy studies of Gd-CeO_2-(LiNa)CO_3 nano composite electrolytes for low temperature SOFG applications

摘要

Electrical properties of 20 mol % Gd doped CeO_2 with varying amounts of (LiNa)CO_3 have been investigated by employing AC-impedance spectroscopic technique. The impedance spectra show a high frequency depressed arc, represents the bulk composite and low frequency incomplete semicircle representing electrode contribution. The bulk resistance of the composites decreases with increasing carbonate content up to 30 wt% (LiNa)CO_3 thereafter the resistance increases, whereas all the compositions show a decrease in resistance with increasing temperature. The typical nature of the impedance spectra of the composite shows the possibility of coexistence of multi ionic transport or existence of space charge effect at the interface of Gd-CeO~2 and carbonate phase. The composite containing 25 wt% (LiNa)CO_3 shows the highest ionic conductivity of 0.1757 S cm at 550 ℃ and lowest activation energy of 0.127 eV in the temperature range 550-800 ℃. A symmetric cell is fabricated with GDC-25 wt% (LiNa)CO_3 electrolyte, NiO-GDC(LiNa)CO_3 anode and lithiated NiO-GDC(LiNa)CO_3 cathode. Pure H~2 and air are used as fuel and oxidant. The cell delivers a maximum power density of 45 mW/cm~2, 58 mW/cm_2 and 92 mW/cm~2 at 450, 500 and 550 ℃, respectively.