Impedance spectroscopy studies of Gd-CeO2-(LiNa)CO3 nano composite electrolytes for low temperature SOFC applications

Electrical properties of 20 mol % Gd doped CeO2 with varying amounts of (LiNa)CO3 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)CO3, 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-CeO2 and carbonate phase. The composite containing 25 wt% (LiNa)CO3 shows the highest ionic conductivity of 0.1757 S cm−1 at 550 °C and lowest activation energy of 0.127 eV in the temperature range 550–800 °C. A symmetric cell is fabricated with GDC-25 wt% (LiNa)CO3 electrolyte, NiO-GDC(LiNa)CO3 anode and lithiated NiO-GDC(LiNa)CO3 cathode. Pure H2 and air are used as fuel and oxidant. The cell delivers a maximum power density of 45 mW/cm2, 58 mW/cm2 and 92 mW/cm2 at 450, 500 and 550 °C, respectively.

► Electrical properties of 20 mol% Gd doped CeO2 with varying amounts of LiNa(CO3) has been investigated.
► The typical nature of impedance spectra of the composite shows the possibility of coexistence of space charge effect at the interface of Gd-CeO2 and carbonate phases.
► The composite containing 25%(LiNa)CO3 shows highest ionic conductivity of 0.1757 S cm−1 at 550 °C and 0.21 S cm−1 at 650 °C respectively. The lowest activation energy of 0.127 eV in the temperature range 550–800 °C.
► Symmetric cells comprises of NiO-GDC(LiNa)CO3//GDC-(LiNa)CO3//LiO-NiO-GDC(LiNa)CO3 were fabricated through die pressing technique and a maximum current density of 92 mW cm−2 was achieved at 550 °C.