The effect of alumina addition on the electrical conductivity of Gd-doped ceria

Abstract

Acceptor doped-ceria is a possible electrolyte material for the IT-SOFC (intermediate temperature solid oxide fuel cell) due to its high oxygen-ion conductivity. However, its use has been limited by its mechanical weakness and the appearance of electronic conductivity in reducing condition. In this study, alumina was selected as an additive in the doped-ceria to see if it increases the oxygen-ion conductivity and mechanical strength. Effects of alumina addition in doped ceria were studied as a function of alumina content and acceptor (Gd) content. The electrical conductivity of (Ce1-x Gd (x) O2-delta)(1-y) + (Al2O3) (y) (x = 0-0.35, y = 0-0.10) was measured by using impedance spectroscopy. The grain conductivity of Ce0.8Gd0.2O2-delta (GDC20) with 5 mol% alumina increased similar to 3 times from that of GDC20 at 300 degrees C. The grain conductivity was even similar to 2 times higher than that of Ce0.9Gd0.1O2-delta (GDC10) at 300 degrees C. The electrical conductivity of GDC20 without alumina addition, measured at 500 degrees C in air, rapidly decreased after exposure to reducing condition (Po-2 similar to 10(-22) stop atm) at 800 degrees C. However, the decrease was much slower in GDC20 with alumina addition, indicating the improved mechanical strength. Among the examined compositions, (Ce0.75Gd0.25 O2-delta)(0.95) + (Al2O3)(0.05) (GDC25A5) showed the highest conductivity at most temperatures.