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 dopedceria 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 (Ce 1−x Gd x O 2−δ ) 1−y + (Al 2 O 3 ) y (x = 0-0.35, y = 0-0.10) was measured by using impedance spectroscopy. The grain conductivity of Ce 0.8 Gd 0.2 O 2-δ (GDC20) with 5 mol% alumina increased ∼3 times from that of GDC20 at 300 • C. The grain conductivity was even ∼2 times higher than that of Ce 0.9 Gd 0.1 O 2−δ (GDC10) at 300 • C. The electrical conductivity of GDC20 without alumina addition, measured at 500 • C in air, rapidly decreased after exposure to reducing condition (Po 2 ∼10 −22 atm) at 800 • C. However, the decrease was much slower in GDC20 with alumina addition, indicating the improved mechanical strength.Among the examined compositions, (Ce 0.75 Gd 0.25 O 2-δ ) 0.95 + (Al 2 O 3 ) 0.05 (GDC25A5) showed the highest conductivity at most temperatures.

Lowering the sintering temperature of Gd-doped ceria by mechanochemical activation

“…The lattice parameter calculated from the XRD patterns of Ce 0.8 Gd 0.2 O 2Àd was 0.5411 AE 0.0002 nm regardless the type of powder used, which is in good agreement with previous reports [10,14,15]. Moreover, the logarithmic grain conductivity (log s) of the sintered pellets was approximately À2.03 and À1.40 S/cm at 500 and 700 8C, respectively, for both the high energy-milled K-and W-powder, which cannot be achieved when the GDC phase is not formed [8,9,16].…”

“…Many attempts have been made to decrease the sintering temperature of GDC, including the use of nano-sized powder produced by various wet-chemical routes [3][4][5] and the addition of sintering aids [6][7][8][9][10]. For practical application, it is important to achieve a sintered density !95% at temperatures 1300 8C.…”

Increased electrical conductivity and the mechanism of samarium‐doped ceria/Al2O3 nanocomposite electrolyte

“…The heterogeneous interface of Al 2 O 3 /YSZ or Al 2 O 3 /ceria has demonstrated much higher ionic conductivity and contributed to the improved conductivities of the composite electrolytes . Alumina addition can also increase the mechanical strength of doped ceria and inhabit its electronic conduction in reducing atmosphere . In addition, as the alumina is dramatically cheaper than the doped ceria, its substitution for ceria matrix can reduce the cost of the composite materials without property degradation .…”

“…Although there is substantial literature involving the effects of alumina addition on the properties of YSZ, the performances and their corresponding mechanisms of the doped ceria/Al 2 O 3 composite have not been elaborated systematically and adequately . In the limited references, Zhang et al .…”

Effect of Al- or Ga-additive on ionic conductivity of thin-film Gd-doped ceria

“…Ga and Al have also been reported as densification-promoters during sintering of bulk samples by enhancing grain-boundary mobility with their smaller atomic radius than Ce 4+ ion [20,21]. For the addition of alumina into a GDC pellet, the grain boundary conductivity of GDC only slightly decreases with up to 5 mol% Al 2 O 3 addition until it shows fast decrease with further addition due to the resultant second phase [22].…”