Ionic and Electronic Conductivities and Fuel Cell Performance of Oxygen Excess-Type Lanthanum Silicates.

Highly dense pellets of an oxygen excess-type lanthanum silicate (La_9.333+xSi₆O_26+1.5x, x > ca. 0.3, OE-LSO) were successfully fabricated, and their electrical conducting properties were studied. The replacement of Si by Al enhanced its conductivity, and the slightly Al-doped OE-LSO specimen [La_9.62(Si_5.79Al_0.21)O_26.33] had excellent features as a solid electrolyte; that is, it had high ionic conductivity and was highly stable under reducing as well as oxidizing conditions at 873-1073 K. In addition, the ionic transference number was higher than 0.99. In the fuel cell utilizing this electrolyte (0.72 mm thick), (La_0.6Sr_0.4)(Co_0.2Fe_0.8)O_3-δ cathode, and Ni-Ce_0.9Gd_0.1O_1.95-δ anode, good performance with the maximum power density of ca. 0.25 W cm^-2 was obtained at 1073 K. In addition, this electrolyte also had high compatibility with these conventional mixed conducting electrodes, according to an analysis near the electrode/electrolyte interfaces after the fuel cell test. [ABSTRACT FROM AUTHOR]