The electrical behaviour of platinum impregnated porous YSZ

Porous sintered cubic yttria-stabilised zirconia (YSZ) samples were impregnated with a platinum salt solution and subsequently reduced to Pt metal to enhance the capacitance. Two impregnation methods were applied: (1) immersion of porous YSZ in a Pt salt solution followed by reduction of the platinum salt, and (2) deposition of Pt in porous YSZ at an electrode by means of electrolysis. The samples were investigated using impedance spectroscopy (IS) at ambient temperature and at 551 °C. The room temperature capacitance of samples prepared by the first method was up to four times larger than that of porous YSZ, while a maximum increase in capacitance of ∼20 times was observed in the electrolytically impregnated samples. Compared to dense composites with a randomly dispersed platinum phase, the preparation of impregnated samples—with a comparable enhancement of the capacitance—resulted in a reduction of the amount of noble metal needed of at least one order of magnitude. At temperatures above 400 °C, YSZ is oxygen ion conducting so that a double layer can be formed at low frequencies at metal/electrolyte interfaces. From the measured double-layer capacitance, which amounts to ∼2.6×102 F/m2 at 551 °C, it was determined that the specific electrode/electrolyte interfacial surface area of electrolytically impregnated samples was in the range of 80–300 m2/m2.