Electrochemical Semipermeability and the Electrode Microsystem in Solid Oxide Electrolyte Cells

Abstract

New evidence is put forward within the framework of a recently introduced model. The electrodes are viewed as measuring the oxygen chemical potential in a “microsystem” which exchanges oxygen at a finite rate with the surrounding gas being analyzed. In high temperature oxygen gauges, the oxygen flux resulting from the electrochemical oxygen semipermeability of the electrolyte can have two effects other than reducing the theoretical emf by the factor false(1−t¯normalefalse) which appears to induce error of second order only. The oxygen semipermeability can obviously modify the oxygen content of the gas analyzed and also can disturb the equilibrium between the electrode microsystem and the analyzed gas. A special experimental setup was assembled to study both phenomena. The results showed that the second is generally far from being negligible and may lead to noticeable measurement error. A new arrangement with a zirconia point electrode is proposed to eliminate this source of error in oxygen gauges working at very high temperatures. The new arrangement was utilized to measure accurately the oxygen semipermeability of a ZrO2‐Y2O3 [9 mole per cent (m/o)] electrolyte at temperatures up to 1650°C. The semipermeability was found to be proportional to false(P3′1/4−P2′1/4false) , where P3′ and P2′ are the equivalent oxygen pressures in the layers of oxygen adsorbed on both bases of the pellet. The activation energy of the electronic conductivity equaled 2.02 eV.

Oxygen permeation through thin mixed‐conducting solid oxide membranes

“…Indeed for the thick oxide films the experimental results are consistent with the theoretical prediction (Alcock and Chan, 1972;Palguev et al, 1972;Fouletier et al, 1976;Dou et al, 1985;Park and Blumenthal, 1989;Bouwmeester et al, 1992). It is obvious, however, that the surface charge transfer reactions can be very important when the oxygen transport resistance in the bulk oxide becomes very small as a result of the increase in ionic and electronic conductivities or the decrease in film thickness.…”

“…In Figure 1 an oxide membrane is schematically divided into the bulk oxide and the adjacent interfaces, emphasizing both solid state diffusion and surface electrochemical reactions in the mass transport of the oxygen species. Among the limited experimental studies on oxygen permeation through fast ionic conductors, almost all studies focused on the oxygen permeation through relatively thick (> 500 pm) stabilized zirconia films which are essentially ionic conductors (Alcock and Chan, 1972;Palguev et al, 1972;Fouletier et al, 1976;Dou et al, 1985;Park and Blumenthal, 1989;Bouwmeester et al, 1992). In these studies, most researchers considered only the oxygen transport through the bulk oxide.…”

The effect of surface coating on the oxygen permeation characteristics of zirconia

“…(1) with the reported electrical conductivity data of 9 YSZ (9 mol% Y 2 O 3 -doped ZrO 2 ). 4,5 As shown, the measured data at 1600 • C match reasonably well with the estimated values. It means that the oxygen flux is mostly limited by the bulk diffusion.…”

“…However, the doped ZrO 2 was only studied for the high temperature (>1000 • C) use due to their low electronic conductivity. [3][4][5] The oxygen permeation studies of zirconia were mostly limited in relatively high oxygen partial pressure (P O 2 ). The oxygen permeation study in low P O 2 is needed for the application such as the oxygen removal from steel melt.…”

Feasibility Study on Advanced Solid-State Oxygen Sensors.

“…Table 1 shows the typical values of Ea and A for several zirconia compositions (24). A typical galvanic cell using a zirconia solid electrolyte is shown in Figure 3 (18,23,(25)(26)(27)(28). A thin plate of zirconia ceramic separates two gas atmospheres having oxygen partial pressures p!…”