Electrochemical Semipermeability and the Electrode Microsystem in Solid Oxide Electrolyte Cells

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 $(1-t{¯}_e)$ 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 ${\mathrm{ZrO}}_2‐Y_2{O}_3$ [9 mole per cent (m/o)] electrolyte at temperatures up to 1650°C. The semipermeability was found to be proportional to$(P_3^{\prime 1/4}-P_2^{\prime 1/4})$, where $P_3^{\prime }$ and $P_2^{\prime }$ 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.