Behaviour of a dense In2O3/ YSZ electrode in oxygen containing atmospheres

Abstract

A study of electrical and electrochemical properties of a dense In2O3 electrode in contact with a single crystal YSZ electrolyte was carried out by d.c. and a.c. methods. As a result, it was found that dense In2O3 electrodes have high electrical conductivity but very low electrochemical activity. In a vicinity of the equilibrium potential and under the anodic polarisation, the rate of Faraday reaction at the In2O3 electrodes was as low as to consider the electrode a blocking one. The blocking properties of the In2O3 electrodes were used to measure the hole conductivity of the YSZ electrolyte in the temperature range between 795 to 1163 K and oxygen partial pressure from 1 to 105 Pa. A comparison with the literature data confirmed that the dense In2O3 electrode blockes the ionic transfer through the YSZ. A set of experiments indicated that the oxygen exchange between the indium oxide surface presented to the oxygen containing gaseous phase and this phase is very poor. A route of the electrode process at O2, In2O3 / YSZ electrode was proposed a limiting stage of which is the discharge of the oxygen ions to the atomic oxygen adsorbed on the electrode surface: $$O_0 ^x \left( {In_2 O_3 } \right)_s = V_0 ^{ \bullet \bullet } \left( {In_2 O_3 } \right)_s + O_{ad} \left( {In_2 O_3 } \right)_s + 2e'\left( {In_2 O_3 } \right).$$ The polarisation resistance decreases when platinum or the praseodymium oxide is deposited on the surface of the In2O3 electrodes. The cathodic polarisation also increases the electrochemical activity of the electrodes. Both the establishment of the steady state of the electrode under polarisation and the recovery of the equilibrium state by the electrode are very long processes, which are probably related to the diffusion mechanism by which the stoichiometry of the indium oxide is changed.