Recovery and Delay of Impurity-Induced Poisoning of Oxygen Exchange Kinetics in Mixed Conducting Oxides Via Controlled Surface Acidity

Abstract

The oxygen exchange kinetics in mixed conducting oxide surfaces are critical to a variety of energy-related technologies, including solid oxide fuel/electrolyser cells (SOFCs/SOECs), permeation membranes, batteries, and sensors. Such devices, however, commonly suffer from performance degradation from impurity-poisoning during long-term operation, for example, chromia poisoning in SOFCs from metal interconnects or silica from furnace refractories. The acidity/basicity of binary additives has recently been found to be a sensitive descriptor for determining the oxygen exchange coefficient (kchem ) of mixed ionic/electronic conducting oxides (MIEC), systematically varing by over 6 orders of magnitude via controlled surface infiltration with binary oxides. These huge variations in kchem are attributed to changes in surface electron concentration induced by the additives.Inspired by these ideas, in this work we first demonstrate the ability to recover the oxygen exchange kinetics of MIEC oxides (e.g. Pr0.1Ce0.9O2-δ (PCO) and Sr(Ti,Fe)O3 (STF)) by counteracting acidic infiltrant’s impact on degradation, e.g. by chromia or silica, by compensating with a basic infiltrant like lithia or calcia. Further, we further demonstrate the ability to enhance impurity tolerance of MIEC oxides by pre-coating basic additives onto the electrodes. Such pre-treatments not only markedly improve the initial kchem of the pristine MIEC oxides, but markedly lower the rate of degradation induced by subsequent coatings with acidic poisons. Electrical conductivity relaxation measurements on porous MIEC specimens were used to examine the impact of infiltrants on kchem . In parallel, the area-specific resistance of screen-printed symmetric cells (cathode|electrolyte|cathode) were examined by electrochemical impedance spectroscopy.