Under high temperatures, oxygen ion migration (driven by concentration gradient), zirconia becomes an excellent conductor of oxygen ions. Oxygen molecules are reduced to oxygen ions at the inner wall electrode (high oxygen side) and enter the zirconia lattice: O2(g) + 4e- → 2O2-(ZrO2)
These oxygen ions migrate within the zirconia, passing through the solid electrolyte to reach the outer wall electrode (the low-oxygen side). At the outer wall electrode, oxygen ions are oxidized back into oxygen molecules and release electrons: 2O2? (ZrO2?) → O? (gas) + 4e?
