Applicability of sodium sulfate as a solid electrolyte for a sulfur oxides sensor

Abstract The electromotive force (EMF) has been measured on SO2O2SO3 concentration cells using undoped and 4 at.% yttrium-doped Na2SO4 as solid electrolytes at temperatures between 920 and 1120 K. Two types of electrolytes prepared by sintering and infiltration have proven to work basically well above 973 K. The observed EMF's are consistent with the values calculated from the Nernst equation in the wide concentration range of SOx, showing that the ionic transference number is unity both in the undoped and yttrium-doped Na2SO4. A large difference in SOx pressures between the anode and the cathode leads to the lowering of the EMF because of the permeation of gases through the macroscopic defects such as pores and cracks in the electrolyte. The experimental results suggest that improvement of the sinterability and the stabilization of the high temperature phase are the indispensable problems to solve for the practical application of Na2SO4 as a solid electrolyte to an SOx sensor.