Thermodynamic study of mixed anionic solid solutions using gradient solid electrolytes System K₂CO₃K₂SO₄

Abstract

The thermodynamic properties of K₂CO₃K₂SO₄ solid solutions with hexagonal structure have been measured using a solid‐state cell, incorporating a composite solid electrolyte with step‐changes in composition. The cell with the onfigurationFormula Pt, CO'₂+O'₂||K₂CO₃|K₂(CO₃)_x(SO₄)_1-x|| CO″₂+O″₂+Pt X =1 X=X was investigated in the temperature range of 925 to 1165 K. The composite gradient solid electrolyte consisted of pure K₂CO₃ at one extremity and the solid solution under study at the other. The Nernstian response of the cell to changes in partial pressures of CO₂ and O₂ at the electrodes and temperature was demonstrated. The activity of K₂CO₃ in the solid solution was measured by three techniques. All three methods gave identical results, indicating unit transport number for K⁺ ions and negligible diffusion potential due to concentration gradients of carbonate and sulfate ions. The activity of K₂CO₃ exhibits positive deviation from Raoult's law. The excess Gibbs energy of mixing of the solid solution can be represented using a subregular solution model