Carbonate content and solvent effects on microstructural and electrical properties of cold sintered SDC-Na2CO3 nanocomposite electrolytes

This study explores the effects of carbonate content and transient solvent type on the densification behavior, microstructural evolution, and electrical conductivity of cold-sintered samarium doped ceria (SDC)-sodium carbonate nanocomposite electrolytes intended for intermediate-temperature solid oxide fuel cell applications. Nanocomposites containing 10-30 wt.% Na 2 CO 3 were fabricated via the cold sintering process, employing either deionized water (DI) or ethylene glycol (EG) as transient solvents. The influence of two different liquid addition methods, mortar-pestle mixing and vapor-phase humidification in a petri-holder, was systematically investigated. It was found that increased carbonate content enhanced densification, with relative densities exceeding 95 % for composites containing ≥20 wt.% Na 2 CO 3 . Although EG exhibited limited solubility for Na 2 CO 3 , it enabled comparable densification due to its higher boiling point, which prolonged the particle rearrangement stage during CSP while maintaining better microstructural homogeneity as compared to the use of water. However, the conductivity of EG-treated samples was generally lower, likely due to residual organic species. The highest ionic conductivity, 68 mS.cm -1 at 600 °C, was recorded for the SDC20N sample humidified with DI water via the petri-holder method. Microstructural analyses revealed that this humidification method promoted inhomogeneity through enhanced carbonate agglomeration. Electrochemical impedance spectroscopy indicated dual conduction behavior, with activation energies ranging from 0.29 to 0.40 eV.