Effect of Alkali Carbonates (Single, Binary, and Ternary) on Doped Ceria: A Composite Electrolyte for Low-Temperature Solid Oxide Fuel Cells.

Samarium-doped ceria (SDC) carbonate has become an attractive electrolyte for fuel cells because of its remarkable ion conductivity and high performance. Different doped ceria-carbonate (single-carbonate SDC, binary-carbonate SDC, and ternary-carbonate SDC) electrolytes were synthesized by the coprecipitation/oxalate method, to optimize the electrochemical performance. The structure; morphology; and thermal, optical, and surface properties have been studied using a variety of techniques. The X-ray diffraction results confirmed the successful incorporation of samarium into ceria as a crystalline structure and inclusion of carbonate, which is amorphous in nature. To analyze the conduction mechanism, direct current conductivity was measured in a H/O atmosphere. Doped ceria-binary carbonate ((Li/Na)CO-SDC) showed the best conductivity of 0.31 S cm and power density of 617 mW cm, at 600 °C. The enhancement in the ionic conductivity and performance of the composites is due to the contribution of hybrid ions (O, H). The crystallite size of the composites was in the range 21-41 nm. For the calculation of band gaps, optical absorption spectra of the synthesized powders were analyzed, and they showed a red shift with the band gap energy in the range 2.6-3.01 eV, when compared to that of pure ceria (3.20 eV).