Preparation of SDC–NC nanocomposite electrolytes with elevated densities: influence of prefiring and sintering treatments on their microstructures and electrical conductivities

Abstract

Sm_0.2Ce_0.8O_1.9–Na₂CO₃ (SDC–NC) nanocomposite powders and electrolytes were prepared through the precipitation of Sm-doped cerium/sodium complex carbonate and its prefiring and sintering operations. Their phase components and microstructures were characterized by XRD, FT-IR, TG-DSC, SEM and TEM, respectively, and, in particular, the sintering performance and oxide ionic and protonic conductivities of SDC–NC nanocomposite electrolytes prepared by prefiring and sintering at different temperatures were studied. It has been found that the SDC–NC nanocomposite powders derived from pre-firing treatments of non-crystalline carbonate precipitates are composed of SDC/NC nanocomposite core–shell structured particles. Moreover, the as-sintered SDC–NC nanocomposite electrolytes are generally made up of densely compacted SDC particles bound by NC phase, while their sintering performances and microstructures are significantly affected by the prefiring and sintering temperatures due to the differences in structural homogeneity and continuity of the NC phase. In addition, the oxide ionic and protonic conductivities of SDC–NC nanocomposite electrolytes can be strongly dependent upon the prefiring and sintering treatments, with the sample S-500-800 (prefired at 500 °C and sintered at 800 °C) showing the highest conductivities, 9.11 and 3.27 mS cm⁻¹ at 600 °C in H₂ and air, respectively. The single cell based on the electrolyte of S-500-800 showed an OCV of 0.99 V and a peak power density of 342 mW cm⁻² at 550 °C. More interestingly, the dependence of electrical performance on the prefiring and sintering temperatures is discussed from the perspective of the significant effects of the prefiring and sintering treatments on the microstructures and interfacial interactions between the phases of disperse SDC nanoparticles and NC, which is homogeneously and continuously filled in between them.