Advanced low-temperature ceramic nanocomposite fuel cells using ultra high ionic conductivity electrolytes synthesized through freeze-dried method and solid-route

Low ionic conductivity and slow reaction kinetics often limit the performance of a ceramic nanocomposite fuel cell (CNFC). Here, we report a novel synthesis method, freeze-dried method, to achieve a record high ionic conductivity for nanocomposite electrolytes (>0.5 S/cm) based on Ce_0.85Sm_0.15O₂ (SDC) and a eutectic mixture of Na₂CO₃, Li₂CO₃, K₂CO₃ (NLK). The highest ionic conductivity (0.55 S/cm) was reached by increasing the carbonate content of the electrolyte to 35 wt%. For the sake of comparison, the nanocomposite electrolytes were also prepared through solid-route. Composite anodes and cathodes for complete fuels were prepared from NiO and La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF), respectively using both solid-route and freeze-dried nanocomposite electrolytes. Complete fuel cells manufactured from these nanocomposite materials produced ∼1.1 W/cm² at 550 °C. The EIS measurements revealed low ohmic losses (0.18 Ω cm²) and even lower charge transfer resistance (0.05 Ω cm²). In addition, it was found that the open-circuit-voltage (OCV) of the CNFCs improved from 1.1 V to 1.2 V when a mixture of air and CO₂ was supplied as compared to the case when only air was supplied at the cathode. Finally, high temperature X-ray diffraction (HT-XRD) revealed stable structures of SDC, NiO and LSCF up to 600 °C, which shows the thermal stability of these fuel cell materials.