Multi-dimensional Structure Synthesis And Property Of Solid Oxygen Ionic Electrolytes

As a promising green energy conversion device, solid oxide fuel cell （SOFC）produces electricity from chemical energy that combines fuel and oxidant, which hashigh efficiency as well as low pollutants. In terms of the reduced cost and longer life,lowering of the operation temperature is the crucial investigation, making the study ofelectrolyte materials for intermediate/low temperature SOFC as a hot spot. As the targetof this work, to develop solid electrolyte materials processing high ionic conductivitybases on two sources to design and synthesize materials: one is to search new materialswith high ionic conductivity and more stability. Besides the traditional electrolytematerial of Y2O3doped ZrO₂（YSZ）, apatite-type lanthanum silicate, co-doped CeO₂and La₂Mo₂O₉are the primary objects; another is to optimize the electrolytemicrostructure to improve conductivity. We not only study three-demensional （3D） bulkelectrolyte, but also two-demensional （2D） film material. In addition, the materials ofone-demensional （1D） nanostructured morphology were also discussed as the solidelectrolyte innovatively.Firstly,3D apatite-type lanthanum silicates (La_9.33+xSi₆O_26+1.5x, LSO) bulkelectrolytes were synthesized via a sol-gel process. The effects of calcinationtemperature, sintering condition and composition on the phase present, microstructureand ionic conductivity of the LSOs have been investigated systemically. Compared withsolid-state reaction, the sintering temperature was lowered a lot substantially by thismethod. Based on2and4probe AC impedance spectroscopy measurements, theionic conductivity of the LSOs was obtained, which is much higher than other reportedvalues. The tune effect of SiO₄tetrahedra on the conductivity was also studied.Secondly,2D Sm³⁺and Nd³⁺co-doped CeO₂（SNDC） thin films were prepared byRF magnetron sputtering, whose fabrication parameters were optimized. The resultsrevealed that the texture in the SNDC film could be tuned by substrate temperature,presenting the conductivity of the film sample increased with the reduction in theintensity of （111） preferred orientation; the residual stress in the film increases asannealing temperature decreases, which leads to in enhanced ionic conductivity.The electrical conductivity of the SNDC film was higher than that of corresponding bulk material.Additionally, in order to improve the conductivity of electrolyte, we furtherincrease specific surface area, as result of which1D La₂Mo₂O₉（LMO）nanostructured materials were prepared by electrospinning technique. The LMOnanofibers have a special microstructure of individual grains chained together.In contrary with traditional LMO material, the nanofibers show stabilization ofthe high temperature phase at room temperature. The conductivity of thenanofibers is2,000times higher than that of corresponding bulk LMO, due tophase stabilization effect and surface fast conduction.Finally, YSZ nanofibers with a series of doped composition were alsoprepared by electrospinning, which shows oxygen ionic conduction asconduction mechanism. The results also confirm the surface fast conduction forthe1D nanostructural materials. In addition, YSZ nanotubes were synthesizedby co-electrospinning. As the solid electrolytes, the nanofibers with highperformances have great potential for the applications in portable devices suchas low temperature micro-SOFCs.