Semiconducting Ferrite (Spinel,Garnet) Materials For Low Temperature Solid Oxide Fuel Cell (LT-SOFC)

Low temperature solid oxide fuel cell(LT-SOFC)is regarded an attractive device because of their unique characteristics such as fuel flexibility,environment friendly and high efficiency.Currently,the SOFC fundamental problems are to search materials with high oxide ion conductivity and reducing the SOFC operated temperature(<600?).Ferrites(spinel and garnet)have a great potential for energy applications.This Thesis work has focused on the development of ferrites for electrolytes in advanced LT-SOFC.The results are presented as five parts in this dissertation work:In the first part:The single-phase Ni-Zn ferrite(Ni_0.4Zn_0.6Fe₂O₄)and their heterostructure composites with Sm_0.2Ce_0.8O₂(SDC)are fabricated as electrolyte membrane for LT-SOFC.The different characterizations verified the single-phase cubic crystalline structure,morphology,well packed microstructure,chemical states and surface analysis of the prepared nanoparticles(NPs).The prepared electrolyte displayed a triple charge conducting nature with a protonic conductivity in the range of 0.012 Scm^-1to 0.048 Scm^-1and LT-SOFC device delivered high power output of760 m W.cm^-2at 550?.In the second part,rare earth(RE)doped Mn-Zn spinel ferrite with the composition of Mn_0.5Zn_0.5X_0.02Fe_1.98O₄(X=Pr,Y,Gd,Ho,Yb)have been developed by analyzing its conduction mechanism at higher temperature.The different characterizations are used to study the single-phase spinel structure,porosity,homogenous grain size and optical bandgap of the prepared nano particles(NPs).The electrical conductivity(1.12x10^-2(?)^-1-cm^-1to 9.52x10^-2(?)^-1-cm^-1)of the as-prepared sample are measured at 40?-300?temperature.The optical,conductive analysis of the synthesized samples suggest that the prepared NPs can be used for energy conversion devices.The third part describes that the garnet ferrites(Sm₃Fe₅O₁₂)doped with(Yb,La)are used to form Sm_3-0.5Yb_0.5Fe₅O₁₂(SYFO)and Sm_3-0.5La_0.5Fe₅O₁₂(SLFO)NPs.The prepared NPs are developed to construct electrolyte membrane for LT-SOFC.Material characterizations and electrochemical analysis of as-prepared samples are performed using standard analytical techniques.The power outputs of the constructed fuel cell devices improved from 310 m W.cm^-2to 650 m W.cm^-2corresponding to a reduction of polarization resistance from 0.92(?)-cm²to 0.45(?)-cm²at 550?.In the fourth part:the single-phase yttrium iron garnets(YIG)doped with RE metal ions are prepared to analyze the complete optical bandgap theory including condition band and valance band alignments.The main standard characterizations of synthesized samples are employed to analyze the basic scientific parameters such as garnet phase,morphology and microstructure of the prepared NPs.The main purpose of this work is to analyze the optical band alignments such as valance band,conduction positions to verify the semiconducting nature of garnet ferrite NPs.The fifth part includes,the semiconducting electrolytes with high oxide ion conductivity are fabricated using Sm_3-1La₁Fe₅O₁₂(SLFO)and Sm_3-1.5La_1.5Fe₅O₁₂(2-SLFO)single phase NPs.It has been found an interesting mechanism during the fuel cell process that the increasing content of La doped garnet ferrite enhanced the transfer of oxygen carrier and enlarged triple phase boundary region(TPB).The 2-SLFO electrolyte membrane can improve the ionic conductivity and reduce the cell polarization resistance,leading to excellent power output of 620 m W.cm^-2.