Study On Semiconductor Ionic Conductor Composite Electrolyte For Solid Oxide Fuel Cell

With the increasingly serious energy crisis and environmental pollution,Solid oxide fuel cell as an efficient energy conversion device has become a hot research topic because of its dual characteristics of high energy conversion efficiency and cleanliness in the operation process.However,after nearly two hundred years of development,SOFC is still difficult to achieve commercialization,which limited by a number of problems caused by it's high operating temperatures,e.g.thermal expansion coefficients mismatching between electrodes and electrolyte,degradation of materials,interfacial reactions between the components,limitation of materials selection,technological difficulties and high cost.Plenty of researches have been executed to reducing the operational temperature of SOFC.One of a promising way is to seek other alternative materials which have enough ionic conductivity at low and intermedium temperatures.Among them,semiconductor ionic conductor composites received widely attention relying on its splendid ionic conductivity at low temperature,which has been confirmed by relevant research.Then,semiconductor ion conductor fuel cell(SICFC)and single-layer fuel cell(SLSOFC)based on such material begin to attract more and more researchers.In this work,two kinds of semiconductor ion conductor composite materials were applied to SICFC and SLSOFC respectively.The operation mechanism and the reasons for the performance improvement of the cells caused by the composite materials were discussed.Firstly,YSZ-ZnO composite was prepared by solid-state mixing method and applied to Ni-NCAL\YSZ-ZnO\Ni-NCAL symmetrical SICFC.The effect of mass ratio of two-phase materials on cell performance was studied.The optimal power density output of 721 mw cm^-2was obtained at the ratio of 5:5,which is still as high as 142 m W cm^-2at 430?.Raman analysis of the material shows that after testing,lithium carbonate is formed in the cell,which is beneficial to improve it's performance.XPS analysis showed that the valence state of elements in the composite has changed with abundant oxygen vacancies were detected,indicating that there was interface effect between the two materials during cell operation,which promoted the generation of oxygen vacancies and the improvement of ionic conductivity.From TEM images,a large number of interfaces were observed,which confirmed the above inference.Then,the anode catalyst LST and ionic conductor SDC were synthesized by sol-gel method and co precipitation method.The composite material of LST-SDC-NCAL was applied to SLSOFC.The test about the effect of the thickness of the functional layer on the cell was shown that the performance increases with the thickness of the electrolyte layer,but the ohmic resistance of the cell increases greatly,which is not conducive to the benign development of the cell.The study about the effect of electrode porosity on the performance of the cell was shown that addition of pore-forming agent on the cathode side did not significantly affect the performance,but the electrode coated with nickel foam as a carrier can promote the performance of the cell.Therefore,the composite material of LST-SDC-NCAL was coated on nickel foam to prepare Ni-LST-SDC-NCAL as the current collector of SLSOFC.The symmetrical electrode cell was studied.The output power density of 222 m W cm^-2was obtained at 550?.In-situ Schottky junction in the device helps to prevent short circuiting as well as promote ion transport.Electrochemical impedance spectroscopy(EIS)analysis of the SLSOFC reveals promising ionic conductivity about 0.09 S cm^-1with the activation energy of0.7 e V.The cell performance was stable during 68 h without any significant degradation.Moreover,the SLSOFC possessed higher tolerance for temperature change than traditional three-layer fuel cell due to the well match of thermal expansion coefficient between electrodes and electrolyte.