Fabrication Of ScSZ Electrolyte For SOFC By Plasma Spray And Research On Cell Performance

Solid oxide fuel cell(SOFC)has attracted much attention due to its high energy conversion efficiency,low pollution emissions,and wide selection of fuels.With the development of SOFC toward medium and low temperature,metal-supported SOFC have gradually emerged,However,the commonly used wet chemical preparation techniques require high temperature sintering(>1100°C)to densify the electrolyte,which limits the use of metal supports.Plasma spraying(PS),is a cost-effective technology with both flexible process and production efficiency,can effectively avoid the influence of the sintering process on the metal matrix.In order to reduce the spraying defects and obtain a high-density electrolyte coating,in this thesis,scandia stabilized zirconia(ScSZ)with excellent conductivity at medium temperature was selected as the electrolyte material,the effects of powder feedstock and plasma spray process on the microstructure and performance of the coating were investigated,focusing on the density of the electrolyte and output performance of the cell.The microstructure and mechanical properties of the coatings were characterized by SEM and nanoindentation tests,respectively.Electrochemical tests were used to characterize the electrochemical properties of the cells.The relationship between the microstructure of the electrolyte coating and the output performance of the cells was discussed.The specific research results are as follows:(1)Agglomerated and melt-crushed ScSZ powders were selected for atmospheric plasma spraying(APS).There are obvious through cracks in the interior of the coating prepared by agglomerated powder,resulting in low open circuit voltage and output performance of the cell.The coating prepared by melt-crushed powder has a uniform structure,weak crack connectivity,and the output performance of the cell is better.The open circuit voltage at 800°C is 0.928 V,and the maximum power density and ohmic impedance are 0.883 W/cm~2 and 0.134Ω·cm~2,respectively.Therefore,the melt-crushed ScSZ powder was subsequently selected for electrolyte densification research.(2)ScSZ electrolyte coatings were prepared by APS on different temperature substrates.With the increase of substrate temperature,the transverse unbonded interface in the coating decreased,the crack network and pore size decreased,and the coating porosity was reduced from 12.29%to 7.73%,which was reduced by about 37%.The single cell prepared on the 600℃substrate has the best electrochemical performance,with an open circuit voltage of 0.934 V at 800°C,maximum power density and ohmic impedance of 0.998 W/cm~2 and 0.076Ω·cm~2,respectively.(3)The density of the ScSZ electrolyte was significantly enhanced by the low-pressure plasma spraying(LPPS).At 7000 Pa,the porosity of the coatings decreased with the decrease of spraying distance.When the pressure was reduced to 4000 Pa,the porosity was further reduced to3.28%.Finally,the single cell prepared by LPPS at a pressure of 4000 Pa and a spraying distance of 325 mm has the best electrochemical performance,at 800℃,the open circuit voltage is 1.008 V,the maximum power density is 0.970 W/cm~2,and the ohmic resistance of the electrolyte is 0.101Ω·cm~2.