Research On Air-tightness And Electrochemical Performance Of Solid Oxide Fuel Cells

Solid Oxide Fuel Cells（SOFC）is an all-solid energy conversion device that directly converts chemical energy in fuel gas into electrical energy.It has the advantages of high energy conversion efficiency and easy modular design.The world’s top ten new energy technologies are of great significance to the energy crisis and the improvement of the ecological environment.The structural types of SOFC are mainly tubular and flat.Flat-type SOFC has become the focus of research due to its high current density and power density,but the problem of airtightness has been one of the key technologies that restrict the development of flat-panel SOFC.The air tightness problem mainly consists of two parts,one is the airtightness of the electrolyte,and another is the sealing airtightness of the sealing material.For the problem of electrolyte tightness,a gas tightness detecting device was designed.Firstly,according to the structural characteristics,detection accuracy and working conditions of the SOFC,the detection method is determined by the pressure drop method and the detection pressure is vacuum degree.Secondly,according to the detection pressure,the vacuum design manual is used to determine the sealing position of the vacuum seal,the sealing material and the sealing pressure.And complete the vacuum design parameters such as the wall thickness of the pipeline,the wall thickness of the vacuum chamber,and the design and selection of the vacuum pump and other accessories;then design the cavity and the fixed fixture,and eliminate the interference phenomenon during the assembly process by three-dimensional simulation.Optimize the model,determine the design;and finally complete the physical assembly.The sealing airtightness problem is related to the performance of the sealing material.For this purpose,a glass-ceramic composite material was developed and filled in the designed battery structure for medium-temperature sintering and packaging,and its related material properties and packaging characteristics were developed.Research.The powder material was ball milled for 5 h,and the average particle size was 10μm.The thermal properties of the material were analyzed by a thermogravimetric analyzer,and the mass loss at 25⁸00℃was only 3.5%.The thermal expansion coefficient of the material is 8¹0×10^-6/K^-1 at 700⁷50°C.It was found by SEM and EDX analysis that the sealing interface has good compatibility and the elements are relatively stable and have no diffusion.The sealing of the airtightness was carried out by introducing N₂ of 2 kPa,and the air leakage rate was measured to be 0.0039 sccm/cm.The hermeticity of the SOFC electrolyte and the sealing material can also be characterized by the open circuit voltage of the battery.Therefore,after the battery is sealed by the above composite material,the electrochemical performance test is performed using a Beit electrochemical workstation.Then,the effects of different H₂ flow rates on the open circuit voltage of the battery and the current density-voltage,current density-power density were studied.The experimental results show that the higher the H₂flow rate,the higher the open circuit voltage of the battery.When the H₂ flow rate is 0.6slm,the open circuit voltage of the battery can reach 1.167V,which is close to the theoretical voltage.When the current density is lower than 100 mA/cm²,the H₂ flow has less influence on the voltage of the battery;when the current density exceeds 100 mA/cm²,the H₂ flow has a great influence on the voltage of the battery,causing a sharp voltage loss,and the loss of voltage is mainly Reflected in the concentration polarization part.The H₂ flow rate is also positively correlated with the power density of the battery.The larger the H₂ flow rate,the higher the power density of the battery,and the maximum power density is 326 mW/cm².Finally,the electrochemical stability of the battery was characterized by constant current discharge.The constant current of 0.8V was 25h,the voltage drop of the battery was 0.796V,and the voltage value showed almost no change,indicating that the electrochemical performance of the battery was stable and no attenuation.