Study On Electricity Induced Degradation In Electrolyte In Solid Oxide Fuel Cell

Solid oxide fuel cell(SOFC)is a new type of power generation system that directly converts chemical energy into electrical energy.It has clean,high-efficiency advantages and broad application prospects.The energy conversion efficiency of SOFC is not limited by the Carnot cycle and can reach 60 to 70%,becoming a hot spot for energy research.In recent years,although research on the flat-panel SOFC has made great progress,the output attenuation of long-term work is still one of the important reasons restricting the commercialization of this technology.The battery attenuation of the SOFC is mainly caused by changes in phase and microstructure of materials and materials occurring in electrode and electrolyte materials under high temperature,high current density and complex atmosphere.At present,related research has focused on the attenuation of electrodes,especially cathodes.However,the problems of electrolyte attenuation have less research.This paper mainly studies the compatibility and diffusion behavior of metal electrode and ceramic electrolyte under the action of electric field when the fuel cell is working,and characterizing the electrochemical and mechanical properties.In this study,yttria-stabilized zirconia(YSZ)was used as the electrolyte material that was prepared by powder dry compression molding and high temperature sintering to make a dense electrolyte sheet,and Pd was used as the electrode to print the surface of electrolyte through screen printing process.After sintering,electrode?electrolyte sample were prepared.The sample was polarized at a current density of 1 A/cm~2 at a working temperature of 850°C and in an air environment.Electrochemical characterization was performed for samples with polarization times of 1 h,50 h,100 h,200 h,and 350 h.Using a scanning electron microscope(SEM)test method to analyze the micromorphology of the poled electrode,and through the SEM attached X-ray energy spectrometer(EDX)linear scanning energy spectrum,X-ray photoelectron spectroscopy(XPS)ion etching depth profile and focused ion beam-transmission electron microscopy(FIB-TEM)analyzed the sample electrode and electrolyte interface.The test results show that The effect of the electric field did not cause significant diffusion between the Pd and the electrolyte,and the noble metal electrode had high stability at a current density of 1 A/cm~2 with a polarization time of 350 h.However,after long-time polarization,the appearance of the electrolyte contacted with the electrode is dark and the microstructure is rough and porous that Pd particles with dimensions much smaller than typical sintered sizes are attached to the surfaces.This phenomenon becomes more pronounced as the polarization time increases.At the same time,electrolyte fracture strength decreases with prolonged polarization time.The study also characterized the interface morphology between the cathode Pd element?the anode Ni element and the YSZ electrolyte of full cell which is at the condition of current density of 0.75 A/cm~2,operating temperature of 750°C and operating time of 4000 hours.Analysis shows that there is no diffusion of electrode elements into the electrolyte by using scanning electron microscopy(SEM)and its accompanying EDX?FIB-TEM spectra and time-of-flight secondary ion mass spectrometry(ToF-SIMS).In addition,it is found that there are two kinds of Pd and YSZ states in the cathode.One is that Pd is agglomerated into small particles dispersed in the voids of the YSZ framework.The other is that Pd is coated with YSZ and the coated Pd particles exhibit a concentration gradient from the center of the sphere to the outside.Furthermore,the influence of polarization current density and polarization time on the mechanical properties of YSZ electrolyte was studied.Using the casting process,screen printing,degreasing and co-sintering processes prepared YSZ wafer with a diameter of 22 mm and a thickness of 0.6 mm as the electrolyte.Using Pd as cathode made half cell.After a different polarization current density and polarization time,testing the hardness and fracture strength of half-cell and using SEM and XPS observe the fracture mode microscopically.Finding the corresponding relationship between the polarization time,the fracture strength and hardness and explain this phenomenon.