Structural Design And Property Of YSZ-glass Composite Seal For Intermediate Temperature Solid Oxide Fuel Cell

Solid oxide fuel cell?SOFC?is a device that directly converts chemical energy of fuels to electric energy.Due to its high efficiency,cleanness and low pollution,it has been considered as an efficient energy converter that can solve energy crisis and environmental problems.Currently,intermediate temperature?600?-800??SOFC technology has become more mature.Its relatively low working temperature can greatly reduce the cost of SOFC and expand the choice of cell components,achieving rapid temperature change and keep the stability,which expands the range of applications in mobile power and transportation.In addition,as far as SOFC's sealants are concerned,lower working temperature has changed the choice of sealants,from high temperature sealants like ceramics,micas and metals from early stage to glass-ceramic sealants now.Therefore,it is meaningful to develop reliable sealants for SOFC.As a kind of high thermally stable and highly deformable sealant with some degree of stiffness and physical integrity,glass-ceramic sealants,that have attracted extensive attention in recent years.However,glass-ceramic sealants will produce serious thermal stress leading to interfacial sealing failure.The reasons can mainly be attributed as follows:first,glass is brittle and prone to cracking below the glass transition temperature?T_g?;second,glass is a thermodynamically unstable phase,which tends to crystallize at elevated working temperature;third,the mismaching of CTE leads to microcrack that reduce the interface sealing effect.In view of the above problems,in this paper,a new composite glass-ceramic sealant developed by adjusting the glass to ceramic ratio,selecting suitable ceramic particles,determining the glass crystallization conditions,etc.In order to solve the above contradictions,comprehensively improving the interface sealing performance.The research contents and corresponding conclusions of this paper are as follows:?1?The effect of two kinds of Y stabilized Zr?YSZ?-glass seals on interfacial tightness,chemical compatibility,thermal stability and cell performance were investigated.The research indicated that,when adding 20 wt%YSZ,H1-20 and H4-20 seals have better comprehensive performance.H1-20 and H4-20 leakrate is below 0.01 sccm cm^-1 under load pressure is 0.2 MPa and the input pressure is 6.8 kPa between 650?and 800?,with the input pressure is gradually increased to 20.4 kPa,H1-20 seal leakrate is increase gradually,and H4-20's is decreased gradually that suggested better comprehensive performance.Through observation and analysis of the microstructure and interface state of H1-20 and H4-20 glass ceramic seals,the interface of sealants with the adjacent metal connector and single battery anode was well combined,and no obvious element diffusion phenomenon was found.In addition,there were a few microcosmic defects in the interior of H1-20,which was consistent with the test results of sealing performance.H1-20 and H4-20 seals were applied in test of single battery.After 5 thermal cycles and 100h constant current test,both of them showed excellent thermal cycles and long-term operation stability.?2?The effect of the number of thermal cycles on the mechanical properties of H1-20 and H4-20 seals and metallic interconnect were studied.The research indicated that,the bond strength of H4-20 and SUS430 interconnect was higher than H1-20 and SUS430interconnect.The shear strength of H4-20 was about 2.6 MPa,and tensile strength was about 22 MPa,while the shear strength decreased from 1.6 MPa to 1.1 MPa and tensile strength decreased from 12 MPa to 4 MPa of H1-20 after 10 thermal cycles,the fracture mode for H1-20 was near to seal interfacial failure and internal failure for H4-20,it was suggested that the interfacial bonding strength and stability of H4-20 and the SUS430interconnect were obviously better than H1-20 and the SUS430 interconnect.With the thermal cycles increased,the internal crystallization phase of the H1-20 increases correspondingly and a few of micro cracks were formed,the thickness of oxidation layer between H1-20 and SUS430 was thin that about 2⁵?m.However,the crystallization phase of H4-20 seal was remains stable with the increase of thermal cycles,and the oxide layer of its adjacent SUS430 interconnect is relatively complete and uniform,with a thickness of about 5⁷?m.These changes in microstructure are the essential reason for the difference in mechanical properties.?3?The crystallization kinetics of H1-20 and H4-20 glass ceramic seals were studied to determine the activation energy for crystallization and Avrami parameters.The research indicated that H4-20 were apparently higher than those of H1-20.The activation energy Ec and Avrami parameter n for H1-20 and H4-20 were calculated as 17.2 kJ.mol^-1 and32.7 kJ.mol^-1,and 3.2 and 2.6,respectively.H4-20 showed better thermal stability in long term SOFC operation.After thermal treatment at 750?,the main crystalline phase for H1-20 and H4-20 were BaMg₂Si₂O₇ and BaSr₂Si₃O₉,respectively.Because the CTEs of two seals were close to adjacent component,crystallization of glass would not produce high thermal stress and reduce sealing performance.