Study On The Structure And Properties Of Sealing Glass For Intermediate Temperature Solid Oxide Fuel Cell

Solid oxide fuel cell(SOFC)is an electrochemical device that directly converts chemical energy stored in fuel and oxidant into electrical energy at medium and high temperature(generally around 600 to 1000?).It has the advantages of low pollution emission,high efficiency of energy conversion and wide adaptability of fuel and is regarded as one of the most promising energy sources in the 21st century.In recent years,the intermediate temperature(600?800?)flat-panel SOFC(ITSOFC)becomes the focus of attention of scholars at home and abroad.ITSOFC has solved many technical problems after many years of development,the preparation process becomes mature with commercial conditions,but the sealing material is still one of the key challenges to limit its commercialization process.As the main sealing material for ITSOFC,glass/glass-ceramic has high research value with the advantages of low cost,good heat treatment,suitable for mass production,etc.In this paper,the components of Boron-Bismuthate glass which is used as a glass-ceramic-based sealan(sealing glass)for ITSOFC stacks were designed.Sealing glass samples were prepared by melt-cooling method,and the effect of the different ZnO content(0?20mol%)on the network structure,glass transition temperature(Tg),softening point(Ts),initial crystallization temperature(Tc),coefficient of thermal expansion(CTE)and chemical stability of sealing glass were investigated.CTE,Tg,Tc,TS and other glass thermal performance parameters were analyzed by differential scanning calorimeter and thermal dilatometer.The glass network structure was analyzed by IR and Raman absorption spectroscopy.The crystallization behavior of glass was studied by X-ray diffraction.The reaction of glass-ceramics with water and the calculation of glass-forming ability(GFA)were used to evaluate the chemical stability of the system and the stability of the glass network.The morphology of the glass-ceramics was analyzed by scanning electron microscopy.The experimental results show that the addition of ZnO can improve the thermal properties of Boron-Bismuthate sealing glass.With the increase of ZnO content,the Tg and Tc of the original glass increased,the Ts increased from 377? to 411?.The CTE of the original glass decreased from 14.5 × 10-6K-1 to 12.4 × 10-6K-1.After heat treated for long-time(500h),the CTE of glass-ceramic is 12.3?12.8 × 10-6K-1 which can match with the coefficient of thermal expansion of adjacent cell components;The main crystaline phase of the B2O3-Bi2O3-ZnO sealing glass is Bi4B2O9 and Bi24B2O39,and the Bi4B2O9 phase precipitates at the low temperature before Bi24B2O39 phase.The addition of ZnO can promote the precipitation of Bi24B2O39 crystals in the sealing glass.The experimental results of FTIR and Raman indicate that the network structure of B2O3-Bi2O3-ZnO system is composed of[BiO3]triangles,[BiO6]octahedrons,[BO3]trihedrons and[BO4]tetrahedron units.In the glass structure,B2O3 is a network forming body and ZnO acts as a network modifier playing a role in filling the network.On the one hand,with the addition of ZnO,network connection degree can be improved,this strengthens the glass structure.On the other hand,the molar content of B2O3 was reduced and the relative content of[BO4]and[BO3]in the glass network was changed by the increase of the content of ZnO,this loose the glass structure.Both of these effects on the stability of the glass network result in the glass forming ability(GFA)i.e.AT(Tc-Tg)fluctuating between 122? and 88?.