Structure Designation And Performance Optimization Of Ceramic And Glass Composite Seals For Planar SOFC

As a new power generation technology, solid oxide fuel cell(SOFC) has became a hot research topic due to its low emissions and high conversion efficiency. Recently, although great progresses were made in the planar SOFC, the high temperature sealing was still a bottleneck in its wide applications.The ceramic-glass was the most frequently used seal materials in planar SOFC. With sealants structure design, a novel glass with relative low glass soften temperature was added into Al2O3 powders to form ceramic-glass composite seals fabricating by tape casting technique in this study. Based on the tested result of leakage rate and microstructure analysis, it was found that the seals with 40wt% glass exhibited excellent seal performance at the leakage rates of only 0.01sccm·cm-1 under gas pressure of 10.2k Pa and compressive load of 0.17 MPa at 750 oC. The AD40 seals showed the desired thermal cycle stability at low leakage rates within 10 thermal cycles. It also exhibited very good interfaces bondage and high temperature stability by glass crystallization phase analysis and interfacial bonding analysis. 0.7W·cm-2 output power and 100 h stable operation were obtained using AD40 seals in SOFC single cell test.The thermal expansion coefficient and high temperature thermal stability of h-BN ceramic were measured by thermal analysis technology and h-BN based sealant was fabricated by tape casting. Based on the tested result of gas tightness, it was found that the seals exhibited excellent seal performance at the leakage rates of only 0.01sccm·cm-1 under gas pressure of 6.8k Pa from 650oC to 800oC and the leakage rate decreased with the increasing of test temperature. Furthermore, the seal property was still far below the limited leakage rate, even the input gas pressure up to 20.4k Pa. And the seals kept low leakage rates within 10 thermal cycles at 750oC. The h-BN ceramic tended to be oxidized as liquid B2O3 membrane at high temperature, so that a strong interface layer between cell or interconnect is formed and the gas leak paths were effectively avoided. In order to improve the properties of h-BN based sealing materials, ceramic-glass composite seal materials were fabricated by adding different proportions of G glass powder into h-BN. The 50wt% glass content seal performed excellent properties through the sealing performance and the micro morphology analysis. The sealing performance was almost unchanged after 10 thermal cycles with the leakage rates of 0.0075sccm·cm-1 under gas pressure of 6.8k Pa at 750oC. The main reasons of low leakage rates were the excellent interfaces bondage and dense structure of h-BN-G50 seal. High voltage output and low attenuation were gained employing h-BN seals in single cell test.