Shape memory alloy/glass composite seal for solid oxide electrolyzer and fuel cells

Widespread use of solid oxide electrolyzer and fuel cells is hindered by a lack of long-term durability of seals caused by thermal expansion mismatch induced cracking. A novel seal design incorporating an engineered thermal expansion gradient in a glass matrix with a TiNiHf shape memory alloy mesh for active stress relief and crack healing is being developed. Thermal expansion coefficient (CTE) measurements of the seal and other cell components show the possibility of a thermal expansion gradient design for the seal. Differential scanning calorimetry and microscopy show that the TiNiHf alloy has shape memory phase transformation temperatures in the desired range of 200–250 °C. The glass partially crystallizes during thermal cycling, as shown by X-ray diffraction and dilatometry; the CTE decreases from 9.3×10-69.3×10-6 to 6.6×10-6∘C-1 after thermal cycling. Neutron diffraction data from TiNiHf /glass composite reveal that the TiNiHf alloy absorbs residual stresses from the glass matrix during austenitic to martensitic phase transformation.