Virginia Tech professor of materials science and engineering Peizhen (Kathy) Lu has developed new barium oxide-, calcium oxide-, magnesia-, and alkali oxide-free glasses that can be used as sealants in both solid oxide fuel cells and solid oxide electrolyzer cells (SOFC/SOEC).
SOFCs operate by separating oxygen ions from air, which pass through a crystal lattice and oxidize a fuel—usually a hydrocarbon. The chemical reaction produces electrons, which flow through an external circuit, creating electricity. Composed of ceramic materials, SOFCs can operate at temperatures as high as 1,000 °C (1,832 °F). An SOFC can also be designed to operate with reversed direction of current flow as a solid oxide electrolyzer cell (SOEC) to split steam to produce hydrogen.
To produce enough power or hydrogen for a particular application, SOFC/SOEC modules are stacked together. Suitable sealant material is required to avoid the mixing of fuel (hydrogen or hydrocarbon) and oxidants (oxygen and air) in solid exide fuel cell, and steam and reactant gases in solid oxide electrolyzer cell, to avoid leaking of the gases.
Seals are a key barrier for the high efficiency and long-term integrity of both cells. Although glasses are the best solution for these particular applications, it is very difficult to design a glass to fulfill all the required properties simultaneously. Lu has invented a new self-healing seal glasses that can be used to seal the modules and the stack.
In addition to being BaO-, CaO-, MgO-, and alkali oxide-free, the invented glass seals also contain little amount of or no B2O3. All the developed glasses in this invention have glass transition temperature in the range of 680-750 ºC, thermal expansion coefficient in the range of 10.5-12.5x10-6/ºC from room temperature to glass transition temperature, and dilatometric softening temperature in the range of 720-820 ºC. The glasses are thermally stable up to 850 ºC. The sealing temperature of the developed glasses does not exceed 1000 ºC. The invented glass is suitable for the cells operating at 700-900 ºC for long term.
Virginia Tech Intellectual Properties is licensing the invention.
The US Department of Energy has provided $365,000 in funding for Lu’s SOFC and solid oxide electrolyzer cell research so far.
K. Lu and M. K. Mahapatra (2008) Network structure and thermal stability study of high temperature seal glass. J. Appl. Phys. 104 074910 doi: 10.1063/1.2979323