Built together as a series of cassettes, solid oxide fuel cells (SOFC) hold the promise of high-efficiency energy conversion, lower operating costs, fuel adaptability, and reliability. Unfortunately, a major drawback is the durability and reliability of the glass seals that bind the cassettes together. PNNL's cassette-less SOFC stack solves these problems by providing increased strength and durability while maintaining appropriate electrical connectivity.

In current SOFC stacks, an anode-supported cell is attached to a steel cell frame and welded to a metal interconnect plate. These individual cassettes form a stack of a certain size for a certain application. To prevent the cassettes from shorting out, each cassette must be separated and electrically isolated, typically by using glass seals. These glass seals tend to have low bonding strength and are typically located on the perimeter of the cassettes and around the gas porting sections. These areas also generally experience the maximum stresses during thermal cycling and tend to be the failure point. Additionally, the stack height dimension changes during the glass sealing step, which causes inconsistency in the electrical contact and lowers yield. A failure of the glass sealing step can cause the entire stack to be scrapped, increasing production costs.

PNNL's approach eliminates the cassette from the stack. The SOFC stack features an interconnect and cell that are electrically isolated from the frame portions of the stack. These frame parts are then welded together to form the stack. The interconnect plates and cells are bonded to the frames by glass seals in a configuration that greatly reduces the glass sealing area and reduces the stress on these areas. These preassembled parts can then be laser-welded together in a stack, turning what had previously been the most fragile part of the system into one of the strongest. This approach also eliminates any dimensional change during the stack assembly, leading to a more robust stack and increasing production yield.