Design consideration of micro thin film solid-oxide fuel cells

Miniaturized planar solid-oxide fuel cells (SOFCs) and stacks can be fabricated by thin film deposition and micromachining. Serious thermal stresses, originating in fabrication and during operation, cause thermal-mechanical instability of the constituent thin films. In this paper, the effect of thin film geometry on thermal stress and mechanical stability is evaluated to optimize the structure of a thin film. A novel design of thin circular electrolyte films for SOFCs is presented by using corrugated structures, with which small thermal stresses and a broad design range of structure parameters can be obtained. Thermal transfer analysis shows that heat loss by solid conduction is serious in thin films with a small radius. But thermal convection and radiation dominate heat loss in large thin films with a radius of several millimetres. Scale-dependent thermal characteristics show the importance of film size and packaging in optimization of thermal isolation for micro SOFCs. A novel flip-flop stack configuration for micro SOFCs is presented. This configuration allows multiple cells to share one reaction chamber, helps to obtain uniform flow fields, and simplifies the flow field network for micro fuel cell stacks.