A circular membrane for nano thin film micro solid oxide fuel cells with enhanced mechanical stability

We demonstrate a new architecture for a low temperature solid oxide fuel cell to enlarge the lateral dimension of the fragile nano thin film electrolyte from the micrometer to millimeter scale with greatly enhanced mechanical stability. The new structure was achieved by simple silicon micromachining processes to change the membrane shape from a square to a circle to reduce buckling-induced stress concentration that often caused membrane fracture. A tapered silicon membrane support with the thickest end of 30 μm was introduced as an effective membrane stress absorber. The new architecture effectively suppressed membrane buckling and decreased the maximum principal stress by 30-40%. The largest lateral dimension of the stable membranes was 3 mm in diameter, and the survival rate was significantly improved over square membranes having the same lateral dimension. Fuel cells with 100 nm-thick electrolytes showed stable open circuit voltages of 1.12 V at 400 °C for more than 8 hours without any membrane failure observed, showing the superior mechanical stability of the new cell architecture that is promising in the further practical applications of such devices.