Solid oxide fuel cells (SOFCs) utilizing nanoscale thin film technology has effectively decreased their operating temperatures from typically required to be in the 800°C to 1000°C range to below 500°C. By the help of silicon micromachining technology, such nanoscale thin film electrolytes were fabricated as a free-standing membrane. However, in order to minimize the internal resistance of the cell, the membrane is usually made to be only a few tens of nanometers in thickness, and subsequently its mechanical stability is poor. The lateral dimension of a fuel cell determines the total power output of this device, and for nano thin film electrolyte SOFCs, enlarging the electrolyte to obtain higher power output without cracking the membrane becomes virtually impossible. In this work, we demonstrated a fabrication method for a new nano thin film SOFC architecture that can provide upward membrane scalability to obtain higher device power, and at the same time enhance membrane mechanical stability for stable fuel cell operation.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 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 to be 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 º C for more than 8 hours without any membrane failure observed, showing the superior mechanical stability of the new cell architecture that are promising in further the practical application of such devices.

Nanoporous platinum electrode thin films were delaminated from yttria-stabilized zirconia (YSZ) substrates via double cantilever beam delamination to reveal the structure located at the interface between electrode and electrolyte. The thermally driven morphological evolution between the electrode top surface and the substrate contact interface of agglomerated nanoporous platinum thin films were compared. We found the temperature required for significant agglomeration to occur was approximately 100 °C higher at the electrolyte contact interface side than at the top surface side. Judging the reaction active site from the electrode top surface could be inaccurate because higher resistance of thermal agglomeration at the interface could retain the reaction active site during fuel cell operation.

We investigated the effect of electrolyte thickness and operating temperature on the heat and mass transfer characteristics of solid oxide fuel cells. We conducted extensive numerical simulations to analyze single cell performance of a planar solid oxide fuel cell (SOFC) with electrolyte thicknesses from 80 to 100 µm and operating temperatures between 700 • C and 800 • C. The commercial computational fluid dynamics (CFD) code was utilized to simulate the transport behavior and electrochemical reactions. As expected, the maximum power density increased with decreasing electrolyte thickness, and the difference became significant when the current density increased among different electrolyte thicknesses at a fixed temperature. Thinner electrolytes are beneficial for volumetric power density due to lower ohmic loss. Moreover, the SOFC performance enhanced with increasing operating temperature, which substantially changed the reaction rate along the channel direction. This study can be used to help design SOFC stacks to achieve enhanced heat and mass transfer during operation.

State-of-the-art micro-solid oxide fuel cells (micro-SOFCs) use ion-conducting ceramic electrolytes with thicknesses in the tens to hundreds of nanometers scale, which enabled a drastic decrease in operating temperature without a decrease in cell performance.

In this work we report a porous silver thin film cathode that was fabricated by a simple inkjet printing process for low-temperature solid oxide fuel cell applications. The electrochemical performance of the inkjet-printed silver cathode was studied at 300-450 °C and was compared with that of silver cathodes that were fabricated by the typical sputtering method. Inkjet-printed silver cathodes showed lower electrochemical impedance due to their porous structure, which facilitated oxygen gaseous diffusion and oxygen surface adsorption-dissociation reactions. A typical sputtered nanoporous silver cathode became essentially dense after the operation and showed high impedance due to a lack of oxygen supply. The results of long-term fuel cell operation show that the cell with an inkjet-printed cathode had a more stable current output for more than 45 h at 400 °C. A porous silver cathode is required for high fuel cell performance, and the simple inkjet printing technique offers an alternative method of fabrication for such a desirable porous structure with the required thermal-morphological stability.