High-Performance Solid Oxide Fuel Cells For Low Temperature Operation

Professor Fritz Prinz
Chair, Department of Mechanical Engineering,
Stanford University, Stanford, CA 94305

Abstract

Fuel cells convert chemical energy directly into electrical energy with higher efficiency when compared to traditional heat expansion engines. Currently, two types of fuel cells are the subject of intense study. Polymer electrolyte membrane fuel cells (PEMFCs), commonly made of proton conducting polymeric membranes, need to be operated below 100°C to keep membranes sufficiently hydrated. In contrast, solid oxide fuel cells (SOFCs) containing solid oxide-ion conducting electrolytes require operational temperatures in excess of 700°C to achieve power densities comparable to that of PEMFCs due to the limited oxide-ion conduction in oxide membranes with thicknesses of a few to tens of micrometers.

Our research shows that sub-micron thin SOFCs consisting of traditional oxide-ion conducting electrolyte materials, such as Yttria Stabilized Zirconia (YSZ), can be operated below 400°C. We have achieved power densities of 200mW/cm2 and 400mW/cm2 at 350°C and 400°C, respectively. The SOFC structures in the present study were fabricated with the help of thin film deposition processing and lithographic silicon etching techniques.

The high power densities achieved are due to both the reduction of electrolyte thickness and the enhanced charge transfer reaction rates at the interfaces between the nano-porous electrodes (cathode and/or anode) and the nano-crystalline thin electrolyte. Strong electro chemical potential gradients are considered the origin for a high density of oxide-ion vacancies in the vicinity of the surface, which in turn lead to fast reaction kinetics and high current density. Improved SOFC performance at low operating temperatures promises new applications in areas such as transportation and portable electronics.

Monday, February 13, 2006
3:30pm
Wu and Chen Auditorium, Levine Building
Reception to follow