Solid Oxide Fuel Cells: Studies of Ionic Conductivity
PI: Clare Grey
Solid oxide fuel cells represent viable fuel cells for static power applications. Current limitations to this technology include
- their high operating temperature, and
-
the relatively slow rate for the 02 ->02- reaction. The need to use high operating temperatures is driven by the relatively slow rates of oxygen ion diffusion across the solid electrolyte at lower temperatures. However, the use of lower temperatures would allow stainless steel components to be used, reducing the costs of the devices. The 02 -> 02- reaction occurs at a three-phase interface, involving air (02), a electronically-conducting cathode material, and the solid electrolyte; the low concentration of this interface results in slow rates for this reaction, limiting the power that can be drawn from the cell.
Our work in this area is focused on two areas. First, we use 170 MAS NMR to study ionic motion (N. Kim and C.P. Grey, Science, 297, 1317-1320, (2002)). Via NMR, we can determine which ions are mobile and the mechanisms by which ions move through the solid. Through this work we can provide insight into possible strategies for improving ionic conductivity.
In a second research area, we are investigating ionic motion across and at interfaces. Improving the rate at which ions move across interfaces represents one step towards solving the 02->02- reaction limitation. In one project, we are investigating CaF2-BaF2 heterostructures. 19F MAS NMR is used to understand the dramatic increases in conductivity seen in these nanostructures and to test models for enhanced conductivities at interfaces. Other related projects involve and investigation of surfacemodified nanoparticles. The use of nanostructures or nanoparticles increases the concentrations of the interfaces, often increasing conductivity and making their investigation easier by NMR. (NSF DMR)