ELECTROCHEMICAL CHARACTERIZATION OF VACUUM PLASMA SPRAYED PLANAR SOLID OXIDE FUEL CELLS AND SHORT STACKS FOR MOBILE APPLICATION

摘要

The requirements for the usage of SOFCs for mobile applications are different compared to those for stationary applications.During the practical operation of a vehicle,the SOFC stack in an Auxiliary Power Unit (APU)will be thermally cycled frequently with several interruptions of the fuel gas supply.Therefore,the cells have to withstand several thousand rapid thermal as well as reduction-oxidation cycles.In contrary to the investigation of SOFCs for stationary application,few investigations have been performed concerning the behaviour of cells and stacks in dynamic operation.This paper concentrates on the investigation of Vacuum Plasma Sprayed (VPS)cell layers with a diameter of 48 mm under operating conditions.The cell layers were deposited on different porous metallic substrates.The microstructure of the cells was characterised before and after operation by optical light microscopy,Scanning Electron Microscopy (SEM),X-Ray Diffraction (XRD)and Energy Dispersive X-ray microanalysis (EDX).The cells were electrochemically characterized by time dependent measurements (life cycle),current-voltage-measurements and impedance spectroscopy.In order to understand the nature of degradation mechanisms,a thorough comparison and discussion is made among the open circuit voltages (OCV),ohmic resistances and the polarisation resistances before and after dynamic operation,respectively.