Impedance of solid oxide fuel cell LSM/YSZ composite cathodes

A number of lanthanum strontium manganate/yttria-stabilized zirconia (LSM/YSZ) composite electrodes are produced with varying composition and processing parameters. The composites are investigated using impedance spectroscopy. General trends related to the oxygen reduction process are extracted from the impedance data. Literature concerning kinetic studies of LSM/YSZ electrodes and related systems is reviewed and compared to new experimental data. From this it is found that at least five processes affect the impedance. Going from high to low frequency, these processes are (i), (ii) two geometry-related contributions interpreted as transport across LSM/YSZ interfaces and through the YSZ of the composite, (iii) a process reflecting competitive reaction steps such as bond breaking and surface diffusion, (iv) gas diffusion in a stagnant gas layer above the electrode structure, and (v) an activation process (inductive) presumably located at the triple phase boundary of electrode, electrolyte, and gas phase. (C) 2001 The Electrochemical Society.