This paper shows that measured impedance in porous (La0.6Sr0.4)(0.99)CoO3-delta cathodes can be dependent on both gas diffusion and electrode kinetics at temperatures above 700 degrees C or below ambient pO(2)S if electrode kinetics are fast. The reaction mechanism is discussed on the basis of measured temperature- and pO(2)-dependences. The degradation was found to be related exclusively to the electrode kinetics and measured about 0.5-1.5 m Omega cm(2) days(-1) depending on temperature with a higher rate measured in moisturised air. We speculate on degradation mechanism that involves formation of strontium hydroxides at catalytically active oxygen vacancy sites at the electrode surface. (C) 2007 Elsevier B.V All rights reserved.