Electrode activation and degradation: Morphology changes of platinum electrodes on YSZ during electrochemical polarisation

During polarisation of dense PLD Pt film electrodes on YSZ changes in the morphology of the anode appeared involving a pronounced electrode activation. These morphology changes or more precisely the formation of bubbles and their cracking were explained by a built up of gas pressure underneath the Pt film due to the evolving oxygen. For the first time a detailed study of this phenomenon was presented, including a characterisation by HRSEM, AFM, in situ optical microscopy, XRD and electrochemical measurements. The appearance and the shape of different kinds of bubbles were discussed and an internal pressure was estimated by using simple geometrical models. A diffusion of oxygen along the interface Pt/YSZ was evidenced. The observed electrode activation was related to an extension of the tpb length during the formation and cracking of the bubbles. A comparison of dense electrodes to differently prepared porous ones clearly showed that a morphology change due to overpressure only occurs on extended gas-tight electrode areas and thus, need not be considered when using sintered paste electrodes.