Impedance of thin film cathodes: Thickness and current collector dependence

• Clean platinum gauze catalyses the oxygen dissociation, thus enhancing the oxygen exchange reaction of a MIEC electrode.
• Platinum can react with La0.6Sr0.4Co0.2Fe0.8O3 –δ(LSCF), becoming catalytically inert.
• Sulphur contamination on the surface of apparently clean gold gauze can rapidly react with LSCF to form SrSO4.
• The chemical capacitance is useful as indicator for a valid measurement of the oxygen exchange rate in thin film EIS measurements.

The influence of the layer thickness of mixed ionic–electronic conducting (MIEC) cathodes and the type of noble metal current collector on the apparent surface exchange resistance is studied with impedance spectroscopy. The impedance data is analyzed with the ‘General Finite Length Diffusion’ transfer function. Also a simple relation is derived for the influence of the electronic sheet resistance of a thin layer on the apparent exchange resistance. These analysis methods are applied to a set of thin, dense layer electrodes of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) deposited on a Ce0.9Gd0.1O1.95 electrolyte by pulsed laser deposition (PLD). The apparent chemical capacitance is used to check the reliability of obtaining the oxygen exchange rate from the layer resistance. Use of a fresh, clean platinum gauze current collector significantly enhances the surface oxygen exchange rate on LSCF. But both ‘noble metal’ current collectors, Pt and Au, cannot be considered to be inert on LSCF.