Outstanding Oxygen Reduction Kinetics of La0.6Sr0.4FeO3−δ Surfaces Decorated with Platinum Nanoparticles

Abstract

La0.6Sr0.4FeO3-δ (LSF64) thin films are prepared by pulsed laser deposition (PLD) on yttria stabilized zirconia single crystals (YSZ) and characterized by electrochemical impedance spectroscopy (EIS) measurements before and after decoration with platinum nanoparticles. The platinum on the surface of LSF64 strongly accelerates the oxygen surface exchange kinetics. Especially at low oxygen partial pressures, the area-specific resistance (ASR) decreases by almost two orders of magnitude (e.g. in 0.25 mbar pO2 from 125 Ωcm2 to ca. 2 Ωcm2 at 600 C). While the pure LSF64 films exhibit severe degradation of the polarization resistance, Pt decorated films degrade much slower and show less scatter between individual samples. Surprisingly, faster oxygen incorporation (=lower polarization resistance) results for lower oxygen partial pressures, which indicates a severe mechanism change compared to undecorated LSF64 surfaces. The obtained results thus also reveal valuable information on the rate-determining step of oxygen exchange on LSF64 surfaces with and without platinum. On undecorated LSF64 surfaces oxygen dissociation is suggested to be rate limiting, while the Pt particles on LSF64 enable fast oxygen dissociation. Consequently, on Pt-decorated LSF64 electrodes a kind of job sharing mechanism results, with oxygen dissociation taking place on Pt and oxide ion formation and incorporation proceeding on the oxide.