In Situ Impedance Analysis of LSC Thin Films during Growth on YSZ and LSGM

The mixed ionic electronic conducting perovskite oxide

La0.6Sr0.4CoO3−δ (LSC) is a very promising cathode material

for application in solid oxide fuel cells (SOFC) due to its

catalytic properties for the oxygen surface exchange and

high electronic conductivity.1 A factor which is essential to

consider in the characterization of LSC is the influence of

lattice strain on the surface exchange resistance and the

chemical capacitance.

Recent findings showed that tensile strained films exhibit

faster surface exchange reaction and oxygen diffusion

compared to compressively strained films.2

In this study, the influence of the two different substrates

Y2O3:ZrO2 (YSZ) and (La,Sr)(Ga,Mg)O3 (LSGM) on LSC thin

films was examined with a novel method allowing in situ

impedance spectroscopy during the PLD process (IPLD).

Thus, it is possible to track charge carrier densities during

growth and to link results with microstructure and strain.3

Matthäus Siebenhofer1, Ghislain M. Rupp1, Jürgen Fleig1, Markus Kubicek1

1TU Wien, Institute of Chemical Technologies and Analytics, Austria

Individual Features

Introduction

The capacitance of the thin film increases linearly withthe thickness of the growing film while current collectorand counter electrode do not change dramatically duringthe deposition process.

Typical Impedance Spectra

The typical impedance spectrafeature three individual arcs indifferent frequency regimes:

• Current Collector (CC) – HF

• Working Electrode (WE) – MF

• Counter Electrode (CE) – LF

Capacitance on Different Substrates

An increase in thechemical capacitance of afactor 1.6 was found fortensile strained LSC thinfilms grown on LSGMcompared to films grownon YSZ single crystals.

Resistive PropertiesA lower oxygen exchange resistance of 1.04 ± 0.02 Ωcm2

is reproducibly found for LSC on LSGM measured at600 °C and 40 μbar O2. This indicates enhancement of theoxygen exchange kinetics by a factor of ∼2 for LSC filmson LSGM compared to films on YSZ.

Experimental I Experimental II

References1 Chunwen, Sun, et al. "Cathode materials for solid oxide fuel cells: a review." Journal

of Solid State Electrochemistry (2010).

2 Kubicek, Markus, et al. "Tensile Lattice Strain Accelerates Oxygen Surface Exchange and Diffusion in La1–xSrxCoO3− δ Thin Films." ACS Nano (2013).

3 Rupp, Ghislain M., et al. "In Situ Impedance Analysis of Oxygen Exchange on Growing La0.6Sr0.4CoO3−δ Thin Films." ACS Applied Energy Materials (2018).

Conclusions• Simultaneous PLD thin film growth and

electrochemical characterization of LSCthin film electrodes

• Very high reproducibility of measurements

• Enhancement of the oxygen exchangekinetics by a factor of 2 for strained LSCfilms on LSGM compared to unstrainedfilms on YSZ

• Higher chemical capacitance in tensilestrained films, suggesting a decrease of theoxygen vacancy formation energy leadingto higher oxygen vacancy concentrations.

Acknowledgements & Contact Information

Fig. 1: Schematics of the IPLD setup and the thin film samples prior to deposition Fig. 2 a) & b) : Photographs of the IPLD setup

a)

b)

Fig. 3: Impedance spectra during a deposition process on YSZ at 600° C and 0,04 mbar p(O2) measured for different thicknesses

Fig. 5: Chemical capacitances of LSC thin films duringgrowth on LSGM and YSZ at 600 °C and 0,04 mbar p(O2)

Fig. 4: Capacitances of the individual features of a LSC thinfilm sample during growth at 600 °C and 0,04 mbar p(O2)

Fig. 6: Resistance of LSC thin films during growth on LSGM and YSZ substrates at 600 °C and 0,04 mbar p(O2)

Fig. 7: Oxygen exchange at the surface ofa tensile strained thin film

Financial support by Austrian Science Fund (FWF) projectsP4509-N16 and P31654 is gratefully acknowledged.

TU Wien - Institute of ChemicalTechnologies and Analytics

matthaeus.siebenhofer@tuwien.ac.at