TY - JOUR

T1 - Closed-Pore Formation in Oxygen Electrodes for Solid Oxide Electrolysis Cells Investigated by Impedance Spectroscopy

AU - Krammer, Martin

AU - Schmid, Alexander

AU - Nenning, Andreas

AU - Bumberger, Andreas Ewald

AU - Siebenhofer, Matthäus

AU - Herzig, Christopher

AU - Limbeck, Andreas

AU - Rameshan, Christoph

AU - Kubicek, Markus

AU - Fleig, Juergen

N1 - Publisher Copyright: © 2023 The Authors. Published by American Chemical Society.

PY - 2023/2/2

Y1 - 2023/2/2

N2 - Electrochemical impedance spectroscopy was used to investigate the chemical capacitance of La0.6Sr0.4CoO3−δ (LSC) thin-film electrodes under anodic polarization (i.e., in the electrolysis mode). For this purpose, electrodes with different microstructures were prepared via pulsed-laser deposition. Analysis of dense electrodes and electrodes with open porosity revealed decreasing chemical capacitances with increasing anodic overpotentials, as expected from defect chemical considerations. However, extremely high chemical capacitance peaks with values in the range of 104 F/cm3 at overpotentials of >140 mV were obtained after annealing for several hours in synthetic air and/or after applying high anodic bias voltages of >750 mV. From the results of several surface analysis techniques and transmission electron microscopy, it is concluded that closed pores develop upon both of these treatments: (i) During annealing, initially open pores get closed by SrSO4, which forms due to strontium segregation in measurement gases with minute traces of sulfur. (ii) The bias treatment causes mechanical failure and morphological changes including closed pores in the bulk of dense films. Under anodic polarization, high-pressure oxygen accumulates in those closed pores, and this causes the capacitance peak. Model calculations based on a real-gas equation allow us to properly predict the experimentally obtained capacitance increase.

AB - Electrochemical impedance spectroscopy was used to investigate the chemical capacitance of La0.6Sr0.4CoO3−δ (LSC) thin-film electrodes under anodic polarization (i.e., in the electrolysis mode). For this purpose, electrodes with different microstructures were prepared via pulsed-laser deposition. Analysis of dense electrodes and electrodes with open porosity revealed decreasing chemical capacitances with increasing anodic overpotentials, as expected from defect chemical considerations. However, extremely high chemical capacitance peaks with values in the range of 104 F/cm3 at overpotentials of >140 mV were obtained after annealing for several hours in synthetic air and/or after applying high anodic bias voltages of >750 mV. From the results of several surface analysis techniques and transmission electron microscopy, it is concluded that closed pores develop upon both of these treatments: (i) During annealing, initially open pores get closed by SrSO4, which forms due to strontium segregation in measurement gases with minute traces of sulfur. (ii) The bias treatment causes mechanical failure and morphological changes including closed pores in the bulk of dense films. Under anodic polarization, high-pressure oxygen accumulates in those closed pores, and this causes the capacitance peak. Model calculations based on a real-gas equation allow us to properly predict the experimentally obtained capacitance increase.

KW - chemical capacitance

KW - degradation mechanism

KW - impedance spectroscopy

KW - LaSrCoO (LSC)

KW - oxygen electrode

KW - pore formation

KW - solid oxide electrolysis cell (SOEC)

KW - thin film

UR - http://www.scopus.com/inward/record.url?scp=85147573181&partnerID=8YFLogxK

U2 - 10.1021/acsami.2c20731

DO - 10.1021/acsami.2c20731

M3 - Article

AN - SCOPUS:85147573181

VL - 15.2023

SP - 8076

EP - 8092

JO - ACS Applied Materials and Interfaces

JF - ACS Applied Materials and Interfaces

SN - 1944-8244

IS - 6

ER -