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CAUSES OF DEGRADATION IN A SOLID OXIDE ELECTROLYSIS STACK
Manganese and O have segregated to the surface and a thick (10 μm) Cr-O layer has also formed
at the surface. Titanium and Si are identified in the interface between the metal and oxide. The effect
of these elements has not yet been measured, however, we suspect that Ti and Si form oxides that are
electrically insulating and will add to the degradation in stack performance.
Conclusions
Several probable causes of degradation have been identified through Argonne’s post-test analyses of
SOEC stack components. In the present work, five causes of degradation were identified through SEM
and EDS studies of selected regions of components from the ½ILS stack. The interconnect was found
to be a source of foreign elements, such as Cr, Mn, Ti and possibly Si, that contribute to degradation
by forming non-conductive interface layers. Chromium was observed to diffuse into the bond layer
reducing its conductivity. A Si-Mn-O capping layer was found within millimeters of the sealing edge of
the steam/hydrogen electrode, and Si-O was distributed throughout the electrode, both of which
would decrease overall conductivity and the number of active sites for steam reduction. The oxygen
electrode densified and delaminated during long-term operation. And, cracks were observed along the
conductive bond layer/interconnect interface in the oxygen electrode compartment. These would
cause serious degradation if they were formed during HTSE operation.
Some additional experiments would help determine the degree of each effect in stack degradation.
Long-term (1 000 h) studies on the conductivity of the coated interconnect plate under dual air and
steam/hydrogen atmospheres on either side of the plate could determine the effect of degradation
due to elemental diffusion out of the plate and segregation to various interfaces. During the same test,
bond layer cracking at the interface could be examined. Finally, a thorough external examination of
stacks upon cooling and a SEM examination of intact stack layers, may help determine when crack
formation in the bond layer on the interconnect plate occurs.
Acknowledgements
The authors would like to thank Nathan Styx and Simon Murphy for their assistance in experimental
measurements.
This work is supported by the US Department of Energy, Office of Nuclear Energy, Science and
Technology, Nuclear Hydrogen Initiative. The submitted manuscript has been created by UChicago
Argonne, LLC as Operator of Argonne National Laboratory under Contract No. DE-AC02-06CH11357
with the US Department of Energy. The US government retains for itself, and others acting on its
behalf, a paid-up, non-exclusive, irrevocable world-wide license in said article to reproduce, prepare
derivative works, distribute copies to the public, and perform publicly and display publicly, by or on
behalf of the government.
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