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CAUSES OF DEGRADATION IN A SOLID OXIDE ELECTROLYSIS STACK
On the steam/hydrogen side of the cell, a capping layer was observed to form over the surface of
the electrode a few millimeters from the sealing edge (Figure 6). This capping layer was composed of
mainly Si-O, although some Mn was also found in this layer. The capping layer disappeared within a
centimeter from the seal. However, Si-O was found dispersed throughout the electrode as shown in
Figure 6. We expect Si-O to increase degradation of the steam/hydrogen electrode by poisoning active
steam reduction sites.
Figure 6: Silicon EDS map (left) and SEM secondary image (right) of a
cross-section of a steam/hydrogen electrode near the sealing edge of the cell
Si Kα
Electrolyte
Electrode
10 μm
Capping
layer
As mentioned before, we found no evidence of conductivity loss in the nickel bond layer or in the
steam/hydrogen flow field. Moreover, the flow field was not corroded or discolored.
The steam/hydrogen side of the interconnect, however, showed large resistances in the
four-point mapping study. Figure 7 shows a composite of an SEM image and corresponding EDS maps
for significant elements in the steam/hydrogen side of the interconnect/bond layer interface.
Figure 7: SEM images and EDS maps of the interface between the interconnect
and bond layer, which bonds the interconnect to the steam/hydrogen flow field
Ni bond layer
Interconnect
152 NUCLEAR PRODUCTION OF HYDROGEN – © OECD/NEA 2010