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Page 16 of 27 Chen et al. Energy Mater. 2025, 5, 500045 https://dx.doi.org/10.20517/energymater.2024.144

standard of 1%·(khr) . In order to enhance the stability of the electrolytic cell, it is imperative to gain a
-1
[23]
comprehensive understanding of the degradation mechanism of the SOEC system . It is currently thought
that the degradation of the SOEC is mainly associated with the cathode, anode, and electrolyte.

Cathode degradation
Ni-YSZ exhibits favorable performance in a majority of scenarios. During electrolysis, the primary forms of
degradation observed in Ni-YSZ are oxidation, migration, agglomeration, depletion, carbon deposition and
poisoning.

The high concentration of steam during the electrolysis process results in the oxidation of Ni particles into
gaseous Ni(OH) , which is subsequently transferred to the surface of the electrolyte. This result increases the
x
ohmic resistance of the electrolytic cell and reduces the TPBs, thereby decreasing the catalytic performance
of the electrode materials . Furthermore, the formation of NiO results in a reduction in the surface
[135]
activity and electronic conductivity of the catalyst. Additionally, the formation of NiO dendrites following
[136]
multiple redox reactions also causes damage to the microstructure of the electrode . In order to avoid the
oxidation of Ni and enhance the electrochemical performance of the electrodes, the incorporation of
partially reducing gases or the doping of metals is typically employed. Chen et al. found that Ce could
inhibit the oxidation of Ni in CO [Figure 9A] . Accordingly, they prepared a Ce-Ni-YSZ cathode by
[137]
2
loading Ni Ce O nanoparticles on the surface of Ni-YSZ, and observed that its anti-CO oxidation
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0.1
2
2-x
performance was markedly superior to that of Ni-YSZ. This material is a promising cathode for CO
2
electrolysis.
In addition, Ni-based materials are prone to oxidation during the electrolysis of CO , resulting in the
2
formation of diverse carbon depositions, including carbon nanotubes, carbon fibers, and amorphous forms.
These deposits diminish the area of the TPBs, obstruct the gas transport channels, and compromise the
stability of the electrode materials. The doping of Cu can increase the concentration of oxygen vacancies,
enhance the conductivity of the material, and accelerate the adsorption and diffusion of CO .
[13]
2
Anode degradation
SOECs typically require high current densities for optimal performance. At higher current densities
(> 0.5 A·cm ), the anode exhibits a more pronounced degradation than the cathode, suggesting that the
-2
degradation of SOECs is mainly related to the anode . It is commonly believed that delamination at the
[138]
anode/electrolyte interface, cation migration, and the generation of deleterious phases represent the primary
causes of anode degradation.

For LSM-based anode materials, delamination represents a significant factor contributing to the
degradation of SOECs. One view is that O is continuously accumulated at the electrode/electrolyte interface
2
during electrolysis, resulting in the formation of localized high oxygen partial pressure sites that lead to
anode delamination [Figure 9B]. Another view is that the cation migration will result in the formation of a
secondary phase, which obstructs the active sites on the TPBs, thereby leading to the deterioration of the
electrolytic cell. Furthermore, anode poisoning represents another potential cause of SOEC degradation.
The interconnects in the SOEC stack are composed of stainless steel. At elevated temperatures, volatile Cr-
based compounds, such as CrO (OH) , decompose into Cr O and other substances that are deposited on
2
3
2
2
the surface of the electrodes and electrolyte . This deposition increases the polarization resistance of the
[139]
[140]
electrodes, leading to SOEC degradation . In order to mitigate the effects of Cr poisoning, it is common
practice to coat conductive materials (e.g., perovskites) on the surface of the interconnects. Sealants and
[141]
reaction gases typically comprise volatile elements, such as B [Figure 9C] and S , which can be
[142]
deposited at the electrode/electrolyte interface. This can block the reaction sites and also damage the pore
structure of the electrodes, resulting in a reduction in the catalytic activity and stability of the electrodes.