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Page 4 of 27 Chen et al. Energy Mater. 2025, 5, 500045 https://dx.doi.org/10.20517/energymater.2024.144

[usually yttria-stabilized zirconia (YSZ)] and are oxidized to oxygen. During electrolysis of H O, CO or
2
2
both of them, the basic chemical reactions can be divided into two half-reactions, one at the cathode and
another at the anode:

At the cathode side:

H O + 2e → H + O (1)
-
2-
2
2
CO + 2e → CO + O 2- (2)
-
2
At the anode side:
2-
2O → O + 4e - (3)
2
CATHODE
Cathodes, also known as fuel electrodes, provide active sites for the decomposition of H 2 O and transport
channels for oxygen ions and gases, so they must have good electronic conductivity and catalytic activity to
improve the efficiency of the electrolytic cells. Meanwhile, they generally have a loose porous structure to
ensure the flow of gases. Since the reaction usually occurs at the triple phase boundaries (TPBs), the cathode
must have high mixed ion-electron conductivity to extend the TPB area. However, long-term stability
issues, such as particle aggregation, carbon deposition, nickel oxidation and sulfur poisoning, hinder further
applications .
[7,8]
Cermet
Cermet materials are commonly used as cathodes. Pure metals have the disadvantages of mismatched
thermal expansion coefficients, poor chemical stability, high-temperature creep, and high cost, making
them unsuitable for direct use as SOEC cathodes . By compositing with metals and ceramics, the
[9]
advantages of both can be combined: excellent electronic conductivity and mechanical strength of metals,
and good high-temperature stability and electrochemical properties of ceramics.

Ni-Y Zr O (Ni-YSZ) has excellent electrocatalytic activity, stability, and low preparation cost, and has
0.92
0.08
2+δ
been successfully commercialized in large-scale applications . Ni, YSZ and pores can be used as transport
[10]
channels for electrons, ions and gases. However, Ni particles tend to aggregate at high temperatures. In
addition, problems such as carbon deposition, Ni oxidation and sulfur poisoning will further limit their
application .
[11]
Recent studies have shown that carbon atoms on the surface of cerium oxide-based materials such as
Sm Ce O (SDC) and Ni-SDC can be trapped as carbon oxide intermediates, mitigating carbon
0.2
2-δ
0.8
deposition during CO electrolysis [Figure 3]. Therefore, as SOEC cathodes, ceria or ceria-based materials
2
can be further investigated.
Compared with Ni-based cermet materials, Cu-based materials have higher electronic conductivity and are
less prone to carbon deposition. However, the catalytic activity of Cu is low, and the composite with
metallic oxides that have higher catalytic activity is an effective method .
[13]