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Page 18 of 27 Chen et al. Energy Mater. 2025, 5, 500045 https://dx.doi.org/10.20517/energymater.2024.144

performed a series of stability tests on a microtubular SOEC with YSZ as the electrolyte at a high voltage of
[147]
2.8 V . The formation of voids at the grain boundaries of the electrolyte interface results in the
propagation of cracks within the electrolyte, leading to delamination, which would impair the performance
of the electrolytic cell, as shown in Figure 9E.

ScSZ-based electrolytes exhibit high ionic conductivity at low to medium temperatures (< 800 °C), about
twice that of YSZ. However, the grains and grain boundaries of ScSZ are subject to damage during the
process of reaction, which in turn affects the conductivity and stability of the electrolyte . LSGM exhibits a
[148]
broad operational temperature range and high ion transfer numbers. However, it displays a discrepancy in
thermal expansion coefficients with Ni-based cathode materials, as well as the formation of LaNiO particles
3
[149]
during electrolysis, which ultimately results in electrolyte rupture . The development of electrolyte
materials suitable for low and medium temperatures will be a key area of focus for research.

STACK AND ECONOMIC BENEFITS
Structure of stacks
The stacking technology of SOEC is similar to that of SOFC, which is mainly classified into planar and
[150]
tubular types [Figure 10A and B]. Planar cells are more prevalent in practical applications due to their
[130]
simple structure, high power density, low internal resistance, and low manufacturing cost . However, the
[130]
fabrication of stacks demands advanced sealing technology and has the risk of gas leakage. The
improvement of planar cells is the development of low-cost sealants. Tubular cells exhibit better thermal
cycling performance, enhanced structural strength and rapid start/stop capabilities. However, the current
trajectory is lengthy, which has resulted in elevated resistance and diminished power density . Reducing
[94]
the inner diameter and preparing microtubular SOECs represents an effective method for enhancing the
performance of tubular cells. Yao et al. prepared a microtubular SOEC with the structure Ni-YSZ/8YSZ/
LSCF-GDC by introducing an insulating ceramic connecting device and employing silver paste as a
collector at the cathode [Figure 10C], which represents a significant improvement compared to that of
[151]
conventional tubular SOECs . The flat-tubular configuration represents a distinctive category of SOEC
stacks, which combines the advantages of both planar and tubular SOECs. This configuration offers high
power density, robust thermal cycling performance, and ease of sealing, rendering it suitable for industrial
applications. As illustrated in Figure 10D, the flat-tubular anode-supported cell without a metal connecting
plate can not only avoid Cr poisoning in the reaction process, but also reduce the manufacturing cost,
[152]
making it a promising candidate for a next-generation SOEC structure .
Economic benefits
Both CO and H are crucial chemical intermediates utilized in the synthesis of a multitude of high-value
2
chemicals, such as ammonia and olefins. At present, the predominant methods of industrial preparation
mainly adopt steam methane reforming and coal gasification. The process will result in the generation of a
considerable quantity of CO and a notable degree of environmental contamination . However, the
[153]
2
electrolysis of CO by SOEC to produce CO, not only can directly consume CO in industrial production,
2
2
but also reduce the consumption of fossil fuels and achieve indirect emission reduction of CO . Blast
2
furnace gas (BFG) is a low calorific value fuel that can be used in a clean and efficient way to produce
organic chemicals by CO reduction. However, the use of ‘green hydrogen’ prepared by SOEC to replace CO
can not only reduce environmental pollution, but also greatly improve economic benefits. Kong et al.
developed a process for value-added recycling of BFG based on BFG-SOFC-SOEC-H 2 [154] . Optimization was
conducted by ASPEN Plus software and the results showed that the process was able to achieve a capture
-1
rate of 99.92% of carbon oxides and a hydrogen production rate of 0.24 kmol·(kmol·BFG) .