Progress and challenges in the research on cathodes for Co-electrolysis of CO₂/H₂O in solid oxide electrolysis cells

Solid oxide electrolytic cell (SOEC) is a green hydrogen production technology, with high efficiency, no use of precious metals, a variety of operating modes and other advantages, at high temperatures can effectively electrolyze CO₂ and H₂O, and the combination of heat sources and green electricity can achieve efficient conversion of electrical energy into chemical energy, such as hydrogen, CO, syngas, thereby helping to reduce carbon dioxide emissions. Compared with low temperature CO₂ electrochemical reduction, CO₂ electrolysis in SOEC has higher current density and energy efficiency. At present, SOEC electrolytic high temperature steam electrolysisi is in a small demonstration stage, only hundreds of kilowatt scale devices can be used worldwide, and the cost per kilowatt is high, but because of its high operating temperature (800 ℃), it can be combined with low-cost thermal energy input in the synthesis process of industrial or downstream industries to reduce the cost of electricity required for hydrogen production. In the context of current energy structure adjustment and dual carbon emission reduction, the energy required for SOEC co-electrolysis can also be derived from redundant or discarded renewable energy, which is expected to further reduce costs, so it is a promising energy conversion and storage technology. At the same time, SOEC co-electrolysis of CO₂/H₂O synthesis gas is in the laboratory stage, especially the cathode material in the operation of carbon deposition led to performance decay and other problems. This review focuses on the development history, basic mechanism and research progress of key cathode materials of SOEC. In the process of co-electrolysis, SOEC cathode plays a vital role in controlling the stability of battery operation. However, the most commonly used Ni-YSZ cermet material has poor stability due to coarsing and agglomeration of Ni. Researchers are exploring ways to improve the stability of cermet electrodes. Attempts are also being made to find cathode materials that can replace cermet electrodes in SOEC co-electrolysis. Perovskite materials have been concerned by researchers due to their good mixed conductivity, carbon resistance, impurity tolerance, REDOX stability and durability, but their relatively low catalytic activity is the main challenge faced by most perovskite-related oxides. The researchers found that the oxygen vacancies on the surface of the material and the active three-phase interface can be increased through impregnation, doping, and dissolving technologies. These oxygen vacancies can be used as the host site to accommodate CO₂ molecules at high temperature, thus reducing the polarization resistance of the electrode and improving the electrochemical performance of the electrode. Moreover, the impregnation method has the advantages of easy operation, high efficiency and low preparation temperature. The doping method has the advantages of simple doping process, no pollution and low cost, and the in situ dissolution method has the advantages of high stability, high efficiency and good performance, and is easy to be popularized later. Therefore, based on the existing problems and challenges of cathode materials such as cermet and perovskite, this paper summarizes the progress in improving the performance and stability of cathode materials by using impregnation, doping and dissolution technologies, and provides technical feasibility analysis for the commercialization of SOEC.