WANG Hongbin ^{1, 3}, WANG Leying ^{1, 3}, LUO Linghong ^{1, 3}, WEN Ge ⁴,
CHENG Liang ^{2, 3}, XU Xu ^{1, 3}, WU Yefan ^{1, 3}
(1. School of Materials Science and Engineering, Jingdezhen Ceramic University, Jingdezhen 333403, Jiangxi, China; 2. National Engineering Research Center for Domestic & Building Ceramics Jingdezhen Ceramic University, Jingdezhen 333001, Jiangxi, China; 3. Jiangxi Provincial Key Laboratory of Fuel Cell Materials and Devices, Jingdezhen Ceramic University, Jingdezhen 333403, Jiangxi, China; 4. School of Mechanical and Electronic Engineering, Jingdezhen Ceramic University, Jingdezhen 333403, Jiangxi, China)

Extended Abstract: [Significance] The concentration of carbon dioxide (CO₂) as the main greenhouse gas continues to rise in the Earth's atmosphere. Reducing CO₂ emissions and converting them into high value-added fuels are necessary strategies to achieve the carbon peaking and carbon neutrality goals. Solid oxide electrolysis cell (SOEC) is an energy conversion device that can efficiently convert CO₂ into high value-added fuels, which has great application prospect in the efficient utilization of renewable energy. The cathode materials used to catalyze the CO₂ reduction reaction is one of the key components of SOEC. In addition to traditional cermet materials, various types of perovskite materials (single perovskite, double perovskite and Ruddlesden-Popper phase) are employed as new cathode materials for SOEC, due to their excellent carbon resistance, improved impurity tolerance, high redox stability and adequate ionic and electronic conductivity. However, the relatively low catalytic activity is the main factor restricting the development of perovskite cathode materials. In order to solve this problem, various methods have been adopted to improve the electrolytic catalytic activity of perovskite cathode materials, such as impregnation, A/B site doping and in-situ exsolution. Among them, the B-site doping with transition metal to promote the metal dissolution of perovskite in reducing atmosphere is considered to be an effective way to improve the electrocatalytic activity of perovskite materials.[Progress] Compared with traditional deposition technology, exsolution is an "inside-out" technology, in which the metal catalyst migrates from the solid lattice and segregates or aggregates on the substrate surface to produce precipitation, namely, the migration of metal ions to the surface of perovskite and the phase transformation into a metal phase. The exsolution technology of perovskite-type materials (ABO₃) is considered to be an effective approach to improve the catalytic activity of perovskite-type materials through nanoparticle modification. Usually, transition metal ions (e.g., Fe, Co, Ni, Cu, Ru, etc.) are incorporated into the B-site of the perovskite lattice during oxidation and then migrate from the main lattice to the surface during reduction, thus forming metal nanoparticles distributed on surface of the parent perovskite and hence metal/perovskite carrier heterogeneous interface. For exsolved perovskite cathode, after reduction, more CO₂RR active sites are generated, which enhances the catalytic activity of CO₂RR. The exsolved perovskite-based catalytic materials exhibit various advantages. (1) Highly active metal nanoparticles and oxygen-rich perovskite support are generated at the same time. (2) The metal/oxide interface promotes the adsorption and dissociation of CO₂, reduces the charge transfer barrier and has a significant catalytic CO₂RR synergistic effect. (3) The anchoring structure effectively inhibits carbon deposition and metal nanoparticle aggregation. (4) The exsolution/dissolution process is reversible in the redox cycle of practical application. In recent years, the introduction of A-site non-stoichiometry to promote exsolution of the first transition metals (e.g., Fe, Co, Ni, Cu) has attracted extensive attention. Exsolution bimetallic nanoparticles also show excellent synergistic effects in various applications, and catalysts modified with bimetallic nanoparticles (e.g., CoFe and NiFe) show significant performance improvements. The ternary/quaternary alloys proved to be more active than mono - or bimetallic catalysts.[Conclusions and Prospects] The research progress of metal/alloy exsolved perovskite SOEC cathodes for CO₂ electrolysis have been discussed in detail, while the exsolution mechanism of cathodes in the CO₂RR electrocatalysis was summarized from the perspectives of active site, oxygen site content, CO₂ adsorption/dissociation, metal-oxide interface co-catalysis and so on. The efficient dissolution methods include B-site doped transition metal elements, A-site non-stoichiometric regulation, reduction condition regulation, phase transition, voltage drive and induced lattice strain. Although anchoring nanoparticles with high catalytic activity to perovskite cathodes through in-situ exsolution has various advantages, there are challenges for large-scale long-term applications, focusing on (1) developing and designing a controllable and efficient exsolution method for stable and durable nanoparticles, (2) identifying the influence of material composition on the synergistic catalytic effect between perovskite carrier and exsolution particles, (3) tracing reversible exsolution/dissolution and analyzing the influence of the structural change of perovskite on the performance of CO₂ electrolysis according to the in-situ characterization method and (4) designing a multi-functional, efficient and stable exsolved perovskite cathode material.
Key words: solid oxide electrolysis cell; perovskite cathode; CO₂ reduction reaction; in-situ exsolution