Solid oxide fuel cell (SOFC) has garnered significant attention due to the clean and efficient energy conversion characteristics, with the performance of cathode materials playing a decisive role in the overall efficiency and lifetime of the device. However, the commercialization of SOFC in the intermediate- to low-temperature range (500–800 ℃) faces two major challenges: insufficient electrocatalytic activity for the oxygen reduction reaction (ORR) at the electrodes and poor long-term operational stability. Although traditional perovskite cathode materials (such as La_1–xSr_xCoO_3–δ, LSC, etc.) exhibit excellent catalytic activity for ORR, they still suffer from issues, such as element segregation, thermal expansion coefficient mismatch, inadequate high-temperature stability, and susceptibility to CO₂/Cr poisoning. In recent years, high-entropy perovskite oxide (HEPO) materials have emerged as a significant research direction for overcoming the limitations of traditional cathode materials by introducing multi-element lattice distortion effects, which demonstrate unique structural stability and performance regulation potential. The high configurational entropy of HEPO materials effectively inhibits cation segregation, enhances phase structural stability, and optimizes oxygen reduction reaction kinetics through the synergistic effect of multiple active sites. Furthermore, high-entropy design can improve the anti-poisoning capability and electronic/ionic conductivity of materials by adjusting the d–band center or oxygen vacancy concentration, providing new insights for the practical application of intermediate- and low-temperature SOFC.

Compared with conventional doping methods, the high-entropy strategy exhibits greater flexibility in component regulation, enabling precise adjustments of the chemical composition, defect characteristics and the disordered/ordered structures of materials, thereby achieving targeted optimization of material properties. In contrast to traditional perovskite materials, the introduction of multiple ions within specific lattices through the high-entropy strategy significantly expands the design space and customization potential of cathode materials, owing to the highly uniform distribution of various elements in the lattice. The preparation methods for high-entropy perovskite materials are relatively diverse, with liquid-phase methods currently being predominantly used to synthesize the high-performance high-entropy perovskite cathode materials. The A-site in the lattice is typically occupied by rare earth or alkaline earth metal cations with larger ionic radii, while the B-site is filled by transition metal cations with relatively smaller ionic radius. HEPO materials exhibit the novel functional characteristics and infinite possibilities, due to the extensive selectivity in elemental composition and content. Depending on the doping elements, they are primarily categorized into ABO₃-type A-site, ABO₃-type B-site, AA'BB'O₆-type and other types of high-entropy perovskite cathode materials. This approach significantly improves the catalytic activity of cathodes, enhances oxygen ion transport capabilities and increases stability, providing new perspectives and solutions to the numerous challenges faced by the traditional SOFC cathode materials, thereby demonstrating cutting-edge and innovative features.

Starting from the design and preparation of high-entropy perovskite materials, the application of high-entropy perovskite cathode materials was focused on, as an emerging and highly potential material system in SOFC. The performance breakthroughs and the mechanism of action are discussed in detail. The high-entropy perovskite material system demonstrates significant enhancement in oxygen reduction activity under medium- and low- temperature operating conditions, effectively suppresses element segregation and simultaneously exhibits excellent CO₂ tolerance, resistance to Cr poisoning and long-term operational stability. The high-entropy strategy has opened new avenues for innovation of SOFC cathode materials. However, current research primarily focuses on the performance enhancement of HEPO, while the elucidation of their mechanisms and theoretical studies still face challenges, mainly manifested in the three aspects. (1) It is necessary to systematically analyze the synergistic mechanisms of multiple elements and quantify the correlation between entropy value and performance through a combination of experimental and theoretical computational methods. (2) It is essential to establish a multi-dimensional evaluation system encompassing electrochemical catalytic activity, oxygen ion transport, chemical compatibility and durability to systematically verify the universality of the four core effects of high entropy under actual SOFC operating conditions. (3) It is crucial to systematically reveal the dynamic regulatory mechanisms of configurational entropy on crystal structure, oxygen vacancy distribution and oxygen reduction kinetics, thereby elucidating the multi-scale correlation laws of entropy-structure-performance.

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.

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.

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.