The interface between electrolyte and cathode is a primary factor affecting the performance of solid oxide fuel cells (SOFCs). Enhancing the chemical compatibility of the interface, fortifying the charge conduction, and mitigating the interdiffusion of elements between the interfaces are imperative to optimize the performance of SOFC single-cells and ensure a long-term operational stability. This review represents the methodologies used to enhance the interface between electrolyte and cathode in recent years. These methodologies encompass the optimization of cathode composition and structure, the design and construction of multilayer composite electrolyte, and interfacial reinforcement methods. These approaches serve as a valuable reference for SOFC development and application.

At the cathode layer, a dense electrolyte and a porous electrolyte backbone are constructed. A solution infiltration technique is utilized to prepare highly active nano-cathodes within the porous electrolyte backbone, thereby eliminating the macroscopic interface between the electrolyte and the cathode. Advanced coating techniques and infiltration technique are employed to modify the cathode surface, thereby enhancing cathode electrochemical performance and single-cell operational durability. The development of novel cathode materials, regulation of component ratios within composite cathodes, and the addition of negative thermal expansion materials prove effective in enhancing the thermal expansion compatibility of the cathode. The thermal-expansion offset enhances long-term electrode durability and ORR activity.

At the electrolyte layer, constructing multi-layer electrolyte films and optimizing the structure of single cell enhance performance and reduce degradation. Multi-layer composite structures improve an electrolyte reliability and a cathode interface chemical compatibility. However, the preparation becomes a challenge and primarily relies on advanced coating technologies. Low-cost, high-density coating technologies are urgently needed, and a hydrothermal in-situ growth technique emerges, thus reducing production costs, while enhancing single-cell performance and long-term durability.

At the electrolyte-cathode interface, the contact between the electrolyte and the cathode directly affects the interface resistance, oxygen ion conduction, and interface bonding strength. Therefore, interface reinforcement can effectively improve the energy efficiency and stability of single cells. The dense nanostructure functional layer (NFL) overcomes the physical limitations of the porous cathode-dense electrolyte interface, thus enhancing single-cell performance, interfacial bonding, and long-term durability.

This review summarizes some research work related to the interface between the electrolyte and cathode in SOFCs, thus providing a reference for the development of high-performance and long-term durability. This review also provides a reference for SOEC research and development since the materials and structure of solid oxide electrolysis cells (SOECs) are similar to those of SOFCs.

The interfacial contact and charge conduction between the electrolyte and cathode have a direct impact on the performance and efficiency of single cells, which is a crucial area in both fundamental research and technological development of SOFCs. The following perspectives for future development are provided.

The development of novel electrolytes and electrode materials represents an effective strategy to address interfacial issues. Concurrently, the exploration of innovative interfacial structural designs can enhance the performance and stability within existing material systems. Future research endeavors should prioritize meeting the practical demands of industrial applications. Furthermore, it is essential to optimize the preparation process. The quality of the interface between the electrolyte and the cathode directly affects the overall performance of SOFCs. Therefore, optimizing the preparation process is of crucial importance. Currently, coating technologies such as pulsed laser deposition (PLD) and chemical vapor deposition (CVD) can achieve a precise preparation of specific compositions and structures. In the future, it is necessary to focus on the research and development of new high-performance, low-cost thin film preparation technologies with large-scale manufacturing capabilities to further improve interface quality. In addition, there is a focus on interdisciplinary research. Various in-situ spectroscopic characterization methods, machine learning and artificial intelligence technologies will also contribute to SOFCs research, including material performance prediction, parameter optimization design, and operating condition performance simulation. This can promote the connection between theoretical models and practical applications, driving SOFCs technology toward higher efficiency and lower costs. Finally, despite significant progress in lab-scale research, the commercialization of SOFCs still faces some challenges. In the next phase, it is necessary to further optimize the cell preparation process and operating conditions, such as electrolyte structure, composite electrode materials, and sintering processes. Reducing costs, improving cell reliability and lifespan can promote SOFCs widespread application in the energy sector.

Solid oxide fuel cells (SOFCs) represent a highly efficient energy conversion technology capable of directly transforming chemical energy from fuels into electricity, with single-cycle efficiencies ranging from 40% to 60% and combined heat-and-power efficiencies reaching up to 60%–90%. Among various SOFCs configurations, planar SOFCs stacks become popular due to their high-power density, modular design, and flexible assembly. However, the compact structure of planar stacks imposes stringent requirements on assembly precision, often leading to a poor "solid-solid" interfacial contact between ceramic single cells and metallic interconnects. This issue results in high internal resistance, reduced output performance, and compromised long-term stability. To address these challenges, cathode contact components are introduced between the single cell and interconnect to optimize interfacial contact, ensuring stable electron transport pathways and mitigating mechanical stress during operation.

The selection and design of cathode contact materials are critical, requiring a balance of high electrical conductivity, chemical stability, thermal expansion coefficient (TEC) compatibility with adjacent components, sufficient porosity for gas diffusion, mechanical strength, and cost-effectiveness. While anode-side contact materials (e.g., nickel mesh or foam) perform well under reducing atmospheres, cathode-side materials face harsher conditions due to high-temperature oxidative environments and the inherent brittleness of ceramic oxides. Consequently, cathode contact materials must meet more rigorous criteria to minimize contact resistance and ensure durability.

This review represents the selection of contact materials, analyzes the influencing factors of contact resistance, and introduces the relevant preparation processes. In terms of material selection, precious metals possess excellent electrical conductivity and sintering activity. However, aside from silver, the material costs are relatively high. Silver itself also faces some issues such as volatility at high temperatures. Perovskite materials have low cost and high stability in cathodic environment, and material systems such as La_0.8Sr_0.2CoO₃ (LSC), La_0.8Sr_0.2Co_0.8Fe_0.2O_3-δ (LSCF), La_0.8Sr_0.2MnO₃ (LSM), LaNi_0.6Fe_0.4O_3−δ (LNF), and LaNi_0.6Fe_0.4O₃(LCN) are used as contact materials for research, and the research goal is how to achieve the trade-off between conductivity, TEC, and sintering activity, and the ASR change during long-term isothermal and thermal cycling is also a key issue. Spinel material is more used in the coating of the linker, which is important in preventing the migration of Cr and protecting the blocker against oxidation. The development of composite materials combines the excellent properties of different materials. For instance, LSCF-Ag composites exhibit a reduced interfacial resistance and an enhanced long-term stability.

Contact resistance is an important factor that affects the overall performance of the battery stack, and the factors influencing contact resistance mainly include interface contact effects, contact area, load strength, elastic modulus, and temperature. Balancing electronic transport and gas diffusion is crucial as excessive contact area under low oxygen conditions may hinder the diffusion of oxygen. The existing research focuses on studying the effects of various factors on contact resistance and battery performance through the combination of experiments and numerical simulations. This integration serves as a mutual validation, enhancing the reliability of the results, saving time and costs, as well as providing a deeper understanding of the underlying physical mechanisms. In terms of the preparation process, in addition to the commonly used methods such as screen printing, spraying, and casting, some novel forming techniques are also applied in the preparation of contact components, such as laser scanning technology, electrophoretic deposition, physical vapor deposition, and magnetron sputtering, each with its own advantages and disadvantages.

Cathode contact components play a pivotal role in determining the efficiency, reliability, and longevity of SOFC stacks. The future development of cathode contact components may focus on several aspects, the first of which is the development of new materials. Innovative cathode materials can be used for the cathode itself and served as candidate materials for the cathode contact layer. It is important to optimize the preparation process. Lab-scale studies can explore various novel or established preparation techniques. However, in industrial production, the choice of preparation processes is constrained by sample stability and cost. Therefore, optimizing the preparation process to compensate for some inherent shortcomings of the materials is a direction worthy of research. Furthermore, the study of contact components will become more complex when considering the actual operating conditions within the stack, such as flow field distribution, temperature distribution, and current distribution. In terms of structural design, concepts such as gradient configuration and asymmetric structures can be applied to achieve the overall performance and structural stability.

In summary, some challenges remain in achieving large-scale commercialization while significant progress is made in cathode contact materials and components. Collaborative efforts integrating material science, engineering, and computational modeling will be a key to advancing SOFCs technology toward widespread adoption in clean energy systems.