In recent years, there has been a growing interest in the use of solid oxide cells (SOCs) for the high-temperature co-electrolysis of CO2 and H2O, particularly when powered by excess electricity from renewable energy sources. This technology is regarded as one of the most promising for sustainable energy systems, offering high efficiency and the ability to generate syngas, a versatile intermediate for synthetic fuels and chemicals. Moreover, it enables efficient energy storage and the use of CO2 as a feedstock, aligning with circular economy principles and supporting deep decarbonization. High-temperature co-electrolysis in SOCs stands out compared to low-temperature electrolyzers by also enabling CO2 conversion, although it requires advanced catalysts and optimized operating conditions to avoid issues such as carbon deposition [1-3]. 
This paper presents the current state of research on catalytic materials and system configurations for the high-temperature co-electrolysis of H2O and CO2 in reversible SOCs. Key scientific challenges discussed include understanding the physicochemical nature of the co-electrolysis process on the fuel electrode and identifying the limiting factors of performance and stability. Development of advanced nanostructured catalysts, particularly those based on fluorite- and perovskite-type oxides, as well as composite systems that offer enhanced reactivity and chemical compatibility with Ni-YSZ cermets and YSZ electrolytes is presented. In addition to the material design, process optimization strategies such as catalyst infiltration into cells and electrode surface engineering are explored to improve the electrochemical performance and long-term durability. The work highlights the emerging methodologies and engineering pathways that form the foundation for next-generation high-efficiency co-electrolysis systems, while outlining the prospects for scalable implementation and integration with renewable energy technologies.