Innovative advances and challenges in solid oxide electrolysis cells: Exploring surface segregation dynamics in perovskite electrodes

Hydrogen generation by means of environmentally friendly approaches is of paramount importance in the field of contemporary science and technology. Solid oxide electrolysis cells (SOECs) represent a high-temperature trajectory of H₂ production, offering highly efficient electrical-to-chemical energy conversion at 400–800 °C. SOECs exhibit numerous advantages over low-temperature electrolysis technologies, including a wide potential performance range, high conversion efficiency, excellent selectivity, and the ability to provide co-electrolysis of H₂O and CO₂, supporting hydrogen energy strategies and carbon emission reduction programs. However, SOECs suffer from unsatisfactory long-term stability, which is caused by a number of microstructurally, chemically, and electrically related factors. In order to address these issues, we present the current review article, which provides a detailed description of the chemical and electrochemical phenomena that occur in SOECs during their real operation, in relation to both internal factors (the composition of functional materials) and external aspects (gas compositions, temperature, and applied potential). An in-depth analysis of these interrelationships enables the rational selection of materials and optimization of SOEC operating conditions. Various strategies for the optimal functioning of fuel electrodes, such as doping, in-situ exsolution, and catalytic advancements, are explored. For oxygen electrodes, performance optimization strategies including the development of novel perovskite materials with tailored surface properties and the incorporation of mixed ionic-electronic conductors to facilitate enhanced oxygen ion transport and electrochemical activity, are comprehensively summarized. Moreover, a particular focus of this review is on the surface segregation behavior of perovskite electrodes, a critical aspect influencing SOEC performance and stability. Recent innovations in SOECs development aimed at mitigating surface segregation, such as doping strategies, surface treatments, and the development of novel perovskite compositions with enhanced stability, are discussed in detail for the first time. Consequently, this work is regarded as a valuable reference in the field of SOECs, particularly in relation to energy materials, degradation processes, solid state ionics, and electrochemistry. By employing these innovative strategies, the long-term stability and efficiency of SOECs can be significantly enhanced, making them more viable for large-scale hydrogen production and carbon reduction initiatives.