Exploring alkali metal doping in solid oxide cells materials: A comprehensive review

Solid Oxide Cells (SOCs) are highly efficient, versatile and fuel flexible electrochemical devices utilized for both power generation and hydrogen production. Continuous efforts are dedicated to improving the efficiency and stability of SOCs through composition optimization, which is also crucial to lower the operating temperature. Traditionally, alkaline-earth dopants have been incorporated at the A-site of perovskite-type (ABO3) electrodes or electrolytes to enhance the electrical properties. However, surface segregation of alkaline-earth is a prevalent issue, leading to performance degradation during long-term operation. In recent years, there has been a growing interest on incorporating alkali metals (Li+, Na+, K+, Rb+ and Cs+) into electrode and electrolyte materials with different crystal structures to improve their properties. Furthermore, the increased basicity of alkali metals has demonstrated the ability to reduce the proton adsorption and migration energies, thereby improving performance in proton-conducting fuel cells. Additionally, alkali metals play a crucial role in the densification of widely used electrolyte materials, leading to higher ionic conductivity. This review offers a comprehensive evaluation and discussion of the latest advancements and trends in alkali metal doping strategies, with a focus on their impact on the cell performance. Additionally, it highlights the potential benefits and challenges associated with adopting this alternative approach for the next generation of SOCs.