Advancing electrochemical devices: the promise of triple ionic–electronic conducting oxides

Abstract Triple ionic–electronic conducting materials represent a key advancement in the development of electrochemical devices, enabling simultaneous transport of electrons, oxygen ions, and protons. This unique property allows triple ionic–electronic conducting materials to overcome the limitations of traditional mixed ionic–electronic conductors by expanding reaction zones from interfacial regions to the material bulk, significantly enhancing reaction kinetics. Triple ionic–electronic conducting materials have shown promise in devices such as solid oxide fuel cells, protonic ceramic cells, and catalytic membrane reactors, delivering improved efficiency, especially at intermediate temperatures. This review provides a concise examination of properties of triple ionic–electronic conducting materials, focusing on the role of perovskite and layered oxide systems. Key mechanisms of conduction, including proton hopping via the Grotthuss mechanism, oxygen ion diffusion through vacancy pathways, and electronic conduction via small-polaron hopping, are critically analysed. Advances in material design, such as doping strategies to stabilise crystal phases and optimise defect chemistry, are highlighted as crucial enablers of high-performance triple ionic–electronic conducting materials. Despite their promise, triple ionic–electronic conducting materials face challenges related to material degradation, phase instability, and scalability. This review discusses recent innovations aimed at addressing these issues, including multi-phase composites and computational modelling for material optimisation. By offering an integrated understanding of triple ionic–electronic conducting materials’ fundamental properties, applications, and challenges, this work aims to guide further research, positioning triple ionic–electronic conducting materials as a promising candidate for the next-generation sustainable energy technologies.