Current trends in solid state ionics: Defect engineering and surface chemistry

This proceedings-perspective paper introduces a new publication format that connects the immediacy of conference reporting with the depth of expert analysis. It summarizes contributions and discussions from the E -MRS 2025 Spring Meeting Symposium K on “ Solid State Ionics: Functional Materials and Devices for Electrochemical Energy Conversion and Storage Applications” , highlighting recent advances and open challenges in the field. Three major research directions are outlined: First, the deliberate control of material defects is shown to govern ionic and electronic transport as well as stability in functional oxides. Second, tailored surface modifications emerge as a powerful tool to tailor oxygen exchange and catalytic activity of mixed conducting electrodes. Third, exsolution of metal particles from oxide hosts is presented as a versatile route to design durable and adaptive catalysts. Together, these developments illustrate how coupling defect control, surface engineering, and exsolution enables next-generation materials for electrochemical energy conversion and storage. • The novel format of this paper bridges conference reports and expert perspectives. • Controlling material defects tunes how ions and electrons move in oxides. • Surface modifications reshape how oxides react with their surrounding atmosphere. • Metal particles that are exsolved from oxides make tougher and smarter catalysts.