• Energy Research

AbstractMixed ionic‐electronic conducting (MIEC) membranes have gained growing interest recently for various promising environmental and energy applications, such as H2and O2production, CO2reduction, O2and H2separation, CO2separation, membrane reactors for production of chemicals, cathode development for solid oxide fuel cells, solar‐driven evaporation and energy‐saving regeneration as well as electrolyzer cells for power‐to‐X technologies. The purpose of this roadmap, written by international specialists in their fields, is to present a snapshot of the state‐of‐the‐art, and provide opinions on the future challenges and opportunities in this complex multidisciplinary research field. As the fundamentals of using MIEC membranes for various applications become increasingly challenging tasks, particularly in view of the growing interdisciplinary nature of this field, a better understanding of the underlying physical and chemical processes is also crucial to enable the career advancement of the next generation of researchers. As an integrated and combined article, it is hoped that this roadmap, covering all these aspects, will be informative to support further progress in academics as well as in the industry‐oriented research toward commercialization of MIEC membranes for different applications.

Nanocrystalline BaCe0.7Zr0.1Y0.1Yb0.1O3−δ (BCZYYb) is designed by a novel strategy with improved proton transport properties at low temperatures (<300 °C). In situ Raman spectroscopy and electrical conductivity relaxation (ECR) are used to quantitatively evaluate the surface exchange coefficients during the hydrogen isotope exchange process. Similar surface exchange coefficients are measured via in situ Raman spectroscopy and ECR measurements, representing new tools to better understand proton transport behaviors at the materials’ interface. The surface exchange coefficient in nanocrystalline BCZYYb is nearly four times higher than that in conventional dense BCZYYb at 300 °C, indicating higher surface mobility of protonic species in the designed BCZYYb membrane. The improved performance originates from the combined interfacial and bulk effects for proton transport at low temperatures. In addition, low‐temperature protonic ceramic fuel cells (PCFCs) are built based on a nanocrystalline BCZYYb electrolyte with improved single‐cell performance at 300 °C, which indicates enhanced proton transport properties in contemporary energy conversion and storage materials can be achieved through interfacial engineering.