Mixed ionic-electronic conducting (MIEC) membranes have gained growing interest recently for various promising environmental and energy applications, such as H 2 and O 2 production, CO 2 reduction, O 2 and H 2 separation, CO 2 separation, 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 powerto-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.

In this paper, we report a detailed study on co-production of H 2 and syngas on La 0.9 Ca 0.1 FeO 3-δ (LCF-91) membranes via water splitting and partial oxidation of methane (POM), respectively. A permeation model shows that the surface reaction on the sweep side is the rate limiting step for this process on a 0.9 mm-thick dense membrane at 990 o C. Hence, sweep side surface modifications such as adding a porous layer and nickel catalysts were applied; the hydrogen production rate from water thermolysis is enhanced by two orders of magnitude to 0.37 μmol/cm 2 •s compared with the results on the unmodified membrane. At the sweep side exit, syngas (H 2 /CO = 2) is produced and negligible solid carbon is found. Yet near the membrane surface on the sweep side, methane can decompose into solid carbon and hydrogen at the surface, or it may be oxidized into CO and CO 2 , depending on the oxygen permeation flux.

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Kinetics data for CO 2 thermochemical reduction in an isothermal membrane reactor is required to identify the rate-limiting steps. Here, we report a detailed reaction kinetics study on this process