Developing technologies to produce renewable and sustainable energy carriers from the sun is widely seen as a global imperative. And while technologies for converting solar irradiance into energy carriers or stored energy predicated on low temperature processes such as photosynthesis, either natural or artificial, or electrolysis offer potential solutions, there is significant recent interest in exploring high-temperature thermochemical or electrochemical pathways because these routes are potentially more efficient.

In a thermochemical process, a concentrated solar resource heats an active non-stoichiometric oxide under conditions that promote spontaneous oxygen defect formation. This reaction produces O₂ by absorbing heat, and is distinctly different than the complicated “OER” mechanism invoked by artificial photosynthesis or electrolysis. This reaction also stores solar energy directly in the defected oxide much like charging a battery. Once “charged,” and if exposed to water or carbon dioxide under conditions that result in gas splitting, the result is molecular H₂ or CO (i.e., solar fuel). Here again, the spontaneous re-oxidation reaction produces fuel using only a chemical potential driving force, and is distinctly different from the low-temperature “HER” processes. Alternatively, if exposed to oxygen from air, an exothermic oxidation reaction releases the stored solar energy as high quality heat (i.e., solar thermal energy). The nonstoichiometric reduced oxide can also be stored for future use much like a battery.

High temperature electrochemical processes that incorporate oxides as electrodes and separators are another promising pathway to produce renewable and sustainable energy carriers using redox-active materials. And while the relevant charge transfer processes are analogous to low-temperature electrolysis, using oxide electrodes and separators at high temperature lowers the electrical potential energy demand for gas splitting, and also decreases electrode losses that arise from charge transfer reactions, thus offering thermodynamic and kinetic advantages over low temperature electrolysis. Here again concentrated solar energy can provide heat and electricity to drive the endothermic electrochemical reactions.

These two high temperature approaches to renewable and sustainable energy carriers have commonalities in the class of functional oxide materials. Effective and efficient redox-active oxides are key to their commercial success, and material discovery efforts are currently underway in laboratories around the globe to understand how oxide composition, structure, and defect chemistry define functionality. The aim of this symposium is to bring together researchers from diverse disciplines who are working on high temperature approaches to fuel production and energy storage. This symposium will highlight advances in redox active metal oxides applied to electrochemical and thermochemical processes inclusive of a number of applications, such as water and carbon dioxide splitting, and thermal energy storage. Presentations will focus on material discovery, classes of oxides, and recent progress or challenges in rational design of materials via computational science. Topics will include defect chemistry, bulk and interfacial chemistry, as well as prediction and realization of new materials. The symposium especially welcomes discussions that advance understanding of fundamental material science issues.

defects diffusion electronic structure energy generation energy storage ionic conductor oxide simulation