(22e) Screening of Metal Oxide Materials for Solar Thermochemical Water Splitting

While solar energy is the most abundant renewable energy resource, the capture, storage, and distribution of it remains a challenge. Solar thermochemical water splitting (STWS) provides a promising route for efficient utilization of this disperse resource since it allows for use of the entire solar spectrum to convert water to an energy dense fuel, H₂. However, despite a significant number of materials having been examined, an optimal redox material to drive this process has yet to be developed.  In order to evaluate potential materials, we have developed a set of screening criteria based on thermodynamic requirements. This criteria stipulates that the reduction enthalpy for the material be greater than 286 kJ/mol, which is the overall enthalpy of the water splitting reaction; however, higher reduction enthalpies will also result in lower extents of reduction at a given operating temperature, and therefore less H₂ production. Thus, we evaluate a large set of metal oxide redox materials based on their calculated reduction enthalpies to determine which potential materials are good STWS candidates.  In this work we will discuss the findings from our thermodynamic screening of metal oxide materials for solar thermochemical water splitting based on the aforementioned criteria using DFT, as well as our experimental validation of these calculations. We will also briefly describe a method we have developed to evaluate metal oxides for STWS based on their water splitting kinetics.