(609c) Evaluating the Effect of Modeling Variables and Experimental Conditions on Material Development 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 this work we focus on developing standardized procedures, both computational and experimental, for assessing new STWS active materials. First, we apply density functional theory (DFT) to assess the effects of a number of variables, including crystal structure, cation disorder, and magnetic ordering, on the predicted solar thermal water splitting behavior of spinel and perovskite metal oxides. Accurate modeling of materials using DFT is particularly challenging for high temperature applications, but we show that all of the variables evaluated can critically impact the predicted STWS behavior and must be modeled accurately in order to predict high-temperature material properties. Experimental results from thermogravimetric analysis and redox cycling in a stagnation flow reactor are presented to validate DFT models. Second, direct comparison of experimental results for new active materials is extremely challenging given the wide variety of water splitting conditions and apparatus configurations used. We evaluate a number of known water splitting metal oxides, including ceria, hercynite (spinel), and SLMA (perovskite), at various experimental conditions in order to allow for a direct comparison and to aid in the effort of developing standard experimental procedures for STWS material development.