(209d) Materials Discovery and Development for Lower Temperature and Near Isothermal Thermochemical H2 Production

Materials discovery and development related to thermochemical materials for H2 production has historically been focused on materials that have large entropy changes and moderate enthalpies, in order that temperature swings between reduction and oxidation steps are minimized and thermal reduction temperatures are reduced below 1400 °C. Isothermal or near-isothermal cycling has been proposed as a means to decrease sensible heating requirements to the solid phase, but theoretical and experimental work has yielded mixed predictions and results. Based on our recent theoretical and experimental work, we postulate that the prior mixed results reported in literature stem from a combination of materials and conditions for isothermal operation (e.g., CeO2-δ at pO2 ~ 10-4 atm and 1400°C-1500 °C), that has been far from those desired for optimal performance. In this work, we implement a materials design concept that identifies and investigates new material classes, compositions, and operating conditions that are ideal for isothermal thermochemical H2 production. Starting from La-Sr-Mn perovskites, which have been theoretically and experimentally identified as having more favorable properties than ceria, we are utilizing high throughput screening coupled to direct DFT computations of down-selected materials for key performance properties such as oxide formation energies and oxygen vacancy formation and migration energies. DFT computation and screening is coupled closely with experimental synthesis of powdered, replica and direct foam compositions that afford enhanced heat and mass transfer properties. Compositions are experimentally characterized through thermogravimetric analysis and relaxation experiments at a larger scale to test the stability and performance of the replica and foamed compositions.