High-Temperature Materials

Schematic depicting a simple, two-step thermochemical cycle based on iron oxide.

Energy security and climate change are two of the most daunting issues facing humanity today. To address these challenges, we are pursuing a novel method of converting concentrated solar energy to chemical fuels using the direct thermochemical conversion of CO2 and H2O to CO and H2, which are the universal building blocks for synthetic fuels. Nonvolatile metal-oxide-based materials, such as those containing cerium oxide or iron oxide, are being investigated for use as the working fluid in a two-step cycle consisting of a high-temperature, oxygen-liberating thermal reduction reaction (up to 1500 °C) and a lower-temperature, carbon monoxide- or hydrogen-producing oxidation reaction (less than 1000 °C). This process is inherently clean and sustainable, as the only net inputs are solar energy and water or carbon dioxide, and the net outputs are hydrogen or carbon monoxide

Solar energy is collected and focused onto the material using an array of mirrors, as seen in the image of this solar concentrator facility.

and oxygen. To realize this concept, we must address and solve the complex chemical, materials science, and engineering problems associated with thermochemical heat engines and the crucial enabling metal-oxide working-materials.

In order to achieve large gas production volumes at high thermal efficiency, it is desirable to maximize conversion for both oxidation and reduction reactions, and it is essential to recover sensible

Transmission electron microscopy is used to probe film thickness and composition of an ALD coated zirconia particle. The CoFe2O4 coating is approximately 2 nm thick and is conformal throughout the sample.

heat between the high- and low-temperature extremes. To date, very little work has been focused on the kinetics and controlling mechanisms of these reactions. We have developed an approach that combines an idealized stagnation flow reactor with model material structures in order to mitigate the effects of morphological instability and grain growth that confound the interpretation of kinetic measurements in dense composites. Nanometer-thick films of reactive materials are deposited onto high-surface-area supports using atomic layer deposition (ALD). We have demonstrated that these novel materials are an effective, tunable platform for fundamental investigations of gas-splitting reactions. In addition, we use laser-based heating methods to achieve high thermal fluxes in order to better approximate the reactive environment found in concentrated solar power applications, as well as to resolve thermal reduction kinetics at relevant time scales. The approach also includes the use of numerical methods that are focused on applying optimization methodologies coupled to reacting flow simulations,inclusive of imbedded kinetic models, as a means to resolve reaction pathways through model-based data reduction.

 

Schematic of the stagnation flow reactor used to measure gas-splitting kinetics. A computational fluid dynamic model was used to design the reactor geometry such that transport gradients in the near-surface region are independent of the radius.

Contact: Tony McDaniel, (925) 294-1440,