(498b) Non-Stoichiometric Perovskite Oxides As High-Temperature Energy Storage Media and Their Application to Concentrating Solar Power Generation and Hydrogen Production

Although there is a significant abundance of solar resource, the intermittency of the resource compromises its deep integration into the U.S. energy portfolio. However, solar-thermal processes such as concentrating solar power (CSP) are unique in that thermal energy can be efficiently stored in engineered heat-absorbing media. The quantity of heat stored and subsequent power-generation efficiency generally increase as temperature increases, motivating solid particulate storage media for high-temperature systems. However, the storage of only sensible energy limits the potential of both the quantity of stored energy as well as the possible applications of the stored energy. For this reason, energy storage media have been engineered to store both sensible heat and reaction heat, a practice known as thermochemical energy storage (TCES).

Here we present the concepts behind the engineering, synthesis, and characterization of novel doped calcium manganese perovskites (CaAl_yMn_1-yO_3-δ). These materials exhibit rapid and reversible reduction/oxidation behavior through the introduction of oxygen vacancies in the material structure: ABO₃ + Î?H â?? ABO_3-δ + δ/2 O₂. This approach allows the storage of chemical energy through thermal reduction without the kinetic limitations inherent in decomposition reactions. The dopant concentrations of this materials family have been optimized in our laboratories to produce the largest energy storage capacity of a high-temperature perovskite system to date.

Additionally, two applications of the material are presented. First, these materials are applied to a CSP system for electricity generation. In this system, the material is first heated and thermally reduced in the incident solar beam of a solar receiver. The material is then stored in large thermally-insulated bins, after which both the sensible and chemical energy can be utilized by a reaction and heat-transfer process with a working fluid. This high-enthalpy working fluid is passed to a turbine to create power on demand, even when the solar resource is unavailable. Secondly, these materials can operate as thermal-to-chemical energy converters, where the thermal reduction results in a chemically energy-rich species which can be used either fully or in part to facilitate subsequent reactions, such as water-splitting for hydrogen generation. In this embodiment, only the chemical energy is useful, and the sensible energy must be recovered to maximize process efficiencies.

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energyâ??s National Nuclear Security Administration under contract DE-AC04-94AL85000. This work is supported by the U.S. Department of Energy, SunShot Initiative, under Award Number DE-FOA-0000805.