Publications

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One promising method for solar energy storage is Solar Thermochemical Hydrogen (STCH) production. This two-step thermochemical process utilizes nonstoichiometric metal oxides to convert solar energy into hydrogen gas. The oxide first undergoes reduction via exposure to heat generated from concentrated solar power. When subsequently exposed to steam, the reduced oxide splits water molecules through its re-oxidation process, thus producing hydrogen gas. The viability of STCH depends on identifying redox-active materials that have fast redox kinetics, structural stability and low reduction temperatures. Complex perovskite oxides show promise for more efficient hydrogen production at lower reduction temperatures than current materials. In this work, a stagnation flow reactor was used to characterize the water splitting capabilities of BaCe_0.25Mn_0.75O₃(BCM). In the future, the method outlined will be used to characterize structural analogues of BCM, to provide insight into the effect of material composition on water splitting behavior and ultimately guide the synthesis of more efficient STCH materials.

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Ruddlesden–Popper (layered perovskite) phases are attracting significant interest because of their unique potential for many applications requiring mixed ionic and electronic conductivity. Here we report a new, previously undiscovered layered perovskite of composition, Ce_xSr_2–xMnO₄ (x = 0.1, 0.2, and 0.3). Furthermore, we demonstrate that this new system is suitable for solar thermochemical hydrogen production (STCH). Synchrotron radiation X-ray diffraction and transmission electron microscopy are performed to characterize this new system. Density functional theory calculations of phase stability and oxygen vacancy formation energy (1.76, 2.24, and 2.66 eV/O atom, respectively with increasing Ce content) reinforce the potential of this phase for STCH application. Experimental hydrogen production results show that this materials system produces 2–3 times more hydrogen than the benchmark STCH oxide ceria at a reduction temperature of 1400 °C and an oxidation temperature of 1000 °C.

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Overall objectives of the project are: Develop a science & engineering basis for the release, ignition, and combustion behavior of hydrogen across its range of use (including high pressure and cryogenic); and, Facilitate the assessment of the safety (risk) of hydrogen systems and enable use of that information for revising regulations, codes, and standards (RCS), and permitting hydrogen fueling stations.

Solar thermochemical hydrogen (STCH) production is one avenue for converting sunlight into hydrogen through concentrating solar thermal technology. STCH is a two-step redox process that begins with concentrated sunlight to thermally reduce a metal oxide around 1500 °C leaving it in an oxygen deficient form. Subsequent exposure of the reduced metal oxide to steam at lower temperature reoxidizes the material and produces hydrogen. The efficiency of this process is dependent on the metal oxide material thermodynamic properties and cycle operating conditions.

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