Metal oxide materials may be used in two-step solar thermochemical water-splitting cycles to renewably produce hydrogen.  Here, we use first-principles density functional calculations to investigate promising oxide materials for use in these cycles.  We present a general analysis of the equilibrium thermodynamics of a two-step metal oxide water splitting cycle, and survey a large number (more than 100) binary oxide redox couples. This analysis strongly suggest the use of non-stoichiometric oxides in gas splitting cycles. Hence, we perform a kinetic and thermodynamic analysis of the mechanism for water splitting on reduced CeO2-x (111). We show the unreactive behaviour at low temperature is caused by kinetically limited diffusion of vacancies from the subsurface to the surface, while the remarkable reduction of reduced CeO2-x(111) at high temperature, where only H2 desorption is slow, may be explained by the formation of a thermodynamically stable hydroxyl layer.

Solar fuels from thermochemical gas splitting

Much attention has been focused on the surface science of titanium dioxide (TiO2) due to its numerous scientific and industrial applications in photocatalysis, electrochemistry,active coatings,gas sensors. Among these studies, many have focused on the interaction of water and the model rutile (110) surface, due to the fundamental role of water in many of the present and potential applications of TiO2. The vast majority of experimental and theoretical understanding of the adsorption behaviour of water on TiO2(110) concerns gas phase adsorption in ultra-high vacuum (UHV) environments (<1x10-10 mbar). Recent work by our group has attempted to characterise the atomic scale structure and composition of the water interface with the 'standard' UHV prepared TiO2(110) surface using STM, surface spectroscopy and surface diffraction techniques.Slightly reduced TiO2(110) samples prepared in UHV before immersion in liquid water at room temperature were found to exhibit a 2x1 overlayer in atomic scale STM. The 2x1 periodicity of the overlayer leads to the formation of phase domains approximately 300 �2 in size. Core and valence level photoelectron spectra show the overlayer is composed solely of OH. The structure of the water-TiO2(110) interface was investigated by surface X-ray diffraction measurements for three environments: a dipped sample, a liquid cell, and an in situ vapour dose. The bestfit model for all three consists of an overlayer composed of hydroxyls bonded either atop Ti5cor in bridging sites.

Structure of the TiO<sub>2</sub>(110) interface with water

Solution routes to nanoscaled tungsten chalcogenides are of interest for catalysts, lubricants, solar, and battery applications. Recently we developed a general solution route to metal chalcogenide nanomaterials from metal alkoxides (cadmium & alkaline earths) and have extended it to include the WEx. Tungsten disulfide (WS2) nanomaterials are accessible through a solvothermal reaction between tungsten (V) ethoxide and hexamethyldisilathiane. TEM/PXRD of the as prepared materials revealed monolayered WS2. Thermal treatment, under an inert atmosphere, formed bulk WS2. Full details on the synthesis and characterization will be discussed. This work was supported in part by The University of New Mexico's Nanoscience & Microsystems REU Program and by the Laboratory Directed Research and Development (LDRD) program at Sandia. 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 Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Synthesis of tungsten disulfide nanomaterials from tungsten alkoxides

High Z ceramic (YAG:Ce, BGO) and nanoparticle (MWO4 M= Ca,Cd,Pb) scintillators are of interest for the production of non-single crystal radiation detectors. These scintillators are being evaluated, due to their chemical stability (non-hygroscopic), to probe particle size/morphology effects on scintillation. To probe these effects, commercial powders were purchased and novel synthetic routes were undertaken to produce high z scintillators with various particle sizes/morphologies. The scintillation behaviors of the various particles were examined with ion beam induced luminescence (IBIL), in situ ion beam transmission electron microscopy; photoluminescence (PL), and cathodoluminescence (CL) spectroscopy techniques. Full details on the synthesis and characterization will be discussed. This work was funded in part by Sandia's Laboratory Directed Research and Development (LDRD) Program. 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 Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

High z ceramic and nanomaterial scintillators

Running a Solid Oxide Electrolysis Cell (SOEC) above a critical current can degrade the cell very quickly. Oxygen bubble formation has been observed in the electrolyte near the oxygen electrode, and seems to be a source of this degradation. Applying a load on a SOEC shifts the oxygen potential away from its equilibrium value, driving oxygen ions from the hydrogen to the oxygen electrode.  This, along with the applied current in the presence of a finite but small electronic conductivity in the electrolyte, is responsible for high oxygen potential under the oxygen electrode. The resulting oxygen pressure in the electrolyte can be large, in certain cases much higher than 1 atm.   Furthermore, these high pressures inside the bubble introduce significant stresses in the oxide that can lead to fracture or delamination of the cell.  We address the problem of homogeneous nucleation of bubbles containing oxygen in the electrolyte under conditions of constant current flow and determine the radius of the critical nucleus and the reversible work for the formation of the critical nucleus. The implications of these results for homogeneous nucleation of bubbles in the oxide of a SOEC will be discussed.

Oxygen bubble nucleation in solid oxide electrolysis cells

For the best drug therapies, you need precise control over the application, distribution, and pharmacokinetics of the drug in order to know where and when the drug is acting effectively. One way to overcome this limitation is with photochemistry. Photochemistry offers a tool with which one can direct drug release using light irradiation.  Compounds of �photo-caged� nitric oxide (NO) that release NO only after photochemical excitation, called photochemical nitric oxide-releasing molecules (photo-NORMs), are promising for controlled release of therapeutic NO.  The use of photo-NORMs provides significant advantages, as the timing, location, and dosage of NO delivered can be easily controlled by the intensity and timing of light irradiation.The described research will discuss using a variety of strategies to create photo-responsive NO releasing materials.  By using nanocrystals, biopolymers, and liposomes, controlled amounts of nitric oxide can be released in biological environments using light irradiation.

Development of photoresponsive materials for nitric oxide delivery

245th National Meeting (2013)

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