Ralph E. Williford

Optimization of Air Electrode for Li/Air Batteries

The effects of carbon microstructure and carbon loading on the performance of Li/air batteries were investigated. The active carbons from various sources were compared, and a dry rolling method was optimized to prepare air electrodes with high mesopore volume. It is found that the capacities of air electrodes improve significantly when the mesopore volume of the carbon source is high. However, for carbons with low mesopore volumes, other factors such as surface activity also play an important role in determining the electrochemical performances of the Li/air batteries. A practical criterion, area-specific capacity, was used to optimize the carbon loading for air electrode. The best area-specific capacity of 13.1 mAh/cm2 was obtained at a carbon loading of 15.1 mg/cm2. Further increasing or decreasing the carbon loading led to a reduced area- specific capacity. Finally, at fixed carbon loading and discharge rates, electrolyte amount was another key factor governing cell performance. A spring mechanism is proposed to explain the formation of the tri-phase regions in air electrodes. After optimizing the parameters listed above, a high capacity of 1,756 mAh/g carbon corresponding to a specific energy of 4,614 Wh/kg carbon was obtained for Li/air batteries operated in a dry air environment.

In situ observations of the early stages of localized corrosion in Type 304 SS using the electrochemical atomic force microscope

In situ, time-lapse images of the early stages of pitting in dilute NaCl solutions, and intergranular corrosion in dilute oxalic acid solutions, have been obtained in Type 304 SS (UNS S30400) using an electrochemical atomic force microscope (ECAFM). A pit was observed to grow from an irregular shape with ledges along the pit walls, to a round pit with an island formation, over a 6-min time span. Grain boundary chromium carbides were exposed, and then partially dissolved, over a 26-min time span. The intergranular corrosion was most prominent along the grain boundary between the carbides, rather than between the carbides and the matrix, leaving the carbides intact via ligaments of matrix material. This study demonstrated the usefulness and complexities in using the ECAFM for studying the early stages in pitting and intergranular corrosion.

Ultralow density, hollow silica foams produced through interfacial reaction and their exceptional properties for environmental and energy applications†

We report a novel, facile, and reproducible method for large-scale production of highly porous, hollow silica foams (hollow spheres) with a robust ultrathin shell of several nanometres through a simple, one-step, bubble-controlled, interfacial hydrolysis reaction. This material has exceptional properties, including ultralow density (0.028 g cm−3, approaching 99% porosity), good thermal stability up to 1000 °C, an exceptionally high capacity for oil uptake from mixed solvents (up to 25.6 cm3 g−1), and a very low thermal conductivity comparable to ultralow density silica aerogels.

Interference-enhanced Raman scattering from TiO 2 /SiO 2 multilayers: measurement and theory

Raman-band intensities for sputter-deposited TiO(2)/SiO(2) multilayer coatings are found to exhibit a strong dependence on excitation wavelength of the probe laser. A model based on standing waves within the stack correctly predicts the magnitude and wavelength dependence of the observed enhancements.

Photocatalytic generation of dissolved oxygen and oxyhemoglobin in whole blood based on the indirect interaction of ultraviolet light with a semiconducting titanium dioxide thin film

Most current artificial lung technologies require the delivery of oxygen to the blood via permeable hollow fibers, depending on membrane diffusivity and differential partial pressure to drive gas exchange. We have identified an alternative approach in which dissolved oxygen (DO) is generated directly from the water content of blood through the indirect interaction of ultraviolet (UV) light with a semiconducting titanium dioxide thin film. This reaction is promoted by photon absorption and displacement of electrons from the photoactive film and yields a cascading displacement of electron “holes” to the aqueous interface resulting in the oxidation of water molecules to form DO. Anatase TiO2 (photocatalyst) and indium tin oxide (ITO) (electrically conductive and light transparent) coatings were deposited onto quartz flow-cell plates by direct current reactive magnetron sputtering. The crystal structure of the films was evaluated by grazing incidence x-ray diffraction, which confirmed that the primary crystal...