Mehmet Kesmez

High Current Density Air-Breathing Laccase Biocathode

Although biofuel cell research has progressed over the past decade, there were still problems with employing enzymes at air-breathing cathodes, because enzymes need to remain hydrated and most enzyme reactions occur in solution and not in gas phase. This research details an approach to the development of an air-breathing biocathode employing direct electron transfer. This laccase biocathode is studied in two different fuel cell configurations: a proton exchange membrane hydrogen/air fuel cell and a direct methanol fuel cell (DMFC) with an anion exchange membrane. The laccase from the Rhus vernificera biocathode with an enzyme loading of 0.224 mg/cm 2 provides fuel crossover tolerance and provides a high operational current density of 50.0 mA/cm 2 and a maximum power density of 8.5 mW/cm 2 in a 40% methanol DMFC. The laccase biocathode shows a lifetime of 290 h in a DMFC. The hydrogen/air fuel cell provides a stable current for a total of 350 discontinuous hours when operated for 8 h daily.

PHOTOCATALYTIC OXIDATION OF ALDEHYDES/PCE USING POROUS ANATASE TITANIA AND VISIBLE-LIGHT-RESPONSIVE BROOKITE TITANIA

We have synthesized an annealed porous aerogel titania (LUAG2), which demonstrates a very high photocatalytic activity for aldehydes and perchloroethylene (PCE) photocatalytic oxidation (PCO) in gas phase under blacklight and fluorescent light irradiation. LUAG2 has a BET surface area of 237 m2/g and a porosity of 0.31 (volume fraction). X-ray diffraction (XRD) analysis shows LUAG2 is nearly pure anatase. It has improved the destruction of PCE and aldehydes as a group by 10–34% with black light compared to Degussa P-25. The optimum water vapor to butyraldehyde molar ratio is around 1/3. LUAG2 also shows better mineralization to CO2 than Degussa P-25 TiO2 does. Under irradiation of a 4 W fluorescent lamp LUAG2 gives a consistently higher conversion than that of Degussa P-25. The highly active photocatalyst indicates potential applications in indoor and outdoor environmental pollution control. A visible-light-responsive TiO2, NTB 200, is also investigated for comparison purposes.

In Situ Ionic/Electric Conductivity Measurement of La0.55Li0.35TiO3 Ceramic at Different Li Insertion Levels

The electrical conductivities of solid La 0.55 Li 0.35 TiO 3 electrolytes at different Li intercalation levels were measured, in situ, using a special cell and electrode design. The relative changes in electrical conductivities of La 0.55 Li 0.35 TiO 3 at different Li insertion levels in liquid electrolytes were monitored by the voltage across the La 0.55 Li 0.35+x TiO 3 powder disk electrode sandwiched between two nickel screens and charged only on one nickel screen. The real electrical conductivities of the La 0.55 Li 0.35+x TiO 3 ceramic at different Li insertion levels x without influence of high-ion-conductivity liquid electrolytes was measured by electrochemical impedance spectroscopy using sintered La 0.55 Li 0.35+x TiO 3 disk electrodes with Au coating on both sides. Lithium was electrochemically inserted into La 0.55 Li 0.35 TiO 3 when the Au coated disk electrodes were immersed into liquid electrolytes with the cell inverted. The impedances of La 0.55 Li 0.35+x TiO 3 electrodes were then measured with the disk electrode suspended above the liquid electrolyte with the cell upright.

Electrochemical Properties Of Copper Oxide Surfaces, Buried Interfaces, And Subsurface Zones And Their Use To Characterize These Entities

Electrochemistry of oxides is an expanding area of oxide characterization. Although, interfacial characterization techniques including surface science methods have contributes substantially to our current understanding of the processes involved in the oxidation of metals and alloys. The characterization of subsurface zones and buried interfaces still remain a major challenge. Copper reactions with oxygen have been studied by high vacuum based techniques of AES, ELS, ISS, XPS. SIMS, LEED. STM, SEXAFS, HEIS and PFDMS and with optical methods, like UV-Vis-NIR, diffuse reflectance spectroscopy, FTIR and photoluminescence spectroscopes. However it has become evident that the processes that produce thermally and plasma grown oxide films on metals and alloys are electrochemical in nature and can be modeled by electrochemical concepts. Therefore, it is important that the oxide over layers, thin films and thick films be characterized by electrochemical means -with electrochemical methods, such as linear potential sweep voltammetry, cyclis voltammetry, galvanostatic reduction and coulometry which allow the identification of copper (I), copper (II) and copper (III) oxides. Interest in copper as a technologically important material needs to be met with greater understanding of the fundamental nature of copper oxide structures. In this study, the authors demonstrate the use of Linear Sweep Voltammetry (LSV) to study buried structures in the thermally grown oxide layers on copper. In particular, LSV can be used to detact reactions at buried interfaces. It also recognizes Cu 3 O 2 and the decomposition of copper oxides at the metal-oxide layers on copper. In particular, LSV can be used to detect reactions at buried interface. The two key parameters that drive oxide growth and decomposition are demonstrated to be oxygen activity and the free energies of formation of the oxides. The complex nature of the oxidation of copper, as well as other metals and alloys, will be described qualitatively using the Modified Cabrera-Mott (C-M) Model. Surface studies of oxidation of metals and alloys need to be supported and complemented by other techniques such as electrochemical methods.