Chad C. Waraksa

EIS Studies of Porous Oxygen Electrodes with Discrete Particles I. Impedance of Oxide Catalyst Supports

Department of Materials Science and Engineering,The Pennsylvania State University, University Park, Pennsylvania 16802, USATwo titanium oxide catalyst supports for the oxygen electrode of unitized regenerative fuel cells were compared by electrochemi-cal impedance spectroscopy ~EIS! techniques. One was a commercial Ebonex sample, which is a mixture of Ti

Ultrathin nanoparticle ZnS and ZnS: Mn films: surface sol-gel synthesis, morphology, photophysical properties

Abstract Ultrathin films of ZnS and Mn-doped ZnS were grown on silicon substrates using surface sol–gel reactions, and the film growth process was characterized by ellipsometry, atomic force microscopy, X-ray photoelectron spectroscopy, UV-visible absorbance and photoluminescence (PL) spectroscopy. The Si substrates were pre-treated by chemical oxidation. On the oxidized Si/SiO x surface, nanoparticulate films of ZnS and Mn-doped ZnS were grown by sequential immersion in aqueous metal acetate and sodium sulfide solutions. During the first four adsorption cycles, there was little film growth, but thereafter the amount of material deposited was linear with the number of adsorption cycles. This behavior is consistent with the formation of ZnS nuclei at low coverage, followed by particle growth in subsequent cycles. PL spectra are consistent with incorporation of Mn 2+ into the ZnS nanoparticles.

Self-assembly of nanostructured composite ZnO/polyaniline films

Abstract Ultrathin composite ZnO/polyaniline (PAN) films were deposited from organic solutions on silicon and ITO substrates using wet layer-by-layer self-assembly technique. The film growth process was characterized by transmission electron microscopy, ellipsometry, atomic force microscopy, IR and UV-visible absorbance and photoluminescence spectroscopy, and electrical measurements. The Si substrates were pre-treated by chemical oxidation. Multilayer films were grown by sequential immersion of the substrate in an ethanolic ZnO sol and PAN solution in dimethyl formamide. The first adsorption cycle resulted in well-packed monoparticulate ZnO layer almost completely covering the substrate, which predetermined the regular growth of densely packed and quite smooth ten-layer ZnO/PAN film. Photoluminescence and IR data assumed chemical interaction between the components in neighbouring layers. The multilayer (ZnO/PAN) 9 ZnO film sandwiched between ITO and Pt electrodes exhibited strong photoelectrical response while both the components were photoelectrically inactive in our experimental conditions. The reversible conversion from insulating to conducting state was observed under irradiation by light with a wavelength below 350 nm.

EIS Studies of Porous Oxygen Electrodes with Discrete Particles II. Transmission Line Modeling

Porous electrodes provide high-surface-area supports for the catalysts of many reactions, but the influences of electrode preparation conditions on electrocatalysts are not always well understood. Electrochemical impedance spectroscopy ~EIS! can provide extensive information about an electrode, but the models describing the spectra are often too idealized to draw useful conclusions. We describe a new model based on an array of parallel, nonuniform transmission lines for predicting the response of porous electrodes. The model incorporates physically realistic elements, such as discrete particles of variable size and adjustable multilayer stacking geometries. Resistance parameters were derived from experimental data for Pt 4Ru4Ir-coated Ti0.9Nb0.1O2 and Ebonex electrodes prepared under varying degrees of oxidative conditioning. The results, which indicate a high degree of impedance at the support-solution interface and consequently, low catalyst utilization, suggest several strategies for improved electrode design.

Artificial photosynthesis in lamellar assemblies of metal poly(pyridyl) complexes and metalloporphyrins

Abstract Multilayer films composed of inorganic colloids (α-zirconium phosphate or HTiNbO 5 ) and organic polycations can be grown in almost any desired sequence on surfaces by electrostatic self-assembly. Control of the edge chemistry of the anionic sheets is essential to the preparation of well organized monolayers and multilayers. Examples are given of layer sequences that incorporate electron donors and acceptors, which undergo photoinduced electron transfer reactions across inorganic spacer layers. Similar stacking sequences can be used to couple light harvesting assemblies, containing energy donors and acceptors, to electron donor-acceptor dyads.

Self-Assembly of Nanoblocks and Molecules in Optical Thin-Film Nanostructures

The growing interest in developing techniques to prepare ultrathin semiconductor nanoparticle films is motivated by the size-dependent electronic and optical properties of semiconductors, which lead to a range of potential applications in electronic and optoelectronic devices, solar cells, photoelectrodes, photocatalysts, and sensors. The wet chemical synthesis of ultrathin semiconductor films represents, in principle, a simple and inexpensive alternative to more technologically demanding chemical vapor deposition (CVD) and physical techniques [1]. However, the realization of practical devices from wet chemical synthesis requires the development of film growth techniques that give similar or better quality films than vapor-phase methods. In particular, precise control of film thickness, crystallinity, and morphology are significant problems to be overcome in wet chemical synthesis.

Supramolecular assemblies formed by newL-lysine derivatives of viologens

L-Lysine derivatives of viologens form supramolecular assemblies of fibers and ribbons in some aromatic solvents, and the charge separation reaction in these self-assembling systems proceeds with a similar efficiency to the MV2+ system.