William H. Smyrl

Quartz Crystal Microbalance Study: Ionic Motion Across Conducting Polymers

In situ monitoring of mass change was performed during electrochemical growth and redox cycling of a conducting polymer(polypyrrole) on a quartz crystal microbalance. For the polypyrrole films grown with large polymeric anions(poly(4-styrenesulfonate) and polyvinylsulfonate), mostly cations and solvent molecules were inserted and removed to compensate charge in polypyrrole. The films formed with medium-sized anions (tosylate) showed both apparent anion and cation motion during the redox process. The films prepared in the presence of small anions (ClO 4 − and BF 4 − ) showed mostly anion motion, but apparent cation motion also became significant for higher oxidation and/or reduction state

Doped Vanadium Oxides as Host Materials for Lithium Intercalation

An improved cathodic material has been obtained by doping vanadium oxide hydrogel with silver. Silver-doped vanadium pentoxides with a silver molar fraction ranging from 0.01 to 1 were synthesized. With the successful doping, the electronic conductivity of V{sub 2}O{sub 5} was increased by 2 to 3 orders of magnitude. The electrochemical performance of the silver doped materials is very high, up to 4 moles of lithium per mole of silver-doped V{sub 2}O{sub 5} were found to be reversibly intercalated. In addition, the lithium diffusion coefficient is found to be high in the silver-doped material and with a smaller dependence on the lithium intercalation level. These enhancements resulted in high rates of insertion and delivered capacities.

Structural and electrochemical properties of three-dimensionally ordered macroporous tin(IV) oxide films

This paper presents a colloidal-crystal templating technique to prepare three-dimensionally ordered macroporous (3DOM) tin(IV) oxide films for use as lithium ion anodes. In principle, 3DOM architectures are expected to diminish diffusional polarization and yield high rates of charge/discharge due to ion diffusion pathlengths on a nanometer scale and ready electrolyte access to relatively large internal electrode/electrolyte interfacial areas. Uniformly-sized polymer spheres were deposited in a close-packed arrangement on a current collecting substrate. A tin(IV) fluid precursor infiltrated the interstitial space between the spheres and was dried. Subsequent calcination removed the polymer sphere template and formed an inverse opal film composed of nanocrystalline SnO2. These films were characterized by SEM, XRD, elemental analysis, BET, CV, and galvanostatic cycling. Large structural changes occurred in these samples as a result of the formation of LixSn (0 ≤ x ≤ 4.4) alloys during cycling. This swelling could not be suppressed by the inclusion of additives to the precursor solution. Morphological changes were absent after cycling at significantly higher rates, possibly due to ohmic losses that prevented the electrochemical reactions from occurring.

Lithium ion insertion in porous metal oxides

Abstract Sol–gel processing of transition metal oxide precursors has been used to produce porous materials of high surface area. The technique has permitted the synthesis of solid amorphous vanadium and manganese oxides that are capable of reversibly intercalating large amounts of lithium ions. Therefore, these materials may function as high capacity (500–600 mAh/g), high-energy positive electrodes in lithium batteries. Methods to improve the kinetics and the cycle performance of these positive electrodes are showing promise.

Colloidal-Crystal-Templated Synthesis of Ordered Macroporous Electrode Materials for Lithium Secondary Batteries

This paper presents a general method of preparing three-dimensionally ordered macroporous (3DOM) electrode materials, including both cathode materials (V 2 O 5 and LiNiO 2 ) and an anode material (SnO 2 ). The method is based on templated precipitation of inorganic precursors within a colloidal crystal of poly(methyl methacrylate) spheres and subsequent chemical conversion. 3DOM electrodes possess several features of interest in the design of novel battery materials, such as high accessible surface areas, continuous networks, and structural features on the nanometer scale. Optimal synthesis conditions and structural features of 3DOM electrode materials are described on the basis of X-ray diffraction, scanning electron microscopy, nitrogen adsorption, and chemical analysis.

Scanning Electrochemical Microscopy of Precursor Sites for Pitting Corrosion on Titanium

Scanning electrochemical microscopy, SECM, of oxide-covered titanium foils ([approximately]50 [angstrom] oxide thickness) immersed in potassium bromide solutions is reported. Electrogeneration of bromine (2 Br[sup [minus]] [r arrow] Br[sub 2] + 2e[sup [minus]]) at the TiO[sub 2] film is shown to occur rapidly at a few microscopic surface sites. The regions of intense faradaic activity observed in SECM images correlate directly with the location of pit nucleation. The direct correspondence between sites of faradaic activity and oxide breakdown provides a means of identifying precursor sites for pit information.

Zirconium oxide nanotubes synthesized via direct electrochemical anodization

Extended and oriented nanostructures are desirable for many applications, but direct fabrication of complex nanostructures with well-aligned morphology, orientation, and surface architectures remains a significant challenge. Here, we report successful robust fabrication of zirconium oxide (ZrO 2 ) nanotubes by a one-step, templateless anodizing process. The nanotubes formed perpendicular to the Zr substrate have an open ended array of continuous, well-aligned conformation with ca. 10 nm hole size. The ZrO 2 nanotubes with a uniform diameter have great potential for chemical sensing, catalysis, optical emission, and nanoelectrode assembly for batteries and electrochemistry.

Detection of Localized Corrosion of Aluminum Alloys Using Fluorescence Microscopy

Confocal laser scanning microscopy was used in an in situ fluorescence mode to investigate localized corrosion of aluminum alloys in the presence of 0.1 M KCl. Fluorescein dye was used to indicate pH changes and surface chemistry over and around the active sites. Al 6061 was found to have at least two kinds of inclusions according to their elemental constituents. Active inclusions that are rich in Mg, Si, and Al show fluorescence activity in early stages of exposure. The inclusions that are rich in Fe, Si, and Cr show no fluorescence activity at the early stages. Al 2024 was also studied and had different fluorescent activities that were associated with different inclusions.

Scanning Electrochemical Microscopy with Simultaneous Independent Topography

4Corrosion Research Center, Department of Chemical Engineering and Materials Science, University of Minnesota,Minneapolis, Minnesota 55455, USAbDepartment of Physics, University of North Carolina at Charlotte, Charlotte, North Carolina 28223, USAABSTRACTA new method to perform scanning electrochemical microscopy (SECM) and topography simultaneously is described here. The newmethod uses a conventional scanning microelectrode to sense species released by local electrochemical reactions on the surface of asample, combined with shear-force feedback to maintain the probe at a constant distance from the surface of the material. By using shear-force feedback, larger electrochemical currents can be detected at the microelectrode because the probe is scanned at a closer distancefrom the surface of the sample. The new method has yielded high lateral resolution topography and SECM images are reported here.

Amorphous Manganese Dioxide: A High Capacity Lithium Intercalation Host

Amorphous manganese dioxide has been synthesized via a room‐temperature sol‐gel route. The material is a stable intercalation host for lithium and the intercalation capacity is greater than . The host remains amorphous in the entire intercalation range and the insertion process is reversible. When used as an intercalation electrode, the material stores energy at the level of . The latter represents an improvement over crystalline manganese oxide materials by factors of two to three. ©1998 The Electrochemical Society