Daniel A. Buttry

In Situ Interfacial Mass Detection with Piezoelectric Transducers

The converse piezoelectric effect, in which an electric field applied across a piezoelectric material induces a stress in that material, has spurred many recent developments in mass measurement techniques. These methods commonly rely on the changes in the vibrational resonant frequency of piezoelectric quartz oscillators that result from changes in mass on the surface of the oscillator. The dependence of frequency on mass has been exploited extensively for mass measurements in vacuum or gas phase, for example, thickness monitors for thin-film preparation and sensors for chemical agents. Advances in piezoelectric methodology in the last decade now allow dynamic measurements of minute mass changes (< 10-9 grams per square centimeter) at surfaces, thin films, and electrode interfaces in liquid media as well. Mass measurements associated with a diverse collection of interfacial processes can be readily performed, including chemical and biological sensors, reactions catalyzed by enzymes immobilized on surfaces, electron transfer at and ion exchange in thin polymer films, and doping reactions of conducting polymers.

Stable silicon-ionic liquid interface for next-generation lithium-ion batteries

We are currently in the midst of a race to discover and develop new battery materials capable of providing high energy-density at low cost. By combining a high-performance Si electrode architecture with a room temperature ionic liquid electrolyte, here we demonstrate a highly energy-dense lithium-ion cell with an impressively long cycling life, maintaining over 75% capacity after 500 cycles. Such high performance is enabled by a stable half-cell coulombic efficiency of 99.97%, averaged over the first 200 cycles. Equally as significant, our detailed characterization elucidates the previously convoluted mechanisms of the solid-electrolyte interphase on Si electrodes. We provide a theoretical simulation to model the interface and microstructural-compositional analyses that confirm our theoretical predictions and allow us to visualize the precise location and constitution of various interfacial components. This work provides new science related to the interfacial stability of Si-based materials while granting positive exposure to ionic liquid electrochemistry.

Mass measurements using isotopically labeled solvents reveal the extent of solvent transport during redox in thin films on electrodes

Transport of solvent during the redox reactions of thin films on electrodes has been identified as a possible influence on both the thermodynamic and kinetic aspects of their electrochemical responses. A variety of methods has been used in attempts to measure solvent content of these films, including ellipsometry and profilimetry. However, those techniques which rely on measurement of thickness suffer from inability to deconvolute the contributions to swelling (or deswelling) from ion and solvent transport. Thus, the situation remains one in which speculation abounds, but accurate measurements are unavailable. In this communication, the authors report on the application of the quartz crystal microbalance (QCM) technique to the determination of solvent transport during redox in thin films of nickel ferrocyanide (the nickel analogue of Prussian Blue) by comparing the difference in the total mass change (comprised of contributions from both ion and solvent transport) which results from use of isotopically substituted solvent. To their knowledge, these experiments represent the first accurate, unambiguous measurements of solvent transport in thin films on electrodes. It is especially significant that these measurements are made in the presence of simultaneous ion transport.

Recent advances in electrochemical DNA hybridization sensors

Even with the advent of industry produced electrochemical DNA analysis chips, electrochemical DNA hybridization detection continues to be an intensive research focus area. The advantages of electrochemical detection continue to inspire efforts to improve selectivity and sensitivity. Here, we summarize the landscape of recent efforts in electrochemical DNA hybridization detection. We specifically focus on some main areas from where novel work continues to originate: redox active molecules designed for specific interaction with double stranded DNA, DNA mimics to eliminate background electrochemical signals, external nanoparticle or enzyme modifications for sensitivity enhancements, split and self-hybridizing single stranded DNA probe modifications, and novel catalytic oxidation techniques. Additionally, we touch on the use of DNA hybridization sensors to monitor alternative biochemical (non-DNA hybridization) processes.

Virtues of composite structures in electrode modification. Preparation and properties of poly (aniline)/nafion composite films

Poly(aniline) (PA) is electropolymerized within thin films of precast Nafion on gold or glassy carbon electrodes. The quartz crystal microbalance (QCM) is used to aid in identification of the ionic species that undergo transport during switching of the PA between its insulating and conducting forms. The QCM frequency changes observed in solutions containing various cationic species suggest that cation transport is dominant for these composite structures. In acidic solution, a consequence of the high transport number for the proton in the composite films is shown to be an enhanced switching rate relative to the simple (non-composite) PA film. The composite PA films appear to be less resistive and therefore more electrochemically well behaved over a wider pH range than the simple PA films.

Liquid Thermoelectrics: Review of Recent And Limited New Data of Thermogalvanic Cell Experiments

Experimental studies on thermogalvanic cells (or thermo-electrochemical cells or simply thermocells) have shown promising results in the past two decades since being introduced in 1825. Recent literature on this topic ranging from aqueous redox couple cells to nonaqueous and molten salt thermogalvanic cells is reviewed and compared. Some limited new experimental data on power generation for the underdeveloped Cu-CuSO4 system are also reported. The Seebeck coefficient values of these experiments fit with a characteristic model extracted from a 1959 paper by deBethune et al. (Journal of the Electrochemical Society, Vol. 106, 1959). The power generation results are compared with the few previously reported values of the Cu-CuSO4 system by Holeschovsky (Analysis of Flooded Flow Fuel Cells and Thermogalvanic Generators, 1994) and Tester et al. (Evaluation of Thermogalvanic Cells for the Conversion of Heat to Electricity, 1992), including those published by Kuzminskii et al. (Journal of Power Sources, Vol. 52, 1994) and Quickenden and Mua (Journal of the Electrochemical Society, Vol. 142, 1995). Condensing the recently published literature, this article presents recent trends and identifies future possibilities or directions for realizing this attractive concept, which has been around for a long time.

Solvent swelling influences the electrochemical behavior and stability of thin films of nitrated poly (styrene)

Abstract The electrochemical behavior and stability of thin films of poly(nitrostyrene) (PNS) and a partially dinitrated derivative of PNS (PDNS) have been examined in acetonitrile. Qualitative information regarding the extent of solvent swelling of these polyelectrolyte films in non-aqueous solvents is obtained using the electrochemical quartz crystal microbalance (EQCM) technique, both by measuring the frequency changes due to solvent swelling and by measuring the conductance (impedance) spectra of the quartz crystal/polymer film composite resonator in the different oxidation states. Extensive solvent swelling as a function of the number of reductive scans is correlated with instability of the films toward dissolution or delamination and with subtle changes in electrochemical behavior. The effectiveness of thermal pretreatments (which presumably induce crosslinks of some type) for enhancing film stability by slowing the rate of swelling is examined. For certain types of films, it is shown that the transport processes which serve to achieve electroneutrality at high scan rates may occur on a different time scale (i.e. faster) than those which serve to attain thermodynamic equilibrium. The implication is that transient, non-equilibrium states may be prepared during switching whose composition is not necessarily that dictated by the equilibrium state, and that manipulation of these transient states to achieve faster switching rates may be done independently of equilibrium considerations, at least in some cases.

Immobilization of amines at carbon fiber surfaces

Abstract The reaction between amines acting as nucleophiles and the CC bonds on the carbon fiber surface acting as electrophilic vinyl groups has not yet been explored. In this contribution it is demonstrated that both thermal reactions and electrochemical oxidation of amines at carbon fibers allow the covalent bonding of these molecules directly to the carbon fiber surface, presumably via nucleophilic attack of the amine at electrophilic CC sites at the surface and subsequent formation of C–N bonds between the surface and the amine. A novel strategy for a quantitative assay of the number of amines attached to the surface is developed in which Fe(CN)63− is electrostatically bound to the protonated, cationic amine sites, followed by electrochemical determination of the amount of bound Fe(CN)63− as a function of its concentration in solution. Analysis of the isotherm for this electrostatic binding process then provides a measure of the number of interfacially immobilized amines. The composition of the amine layer is also probed using X-ray photoelectron spectroscopy (XPS). Mechanisms are discussed by which attachment of amines at the electrophilic vinyl groups of the carbon fibers can occur. The likely influence that this type of reaction has on the interfacial shear strength in carbon fiber/epoxy composite materials is also discussed.

Dimercaptan‐Polyaniline Cathodes for Lithium Batteries: Addition of a Polypyrrole Derivative for Rapid Charging

A polymer composite cathode prepared from polyaniline and 2,5-dimercapto-1, 3,4-thiadiazole shows high gravimetric energy density when it is coupled with a lithium anode. However, charging and discharging currents should be 0.05 mA/sq cm or less, otherwise the cycle life is shortened. Addition of a polypyrrole derivative, poly(3-butylcarboxylate- 4-methylpyrrole), to the composite cathode enabled rapid charging at 0.2 mA/sq cm without undue deterioration of the energy density, but it was not effective for rapid discharging. This effect of the polypyrrole derivative may be ascribale to the electrical conductivity in its oxidized state.

A SECM Study of Heterogeneous Redox Activity at AA2024 Surfaces

Scanning electrochemical microscopy (SECM) was used to spatially resolve the heterogeneous cathodic activity at AA2U24 surfaces. Experiments used a 10 μm diameter Pt microelectrode in a solution containing the protonated form of (dimethylamino) methylferrocene [DMAFc + , i.e., the Fe(II) state]. The tip was brought near the alloy surface while held at a potential of 0.65 V vs. SCE, where DMAFc + is oxidized to DMAFc 2+ [i.e., the Fe(III) state]. The AA2024 substrate was held at -0.75 V, where the DMAFc 2+ produced near the probe tip is reduced back to DMAFc + at regions on the surface that were cathodically active. Lateral variation in the DMAFc + oxidation current at the tip arises either from a decrease of the diffusive delivery of DMAFc + to the tip due to proximity to the surface or from a positive feedback mechanism in which the DMAFc 2+ that had been oxidized at the probe tip was reduced at the substrate. The images show locally high redox reactivity which is attributed to second phase, intermetallic inclusions. Comparison of the SECM images with scanning electron microscopy-energy dispersive spectroscopy images shows that the regions of high redox reactivity correlate with the locations of the intermetallic particles.