Johna Leddy

Density and solubility of nafion: recast, annealed, and commercial films.

The density of Nafion membranes wetted in water and acetonitrile and the solubility of Nafion in a 50:50 ethanol/water mixture are reported. Commercially available membranes, solution recast membranes, and recast membranes thermally processed for varying lengths of time were examined. Unheated recast membranes were found to be ∼20% less dense in water than both commercial membranes and recast membranes heated at 140 °C for 40, 50, and 60 min. For heating times of ≥40 min, the density of recast membranes in water was invariant and equal to the density of commercial films. Similarly, in acetonitrile, commercial membranes and films heated for 1 h had the same density; unheated recast films were ∼25% less dense. Nafion density in acetonitrile was ∼15% less than that in water. Acid pretreatment reduced Nafion film density by ∼15%. Unheated recast films were 22-100% soluble in a sonicated ethanol/water mixture. Commercial membranes and recast films heated for as little as 10 min were insoluble under the same conditions.

Enzymatically prepared poly(hydroquinone) as a mediator for amperometric glucose sensors

Abstract Poly(hydroquinone) (PHQ), synthesized from glucose-β- d -hydroquinone by peroxidase-catalyzed polymerization in aqueous solution and placed on glassy carbon electrodes, behaves as a redox mediator for glucose sensing. The highly selective nature of enzymatic catalysis leads to PHQ with a unique structure which is more soluble in organic solvents and more electrochemically active, as compared to that prepared via electrochemical methods. A glucose sensor is constructed in a pellet form with PHQ, glucose oxidase (GOD) and graphite powder. PHQ retains its redox activity and reversibility in the solid state and effectively mediates the electron transfer between the electrode and GOD. Resulting glucose biosensors possess sub-minute response times over a dynamic range from 1 to 30 mM. The PHQ mediator permits sensor operation at 100 mV (versus SCE), thereby reducing susceptibility toward common endogenous, easily oxidizable interferences.

Magnetized Nickel Electrodes for Improved Charge and Discharge Rates in Nickel Metal Hydride and Nickel Cadmium Batteries

Nickel hydroxide electrodes serve as positive electrodes in several batteries including nickel metal hydride and nickel cadmium batteries. Nickel hydroxide slurries are coated onto platinum electrodes and allowed to dry either with or without an external magnetic field. Once dried, the external magnet is removed. Films are also formed that incorporate chemically inert, silaneshrouded magnetite microparticles. Magnetized films exhibit larger cyclic voltammetric currents than corresponding nonmagnetized films. Magnetized films generate currents that are 1.25 to 1.79 times that of nonmagnetized films containing no microparticles. Results are consistent with a magnetically facilitated increase in charge and discharge rates.

Chronopotentiometry in thin-layer electrochemical cells: a new look at transition–time derivations including multicomponent systems

A complete derivation is presented for concentration profiles and transition times in a thin layer cell under constant current conditions. Expressions for the concentration across a thin layer cell and the transition time are presented under conditions where the diffusion layer is extremely small (short times) and extremely large (long times) compared to the thickness of the thin layer cell. Excellent agreement with those previously reported in the literature is found. Application to thin layer spectroelectrochemical cells is demonstrated.

Detection of Acetone on Human Breath Using Cyclic Voltammetry

A cyclic voltammetric measurement protocol for acetone concentration collected in the vapor phase and measured in solution is demonstrated for acetone concentrations across the human physiological range, 1 μ Mt o 10 mM at platinum electrodes in 0.5 M H2SO4. Effects arise through adsorption of acetone from the gas phase onto a platinum surface and hydrogen in acidic solution within the voltammetric butterfly region. The protocol is demonstrated to yield breath acetone concentration on a human subject within the physiological range and consistent with ketone urine test strip.