Leon S. Van Dyke

Use of a coulometric assay technique to study the variables affecting deuterium loading levels within palladium electrodes

Abstract We report in this paper measurements of hydrogen (H) and deuterium (D) loading stoichiometries in Pd electrodes. We accomplished these analyses using an electrochemical method developed for in situ determination of palladium deuteride stoichiometries. The electrochemical method quantifies the amount of deuterium incorporated into the metal lattice by collecting the charge released during the potential controlled discharge of deuterium loaded Pd electrodes. In addition, ex situ gravimetric analyses were used to confirm electrochemically measured D/Pd atom ratios. Gravimetric analyses were also used in cases where the diameter of the Pd electrode precluded the relatively slow diffusion-limited electrochemical discharge method. A variety of electrolytic factors were studied to determine what conditions, if any, promote the greatest absorption of deuterium into the Pd lattice. We observed loading values of 0.73 ± 0.02 deuterium atoms per Pd lattice atom under all the electrolytic conditions studied in LiOD and D2SO4 solutions. As found in previous studies, H/Pd values were approximately 10% higher than D/Pd values. These measurements of D/Pd stoichiometries indicate that interfacial parameters, current density, pD, charging time and surface purity have negligible effect on the maximum deuterium concentration within Pd electrodes.

Electrochemical Investigation of Electronically Conductive Polymers

Electronically conductive polymers are a fascinating new class of materials with unique electronic, electrochemical, and optical properties (1). One of the most interesting aspects of these polymers is that they can be reversibly “switched” between electronically insulating and electronically conductive states. Numerous researchers in a variety of conductor transition (1). In addition to being an interesting scientific phenomenon, this switching process plays an integral role in nearly all of the proposed chemical applications of electronically conductive polymers (2–13)

Template-Synthesis: A Method for Enhancing the Ionic and Electronic Conductivity in Electronically Conductive Polymers

Abstract : Template-synthesis entails the synthesis of an electronically conductive polymer (or other material) within the pores of a microporous membrane. The membranes used have cylindrica pores of equivalent pore diameter; as a result, polymeric fibers are obtained, where the diameters of the fibers are determined by the diameter of the pores in the template membrane. We show in this paper that template-synthesized polypyrrole fibers show faster rates of charge transport, during electrochemical undoping, and dramatically higher electronic conductivitie than conventional forms (e.g. electrochemically-synthesized film) of this polymer.

A Simple Chemical Procedure for Extending the Conductive State of Polypyrrole to More Negative Potentials

Abstract : The electronically conductive polymer polypyrrole is an electronic conductor at potentials positive of ca. -0.4 V vs. the saturated calomel electrode (SCE) and an electronic insulator at potentials negative of this value. As a result of this potential-dependent conductor/insulator transition, a polypyrrole film can be used as an electrode for redox couples with E(o)s positive of ca. -0.4 V vs. SCE but cannot be used as an electrode for couples with E(o)s negative of this value. We have discovered a simple chemical procedure that extends the conductive state of polypyrrole to ca. -1.1 V vs. SCE. This procedure entails treating the polypyrrole film with aqueous sodium hydroxide. We demonstrate this extension of the conductive state to more negative potentials in this paper. We also propose, and test, a chemical model that explains the extension of the conductive state

Fibrillar electronically conductive polymers show enhanced rates of charge transport

Abstract : Many electronically conductive polymers can be reversibly switched between electronically insulating and electronically conducting states. For polyrrole, this redox switching reaction can be written as - (Pyrrole)-x+ Boron Tetrafluoride Anion 4- ---- -(Py+BF4(-)n - (PY)(x-n)- + ne(-) where Py and Py(+) are reduced and oxidized monomer unites in the polypyrrole film and BF4(-) is a charge balancing counter-ion, initially present in a contacting solution phase. Equation 1 shows that ions must be incorporated into, or expelled from, the polymer phase during the redox switching reaction. In many cases, the rate of this reaction is controlled by ion-transport in the polymer phase (3,4). The switching reaction plays an integral role in nearly all of the proposed applications of electronically conductive polymers (5-7). In most cases, significant benefit would accrue if the rate of this reaction could be accelerated. The above discussion suggests that one approach for enhancing the rate of the switching reaction would be to enhance the rate of charge-transport in the polymer phase. We would have recently described a procedure for controlling the supermolecular structures of electronically conductive polymers (8). This procedure yields polymers with fibrillar supermolecular structures. We have shown the polypyrrole films which have this fibrillar supermolecular structure support higher rates of reductive charge-transport than conventional polypyrrole films. We report preliminary results of these investigation in this communication. Electronically conductive polymers, Polypyrrole, Oxidized monomer units, Supermolecular, Fibrillar supermolecular structure. Charged particles.

Modification of Fluoropolymer Surfaces with Electronically Conductive Polymers

Abstract We describe methods for coating fluoropolymer surfaces with thin films of electronically conductive polymers. Modification of the fluoropolymer surface prior to coating with conductive polymer is necessary to achieve good adhesion between the fluoropolymer membrane and the conductive polymer coating. We describe four different procedures for modifying the fluoropolymer surface so as to promote strong adhesion. These procedures are based on a wet chemical treatment of the fluoropolymer or on exposure of the fluoropolymer surface to a hydrogen plasma, an ultraviolet lasr or an electron beam. Finally, we show that it is possible to ‘write’ patterns with the conductive polymer onto the fluoropolymer surface.

UV laser ablation of electronically conductive polymers

Abstract The UV laser ablation of thin polypyrrole and polyaniline films coated on an insulating substrate is described. UV laser ablation is used to pattern the conductive polymer coating; patterns with submillimeter features are easily obtained with edge resolution on the order of a few microns.

Electrochemical evaluation of charge-transport rates in electronically conductive polymers

Abstract The theoretical and experimental aspects of a new current-pulse method for electrochemical investigations of charge-transport rates in thin redox active films on electrode surfaces are described. This method yields an apparent diffusion coefficient, D app , which is a quantitative measure of the rate of the charge-transport process in the film. This method is ideally suited for solving the myriad problems associated with electrochemical analyses of electronically conductive polymers (e.g. polypyrrole, polyaniline, etc.). When applied to such polymers, the D app obtained is a quantitative measure of the rate of the insulator-to-conductor switching reaction. We have used this method to obtain what we believe are the first reliable electrochemically-generated values of D app for the polymer polypyrrole.