PhD, University of Cincinnati, 2002, Engineering : Materials Science

This work was focused on the investigation of charge and discharge properties of polypyrrole/polyimide (PPy/PI) composites. Capacitive and accumulative properties of PPy/PI composites were studied in details targeting application of the composite in polymer based charge storage devices: supercapacitors and polymer batteries. Polyimide was chosen as a matrix because of its excellent mechanical properties and electroactivity. Composites were prepared electrochemically on stainless steel, and studied by potential step amperometry and electrochemical impedance spectroscopy. The composition of the composite was studied by FTIR. Mechanism for PAAc conversion to PI was studied by FTIR ands DSC. Morphology was determined by SEM. Doping-dedoping of PPy in the composite in competition with doping-dedoping of PI along with formation of double electric layers were found to be responsible for a difference between discharge behaviors of PPy and PPy/PI composite. Charge storage ability was greatly affected by PPy. PPy along with factor of preconversion of poly(amic acid) (PAAc) matrix to PI was found to play a key role in charge storage properties of PPy/PI composite. DC polarization was found to alter the supercapacitance of the composite. Two mechanisms: orientation polarization and ion jump polarization were suggested to be responsible for supercapacitance in double electric layer. PPy/PI composite can be considered as a promising material for use in supercapacitors as a material for active polymer electrodes in polymer batteries. Additional advantage of use of PPy as a filler for PI matrix is the reduction of activation energy to conversion to polyimide. This was shown by differential scanning calorimetry and FTIR. Activation energy of the reaction of imidization can be reduced significantly by the presence of PPy.

Committee: Dr. Jude O. Iroh (Advisor) Subjects:

Doctor of Philosophy, Case Western Reserve University, 2004, Chemistry

The electrochemical properties of carbon films prepared by catalytic chemical vapor deposition on clean Ni(111), using an equimolar CO:CH4 mixture at a total pressure ca. 2 x 10-5 kPa (1.5 x10-4 Torr) as the carbon source, have been examined under ultrahigh vacuum (UHV) conditions (6.7 x 10-11 kPa) in pre-electrolyzed LiClO4-poly(ethylene)oxide (PEO) solutions (1 Li+:36 ethylene oxide units) at ca. 55°C. All steps involved, including carbon film preparation, electrochemical cell assembly and electrolyte prelectrolysis were carried out in the same UHV chamber under highly controlled conditions without exposure to the ambient atmosphere. The electrochemistry of glassy carbon electrodes prepared and characterized in UHV was observed in a non-aqueous electrolyte, 1M LiPF6 in Diethyl Carbonate: Ethyl Methyl Carbonate (DEC:EMC). This combination of ex-situ spectroscopic and electrochemical characterization techniques was achieved by the construction of a custom built ultrahigh vacuum (UHV) compatible system, which allows in-situ ultra-purification and mass spectrometric analysis of electrolytes. In addition, it enables electrochemical testing of carbon electrodes cleaned and characterized in a separate UHV chamber, equipped with an array of surface preparative and spectroscopic techniques. Specimens were transferred between the two chambers using a UHV compatible portable chamber, making it possible to perform surface characterization before and after electrochemical experiments with X-ray photoelectron spectroscopy (XPS). Electrodepositon of Al from MeEtimCl/AlCl3 onto a metal substrate characterized using AES in ultrahigh vacuum was achieved in a redesigned UHV system and an independently pumped liquid handling/introduction chamber. The room temperature molten salt used (MeEtimCl/AlCl3) is a moisture sensitive salt that has been used as an Al plating bath solution for decades. Coupling the room temperature molten salt with UHV produces a unique liquid electrolyte base (open full item for complete abstract)

Committee: Daniel Scherson (Advisor) Subjects: Chemistry, Physical