Nanayakkara L. D. Somasiri

Electrochemical Characteristics of “Polyaniline” Cathodes and Anodes in Aqueous Electrolytes

Abstract The quinoid-benzenoid-diimine form, (=(C6H4)=N-(C6H4)-N=)x of “polyaniline” shows excellent cathode characteristics including recyclability when used in conjunction with a zinc anode in an aqueous electrolyte of (l. 0M ZnCl2 + 0. 5M NH4Cl) having a pH of ∼ 4. The reduced form of this material, (-(C6H4)-N(H)-(C6H4)-N(H)-)x can be used as an anode in conjunction with a Pb02 cathode in an aqueous 0.5M Pb(BF4)2 electrolyte.

Physical Characterization of Some Polyaniline, (øN)x

Abstract Polyaniline, (4oSN) is found to exhibit a low energy absorption edge beginning near 1800 cm−1 (ca: 0.22 eV), and a strong anion-induced absorption from about 800 to 1200 cm−1. Electrical conductivity has an activation energy of 0.05 (15%) eV consistent with an anion-induced energy gap of about 0.1 eV.

Polyaniline: Protonic Acid Doping to the Metallic Regime

Abstract “Polyaniline” has been synthesized in various forms both chemically and electrochemically in aqueous media. The quinoid-benzenoid-diimine form, an insulator, is doped by dilute aqueous protonic acids to the metallic regime ([sgrave] ∼ 5 ohm−1cm−1; compressed pellet) to give the corresponding iminium salt. The polymer is not oxidized during the doping process. This represents a new type of p-doping phenomenon in a conducting polymer. Both these forms of polyaniline are stable in the presence of air and/ or water. The doping process is reversed by treatment with aqueous alkali. The mechanism by which doping occurs is discussed.

Polyaniline: Synthesis and Characterization of the Emeraldine Oxidation State by Elemental Analysis

Detailed experimental procedures are given for the chemical synthesis from aniline of analytically pure emeraldine hydrochloride, a highly conducting polymer derived from the emeraldine oxidation state of polyaniline, which contains equal numbers of oxidized and reduced repeat units, the non-protonated base form of which has the composition,. In the as-synthesized polymer, ∼ 42% of the nitrogen atoms are protonated i.e. “doped”. Treatment of this material with 1.0M aqueous HCl gives by elemental analysis, the most highly conducting (metallic) form of the emeraldine oxidation state of polyaniline in which 50% of the nitrogen atoms are protonated. Experimental details are given for converting the as-formed emeraldine hydrochloride to analytically pure emeraldine base. The conductivities of samples of emeraldine base protonated by aqueous HCl to various extents as determined by elemental analysis are reported. Electrochemical studies involving the emeraldine base are consistent with its having a composition very close to the proposed composition involving equal numbers of oxidized and reduced repeat units.

Electronic structure of some polyanilines

Abstract We present some photoelectron spectroscopy data relevant to the chemical and electronic structure of certain members of the polyaniline family of conducting polymers.

Polyaniline: characterization as a cathode active material in rechargeable batteries in aqueous electrolytes

An analytically pure form of chemically synthesized polyaniline having the emeraldine oxidation state has been used as a cathode active material together with a Zn anode in the fabrication of rechargeable cells in 1.0 M aqueous ZnCl2 electrolyte (pH∼4). The experimental capacity and energy density based only on the weight of polymer employed in constructing the cell are 151.5 Ah kg−1 and 159.1 Wh kg−1 respectively at a constant discharge current of 0.75 mA cm−2 (average discharge voltage 1.05V). The cell reactions in the charge and discharge processes have been determined. The modified capacity and energy density, when taking into account the calculated weights of Zn and HCl involved in the discharge reactions, are 109.3 Ah kg−1 and 114.8 Wh kg−1 respectively. The cell shows excellent recyclability and coulombic efficiency.

Spectroscopic Characterization of Some Polyanilines

Some previous studies of polyaniline, or (oN)x, using infrared spectroscopy, X-ray photoelectron spectroscopy and NMR, are reviewed. New results involving the optical absorption spectra of free-standing, electrochemically prepared (oN)x, in both the insulating (2A) and conducting (2S) form are presented. Use is made of spectra of nigrosine, which is a model molecule representative of a short (oN)x chain.