Electrochemical Preparation And Properties Of Polypyrrole Membrane

A pH sensor was fabricated from polypyrrole (PPy) on Pt wire. PPy was prepared electrochemically using 0.1mol/L Py aqueous solution with and without 0.1mol/L NaHCO3 or 0.1mol/L TsONa, and characterized by infrared absorption spectrum (IR), UV-vis spectrum and electrochemical impedance spectroscopy (EIS). The electrochemically synthesized non-doped PPy as pH-indicator electrode gave satisfactory potentiometric properties: sub-Nernstian response with a slope, of 49.32mV/pH at buffer solutions of pH 3 to 10, excellent linearity, of -0.9971, and relatively fast response time and less by far ionic selective coefficient to conventional positive ions such as K+ and Na+. It was indicated that sub-Nernstian response slope and transform coefficient of Pt/PPy approximated to those of PPy doped with HCO3-, which were by far larger than those of PPy doped with TsO-. The degradation mechanism of conducting polypyrrole(PPy) in basic solution was studied by using Chronocolometry and Cyclic voltammetry(CV),FTIR spectroscopy,UV-vis spectroscopy. There was a pair of redox current peaks on CV for Pt/PPy electrode in acid solution. However,the redox activity of PPy decreased observably due to degradation of PPy in basic solution. FTIR spectroscopy and UV-vis spectroscopy indicated that degradation of PPy was relative to change of structure of PPy in basic solution. The degradation of PPy was ascribed to attack of OH-ion. OH-ion not only attacks on β-position of PPy to form carbonyl group but also attacks on α-position to form carbonyl group. Electrochemical properties of PPy electropolymerized on graphite and Pt wire were studied, and the mechanism of anion intercalation/extraction in PPy was investigated. Scanning Electron Microscope (SEM) was used to analyze structural difference of graphite/PPy, Pt/PPy and graphite/PPy/CNP electrodes. Cyclic voltammetry (CV) and Electrochemical impedance spectroscopy (EIS) were applied to study these electrodes in 0.1mol/L LiClO4 aqueous solution, 0.1mol/L LiClO4 CH3CN solution and PC solution. Cyclic voltammetry showed that graphite/PPy and graphite/PPy/CNP electrodes displayed redox activity. From redox processes the calculated Coulomb of graphite/PPy electrode was more than that of Pt/PPy electrode. In Li+ aqueous electrolyte calculated Coulomb of graphite/PPy electrode was more than that of bare graphite by 41.59%, and calculated Coulomb of graphite/PPy/CNP electrode was more than that of bare graphite by 70.54%. The charge transfer resistance of graphite/PPy electrode in different electrolyte was smaller than that of Pt/PPy electrode obviously, besides the double layer capacitance of the former was larger than that of the latter in corresponding electrolyte.