On Propagation Mechanism of the Electrochemically Doped Conductive Layer in Polypyrrole Films by Means of the Analysis of Linear Sweep Anodic Voltammograms

Abstract

Received December719881Accepted March13989 L lnear sweep anodic voLtamDgrams of poLypyrrLe fi Lms eLectrochemicaLy depSi ted n gLassy carbon eLectrodes were decomposed into a sigmoidaL (capacitive) and a peak-shaped faradaic) component by numerica1manlpuLatiQn of the voLtamDgrams The faradaic c( pQnent exhibited a symmetrc wavefon The peak cu rrent had a Linear variat ion with the pQtentlaL sweep rate v Varlatn of the peak potent iaL with v waS equ ivaLent to that wi th the th ickness of the fim These observat ions couLd not be expai ned by ei ther diffusion or the ordinary surface wave Predicted doping mechanism is as foLowsThe poLypyrroLe oxidized at the substrate eLect rode works as a conduct ive eLect rode for Qxldizing the reduced pQLypyrroLe on it The oxldat ion is cont roLted by the charge t r ansferrateConsequentLythecnductiveLayerispropagatedfromthesubstrateeectrdeup to the thickness of the poymer fi Lrr Equat ions for the voLtammPgram of th is modet were derived and had twQ parameters and nFvk R where 1s the anOdc transfer coef f lc lent and k the charge t ransfer rate constant The theoret lcaL votammogram showed an apProxlmateLy symmet ric shaPe The theoret icaL peak potent ia showed tinear variat ion to v forsmavaLuesofnFvkRTThetheoreticaLpeakcurrentwasproPortnaLtov and i ndependent f k The theoret icat predictons agreed with the experments 1IN11(N An interesting feature of conducting PoLymers is aswltchingprocessbetweentheinsuatingandthe cnduct ing states When Poymers such as Potypyr-roLe Poythphene and PoLyani L ine are oxidized to adopingstatethecnductivityisprovidedbythe 1-3) movement Qf poLarons and bipoLarons The potarons and bipotarons disapPear at a reduced Or undoping state and then the poymer becomes insuLating This switching can be contrOLed effiClentLy and convenient Ly by eLect rochemica doping and un-dopin9 techniques when the pQLymer is coated or eLectropo1ymerized on a substrate eLectrode When the poLymer has high density of the charge with ex-ceUent reversib1Lity for the switching it can be