Strujni elektrohemijski oscilator

Abstract

Ova doktorska disertacija se bavi potenciodinamičkim ispitivanjem ponašanja struje pri anodnoj polarizaciji bakarne elektrode, u prisistvu 1M CF3COOH (trifluorosirćetna kiselina). Poseban naglasak je dat na ispitivanje strujnih oscilacija koje se generišu u odreĎenoj oblasti potencijala (oscilatorna oblast, oblast OsS). Pojava strujnih oscilacija ukazuje da se elektrohemijski sistem Cu|1M CF3COOH moţe okarakterisati kao strujni elektrohemijski oscilator. Uočena oscilatorna oblast na struja-potencijal polarizacionim krivama se nalazi izmeĎu dve oblasti stabilnih stacionarnih stanja, naime izmeĎu oblasti aktivnog rastvaranja bakarne elektrode (oblast SSS1) i oblasti njene pasivacije (oblast SSS2). Primenom ciklične voltametrije ustanovljeno je da se strujne oscilacije javljaju pri oba smera polarizacije, anodnom i katodnom smeru. Prelaz SSS1OsS karakteriše zanemarljivo mali histerezis (5 mV), dok je širina histerezisa na prelazu OsSSSS2 značajno veća (34 mV). Bifurkaciona analiza je pokazala da se prelaz SSS1OsS odvija preko superkritične Hopfove bifurkacije, dok je prelaz OsSSSS2 okarakterisan homokliničnom bifurkacijom. Tafelova analiza je pokazala da se anodno rastvaranje bakarne elektrode odvija preko mehanizma jednoelektronskog prenosa naelektrisanja. Rendgeno-difrakcionom analizom ustanovljeno je da oksidi bakra (CuO i Cu2O) ne ulaze u sastav pasivnog sloja. Difrakciona refleksija na 2 = 7,95, koja nije mogla biti indeksirana, ulazuje da se u sastavu pasivnog sloja nalazi faza velike elementarne ćelije, najverovatnije so koju čine Cu(I) i/ili Cu(II) trifluoroacetat. Dobijena mikro-porozna struktura površine bakarne elektrode koja je bila izloţena potencijalima unutar oscilatorne oblasti je detektovana primenom mikroskopije atomskih sila, što ukazuje na tačkastu (piting) koroziju. Na osnovu ispitivanja uticaja temperature elektrolitičke ćelije na oscilatorno ponašanje struje, naĎeno je da se unutar temperaturskog intervala 5 – 52 C strujne oscilacije javljaju na polarizacionim krivama; strujne oscilacije nisu bile opaţene kada je temperatura elektrolitičke ćelije iznosila 55 C...

This doctoral dissertation deals with potentiodynamic examination of current response during the anodic polarization of copper electrode in the presence of 1M CF3COOH (trifluoroacetic acid). Particular focus is given on investigation of the current oscillations that are generated in certain potential region (oscillatory region, region OsS). Appearance of the current oscillations indicates that the electrochemical system Cu|1M CF3COOH can be classified as a current electrochemical oscillator. The observed oscillatory region at the current-potential polarization curve is situated between two regions of stable steady states, namely between the region of active dissolution of copper electrode (region SSS1) and the region of its passivation (region SSS2). It was determined that the current oscillations occur in anodic and cathodic direction of polarization, by applying of cyclic voltammetry. The transition SSS1OsS is characterized by negligible hysteresis (5 mV), while the width of hysteresis at the transition OsSSSS2 is significantly higher (34 mV). Bifurcation analysis showed that the transition SSS1OsS goes via supercritical Hopf bifurcation, while the transition OsSSSS2 is characterize by homoclinic bifurcation. The Tafel analysis showed that the anodic dissolution of copper electrode immersed in 1M CF3COOH goes via one-electron charge transfer step. X-ray diffraction analysis showed absence of copper oxides (Cu2O and CuO) in passive layer. Diffraction reflections at 2 = 7.95, which could not be indexed, indicates presence of phase with large unit cell in passive layer, most probably salt composed of Cu(I) or/and Cu(II) trifluoroacetate. Obtained micro-porous structure of the copper electrode surface, which was exposed to potentials within oscillatory region was detected by using atomic force microscopy, this indicates a pitting corrosion. Based on the investigation of the temperature effect on current oscillatory behavior, it was found that within temperature interval ranged from 5 °C to 52 °C, current oscillations occur on polarization curves...