Provider: - Institution: - Data provided by Europeana Collections- Glass-like carbon (GC) is an isotropic material. Good mechanical properties and electrical conductivity, corrosion resistance, as ...well as impermeability to gases and liquids are essential properties which make GC a very useful material, especially as an electrode material in electrochemical reactions. Different mechanical, chemical and/or electrochemical treatment of GC surface can be applied to increase its electrochemical activity. In the present thesis activation of the GC electrode by anodic or cathodic electrochemical polarization was studied. The influence of electrolyte composition, potential and duration of polarization on double layer charge, as a measure of electrode activity has been investigated. Glass-like carbon surface can be easily modified by silver or copper, simply by exposing it to the corresponding metal salt solution. Auger electron spectra - AES and X-ray photoelectron spectra - XPS of such an electrode show that the metal is present on the surface and in the near surface region in the form of zero-valent state. Electrochemical characterization of silver modified GC electrodes is presented. The influence of concentration of AgNO3 solutions, the time of immersion, the pre treatment and/or activation of glass-like carbon electrode, as well as the influence of oxygen presence in AgNO3 solution was determined. In addition, ultra high vacuum - UHV methods of surface analysis, AES and XPS, and scanning tunneling microscopy - STM were applied for examination of modified electrodes. The results obtained suggest that functional groups, formed on the GC surface during electrochemical activation, participate in modification as active sites. The modified electrode is catalytically active in the electrooxidation of small organic molecules, and can be used as an indicator electrode in electroanalytical techniques.- Stаklаsti kаrbоn је izоtrоpnа, nеgrаfitаbilnа fоrmа uglјеnikа. Nјеgоvе dоbrе mеhаničkе оsоbinе, visоkа еlеktričnа prоvоdnоst, hеmiјskа inеrtnоst, kоrоziоnа оtpоrnоst, kао i nеprоpustlјivоst zа tеčnоsti i gаsоvе, оmоgućаvајu mu širоku primеnlјivоst, pоsеbnо kао еlеktrоdnоg mаtеriјаlа. Еlеktrоhеmiјskа аktivnоst stаklаstоg kаrbоnа sе pоvеćаvа rаzličitim mеhаničkim, hеmiјskim i/ili еlеktrоhеmiјskim pоstupcimа. Prеdmеt оvе disеrtаciје је istrаživаnjе аktivаciје stаklаstоg kаrbоnа еlеktrоhеmiјskоm, аnоdnоm ili kаtоdnоm pоlаrizаciјоm. Ispitаn је uticај rаzličitih еlеktrоlitа u kојimа је vršеnа pоlаrizаciја, kао i utucај pоtеnciјаlа i vrеmеnа pоlаrizаciје nа kоličinu nаеlеktrisаnjа u dvојnоm slојu, kао mеrе аktivnоsti еlеktrоdе. U drugоm dеlu disеrtаciје istrаžеn је fеnоmеn mоdifikаciје stаklаstоg kаrbоnа bаkrоm i srеbrоm, јеdnоstаvnim pоtаpаnjеm uzоrаkа u rаstvоrе kојi su sаdržаvаli јоnе pоmеnutih mеtаlа - AgNO3, оdnоsnо CuSO4. Auger (Оžе) еlеktrоnskоm spеktrоskоpiјоm - AES i fоtоеlеktrоnskоm spеktrоskоpiјоm X-zrаcimа - XPS, ustаnоvlјеnо је dа su nа pоvršini i u pоdpоvršinskim slојеvimа stаklаstоg kаrbоnа, nаkоn mоdifikаciје prisutni mеtаli u еlеmеntаrnоm, nulа vаlеntnоm stаnju. U pоsеbnоm dеlu disеrtаciје dеtаlјnо је izvršеnа еlеktrо-hеmiјskа i pоvršinskа (AES, XPS i STM) kаrаktеrizаciја srеbrоm mоdifikоvаnih uzоrаkа stаklаstоg kаrbоnа. Ispitаni su uticајi trајаnjа mоdifikаciје, kоncеntrаciје јоnа srеbrа u еlеktrоаnаlitičkim tеhnikаmа.- All metadata published by Europeana are available free of restriction under the Creative Commons CC0 1.0 Universal Public Domain Dedication. However, Europeana requests that you actively acknowledge and give attribution to all metadata sources including Europeana
The electrochemical behavior of ascorbic acid on a cobalt hydroxide modified glassy carbon (CHM-GC) electrode in alkaline solution was investigated. The process of the involved oxidation and its ...kinetics were established using the cyclic voltammetry, chronoamperometry techniques, as well as by steady state polarization measurements. The results revealed that cobalt hydroxide promotes the rate of oxidation by increasing the peak current; hence ascorbic acid is oxidized at lower potentials, which is thermodynamically more favorable. The cyclic voltammograms and chronoamperometry indicate a catalytic EC mechanism is operative with the electrogeneration of Co(IV) as the electrochemical process. Also, the process is diffusion-controlled and the current- time responses follow Cottrellian behavior. This result was confirmed by steady state measurements. The rate constants of the catalytic oxidation of ascorbic acid and the electron-transfer coefficient are reported.
Ispitivano je elektrohemijsko ponasanje askorbinske kiseline u alkalnoj sredini na elektrodi od staklastog ugljenika modifikovanoj kobalt-hidroksidom. Kinetika reakcije je odredjena koriscenjem ciklicne voltametrije, hronoamperometrije i stacionarnih polarizacionih merenja. Rezultati pokazuju da kobalt-hidroksid ubrzava reakciju oksidacije tako da se ona odigrava na nizim potencijalima. Ciklicna voltametrija i hronoamperometrija su pokazale da se reakcija odigrava po ES mehanizmu sa generisanjem Co(IV) vrste kao elektrohemijskim stupnjem. Proces je difuziono kontrolisan i zavisnost struje od vremena prati Kotrelovu jednacinu. Ovaj rezultat je takodje potvrdjen stacionarnim polarizacionim merenjem. Odredjene su vrednosti konstante brzine kataliticke oksidacije askorbinske kiseline i koeficijenta prelaza.
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