[lic] Kemian tekniikan korkeakoulu / CHEM

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Browsing [lic] Kemian tekniikan korkeakoulu / CHEM by Degree programme/Major subject "Fysikaalinen kemia"

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  • Biomimetic Oxygen Reduction at Liquid-Liquid Interfaces: From Electrocatalysis to Fuel Cell Applications
    (2012) Peljo, Pekka
     School of Chemical Engineering | Licentiate thesis
    Research on new electro catalysts materials is important, because of the high price and restricted availability of the best available catalyst, platinum. In nature, oxygen reduction in cell respiration is catalysed by an iron porphyrin/copper center. Hence, similar biomimetic structures could be highly active and selective molecular catalysts. In this thesis oxygen reduction catalysed by a molecular catalyst is studied with electrochemistry at the interface between two immiscible electrolyte solutions (ITIES). Firstly, a hybrid fuel cell utilizing a liquid-liquid interface for H2O2 production is demonstrated. In this fuel cell hydrogen is oxidized at the anode as usual, but oxygen reduction catalysed by a cobalt porphyrin takes place at the water-1,2-dichlorobenzene interface by a redox mediator, which is regenerated at the cathode. Oxygen reduction is coupled with proton transfer from water to the organic phase to form hydrogen peroxide, which is extracted into an aqueous phase. Secondly, electrocatalysis of oxygen reduction by cofacial "Pacman" porphyrins is investigated at the lTIES. The experiments and density functional theory calculations show that oxygen reduction to H2O2 is catalysed when oxygen is bound on the exo side of the molecule, while four-electron reduction takes place with oxygen bound on the endo side of the molecule. A new mechanism is presented to explain the results.
  • The dissolution kinetics of sphalerite concentrates
    (2005) Aaltonen, Mari
     Licentiate thesis
    In the literature part of the thesis, an overview of the mechanisms and kinetics of oxidative sphalerite dissolution was given. The factors affecting the rate of dissolution and some methods of study were briefly described. In the experimental part various methods were used. In batch dissolution experiments with manganese dioxide and ferric ions as the oxidising species, it was found that MnO2 affects the dissolution of a sphalerite concentrate by two mechanisms: by directly oxidising the sulphur in the mineral and by regenerating the active ferric species. The results also suggested further oxidation of the elemental sulphur layer by the manganese species. The dissolution behaviour of two sphalerite concentrates was studied by batch dissolution experiments using ferric ions as the oxidant. Fractions with particle sizes of < 37 µm and > 37 µm were used. The measurement parameters were chosen to match those in industrial scale dissolution. The average zinc conversions for the fractions were from 45 to 74 mass percent after 3 hours dissolution. The conversions were strongly effected by the size fraction of the concentrate, temperature and the concentration of iron in the solution. The effects of the sulphuric acid and zinc concentrations were on average negligible. As expected, the concentrate fraction with the largest surface area per gram had the highest conversion and the conversions decreased with decreasing surface area. The average conversion divided by the surface area of the concentrate was 15 m-% higher for the concentrate with a higher concentration of iron in the lattice. A rotating ring disc electrode was constructed, in which a pressed concentrate pellet was used as the disc. The Fe2+ ions formed by the dissolution of ZnS in the disc were detected on the platinum ring by oxidising them back to the ferric form. The measured current was used to determine the rate of dissolution. The method is fast and thus can be used for rapid comparison of the dissolution characteristics of different concentrate fractions under varying conditions. In addition, the method allows for the effects of kinetics and transport processes on the current to be separated, allowing a closer study of the factors affecting the kinetics of the reaction. Theoretical calculations of the rate of mass transfer showed, that kinetics are rate limiting under these conditions. Increasing the mass transport in the solution will not increase the rate of the dissolution process; the conditions have to be made more favourable for faster kinetics. A mineral-carbon paste electrode was constructed by mixing sphalerite concentrate with fine carbon powder and oil. Cyclic voltammetric measurements showed the carbon-oil paste electrode to be inert under the conditions used. The voltammetric and potentiostatic measurements conducted on the modified mineral electrode showed the effect of the electrode potential on the rate of dissolution. The oxidation of the sulphide began above 0.8 V vs. Ag/AgCl and the rate was increased with increasing potential until a maximum was reached at 1.2 V vs. Ag/AgCl.
  • Electrocatalysis of organic molecules on platinum catalysts surfaces: from the fundamentals to the polymer electrolyte fuel cell applications
    (2009) Santasalo, Annukka
     Kemian ja materiaalitieteiden tiedekunta | Licentiate thesis
    Orgaanisia polttoaineita käyttäviä polymeerielektrolyyttipolttokennoja (PEPK) voidaan käyttää energianlähteinä pienissä, kannettavissa sovellutuksissa korkeiden tehotiheyksiensä vuoksi. Nestemäiset polttoaineet kuten alkoholit ovat kiinnostavia polttoaineita kuluttajasovellutuksiin, koska ne ovat turvallisempia ja helpompia käyttää kuin kaasumaiset polttoaineet. Vaikka orgaanisia polttoainevaihtoehtoja on tutkittu jo vuosikymmeniä, niiden adsorptiota ja hapettumista platinakatalyyttien pinnalla ei vielä tunneta kunnolla, mikä on edellytyksenä käytännön sovellusten suunnittelussa. Työn kirjallisessa osassa käsitellään orgaanisten molekyylien elektrokatalyysiä eli niiden adsorboitumista sekä hapettumista erilaisille platinakatalyyttipinnoille. Näihin ilmiöihin vaikuttavat erityisesti valittu elektrodimateriaali, liuoksissa olevat ionit ja molekyylit sekä elektrodin potentiaali, joiden matemaattisia tarkasteluja voidaan käyttää hyväksi arvioitaessa elektrodimateriaalin soveltuvuutta tietyn orgaanisen aineen elektrokatalyysiin. Kokeellinen osa koostuu kahdesta julkaistusta artikkelista sekä lisämittauksista yksikide-elektrodeilla. Ensimmäisessä artikkelissa on tutkittu erilaisten orgaanisten, pienimolekyylimassaisten komponenttien kulkeutumista paljon käytetyn Nafion 115 membraanin läpi ajan funktiona sekä näiden polttoaineiden suorituskykyä PEPK:ssa. Metanoli pienikokoisimpana, varautumattomana molekyylinä kulkeutui nopeitten tutkitun membraanin läpi, mutta sillä saatiin korkeimmat virrantiheydet platina-ruteniumkatalysoidussa polttokennossa. Vaikka muut molekyylit eivät saavuttaneet metanolin kaltaisia virrantiheyksiä, isopropanolilla saavutettiin metanolia huomattavasti korkeampi avoimen virtapiirin jännite. Toisessa julkaisussa on näiden tulosten pohjalta tutkittu metanolin, isopropanolin sekä niiden muodostaman seoksen hapettumista elektrodeilla, joiden pinta-atomit ovat järjestäytyneet yhden kiderakenteen mukaisesti. Korkeimmat virrantiheydet alkoholiseokselle kummassakin happamassa elektrolyytissä saatiin Pt(111) kidepinnalla, joten lisämittauksia suoritettiin elektrodeilla, joilla oli Pt(111) suuntautuneet terassit sekä Pt(100) tai Pt(110) suuntautuneet askelmat. Tämän lisäksi 2- propanolin sekä alkoholiseoksen hapettumistuotteita tutkittiin infrapunaspektroskopialla, jolla havaittiin että molemmat puhtaat alkoholit alkoholiseoksesta sekä adsorboituvat että hapettuvat Pt(111) pinnalla. Valitettavasti selvyyttä siihen miten alkoholiseos edesauttaa isopropanolin hapettumista, ei näillä mittausmenetelmillä saatu.
  • Kuparibentsoaattikompleksien sähkökemiallinen karakterisointi
    (2010) Repo, Eveliina
     School of Chemical Engineering | Licentiate thesis
    In this work electrochemistry of immobilized and free Cu(II) benzoate compexes were studied. The literature part included an introduction of the grafting technique of electrode surface by reduction of diazonium salts, the properties of the grafted layers and the parameters that affect their properties, the properties of Cu(II) benzoate complexes in the solution and solid phase, and the effects of amine ligands on the properties of Cu(II) benzoates. In the experimental part the properties of the grafted electrodes as well as free Cu(II)-benzoate complexes were studied. At first, the blocking effect of benzoate groups immobilized on the gassy carbon and gold electrodes was investigated. The blocking was much more significant in the case of glassy carbon than gold. This was attributed to the lateral orientation of benzoate groups on the gold surface. In addition, the electrochemical properties of immobilized Cu(II) benzoate complexes were studied using cyclic voltammetry. Complexes formed on the god surface were unstable. The reaction mechanism of the Cu(II) benzoates grafted on the glassy carbon electrode was best described by the ECEC mechanism. Cu(II) centres were presented to locate in different environments on the layer and the large values of the peak widths observed in cyclic voltammograms were explained by the deviation of formal potential of Cu(II). Finally, the properties of free Cu(II) benzoate complexes with different amine ligands were studied. Amine ligands affected the stability of the complexes. The complex with pyridine ligands was found to be unstable. The characteristics of cyclic voltammograms of Cu(II) benzoate with bipyridine ligands indicated on the disproportionation reaction mechanism.
  • Studies of synthesis, oxidation and surface assembly of cobalt and gold nanoparticles
    (2011) Doan, Nguyet
     School of Chemical Engineering | Licentiate thesis