[lic] Kemian tekniikan korkeakoulu / CHEM

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Browsing [lic] Kemian tekniikan korkeakoulu / CHEM by Department "Kemian laitos"

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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.
  • 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