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Author:Peljo, Pekka
Title:Biomimetic Oxygen Reduction at Liquid-Liquid Interfaces: From Electrocatalysis to Fuel Cell Applications
Biomimeettinen hapen pelkistys neste-nesterajapinnalla; elektrokatalyysistä polttokennosovelluksiin
Publication type:Licentiate thesis
Publication year:2012
Pages:ix + 44 s. + liitt. 48      Language:   eng
Department/School:Kemian laitos
Main subject:Fysikaalinen kemia   (Kem-31)
Supervisor:Kontturi, Kyösti
Instructor:Murtomäki, Lasse
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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In the closed network of Learning Centre you can read digital and digitized theses not available in the open network.

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Location:P1 Ark Aalto  2343   | Archive
Keywords:oxygen reduction
electrocatalysis
ITIES
hapen pelkistys
elektrokatalyysi
Abstract (eng): 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.
Abstract (fin): Uusien elektrokatalyyttimateriaalien tutkimus on tärkeää, koska paras saatavilla oleva katalyytti, platina, on hyvin kallista ja sitä on saatavilla rajallisesti.
Yksi mahdollisuus on ottaa mallia luonnosta: soluhengityksessä happi pelkistyy rautaporfyriinin ja kupariatomin muodostamassa aktiivisessa keskuksessa, jota jäljittelemällä voitaisiin saada aktiivisia ja selektiivisiä molekulaarisia katalyytteja.
Tässä työssä tutkittiin molekulaaristen katalyyttien katalysoimaa hapen pelkistystä neste-nesterajapinnalla.

Työssä esitellään vetyperoksidia tuottava neste-nesterajapintaa hyödyntävä molekulaarinen hybridipolttokenno.
Vedyn hapetus tapahtuu anodilla kuten normaalissakin polttokennossa, mutta happi pelkistyy kobolttiporfyriinin katalysoimana vesi-1,2-diklooribentseenirajapinnalla.
Pelkistimenä käytetään redoxmediaattoria, joka regeneroidaan katodilla.
Hapen pelkistys vaatii protonin siirron vesifaasista öljyfaasiin, ja syntyvä vetyperoksidi uutetaan vesifaasiin.

Toiseksi tutkittiin "Pacman"-porfyriinien katalysoimaa hapen pelkistystä nestenesterajapinnalla.
Kokeet ja teoreettiset tiheysfunktionaalilaskut osoittavat, että vetyperoksidia syntyy hapen sitoutuessa katalyytin ulkopuolelle, ja pelkistys vedeksi tapahtuu hapen sitoutuessa porfyriinin sisälle.
Tulokset voidaan selittää uudella reaktiomekanismilla.
ED:2012-09-04
INSSI record number: 45203
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