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Aalto University publication series

DOCTORAL DISSERTATIONS 39/2013

Proton Transfer Controlled Reactions

at Liquid-Liquid Interfaces

Pekka Peljo

Doctoral dissertation for the degree of Doctor of Science in

Technology to be presented with due permission of the School of Chemical Technology for public examination and debate in Auditorium KE2 (Komppa Auditorium) at the Aalto University School of Chemical Technology (Espoo, Finland) on the 5th of April, 2013, at 12 noon.

Aalto University School of Chemical Technology Department of Chemistry Research Group of Physical Chemistry and Electrochemistry Supervising professor Professor Kyösti Kontturi Thesis advisor Dr. Lasse Murtomäki Preliminary examiners Professor Robert Dryfe, University of Manchester, United Kingdom Professor Bin Su, Zhejiang University, China Opponent Professor Zdeněk Samec, J. Heyrovský Institute of Physical Chemistry of ASCR, Czech Republic Aalto University publication series DOCTORAL DISSERTATIONS 39/2013 © Pekka Peljo ISBN 978-952-60-5050-8 (printed) ISBN 978-952-60-5049-2 (pdf) ISSN-L 1799-4934 ISSN 1799-4934 (printed) ISSN 1799-4942 (pdf) http://urn.fi/URN:ISBN:978-952-60-5049-2 Unigrafia Oy Helsinki 2013 Finland Abstract Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Pekka Peljo Name of the doctoral dissertation Proton Transfer Controlled Reactions at Liquid-Liquid Interfaces Publisher School of Chemical Technology Unit Department of Chemistry Series Aalto University publication series DOCTORAL DISSERTATIONS 39/2013 Field of research Physical Chemistry Manuscript submitted 10 December 2012 Date of the defence 5 April 2013 Permission to publish granted (date) 12 February 2013 Language English Monograph Article dissertation (summary + original articles) Abstract Electrochemistry at liquid-liquid interfaces has been a versatile area of contemporary electrochemistry for almost 40 years, with research mainly focusing on the aqueous-organic solution interface. The Galvani potential difference across such an interface, controlling the distribution of ions between the phases, can be generated either chemically or with an external voltage source. An aqueous-organic solvent interface shares similaritieswith the cell membrane, where several important biological reactions such as photosynthesis or cell respiration take place. Hence electrochemistry at liquid-liquid interfaces is an excellent means to study biomimetic oxygen reduction. In this reaction, proton transfer across the interface controlled by the Galvani potential difference is coupled with electron transfer. Therefore oxygen reduction in the oil phase mediated by an electron donor occurs only at potentials where proton transfer becomes feasible.

In this thesis oxygen and hydrogen peroxide reduction by 1,2-diferrocenylethane was investigated. The results show that the reduction of hydrogen peroxide is faster than oxygen reduction, but both reactions were slow due to the low thermodynamic driving force. The reaction rate can be increased by the addition of molecular catalysts, and electrochemistry at liquid-liquid interfaces provides an excellent means to compare the activity and selectivity of the catalysts. Cofacial biscobalt porphyrins, biomimetic analogues of the active centre of cytochrome c oxidase responsible of oxygen reduction in nature, were investigated.

Surprisingly, significant amounts of hydrogen peroxide were produced, contradicting previous results. The reaction was shown to proceed to hydrogen peroxide when oxygen was bound to the exo side (dock-on) of the catalyst, while four-electron reduction took place with oxygen bound to the endo side (dock-in) of the molecule.

A proof of concept of a novel type of a fuel cell utilising the liquid-liquid interface is presented.

In this fuel cell hydrogen is oxidized on the anode as in a conventional fuel cell, but oxygen reduction takes place at the liquid-liquid interface. The redox mediator in the oil phase is regenerated at the cathode, completing the electric circuit.

Proton transfer across the interface was also utilised for performing acid catalysed SN1 substitutions on ferrocene methanol. This is a novel method to perform synthesis of organic chemicals, as the presence of protons is controlled by the applied Galvani potential difference.

In situ biphasic electrospray ionization mass spectroscopy was demonstrated to be a very efficient way to follow this kind of reactions.

–  –  –

Tekijä Pekka Peljo Väitöskirjan nimi Protonin siirron kontrolloimat reaktiot neste-nesterajapinnalla Julkaisija Kemian tekniikan korkeakoulu Yksikkö Kemian laitos Sarja Aalto University publication series DOCTORAL DISSERTATIONS 39/2013 Tutkimusala Fysikaalinen kemia Käsikirjoituksen pvm 10.12.2012 Väitöspäivä 05.04.2013 Julkaisuluvan myöntämispäivä 12.02.2013 Kieli Englanti Monografia Yhdistelmäväitöskirja (yhteenveto-osa + erillisartikkelit) Tiivistelmä Neste-nesterajapintojen sähkökemia on ollut yksi modernin sähkökemian osa-alueista jo lähes 40 vuoden ajan. Tutkimus on pääasiassa keskittynyt varauksensiirtoon veden ja orgaanisen liuoksen välisellä rajapinnalla. Faasien välinen galvaanipotentiaaliero, joka kontrolloi ionien jakautumista niiden välillä, saadaan aikaan joko kemiallisesti tai ulkoisella jännitelähteellä. Monet luonnossa tapahtuvat tärkeät reaktiot, kuten fotosynteesi tai soluhengitys, tapahtuvat solukalvossa, joka muistuttaa veden ja orgaanisen liottimen rajapintaa. Siksi nestenesterajapintojen sähkökemia on erinomainen tapa tutkia bio- mimeettistä hapen pelkistystä.





Hapen pelkistyksessä galvaanipotentiaalieron kontrolloima protonin siirto kytkeytyy yhteen elektroninsiirron kanssa. Happi pelkistyy orgaanisessa faasissa vain, kun faasien välinen galvaanipotentiaaliero on niin suuri, että protoni voi siirtyä rajapinnan yli.

Tässä työssä tutkittiin hapen ja vetyperoksidin pelkistämistä 1,2-diferrosenyylietaanilla.

Tulokset osoittivat, että vetyperoksidin pelkistys on hapen pelkistystä nopeampaa, mutta molemmat reaktiot ovat hitaita heikon termodynaamisen ajavan voiman takia. Reaktiota voidaan nopeuttaa käyttämällä molekulaarisia katalyyttejä, ja neste-nesterajapintojen sähkökemia on erinomainen tapa vertailla eri katalyyttien selektiivisyyttä ja aktiivisuutta.

Työssä tutkittiin sytokromi-c-oksidaasin aktiivista keskusta muistuttavia biskobolttiporfyriinejä, sillä sytokromi-c-oksidaasi on ainoa luonnollinen happea pelkistävä entsyymi.

Yllätykseksemme nämä katalyytit tuottivat merkittäviä määriä vetyperoksidia edellisten tulosten vastaisesti. Tulokset osoittivat, että vetyperoksidia syntyy hapen sitoutuessa katalyytin ulkopuolelle, ja pelkistys vedeksi tapahtuu hapen sitoutuessa bisporfyriinin sisälle, joten hapen pelkistys biskobolttiporfyriineillä tapahtuu ”dock-on/dock-in” mekanismin mukaisesti. Hapen pelkistystä neste-nesterajapinnalla voidaan myös käyttää uudenlaisessa polttokennossa. Kennossa vety hapettuu anodilla kuten tyypillisessäkin polttokennossa, mutta happi pelkistyy neste-nesterajapinnalla. Redoxmediaattori regeneroidaan katodilla, mikä sulkee sähköisen virtapiirin.

Protonin siirtoa neste-nesterajapinnan yli voidaan käyttää myös katalysoimaan ferroseenimetanolin SN1-substituutiota. Tässä uudenlaisessa orgaanisten kemikaalien synteesimenetelmässä reaktio voidaan aloittaa tai lopettaa kontrolloimalla galvaanipotentiaalieron avulla katalyytin eli protonin konsentraatiota orgaanisessa faasissa.

Kaksifaasinen elektronisuihkuionisaatiomassaspektroskopia osoittautui erinomaiseksi tekniikaksi tämänkaltaisten reaktioiden seurantaan ja reaktiotuotteiden analysointiin.

Avainsanat neste-nesterajapinnat, sähkökemia, elektrokatalyysi, hapen pelkistys, protoninsiirtokatalyysi, polttokennot, protoninsiirtoon kytketty elektroninsiirto ISBN (painettu) 978-952-60-5050-8 ISBN (pdf) 978-952-60-5049-2 ISSN-L 1799-4934 ISSN (painettu) 1799-4934 ISSN (pdf) 1799-4942 Julkaisupaikka Espoo Painopaikka Helsinki Vuosi 2013 Sivumäärä 158 urn http://urn.fi/URN:ISBN:978-952-60-5049-2 Preface The work presented in this thesis was carried out mainly at the Research Group of Physical Chemistry and Electrochemistry, Department of Chemistry, Aalto University between December 2009 and December 2012. The work for Publication I and partly for III was performed at Laboratoire d’Electrochimie Physique et Analytique, Ecole Polytechnique Fédérale de Lausanne, Switzerland, between September 2011 and February 2012. I am grateful for the financial support for this project from the Academy of Finland and for my visit to Switzerland from the Magnus Ehrnrooth foundation.

Firstly, I would like to express my gratitude for my supervisor Prof. Kyösti Kontturi for giving me the opportunity and arranging the funding to study this interesting topic for my post graduate studies. I would also like to thank my thesis advisor Dr. Lasse Murtomäki for all the helpful discussions and suggestions during this work, as well as Dr. Tanja Kallio for her help and comments regarding especially the fuel cells but also other parts of this work.

Additionally, I am also grateful for Dr. Christoffer Johans for all the discussions concerning the electrochemistry at liquid-liquid interfaces.

Secondly, I am grateful to Prof. Hubert Girault for the opportunity to spend six months at LEPA, as well as for all the helpful discussions, constant enthusiasm and exiting new ideas during this work. Related to my time in Lausanne, I want to thank my co-authors Mr.

Haiqiang Deng, Ms. Peiyu Ge and Dr. Fernando Cortés-Salazar for the help, input and company during this work and Mr. Liang Qiao for sparing some time to try something new with his ESI-MS set-up. I also want to thank Mrs. Astrid Olaya for her input and suggestions, and for her patience with the SSHG set-up. Additionally, I wish to thank all the people at LEPA, especially Dr. Micheal Scanlon and Dr. Kathryn Toghill, for the good time in Lausanne. Also not forgetting the Chinese group, it was very nice to go hiking or skiing on the Swiss Alps.

I am also grateful to my other co-authors Dr. Hai-Jun Xu, Dr. Michel Meyer, Dr. Claude P.

Gros and Prof. Jean-Michel Barbe from Institut de Chimie Moléculaire de l’Université de Bourgogne, Dijon, for fruitful collaboration and for all the help, suggestions and feedback during the preparation of the manuscript. Prof. Kari Laasonen from Aalto University is acknowledged for coming to our rescue with his DFT calculations when experimental results were giving unexpected results.

Special thanks belong to my summer workers Ms. Taina Rauhala, Mr. Taneli Rajala and Mr Carsten Mecke for all the good work they did when I was away sailing. The valuable help from Mr. David Lloyd, Dr. Ben Wilson and Dr. Kathryn Toghill for proof-reading the thesis is gratefully acknowledged.

Many thanks belong to all the personnel and PhD students of the laboratory of Physical Chemistry and Electrochemistry. Special thanks go for all the people in the fuel cell group, Dr. Annukka Santasalo-Aarnio, Mr. Petri Kanninen and Mr. Sami Tuomi, for all the help and suggestions during this work, and I also want to thank Petri for sharing the office with me for the past years. Big thanks also for Dr. Kirsi Yliniemi, Dr. Ben Wilson, Lic. Sc. (Tech.) Nguyet Doan, Ms. Maija Huuppola, Mr. David Loyd, Ms. Elina Pohjakallio and Mr. Tuomas Vainikka. It has been a pleasure to share my lunch and coffee breaks with you and to work here with you, making my life at FyKe a pleasant experience. Whenever I had some technical or theoretical problems, you were always ready to help. Thank you also for the technical staff of the lab, especially Dr. Annu Kontturi and Mrs. Marjut Vähänikkilä.

Finally, I would like to thank all my family and friends for being there as a counterbalance to my work. I am grateful for all your help and support with my life in general. It is good to know that you are there ready to share my problems or just go sailing with me. And to Katja, thank you for making the last few years much better just by being there.

Espoo, 24.1.2013 Pekka Peljo Contents 1 Introduction

2 Electrochemistry at Liquid-Liquid Interfaces

2.1 Interface between Two Immiscible Electrolyte Solutions

2.2 Structure of the Liquid-Liquid Interface

2.3 Thermodynamics of the ITIES

2.4 Charge Transfer at the Liquid-Liquid Interface

2.4.1 Ion Transfer at the Liquid-Liquid Interface

2.4.2 Facilitated Ion Transfer at the Liquid-Liquid Interface

2.4.3 Electron Transfer at the Liquid-Liquid Interface

2.4.4 Photoinduced Charge Transfer at Liquid-Liquid Interfaces

3 Experimental Procedures

3.1 Four-Electrode Cell Experiments

3.2 Two-Phase Reactions with Chemically Controlled Polarisation

3.2.1 Analysis of the H2O2 Produced in the Two-Phase Reaction

3.3 Ultramicroelectrode Experiments

3.4 Electrospray Ionization Mass Spectrometry

3.5 Fuel Cell Experiments

4 Proton-coupled Electron Transfer at Liquid-Liquid Interfaces

4.1 Proton-coupled Electron Transfer Reactions

4.2 Oxygen Reduction at the ITIES

4.2.1 Oxygen and Hydrogen Peroxide Reduction by 1,2-diferrocenylethane.................. 25 5 Electrocatalysis at the ITIES

5.1 Colloidal Electrocatalysis at the ITIES

5.2 Molecular Electrocatalysis at the ITIES

5.2.1 Biomimetic Catalysis for Oxygen Reduction with Cofacial Porphyrins................. 37 6 Proton Transfer Catalysed Reactions at Liquid-Liquid Interfaces

6.1 Cyclic Voltammetry of Ferrocene Methanol in a Four-Electrode Cell

6.2 Proton Transfer Catalysed SN1 Substitution to Ferrocene Methanol

7 Fuel Cell Utilising a Liquid-Liquid Interface

8 Conclusions

8.1 Recommendations for Further Work

References

List of Publications This thesis consists of an overview and of the following publications, which are referred to in the text by their Roman numerals.



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