UCL Department of Chemistry European Synchrotron Radiation Facility Dutch-Belgian Beamline Formation and Electrocatalysis Studies of Nickel and Iron Sulfide Catalysts using in situ XAS Thesis submitted for the degree of Doctor of Engineering (EngD) by Husn-Ubayda Islam Supervisors Prof. Richard Catlow, Prof. Gopinathan Sankar, and Dr. Wim Bras August 2016 Declaration I, Husn-Ubayda Islam confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. Signed: Date: Abstract X-ray absorption spectroscopy (XAS) is an atom specific characterisation technique. It is particularly useful for understanding dilute systems of short range order. When used in situ during reaction processes, the technique is a powerful tool to study the evolving local structure of materials. In this thesis, XAS is used to understand the synthesis, stability, and electrocatalytic activity of iron sulfides. A popular route to the synthesis of nanoparticulate sulfides is the solvothermal decomposition of transition metal dithiocarbamates. These single source precursors are typically dissolved in a coordinating solvent and heated rapidly. The coordinating solvent acts as a heat sink and capping agent but its role in each decomposition process is less understood. Here, it is shown through ex situ and in situ XAS that the coordinating solvent has significant effect on the starting material and decomposition process through coordination to the transition metal centre and reaction with the dithiocarbamate backbone. Case studies include the decomposition of zinc dimethyl, and nickel and iron diisobutyl dithiocarbamates in oleylamine. The solvothermal decomposition of iron or iron and nickel diisobutyl dithiocarbamate in the presence of thiuram disulfide results in the formation of Fe3S4 or NiFe2S4 nanoparticles. These inverse spinel structures are formed as hexagonal sheets with 001 and 111 surfaces which are predicted to be electrocatalytically active. The oxidation of the systems in electrolyte during cyclic voltammetry – a process that is thought to reduce catalytic activity – is investigated by in situ XAS. Acknowledgments I walked into the department of chemistry about a decade ago and never looked back. It was the warm welcome I received from Saeed, and the relaxed attitude of Dewi Lewis that convinced my otherwise hesitant and unsure self. I would like to thank them for that initial push. Four years later, I met my Masters supervisor Adam McKay. He had an interest in instrumentation and characterisation that I could relate to, and his dedication and determination were inspirational. He also convinced me to continue in research and although I didn’t take a PhD with him, the impact he had on my life and the confidence he instilled in me was vast. Thanks Adam. I was fortunate to work under the supervision of four great researchers over the next four years. I thank Nora de Leeuw for taking me on and giving me opportunities that I could only have dreamed of. She is a woman whom I greatly admire, and I look forward to working with her in the future. I would like to thank Wim Bras for being a brilliant industrial supervisor and an even better guardian when I moved to France three years ago. Wim is the ambassador of political incorrectness but his advice is sound and he has always had my best interests at heart. I would also like to thank Richard Catlow for keeping a keen eye on my work and making sure I was on track. Finally, a special thanks is given to Gopinathan Sankar. I was very lucky to be taken under his wings: his enthusiastic ideas and suggestions formed the pillars of this thesis, and when I realised he could manipulate EXAFS software like a don, I learnt some of that from him too. Nora’s CO2 consortium was a wonderful group to be a part of. It was designed as a pool of resources and expertise that we could all benefit from in order to produce something significant. Through this group I met Nathan whose passion for scientific research was commendable, and passion for chocolate endearing. I thank him for being my closest ally through these four years with everything that that entailed. I would also like to thank Alberto, Josie, and Maxime, as well as Graeme Hogarth, Katherine Holt, Mariette Wolthers, and Meleke Balk. It becomes evident in following chapters that their contributions to my work are critical. I thank them for their input, extensive discussion, and beamtime assistance. Also, thank you Anna and Siti; as fellow students you should not have been as patient with me as you were. Thank you so much for your help, your presence at beamtimes and your materials. I thank Sankars and Richard’s “old” group at the KLB as they were my mentors during the first EngD year. Speaking technically, Andy, Jon and Martin taught me software basics, and Vlad sat with me through my first ever beamtime. On a personal level, I had the time of my life with these guys and I consider them friends along with Rozie, Jeff, Nazar, and Tiffany. They were and are inspirational. The second and third year of my EngD were completed at the ESRF. I will never forget the kindness of all the beamline staff, especially Dip who took care of my needs during countless beamtimes, as well as giving me time off the books; Dirk who on a number of occasions quietly scoured the whole synchrotron to find me a tool that I could benefit from; Florian who said “Salut Ooshna” to me every morning; the dubble act Giuseppe and Daniel; my unlikely best friend Alessandro; and the occasional, friendly faces of Halina and Jim. Thanks also to Sergey and Alex. A special acknowledgment is reserved for the CRG liaison officer Murielle; she dealt with an immense out-of-hours workload on my behalf starting with finding me accommodation, a bank, an insurer, becoming my guarantor, and continuing to support me. I am eternally grateful to her because she made life in France that much easier. When I came back from France in my final year, I met the “new” Sankar group. Huw Glen, Ian, Abdul, Zarrin, and Anastasia were a pleasure to work with. Though young, they are wise, respectful, and intelligent beyond their years. They work very well together, and under the guidance of Sankar, are a formidable team. A special thanks is given to Tom Daley (not the diver) for always having my back. We started our undergrad and our EngD’s at the same time, and are likely to finish together. He has been a loyal and professional colleague. My friends Iman, Meetal, Leila, and Sacha fall into the same category. I am grateful that I got to experience this journey with them. Finally, I would like to thank my family. I am lucky to belong to this one because it is full of wonderful characters including my three brothers Humza, Yaqoub, and Yusuf, and my cute sister Hufsa, as well as mum, dad, and my gran. They have seen me at my very best and absolute worst but have remained patient and loving. The constant encouragement I get from mum, and her unfaltering conviction, makes impossible things possible. I am a lucky woman who has had opportunities that women from my background do not always have access to, and this is in part due to the progressive attitude of my parents. My family includes my closest and dearest friends Safia, Shazna, and Ateeqa, and my amazing aunts, uncles and cousins. I would like to thank them all for their support and encouragement. I am glad to say I’m almost there thanks to you! Contents List of Figures ......................................................................................................................... 9 List of Tables ........................................................................................................................ 16 List of Equations .................................................................................................................. 17 List of Samples ..................................................................................................................... 18 List of Communications ...................................................................................................... 19 Chapter 1 Overview ............................................................................................................. 20 Chapter 1 .............................................................................................................................. 21 Iron sulfides: structure, synthesis, and applications ......................................................... 21 1.1 Introduction ............................................................................................................. 21 1.1.1 The sulfur cycle ................................................................................................................. 22 1.1.2 Deep sea hydrothermal vents ............................................................................................. 23 1.1.3 Iron sulfur world theory ..................................................................................................... 24 1.1.4 Iron sulfides in nature ........................................................................................................ 25 1.2 Iron sulfide minerals ............................................................................................... 26 1.2.1 Iron sulfide clusters ............................................................................................................ 26 1.2.2 Mackinawite .....................................................................................................................