Energy Storage and Conversion Applications of Transition Metal Oxide Nanoflakes. A thesis submitted to the University of Dublin, Trinity College Dublin for the degree of Doctor of Philosophy in Chemistry by Aurélie A.S. Rovetta Under the supervision of Prof. Michael E.G. Lyons. School of Chemistry & CRANN Trinity College Dublin 2017 Energy Storage and Conversion Applications of Transition Metal Oxide Nanoflakes. Aurélie A.S. Rovetta Abstract In this work, MoO3 and Co(OH)2 were prepared via liquid phase exfoliation (LPE) and tested for application as supercapacitor materials and for a catalyst material for the oxygen evolution reaction (Co(OH)2 only). LPE was shown to be an effective synthetic route to prepare large quantities of high quality few layer 2-D nanosheets. When combined with liquid cascade centrifugation it allowed the size selection of the flakes within a narrow range. In chapter 4, the intercalation of lithium and potassium into MoO3 film was studied. For potassium intercalation, the influence of the support was the first parameter examined. Three carbon based support, glassy carbon, edge and basal plane pyrolytic graphite, were drop coated with the MoO3 flake suspension and double layer capacitance values of 11 mF g-1 for glassy carbon, 20 mF g-1 for pyrolytic graphite edge plane and 43 mF g-1 for basal plane were observed. The influence of the coating technique was assessed. The suspension was sprayed and phase transferred onto an ITO support electrodes and were found to have double layer capacitance values of 68 and 26 mF g-1 respectively. Lithium intercalation, for sprayed and phase transferred films displayed double layer values of 25 and 139 mF g-1 respectively. Impedance spectroscopy investigation on the pseudocapacitive behaviour in each medium lead to respective value of 20 and 840 mF g-1 for potassium and lithium intercalations. Sprayed molybdenum oxide films were found to be comparable to the state of the art Fe2O3 anode materials, with an energy storage ability of 0.57 kJ g-1. In chapter 5, cobalt hydroxide was examined for its energy storage applications and activity for the oxygen evolution reaction. Porous glassy carbon and nickel foam support electrodes were used and compared, with Co(OH)2 coated on the latter showing to be superior for both applications. After evaluating the influence of the Co(OH)2 flake size on the performance of the catalyst prepared via spray coating, a standard size (mean size 84 nm) was chosen as it offered the best compromise between preparation time/yield and activity. Both capacitive and catalytic performances were evaluated as a function of Co(OH)2 mass loading and an optimum loading of 1/2 Energy Storage and Conversion Applications of Transition Metal Oxide Nanoflakes. Aurélie A.S. Rovetta 1 mg cm-2 and 0.89 mg cm-2 was found for supercapacitor and OER applications respectively. Both coated supports compared favourably with the current state of the regarding the supercapacitive behaviour reaching capacitance values of 400 and 2000 F g-1, GC and Ni foams. For glassy carbon, the overpotential value at 10 mA cm-2 decreased from 870 mV down to 380 mV, with a small mass loading dependency. The OER catalytic properties of Co(OH)2 flakes on Ni foam presented a mass loading goldilocks region, emphasising the compromise between amount of catalyst deposited and film conductivity/diffusion limitations. The overpotential at 10 mA cm-2 for a bare Ni foam was comparable to a coated GC foam with a value of 400 mV. This value was lowered for Co(OH)2/Ni foam, reaching an optimal value of 280 mV with a mass loading of 0.89 mg cm-2. This system had a TOF of 2.08x10-3 s-1 and a Tafel slope value of 58 -1 mV dec . Moreover, all Co(OH)2 coated electrodes were shown to be stable for 24-hours at 10 mA cm-2. Electrical representation using equivalent circuits of the bare and coated foams was performed using electrochemical impedance spectroscopy. In chapter 6, the work focused on testing Co(OH)2 under conditions similar to that used in industrial electrolysers by operating at elevated temperatures, in more concentrated alkaline solution and at higher current densities. When studying the system in different alkaline solutions the influence of the viscosity of the electrolyte was shown to affect the performances of the Co(OH)2 coated nickel foams with an optimal concentration of 5 M NaOH chosen. The -2 overpotential values of Co(OH)2/Ni foam at 50 °C, 10 and 100 mA cm , were measured to be 162 mV and 201 mV respectively. When in a two-electrode cell configuration, where the Co(OH)2 coated foam is both the anode and cathode in the absence of a reference electrode which corresponds to an industrial electrolyser configuration, a cell voltage of 2.0 V was observed at -2 100 mA cm . In addition it was shown that Co(OH)2 was stable at current densities up to 500 mA cm-2 for at least 24 hours. 2/2 Declaration I declare that the work in this thesis has not been submitted as an exercise for a degree at this or any other university and it is entirely my own work. Due acknowledgment and references are given to others were appropriate. I agree to deposit this thesis in the University’s open access institutional repository or allow the library to do so on my behalf, subject to Irish Copyright Legislation and Trinity College Library conditions of use and acknowledgement. Aurélie Rovetta, October 2017 ______________________ i Acknowledgments First of all, I would like to thank my supervisor Prof. Michael Lyons for giving me the chance of learning and growing with this Ph.D. opportunity. The past four years were not t always the easiest but they made this experience even more precious and valuable. I discovered Ireland and fell in love with the country and its people. Despite my Fr-English, more often written than spoken, we had laughs, constructive conversation, unique experiences (including a student mixture) and so much more. I would like to thank Mike for his professional advice and all the memories that I wouldn’t have if he didn’t take that bet on “the French girl”. I would also like to thank Damaris, Patsy, Mark, Tom, Noelle, Tess, Helene and all the other people I forgot to name who were there to make all moments memorable and so enjoyable. No typical working days indeed but the atmosphere made me want more. Thank you! I would like to express a special thank you to Dr. Guy Broze who was my final year master’s supervisor in Belgium. Guy, you are the one who gave me that speech about how a thesis wasn’t the end of the funnel but was the adventure opening to new life perspectives. You guided me and made me believe in myself telling me that my head was built to face such challenges. Despite being far away from each other (that can be sorted) I wanted you to know that you will always have a special place in my life and what it’s about to become. When I first arrived in Trinity, everything changed, new country, new language, new habits, like some people say “It was tough at the top”. Then that lovely, not so little, lovely blonde came into my life. I first had to get your name, Michelle, the Cabra accent can be so strong!! You were here every step of the way and God knows that administrative work is a worldwide maze. You made me improve my English, and the accent was a big part of the problem, that thanks to you I did pass that English test in one go. We went through hell and back, tears, laughs, trips, parties... I don’t need to go further you are part of my life for good. After all you taught me that wine wasn’t only a heritage from my country but on a more philosophical note a “glass of grapes”. I made fantastic friends, Bryan, Rob, Colm, Eoin, Andy, Hugo who understand what a Ph.D. life is like. A lovely mess if I may add, the barbecues, the dancing, the wizard tournament, all were ii fantastic adventures. I would like to say to all my “old” friends, Nathalie, Lucas, Angeline and the others that there is no reason to be afraid they are unique and will be forever in my heart. When I finally got the courage to start getting into shape, I met the wonderful Tamara. “Hey how are you doing? …. What are you studying?... No way!!!”. These few words are how all of it started. Well I am still not that good in volleyball but I met a great friend who I will be in my heart forever. We were all like healthy mind in an healthy body, such a wonderful excuse to book a tapas bar . We had deep meaningful conversation about almost (any)everything, and despite your “Yorkshire” accent I intend to keep that going. I wish you all the best and thank you for all these memories making our student life that much better. What I didn’t expect during this Ph.D. was to be part of a fantastic Irish family. Frances and Philip, not a degree, blood bonds or a metallic ring deny the fact that you are my family and that I am forever grateful of all the kindness and happiness you brought me. You are both wonderful people and I felt lucky and blessed to be able to discover Zaconey, the 51, Slatterys, Searsons, the School House … well our own version of the 12 pubs of Christmas together.