This document is downloaded from DR‑NTU (https://dr.ntu.edu.sg) Nanyang Technological University, Singapore. The electro‑oxidation of C1, C2 and C3 saturated alcohols on nickel‑cobalt oxides Sun, Shengnan 2018 Sun, S. (2018). The electro‑oxidation of C1, C2 and C3 saturated alcohols on nickel‑cobalt oxides. Doctoral thesis, Nanyang Technological University, Singapore. http://hdl.handle.net/10356/73364 https://doi.org/10.32657/10356/73364 Downloaded on 05 Oct 2021 17:14:59 SGT THE ELECTRO-OXIDATION OF C1, C2 AND C3 SATURATED ALCOHOLS ON NICKEL-COBALT OXIDES SUN SHENGNAN SCHOOL OF MATERIALS SCIENCE AND ENGINEERING 2017 THE ELECTRO-OXIDATION OF C1, C2 AND C3 SATURATED ALCOHOLS ON NICKEL-COBALT OXIDES SUN SHENGNAN SCHOOL OF MATERIALS SCIENCE AND ENGINEERING A thesis submitted to the Nanyang Technological University in partial fulfilment of the requirement for the degree of Doctor of Philosophy 2017 Statement of Originality I hereby certify that the work embodied in this thesis is the result of original research and has not been submitted for a higher degree to any other University or Institution. 08-Aug-2017 . Date Sun Shengnan Abstract Abstract The energy and environment problems are becoming focus in recent decades. The electro- oxidation of small molecules is attracting an increasing interest in many fields like water splitting, fuel cell, environmental protection, and fine chemical industry. Hydrogen, water, urea, and alcohols is becoming the major objects due to their simple molecule structure and availability in energy and fine chemistry industry. Water splitting is based on the bond cleavage of hydrogen and the bond formation of oxygen and oxygen by applying external energy to obtain hydrogen as clean energy. In fuel cells, the oxidation of fuels like hydrogen and alcohol plays the key role in obtaining high voltage and high efficiency. In the field of environmental protection, the substance with potential toxicity can be converted into environment-friendly substance by electro-oxidation. In fine chemical industry, converting alcohols to value-added chemicals by electrochemical method has also become the hot topic. This thesis is focused on the electro-oxidation of small molecular (C1, C2, and C3) alcohols on Ni-Co hydroxides and Ni-Co oxides in alkaline. The Ni-Co hydroxides with various Ni contents were prepared by electrodeposition, and Ni-Co oxides were obtained by calcinating the corresponding Ni-Co hydroxides. For C1 alcohol methanol, the investigation was given to the Ni effect in Ni-Co hydroxides and Ni-Co oxides for methanol oxidation reaction. Cyclic voltammetry (CV) and chronoamperometry (CA) methods were used to compare the methanol oxidation activity. The results show that as the Ni content increases, the methanol oxidation activity on Ni-Co hydroxides increases, while the activity on Ni-Co oxides exhibits a volcano-shaped trend. The highest activity on Ni-Co oxides was found at the atomic ratio of Ni / (Ni + Co) = 46%. By conducting electrochemical impedance spectroscopy (EIS), it was found that Ni can promote the adsorption of intermediate products. It suggests that this best ratio of 46% for the methanol electro-oxidation was due to the balance of the adsorption of intermediate products and methanol oxidation onset potential. For C2 alcohols, ethanol and ethylene glycol, the study was performed to reveal the Ni effect of Ni-Co oxides on the oxidation activity and the i Abstract product selectivity. The similar volcano-shaped trend was also obtained, i.e. the ratio of 46% is the optimal one for the two alcohol oxidation reactions. The oxidation products were analyzed by nuclear magnetic resonance (NMR) technique and it was found that the functional groups were converted from -OH to -COOH. The electro-oxidation of C3 saturated alcohols was studied on Co3O4. It shows that C3 saturated alcohols had different reaction rates on Co3O4, which presented the following order: glycerol (GLY) > 1,2- propanediol (1,2-P) > 1,3-propanediol (1,3-P) > 1-propanol (1-P) > 2-propanol (2-P). Through NMR analysis, we found that for the adjacent hydroxyl groups, the C-C bond can be readily broken up. In future work, we plan to compare Ni/Co effect in different coordination environments on alcohol oxidation. NixCo1-xAl2O4, ZnCo2-xNixO4, and LaCo1-xNixO3, three systems were chosen to fix Ni and Co in tetrahedral sites and octahedral sites, respectively. The glycerol oxidation will be compared on cobalt based oxides with cobalt in different coordination environments to investigate the coordination effect. Finally, dihydric alcohol (C2-C4) oxidation on Co3O4 will be compared to study the position effect of hydroxyl group on oxidation rate. ii Acknowledgements Acknowledgements I would like to appreciate my supervisor Prof. Jason Xu Zhichuan for his advice and guidance during my PhD study. Prof. Xu made me know what is research and how to do research in a correct way. During these years, Prof. Xu gave me a lot of help on my research and he helped me open another door. I would like to thank my TAC members Prof. Alex Yan Qingyu and Prof. Zhang Qichun for their comments on my work. I would like to thank Dr. Sun Libo, Dr. Wang Zilong, and Dr. Ren Xiao for their help for characterization. A great gratitude will be given to all the group members, technical staffs, and administrative staffs. iii Acknowledgements iv Table of Contents Table of Contents Abstract .............................................................................................................................. i Acknowledgements .......................................................................................................... iii Table of Contents ............................................................................................................v Figure Captions ................................................................................................................ xi Abbreviations ................................................................................................................. xix Chapter 1 Introduction ..................................................................................................1 1.1 Background ..............................................................................................................2 1.2 Electro-oxidation of Small Molecules.......................................................................2 1.2.1 Hydrogen Evolution .......................................................................................3 1.2.2 Fuel Cell .........................................................................................................4 1.2.3 Value-added Products from C3 saturated Alcohol Oxidation .......................5 1.2.4 Investigation Goal and Motivation ................................................................7 1.3 Dissertation Overview ...............................................................................................8 1.4 Findings and Outcomes/Originality ........................................................................10 References ..........................................................................................................................11 Chapter 2 Literature Review ..................................................................................... 17 2.1 Alcohol Electro-oxidation ...................................................................................... 18 2.1.1 Methanol Oxidation on Pt ........................................................................... 18 2.1.2 Ethanol and Ethylene Glycol Oxidation on Pt ............................................ 20 v Table of Contents 2.1.3 Value-added Products from C3 Saturated Alcohol Oxidation .................... 22 2.1.4 Alcohol Oxidation on Ni and Co Based Materials ..................................... 27 2.1.5 Alcohol Oxidation Mechanism on Ni and Co Based Materials .................. 29 2.1.6 Effect of OH- Concentration on Electro-oxidation Reaction in Alkaline ... 30 2.1.7 Effect of Cations on Electro-oxidation Reaction in Alkaline ..................... 30 2.2 Question: Effect of Ni on Alcohol Oxidation in Ni-Co Hydroxides and Oxides .. 31 2.3 Question: Electro-oxidation of C3 Alcohols on Co3O4 .......................................... 32 2.4 PhD in context of literature .................................................................................... 32 References ......................................................................................................................... 33 Chapter 3 Experimental Methodology ......................................................................37 3.1 Rationale for selection of Methods/Materials/Simulations .....................................38 3.2 Electrode Preparation ..............................................................................................39 3.3 Material Characterization ........................................................................................40 3.3.1 X-ray Absorption Fine Structure ................................................................40 3.3.2 Scanning Electron Microscopy ...................................................................42 3.4 Electrochemical Setup .............................................................................................41 3.5 Electrochemical Test ...............................................................................................43 3.5.1 Cyclic Voltammetry .....................................................................................43