Metal sulfides for electrochemical energy storage and conversion
i Abstract Electrochemical energy storage and conversion devices are regarded as one of the most attractive technologies to overcome the crisis of fossil fuel exhaustion and the global pollution. The key to advance these technologies is to explore suitable materials with various advantages of good performance, such as high stability, low cost, and environmental friendliness. The emerging twodimensional (2D) molybdenum sulfide (MoS2) has shown vast potential for renewable energy storage and
... gy storage and conversion applications, due to its intriguing physicochemical properties. Nevertheless, several issues handicap the commercial application of MoS2, including rapid structure degradation, low electrical conductivity, and sluggish charge transfer kinetics. Therefore, scientific research and breakthroughs are highly desirable to address these issues and satisfy the requirements for practical use. The main aim of this thesis is to investigate MoS2-based composites with engineered nanostructures as prospective electrodes for energy storage and conversion devices with good performance, high stability, and excellent safety. By virtue of the scrupulous design and smart hybridization of nanoarchitectures, exceptional properties and performance could be achieved. With this in view, novel MoS2/Ni3S2 heterostructures, flexible MoS2 electrodes supported on different substrates and hierarchical MoS2 hollow nanotubes have been developed and designed by facile synthetic routes. Meanwhile, the effect of different nanostructures on the electrochemical performance of energy storage and conversion devices is fundamentally investigated to provide in-depth studies on the relationship between structure and performance. The relevant studies in the thesis are divided into five parts, including Ni3S2@MoS2 core/shell nanorod arrays on Ni foam as the supercapacitor electrode (Chapter 4), honeycomb-like MoS2 nanoarchitectures anchored into graphene foam (GF) for enhanced lithium storage (Chapter 5), MoS2 architectures supported on graphene foam/carbon Abstract ii nanotube (GF/CNT) hybrid films: highly integrated frameworks with ideal contact for superior lithium storage (Chapter 6), MoS2 nanosheets decorated Ni3S2@MoS2 coaxial nanofibers for enhanced Na-ion storage (Chapter 7) and active sites-enriched hierarchical MoS2 nanotubes: highly active and stable architecture for boosting hydrogen evolution and lithium storage (Chapter 8). As the in-depth understanding of electrochemical reaction mechanisms is significant for advancing different energy storage and conversion devices, this thesis also performs the fundamental investigation of the lithium/sodium storage mechanisms, and the mechanisms of hydrogen evolution reaction (HER). The cause for enhanced performance has been also carefully explored. It is hoped that all these studies could shed more light on the fundamental understanding. Acknowledgements iii Acknowledgements My deepest gratitude is given to my supervisor Prof. Shen Zexiang for his incessant encouragement, insightful guidance and continual support during my Ph.D. career. I really appreciate the persistent support from my supervisor since he always respects my research project and encourages me whenever I encounter difficulty. I learn a lot from him not only the academic research, but also about how to be a professional scientist. I also truly express my gratitude to my co-supervisor Prof. Lin Jianyi for his high trust, constructive guidance and continual patience in me. He is always a brilliant and religious scientist, and he has taught me a lot of professional electrochemical knowledge. His diligence and serious thinking fully affect me. I would like to especially acknowledge my mentor, Assoc. Professor Alex Yan Qingyu for his good suggestions to my work. My gratitude also gives to all the colleagues for their helpful discussion and collaboration in research. I wish to acknowledge all the colleagues, especially Dr.