Two-dimensional materials for energy storage and generation

Energy is probably the most important factor influencing our everyday life. In fact, we need energy to power up our houses, vehicles, buildings and electronic devices. Storage and generation are the fundamental factors that influence the ways energy can be deployed and produced, so careful strategies have to be designed for their optimization. In particular, the materials used for these technologies should be earth abundant, environmental friendly and cheap. All these requirements are met by two-dimensional (2D) materials (i.e., graphene, transition metal dichalcogenides, etc.), that are currently representing a viable solution to the energy management. In this context, the research works presented in this thesis concern the use of 2D materials in both energy storage and generation devices. In particular, the thesis is organized as follows: Chapter 1 describes the discovery, properties, production and some applications of 2D materials (in particular graphene and transition metal dichalcogenides). Chapter 2 concerns the use of 2D materials in energy storage applications, specifically in electrochemical double layer capacitors. The working principle and main properties of this kind of devices will be thoroughly introduced. Herein, two projects are reported concerning the use of graphene flakes (produced through a wet-jet milling system) as active material for the fabrication of electrodes for electrochemical double layer capacitors. The first project is about the physico-chemical effects raising from the flow of the electrolyte ions on the graphene flakes surface. Our results show that graphene flakes act as “ion sliding” surfaces for the electrolyte ions. The second project, presented in this chapter, shows that the graphene flakes produced by wet-jet milling can be used for the design of high-areal performance electrodes for flexible supercapacitors. These projects are the results of a collaboration with Doctor Francesco Bonaccorso (Istituto Italiano di Tecnologia, Genova, Italy). Chapter 3 deals with energy generation devices, specifically perovskite solar cells. Perovskite materials are now at the centre of huge research efforts for their application in photovoltaics. In this chapter, the main properties of perovskite materials, their use in solar cells and the limits of the resulting devices will be discussed. Finally, the preliminary results on the use of transition metal dichalcogenides flakes in low-dimensional perovskite solar cells will be reported. The aim of this study is to improve the charge collection and the stability of perovskite-based devices. The reported works are carried out in collaboration with Doctor Francesco Bonaccorso (Istituto Italiano di Tecnologia, Genova, Italy), Professor Mohammad Khaja Nazeeruddin (École Polytechnique Fédérale de Lausanne, Sion, Valais) and Professor Giulia Grancini (Università di Pavia, Italy)