Graphene-based Supercapacitors

In Chapter I, the current worldwide energy scenario is thoroughly presented, along with the recent development in renewable technologies. The crucial need of energy storage devices is presented. Electrical storage technologies, with a focus on electrochemical storage, are reviewed. Chapter II deals with the fundamentals of Supercapacitors such as operating principles and cell architectures. Moreover, the history of Graphene is reported with the recent development on its synthesis and production. Materials used to enhance the performance of Graphene-based Supercapacitors are presented. Chapter III is focused on the electrochemical characterization of Graphene-based Supercapacitors with the different measurements available for the performance evaluation and the key parameters. In Chapter IV, a comparison study was performed among several graphene composites containing metal oxides or metal dichalcogenides. However, this chapter was aimed to in-situ synthesize a hybrid 1T-2H-molybdenum disulphide together with the reduction of graphene oxide by one-pot hydrothermal synthesis. The supercapacitor resulting from this innovative hybrid demonstrates outstanding electrochemical performance with a stability up to 50.000 cycles. Chapter V deals with the hydrothermal synthesis of reduced graphene oxide aerogel decorated with molybdenum oxide particles. This work was carried out to demonstrate the feasibility of the concomitant hydrothermal processes using the L-ascorbic acid (Vitamin C) as reducing agent. The addition of this green reducing agent induces a better reduction of graphene oxide and a higher reproducibility of the desired chemical reduction yield. The presence of molybdenum oxide particles permits to increase the specific capacitance using Faradaic processes. As-synthesized materials are tested in micro-supercapacitors in Chapter VI. PDMS-based micro-supercapacitors were fabricated through a simple photolithographic process. Moreover, the use of a conductive binder, PEDOT:PSS, is investigated. The binder induces the formation of a spring-like rod configuration with the embedded active material. This spatial conformation is determined by the filling of the interdigitated channels by capillarity. As-fabricated micro-supercapacitors show high flexibility and good cycling stability. Finally, Chapter VII presents the integration of supercapacitor devices to textiles fabrics. Two different works are presented: synthesis and characterization of an in-situ reduced graphene oxide aerogels onto a copper wire; and fabrication of exfoliated graphene-based wearable supercapacitors. The first part shows a peculiar morphology of the aerogel wadded around the current collector. The fabricated device demonstrates outstanding electrochemical properties in comparison with state-of-the-art works. Moreover, flexibility tests are performed and results are encouraging. In the second part, high performance exfoliated graphene-based wearable supercapacitors are studied. The padding method allows to produce 100 meters of textile fabrics coated with electrochemical exfoliated graphene. Obtained results are promising but, more importantly, the approach used is scalable and cost-effective. The experimental part of this thesis has been carried out in the Center for Sustainable Future Technologies (Istituto Italiano di Tecnologia, Torino), in the Department of Applied Science and Technology (Politecnico di Torino), in the School of Chemistry and the National Graphene Institute (The University of Manchester, UK). The work was mainly focused on the synthesis and development of active materials prior to be tested for electrode in supercapacitor applications.