Microwave Hydrothermal Synthesis Of Metal Oxide/graphene Composites And Their Application In Supercapacitor

There is a rising requirement for the exploitation and use of environmentally friendly and non-polluting new energy sources（wind,water,solar,etc.）to replace conventional energy sources in contemporary society as a result of the depletion of traditional energy sources and environmental problems that are emerging with the development.Therefore,one of the feasible and effective methods to cover the conventional energy sources is to research and develop new technologies for the storage of eco-friendly forms of energy.Thanks to its high power density,speedy charging and discharging,and long cycle life,together with its superior energy storage capabilities,supercapacitors（SCs）have an optimistic future.Researchers have concentrated on a lot of researches on the electrode materials within the supercapacitors since their energy storage properties are still lacking and far below the desired high energy density requirements.The researches reveal that suitable materials for supercapacitor electrodes should have a large specific surface area,good electron/ion conductivity,and other properties.This work studies the use of metal oxide（and metal）and reduced graphene oxide composites（rGO）as supercapacitor electrodes.The composites are made by mixing metal and metal oxide/reduced graphene oxide using a straightforward and time-free microwave hydrothermal method.The details of the study are presented as follows:（1）With the help of a quick and effective microwave hydrothermal process,Zn Fe₂O₄/rGO composites using ZnCl₂,FeCl₃·6H₂O,and graphene oxide solution（GO）as precursor solutions are created in a single step.Its electrochemical properties as supercapacitor electrode materials are then examined.It is necessary to systematically compare the effects of various reduced graphene oxide contents on the structure,morphology,and electrochemical characteristics of Zn Fe₂O₄/rGO composites.The increase of the material’s electrochemical characteristics is achieved by the addition of reduced graphene oxide and the synergistic interaction of Zn Fe₂O₄ with rGO.The generated Zn Fe₂O₄/rGO composite with the best rGO content displays a specific capacitance of 628 F g^-1 at a current density of 1 A g^-1,significantly higher than that of pure Zn Fe₂O₄,which displays a specific capacitance of 68 F g^-1 at a current density of 1 A g^-1.The Zn Fe₂O₄/rGO composite is used in a symmetric supercapacitor with 2500 cycles at a current density of 1 A g^-1 and a capacity retention of 89%.（2）A one-step highly effective microwave hydrothermal method is used to regulate the products through operating the reaction time and create composite material which contains ruthenium and ruthenium oxide nanoparticles attached to graphene by using RuCl₃·n H₂O and graphene oxide solution as the precursor solution.Another work is conducted within this research that it systematically studies the impacts of microwave hydrothermal reaction time on the morphology,structure,and electrochemical characteristics of the products.Research results reveal that the reaction time had an impact on the products.Of all the composites made,the Ru O₂@Ru/rGO composite has both Ru O₂and Ru particles in a variety of redox states and,as a result,owns advantageous electrochemical capabilities.The specific capacitance reaches 3190 F g^-1 at a current density of 1 A g^-1 in the three-electrode test.It is used for cycling tests of symmetrical supercapacitors,and the capacity retention rate could reach 84%after 20,000 cycles at a current density of 5 A g^-1.