Green,High-Performance Supercapacitors Based on Biomass-derived Carbon Electrodes

Author:Asim AMohammed Ahmed

Supervisor:zhu zhi hong


Degree Year:2019





Recently,global warming,climate change and energy consumption have become one of the main environmental challenges facing the world.These challenges combined with energy security issues,have called for the need to increase energy generation from ecological and sustainable sources,as well as new technologies associated with energy conversion and storage.Because,more alternative energy sources,in the form of electrical energy,could not be available contentiously,Therefore,the realistic solution is that the energy can be stored electrochemically in chemical energy storage devices(batteries)and electrochemical capacitors.The performance of electrochemical energy storage involves complex and interrelated physical and chemical processes between electrode materials and electrolytes.The different requirements of multifunctional nanostructured composite material,such as structural and electrochemical properties,must be designed and optimized at the same time.Electrochemical capacitors,thanks to its capability to offer high power performance,high efficiency and extremely long cycle life have attracted considerable attention,as they can integrate or even replace the batteries in the field of energy storage,particularly when high power delivery or uptake is needed.However,supercapacitors usually carry low energy stored per unit of volume and weight compared to batteries.In fact,the properties of the electrodes and electrolyte materials have a significant effect on the final electrochemical performance of the device,thus,it is expected that the engineered nanostructured materials can enhance the energy density,power density,the cycle lifetime of the final supercapacitor device.To meet the requirements of electronic devices,advanced nanostructured electrode materials have been developed in the field of electrochemical capacitor technologies.This thesis focused on the selection,fabrication,and testing of physical and electrochemical performance of the novel hierarchically structured biomass-derived carbons for use as new advanced electrodes for electrochemical capacitors.In another approach,the purpose of this research project is to utilize a range of tools to explore a new ecofriendly electrode material through simple method to manufacture flexible high-performance electrochemical capacitor.The thesis starts with a description of the electrochemical energy storage systems and the comparison between dissimilar electrochemical energy storage technologies,tailed by a brief description of the energy storage mechanisms for different types of electrochemical capacitors.The study,focuses on the improving the electrochemical performances of electrochemical capacitors based on faradaic(metal oxides)and non-faradaic(biomass-derived carbon)materials.In the first part,two different activated carbon structures were derived from low-cost(waste)biomass precursor via KOH and H3PO4 activations for the symmetric supercapacitor device.The synthesized flexible all-solid-state supercapacitor exhibits excellent rate performance and stable cycling,even under a high operating voltage widow of 1.6 V using polymer gel electrolyte(PVA-KOH).Which highlight the possibility of using the waste baobab fruit shell to produce low-cost,high-performance green carbon-based electrode materials for application in electrochemical energy storage technologies.Secondly,flexible all-solid-state hybrid electrochemical capacitor device was synthesized based on a hybrid composite of metal oxide(MrnO2)supported onto faidherbia albida fruit shell(waste)derived activated carbon.The nanowire-like structure of MnO2 has been grafted onto activated carbon derived from biomass through a hydrothermal synthesis method.Benefiting from the combination of a high specific surface area of baobab fruit shell carbon and high specific capacitance of MrnO2,the flexible all-solid-state a hybrid supercapacitor presents excellent electrochemical performance in the operating voltage window of>1.6 V.Growth process leading to further improve the capacitance and energy density.In the third part of the dissertation,asymmetric supercapacitor based on multi-heteroatom self-doped porous carbon derived from the hyphaene fruit shell(waste biomass)as negative electrode with NiMoO4/NiCo2O4 hybrid nanostructure as positive electrode.The synthesized asymmetric all-solid-state supercapacitor offered prominent electrochemical performances within a high voltage window of 1.8 V.Which indicate that Hyphaene fruit shell derived multi-heteroatom doped carbon have a considerable potential application in the field of energy storage systems.Overall,the preparation of the electrodes in this research project was carried out by using simple and low-cost hydrothermal method,which holds great potential to produce eco-friendly and high electrochemical performance supercapacitors.The results from the studies are presented in this thesis together with the scientific research papers.