Fabrication And Electrochemical Performance Of Cu?OH?₂ And CuO Electrode Materials Based On Copper Foam

With the rapid development of global economy,the human society's increasing dependence on energy has been grown ever than before.With greenhouse effect and climate change caused by the wide use of fossil fuels,more and more attention has been focused on the clean and renewable energy sources and their conversion and storage devices.Supercapacitors,which has been designated by the US department of Energy one of the future energy storage systems as important as batteries,have attracted much attention and have been used in many areas,such as hybrid cars,clean source energy collection and conversion,high power density machinery and portable devices,since their long life cycle,high power density,large current charging and discharging and safe characteristics.According to the energy storage mechanisms,the supercapacitors can be classified into two types,one is electrical double layer capacitors?EDLCs?and the other is faradaic pseudocapacitors.EDLCs primarily make use of carbon materials as the active materials and store energy by accumulating charges in the electrostatic double layer.Pseudocapacitors store charges by using the faradaic redox reaction and could provide nearly ten times higher capacitance than EDLCs,because they not only react at the surface but also in the bulk of electrode materials.The conducting polymers and metal oxides/hydroxide have been widely applied to the electrode materials of pseudocapacitors.Though the pseudocapacitors materials could provide much more specific capacitance than the EDLCs materials,the poor stability and low rate capacity limited their practical applications.Hence,the researchers focused on seeking for cost effective,environmentally friendly and excellent electrochemical performance electrode materials.In this thesis the surface oxidation and electrochemical anodization methods have been used to fabricated different morphologies of CuO and Cu?OH?₂ electrode materials.Also the synthesis principles have been investigated to enhance the specific capacitance,the rate capacity and the cycle life,and lower the intrinsic resistance.The main contents are as follows:?1?The mesoporous Cu?OH?₂ nanorods have been synthesized on the copper foam substrate through surface oxidation method under ice bath condition.The Cu?OH?₂ nanorods exhibit 3D connect and quasi-connect structures,forming a 3D network.Such unique structures can provide numerous active sites for redox reactions and improve the specific capacitance of the electrode.The Cu?OH?₂/Cu foam electrode exhibits a high specific capacitance of 2.151 F cm^-2 at a scan rate of 2 m V s^-1,low equivalent series resistance?RESR?of 0.581 ? cm^-2.In addition,an asymmetric supercapacitor is assembled by using the mesoporous Cu?OH?₂ as positive electrode and activated carbon as negative electrode.The device can deliver a high energy density of 4.152 m W h cm-3 and a high power density of 383.222 m W cm-3,but also achieves a good durability performance of 73.4 % capacitance retention after 2000 cycles.?2?The morphology controllable chrysanthemum-like and ball of yarn like CuO micro/nanostructures have been synthesized on the Cu foam substrate by one step chemical surface oxidation method in alkaline condition by using?NH4?2S4O8 as oxidizing agent.The chrysanthemum-like CuO/Cu foam electrode has exhibit a high capacitance of 1641.4 m F cm^-2,good rate capability?77.2 % retention upon increasing the current density by 10 times?and good cyclability?79 % retention after 10000 cycles?.The ball of yarn like CuO/Cu foam electrode has exhibit a specific capacitance of 762.55 m F cm^-2 at a current density of 2 m A cm^-2,excellent cycling stability?98.11 % retention after 20000 cycles?and low equivalent series resistance?RESR?of 0.6225 ? cm^-2.?3?The Cu?OH?₂ nanorods have been fabricated on the copper foam substrate by electrochemical anodization method under ice bath condition.The cross-section of the Cu?OH?₂ nanords exhibits corner extended polygonal shape,which could can maximize the contact area between Cu?OH?₂ nanorods and electrolyte and improve the insertion and deinsertion of the ions in the electrolyte.The synthesis parameters have been optimized,and a high specific capacitance of 1.8886 F cm^-2 at a scan rate of 2 m V s^-1,good coulombic efficiency of Cu?OH?₂ achieved of 84.7 % at 2 m A cm^-2,low intrinsic resistance(0.792 ? cm^-2)and good cycling stability?87.23 % capacitance retention after 5000 cycles?were achieved.?4?The leaf-like CuO-Cu₂O nanosheets have been prepared on copper foam by one step simple electrochemical anodization method,which can be used as advanced binder-free supercapacitor electrode.The surface of the copper foam substrate has been fully covered by the leaf-like ultrathin nanostructures,the unique morphologies can provide numerous active sites for redox reaction.The performance of CuO-Cu₂O/Cu foam electrode was optimized through controlling and restraining the current density and reaction time.The prepared electrode exhibits a very high specific capacitance(1.954 F cm^-2 at scan rate of 2 m V s^-1),excellent durability?120 % retention after 5000 cycles?and remarkable rate capability?91.8 % retention upon increasing the current density by 10 times?.In conclusion,this thesis has adopted different synthesized and prepared parameters to achieve excellent electrochemical performance materials,which exhibit different morphologies and nano/micro structures.The electrode materials involved in this paper,those are CuO and Cu?OH?₂,are rich reserve,relatively low cost and environmental benign.Hope these works could provide new theoretical and technical guidance for the research of transition metal oxide electrode materials.