Synthesis And Supercapacitive Properties Of Bimetallic Oxalate Two-Dimensional Porous Sheets

With the continuous consumption of fossil fuels,the increase of environmental pollution and the rapid development of electric vehicles and mobile electronic devices,it is receiving widespread attention worldwide to develop advanced energy conversion and storage technologies while develop clean,efficient and sustainable new energy sources.As a new type of environmentally-friendly and high-efficiency energy storage device,supercapacitor has many advantages such as high power density,long cycle life and high charge-discharge efficiency etc,so as to it widely used in industrial,communications,military and transportation.At present,developing high-performance,low-price and environment friendly electrode materials is the main direction of supercapacitor development.In recent years,the transition metal oxalate has become a hot spot in the research of supercapacitor electrode materials due to its higher energy density and better electrochemical stability than its oxides and hydroxides.Meanwhile,the two-dimensional(2D)porous structural material is considered to have more excellent electrochemical properties than zero-dimensional and one-dimensional materials due to its rich pore structure and large specific surface area which has attracted much attention of researchers.In this thesis,many kinds of bimetallic oxalate 2D porous sheets were successfully prepared through hydrothermal method by using oxalic acid as a ligand.The supercapacitance properties of obtained simples were also studied.The main research contents and conclusions of this paper include the following three aspects:Firstly,using cobalt nitrate and copper nitrate as metal sources,three kinds of copper-cobalt-oxalate sheets with 2D porous structure were successfully prepared through hydrothermal reaction at 200°C for 5,10 and 20 h.The SEM analysis showed that the prepared sample with the reaction time of 10 h(Cu-Co-OA-10)had the best morphology.Cu-Co-OA-10 is a porous nanosheet array structure formed by 2D nanosheet interweaving.The specific surface area of Cu-Co-OA-10 is 47.049 m~2/g.The specific capacitance of the Cu-Co-OA-10 electrode is 1169.55 F/g.The supercapacitor(Cu-Co-OA-10//AC)was assembled with AC and Cu-Co-OA-10.Its energy density and power density can reach to 28.88 Wh/kg and 10800 W/kg,respectively.After 2000 cycles of charge and discharge,the specific capacitance of Cu-Co-OA-10//AC can still be maintained at 95.26%indicating its good application potential.Secondly,using different proportions of manganese chloride and cobalt nitrate as metal sources,three kinds of different manganese-cobalt-oxalate sheets wih 2D porous structure were successfully prepared at 200°C for 10 h.The morphology of the three samples were analyzed by SEM.It was found that when the ratio of manganese to cobalt was 1:2,the structure and morphology of the obtained sample(Mn-Co-OA-1-2)was optimal.The specific surface area of Mn-Co-OA-1-2 is66.192 m~2/g.The specific capacitance of the prepared Mn-Co-OA-1-2 electrode is2485.71 F/g.The energy density of the assembled Mn-Co-OA-1-2//AC can reach to33.10 Wh/kg,the power density can reach to 9000 W/kg,and the specific capacitance retention rate is 97.87%(after 2500 charge-discharge cycles at 6 A/g),which indicates that the Mn-Co-OA-1-2 material has excellent supercapacitor energy storage performance.Thirdly,using cobalt nitrate and zinc nitrate as the metal source,zinc-cobalt-oxalate 2D porous sheets(Zn-Co-OA)were successfully prepared at200°C for 10 h.Zn-Co-OA was a mixture of cobalt oxalate and zinc oxalate,and its surface has a weed-like substance formed by the assembly of crosslinked nanosheets.The specific surface area of Zn-Co-OA was 34.64 m~2/g.The specific capacitance of Zn-Co-OA electrode can reach to 1906.50 F/g.In addition,the assembled Zn-Co-OA//AC asymmetric supercapacitor possesses an energy density of up to 24.75Wh/kg,a power density of up to 9000 W/kg and a capacitance retention of 96.97%(after 2500 charge-discharge cycles at 6 A/g),which are shows that Zn-Co-OA//AC has outstanding energy storage performance.