Controlled Synthesis And Electrochemical Application Of Nanostructured 3d Transition Metals And Their Compounds

Due to the outstanding physical and chemical properties,3d metals and their compound nanomaterials are regarded as the most promising substances to substitute for traditional materials which are playing important roles in catalysis,energy,sensing,biomedicine but exist problems and disadvantages.Although the 3d transition metals and their compound nanomaterials have many advantages including large theoretical capacity,there are still problems such as the electrode collapse and the insufficient conductivity.Therefore,through controlled synthesis of these materials,the effects of structure on performance can be investigated and regulated,so that their performance can be controllably improved and put into electrochemical applications.Based on this,the main contents of this thesis are sumarried as follows:(1)Thickness-control of ultrathin Co(OH)2 nanosheets with enhanced oxygen evolution reaction performanceTwo-dimensional nanomaterials have high specific surface areas and abundant surface electrochemical active sites.Co(OH)2 can afford Co3+ to serve as the catalytically active sites.Combined with the advantages of 2D nanomaterials and Co(OH)2,the catalytic performance of OER can be greatly enhanced.By using cobalt coordination compound as the precursor,the ultrathin two-dimensional cobalt hydroxide was synthesized by mixed solventhermal method(H2O+C2H5OH).After changing the reaction time and temperature of hydrothermal reaction,the thickness of Co(OH)2 nanosheets can be adjusted and Co(OH)2 nanosheets with three different thicknesses were obtained.And a comparison of OER catalytic performance was carried out on two-dimensional nanosheets with three different thicknesses of Co(OH)2.The effect of thickness on OER catalytic performance was explored and we drew a conclusion that the thinner nanosheets are,the better performances.When the thickness of Co(OH)2 nanosheets is about 4 nm,it has a low onset potential and a low overpotential of 327 mV at a current density of 10 mA ·cm-2,low Tafel slope(78 mV dec-1)and strong stability with a negligible decline of current density for 6 h,which shows better catalytic performance than that of commercial IrO2 in 1 M KOH alkaline electrolyte.(2)Synthesis of 3D titanium dioxide and tin dioxide double-layered hollow prisms with enhanced lithium storage performanceHollow nanomaterials with large surface area and additional free volume enable increasing contacting area,active sites,and offer the enough volume to buffer the pressure during their reactions.Combined with the high theoretical capacities of TiO2 and SnO2,they are beneficial to improve lithium storage performances.By using a facile one-step double hydrolysis route to prepare brand new a-Fe2O3 hollow prisms,and novel three-dimensional double-layered titanium dioxide and tin dioxide hollow prisms were obtained through ultrasonic hydrolysis/calcination and hydrothermal methods with the as-prepared a-Fe2O3 hollow prisms as hard templates.The samples of TiO2 and SnO2 3D double-layer hollow prism were applied to the lithium ion battery respectively.As anode material for LIB,the achieved TiO2 double layered hollow prisms deliver a high specific capacity of about 150 mAh·g-1 at a current density of 1 C over 500 cycles.And the as-prepared SnO2 double layered hollow prisms show a high reversible capacity of 630 mAh g'1 at a current density of 100 mA·g-1 after 370 cycles,as well as an excellent rate capability.Fast lithium charge/discharge performance is investigated with a capacity of 410 mAh· g-1 at a high current density of 800 mA·g-1.These performances exceed those of most similar materials previously reported.Our SnO2@C double-layered hollow prisms have a higher discharged specific capacity of 850 mAh·g-1 over 20 cycles and an improved capacity of 1200 mAh· g-1 after 170 cycles.(3)Synthesis of Co9S8/C nanotubes and Co(OH)2/Co3O4 composite nanomaterials for high rate-performance supercapacitor electrodeComposite nanomaterials can make up for the deficiency of single materials and achieve superior performance through synergistic effect.At the same time,the Co-based nanomaterials emerge as promising electrode materials of supercapacitors because of their rich redox reaction sites.Herein,we used simple hydrothermal method to obtain sol containing Co,and this sol was calcined in N2 to form Co9S8/C nanotubes;Furthermore,Co(OH)2/Co3O4 composite nanomaterials were prepared by using one-step hydrothermal method.The above two composite materials were applied as electrode materials of the supercapacitor.The Co9Ss/C nanotubes show the specific capacitance of about 120 F·g-1 at 4 A·g-1 current density.And the specific capacitance remains 99%over 1000 cycles;The Co(OH)2/Co3O4 composite nanomaterials show the specific capacitance of about 400 F g"1 at 4 A·g-1 current density.And the specific capacitance remains 99.5%,as high as 398.1 F· g-1 over 1000 cycles.(4)Synthesis of Cu@polymer nanocomposites and their application as nonenzymatic glucose sensorsAs the coating layer,the polymer has the function of slowing dovn the corrosion and dissolution of nanoparticles,while the copper nanoparticles have the advantages of high conductivity and low cost.By combining the advantages of the composite structure,the electric sensing characteristics of Cu nanoparticles can be utilized.A one-step self-activated route was used for synthesizing novel core-shell Cu@polymer nanocomposites.The Cu@polymer nanocomposites can be applied as a nonenzymatic sensor for glucose detection.The as-prepared Cu@polymer nanocomposite modified electrode shows high sensitivity up to 1417.1 ?A·cm-2·mM-1,a low detection limit(10 ?M),good linear dependence in a wide range from 0.01 mM to 1 mM,good selectivity and strong anti-interference capability.At the same time,it solves the problem of corrosion and poisoning of the catalyst successfully.