Controllable Preparation And Electrochemical Performance Of MOFs Based Functional Materials

Supercapacitor is an especially promising energy storage technology to efficiently utilized new sustainable energy sources owing to its highly power density,fast charge/discharge rate and long cycle life.Carbon-based materials,conducting polymers and metal oxides/hydroxides are main three kinds of electrode materials for supercapacitors,which have been extensively investigated.Compared with these conventional electrode materials,metal-organic frameworks?MOFs?are one of the most suitable advanced functional materials to be applied as electrode for supercapacitors because of the following reasons:?1?deriving carbon materials through carbonization;?2?deriving oxide materials through annealing;?3?partial conductive MOFs itself can be used as electrode active materials of supercapacitors.Considering the MOFs with special structure,compositon and characteristics can be functionally modified,so that the morphology and electrochemical performance of these MOFs and their derived materials can be purposefully improved.The research work in this papar is mainly focused on the conductive anionic Co-MOF with zeolite framework.The main contents are described as follows:?1?Study on the electrochemical performance of the conductive Co-MOF with anionic framework.Firstly,the conductivity of the anionic Co-MOF is 1.42×10^-3S·cm^-1,which has been measured by the four-probe method.Second,adjusted the reaction time and temperature of Co-MOF in-situ growth on nickel foam,and characterized the morphology,structure and electrochemical performance.It can be determined that 70?,36 h and 3 M KOH are the optimal reaction temperature,time and electrolyte,respectively.The Co-MOF electrode exhibited a specific capacitance of 236.2 F g^-1at 1 A g^-1 and a capacitance retention of 51.40%at 15 A g^-1.Additionally,after 3000 cycles,64.04%capacity is still retained.It is proved that Co-MOF has relatively good rate performance and cycle stability as an electrode active material for supercapacitors.?2?Study on the effect of cetyltrimethylammonium bromide?CTAB?on the electrochemical performance of the anionic conductive Co-MOF.Firstly,added different amounts of CTAB to the precursor of Co-MOF,and then obtained the required electrodes through solvothermal reaction.The optimal CTAB addition amount was determined by characterizing the morphology,structure,composition and electrochemical performance.The experiment proved that the adding CTAB molar ratio of 6 times that of the H₆TATAT shows the highest capacitance,which is 334.0 F g^-1at 1 A g^-1and retains 77.92%after 3000 cycles.Meanwhile,the electrochemical reaction mechanism of Co-MOF can be inferred from the experimental data.In addition,the influence of carbon fiber paper as current collector to replace nickel foam was studied as well as the electrochemical performance of CTAB modified Co-MOF grown on carbon fiber paper.Experiments prove that the addition of CTAB can improve the dispersion,element distribution and microstructure of Co-MOF on the current collectors to further increase the capacitance.?3?Study on the effect of viologen with dicationic properties on the electrochemical performance of the anionic conductive Co-MOF.Firstly,viologen with different structures were used to activate Co-MOF electrode materials,and the modification effect of viologen with different molecular sizes and main structures were clarified.Experiments proved that the Vio 3 is the best electrochemical modifier.And then,studied the influence of the adsorption amount of viologen on the electrochemical performance of Co-MOF electrodes and 9.69×10^-2 m mol is the best adsorption capacity.?4?Study on the electrochemical performance of the derived carbon materials from an anionic Co-MOF with zeolite framework.By controlling the reaction time of the Co-MOF precursor and studied the morphology,composition and electrochemical performance of the derived carbon materials after carbonization.And N-doped porous carbons were obtained.In order to improve the capacitance of the derived carbons,viologens with bisthiazole group were selected to modify the Co-MOF precursor before carbonization and then S-doped porous carbon was obtained.Scanning electron microscopy and transmission electron microscopy proved that the micro-morphology of derived carbon maintained the 14-hedron structure of Co-MOF crystal particles with loose porous with a sponge-like structure.And the specific capacitance increased from 103.2 F g^-1to 220.1 F g^-1 at 1 A g^-1 after viologen modification.?5?Study on the electrochemical performance of the derived metal oxide materials from an anionic Co-MOF with zeolite framework.By adjusting the ratio of nickel nitrate and cobalt nitrate used in the synthesis process,mixed Ni/Co-MOF precursors with different metel contents were obtained.After annealing in air atmosphere,Ni_xCo_3-xO₄were obtained.Characterized the morphology,structure and electrochemical performance to determine the optimal metal ratio and the optimal metal ratio is determined to be Ni/Co=1/2.Additionally,to further increase the capacitance of derived Ni_xCo_3-xO₄,the Ni/Co-MOF precursor was activated by a methanol solution of cobalt nitrate before annealing,resulting in the specific capacitance increased from 579.2 F g^-1 to 628.8 F g^-1.