Optimization Of Electrical Energy Storage Based On Nickel-(thiophene-2,5-dicarboxylic Acid) Framework Materials

Supercapacitors have attracted great attention due to their significant impact on alleviating energy and environmental crises,and promoting the improvement of people’s living standards.They are a hot field of chemical and material research today.Therefore,further development of electrode materials and related devices for supercapacitors with superior performance is of great significance in meeting the growing demand for high-performance power supply in current social life.The preparation of porous nanostructures with high specific surface area and abundant active sites is an important way to obtain materials with excellent chemical activity and storage capacity.Therefore,metal organic framework（MOF）is considered as an ideal material for electrochemical energy storage applications.In particular,nickel-based organic framework materials are considered as potential electrode materials for supercapacitors because they exhibit good electrochemical properties.However,there are few high-performance electrochemical energy conversion and storage materials based on conventional Ni-based MOF,mainly because of their relatively poor electrical conductivity and stability,and relatively slow electron and ion transport,thus limiting the utilization of active sites in their redox reactions,which in turn inhibit their electrochemical performance.Therefore,the optimization of electrical energy storage based on conventional Ni-MOF materials is of great research importance.Based on this,this thesis uses different strategies to optimize the conventional nickel-（2,5-thiophene dicarboxylic acid）framework material（Ni-MOF）for electric energy storage,with the following main studies:1.Co-Ni bimetallic synergistic strategy:Ni-MOF（{Ni₃（OH）₂（tdc）₂（H₂O）₄}n,H2tdc=2,5thiophene dicarboxylic acid）was used as a model to construct bimetallic Co/Ni-MOF with the same crystal structure as Ni-MOF by introducing Co2+to replace part of Ni²⁺ in Ni-MOF.Compared with Ni-MOF,the bimetallic Co/Ni-MOF exhibits significantly higher reactivity and conductivity compared to Ni-MOF,and thus exhibits superior electrochemical properties.The Co/Ni-MOF-2:1 bimetallic material with an optimal Co:Ni ratio exhibits higher specific capacitance（610 F g-1 at a current density of 0.5 A g-1）,better rate performance（88%retention of specific capacitance for Co/Ni-MOF-2:1 when increasing from 0.5 A g-1 to 5 A g-1）and cycling stability（72%retention of specific capacitance after 5000 cycles）.In addition,the asymmetric supercapacitor composed of Co/Ni-MOF-2:1 and activated carbon exhibited high specific capacitance（228 F g-1 at a current density of 0.5 A g-1）and good cycling stability（95.5%capacity retention after 5000 cycles at 5 A g-1）.2.Template derivatization strategy:Ni-MOF/Ni（OH）₂/Ni₃S₂ complexes were prepared by one-step hydrothermal derivatization using Ni-MOF as the precursor template.NiMOF/Ni（OH）2/Ni3S2 has a unique layered structure,which not only enhances the abundant redox reaction active sites,but also provides an effective contact area for the electrolyte and reduce the volume strain.In addition,the Ni3S2 component has high electrical conductivity as well as Ni（OH）2 has a high theoretical specific capacity.Therefore,the NiMOF/Ni（OH）2/Ni3S2 complex has significantly improved electrochemical performance compared to the Ni-MOF precursor.Among them,the specific capacitance of NiMOF/Ni（OH）2/Ni3S2 is 543 F g-1 at a current density of 0.5 A g-1（Ni-MOF:425 F g-1）,the retention of specific capacitance of current density from 0.5 A g-1 to 5 A g-1 is 56%（Ni-MOF:29%）,and the retention of specific capacitance of 4000 cycles is 88%（Ni-MOF:34%）.3.Strategy of constructing heterostructures:Using a simple and efficient solvent reaction,ZIF-67,ZIF-8 and MIL-100 nano-MOF structures were successfully grown on Ni-MOF to construct heterostructures with special morphology,which can not only prevent the agglomeration of Ni-MOF microrods to a certain extent,but also promote the electrochemical reaction.The specific capacitance of 2C-ZIF-67@Ni-MOF is 941 F g-1 at a current density of 0.5 A g-1.The specific capacitance retention of 86%for current densities from 0.5 A g-1 to 5 A g-1 and 73%for 1000 cycles were significantly higher than that of Ni-MOF.Similarly,the electrical energy storage performance of ZIF-8@Ni-MOF and MIL-100@Ni-MOF was significantly improved compared to that of Ni-MOF.