Performance Of Ni And Co-based Coordination Polymer Materials And Their Derived Nanostructures For Supercapacitors

Increasing environmental exacerbation and energy shortages promote the development of renewable energy as a top priority.As a new type of energy storage device,supercapacitors have attracted wide attention around world.Although supercapacitors have higher power density,their energy density has still been lower,which has greatly restricted their development and application.Electrode materials,as an important component of supercapacitors,play a crucial role in increasing device capacity.Therefore,the research and development of electrode materials with high specific capacitance,while maintaining high power density,has be paid close attention.Coordination polymer materials?CPs?,as a new type of porous material,have numerous advantages,such as adjustable pore size,facile surface modification and functionalization,etc.,and have still been focused on.In this work,we have attempted to fabricate highly porous carbon by carbonizing highly crystalline CPs and focused on the detailed characterization of structure reorganization for supercapacitors with high power density and energy density.Here,we proposed a facile one step hydrothermal method for the synthsis of crystalline CPs,which were prepared from metal X(Ni²⁺,Co²⁺)salts as the main body and dimercaptobenzimidazole as the guest under the solvent system of DMF.Furthermore,porous carbon materials based on Ni-CP and Co-CP were derived by chemical vapor deposition.Structures of Ni-CP and Co-CP were characterized by infrared spectroscopy,thermogravimetric analysis,X-ray diffraction,scanning electron microscopy,Raman spectroscopy,and specific surface area analysis.Porous carbon materials derived from Ni-CP and Co-CP were tested in 6 mol/L KOH electrolyte by AC impedance analysis,cyclic voltammetry.Specially,Charging and discharging tests were used to characterize the electrochemical performance.1.Ni-CP and Co-CP nanoparticles were prepared by solvothermal methods through self-assembly between Ni salt or Co salt and dimercaptobenzimidazole.Then,carbon coating X-CP/C derivatives were prepared at acetylene as carbon source by chemical vapor deposition.The resultant materials were applied in the electrode materials of supercapacitors.As a result,the worse conductivity of CPs can be overcame and the electrochemical characteristics of CPs will be improved.2.When chemical vapor deposition is performed at 600?,high conductive carbon nanotubes are grown on the surface of X-CPs so that their conductivity and specific capacitance have been improved,especially,the specific surface area of Ni-CP increased to 450 m²/g.In addition,the diameter of Ni-CP particles was reduced to 5 nm,the specific capacity of 120 F/g can be obtained at 1 A/g discharge,and capacity retention rate of 95.2% can be held after 1000 charge-discharge cycles.Co-CP partlcles,entangled by carbon nanotubes grown on their paticle surface by chemical vapor carbon deposition,were converted into nanosphere cross-linked short rods.Consequently,specific surface area of Co-CP derivatives of 194 m²/g,specific capacity of 104 F/g at 1 A/g charge-discharge test,capacity retention rate of 98% after 1000 charge-discharge cycles were maintained.3.In order to improve the poor conductivity of CPs,ferrocene was introduced into X-CP materials as catalyst.Accordingly,Ni/Co-CP-b-Fe/CNTs composites were derived by catalytic chemical vapor deposition from CNTs networks grown in situ on the particles surface,following the removal of Fe catalyst inside Ni/Co-CP-b-CNTs porous materials.ID/IG values of Raman spectroscopy composites were minimized with increase of graphitization degree for Ni/Co-CP-b-Fe/CNTs,contributive to improving their conductivity.Correspondingly,The specific surface area of Ni-CP-b-CNTs was increased from 105 m²/g to 293 m²/g,a nearly threefold more increase than Ni-CP composite,resulting in its average pore diameter decreased from 11 nm to 6 nm.Likewise,for Co-CP-b-CNTs composite,the micropore pore volume and specific surface area were also enhanced,specific surface area enlarged from 93 m²/g to 238 m²/g,a twofold increase,and the average pore diameter decreased from 10 nm to 6 nm.The results indicated that this method can achieve the purpose of pore structure modification.Specific capacitances of 152 F/g for Ni-CP-b-CNTs and 160 F/g for Co-CP-b-CNTs can be obtained at a discharge current density of 1 A/g.4.In order to verify the effect of CNTs and CP-derived carbon composites on improving electrical conductivity,CNTs were applied to Ni-CP,Co-CP composites for supercapacitors by a physical hybrid method.Because of these precursors winded by CNTs network,their electrochemical results were better than these precursors,origining from their more micropore pore volume and the total pore volume,lowere average pore diameter,and improved overall conductivity.Consequently,the special capacities and discharge capacity retention rates were totally improved.5.X-CPs supported on CNTs?X-CP@CNTs?were synthesize in Ni or Co salts,dimercaptobenzimidazole and CNTs chemically mixed by solvothermal method.Based on X-CPs loaded on CNTs network,with specific surface area upgraded and the average pore size reduced,Specific capacitances of 160 F/g for Ni-CP@CNTs and 91 F/g for Co-CP@CNTs can be obtained at a discharge current density of 1 A/g.