Green Chemical Preparation And Capacitance Properties Of MOFs And Their Composites

MOFs and their composites have great potential as supercapacitor materials.The rapid and pollution-free synthesis of such materials is of great significance for promoting industrial applications.Electrochemical and ball milling are two green methods that have many advantages over traditional methods.In this paper,the two methods are used to synthesize MOFs and their composites.Then we studied the influence of reaction conditions,and explored the capacitance properties of the products.The specific research is as follows:（1）Ni₃（BTC）₂·12H₂O was synthesized by electrochemical method.The effects of reaction temperature and voltage were studied.The capacitance properties of the products were tested.It was found that both temperature and voltage have an effect on the yield and size.When either of the two conditions rises,the size of the output gradually increases.The product was tested for capacitance and found to have a mass-to-capacitance of 95.1 F/g at a capacitance density of 1 A/g.（2）A mechanical ball milling method is proposed for ultra-rapid synthesis of a Ni-based metal organic skeleton.Here,Ni-BTC,Ni-FA and Ni-OA are synthesized.The XRD results of Ni-BTC showed that the crystallinity of the products that obtained at different reaction times（1-180 min）were not significantly different,and the stable product was obtained only at the fastest rate within 1 min.The product can even be obtained at 10 Hz in 1 min without any solvent assistance.Increasing the milling time,increasing the mechanical frequency and adding an auxiliary solvent will increase the yield,while the type of auxiliary solvent has little effect on the results.Water is the best choice considering green and environmental friendliness.The method is fast,efficient,environmentally friendly,and has good scalability（gram size）and scalability of other MOFs.Ni-FA and Ni-OA were synthesized by mechanical ball milling.It was found that Ni-FA can be synthesized in 5 minutes and Ni-OA can be synthesized in 1 minute.The capacitance performance of the two products was found to be found:the mass-to-capacity capacitance measured by Ni-FA at 1A/g was 903.3F/g,and the capacitance retention rate of 200 cycles at 3A/g was79%;Ni-OA was The mass specific capacitance measured at 1 A/g was 656.7 F/g,and the capacitance retention rate of 200 cycles at 3 A/g was 80%.（3）GO was reduced by mechanical ball milling.After a series of tests and characterization,it was found that the ball milling method can restore GO to a certain extent,but the reduction is not complete,and there is still a large amount of raw materials remaining after reduction.Then we synthesized the Ni-OA/graphene composite by ball milling,and explored the influence of different rGO addition on its capacitance performance.It was found that the addition of rGO significantly improved the capacitance,rate and cycle performance of the material.When the addition amount is 2%,the mass-to-capacitance of the material reaches a maximum value of 867.5F/g.As the amount of addition increases,the material’s rate performance is continuously improved,compared with the material with 2%added and no rGO added.The cycle performance test displayed that after 500 cycles of 1A/g,the capacitance retention of the material with a 2%addition was 66%,which was also significantly improved compared to the 41%not added.