Study On Preparation Of Graphene/Nickel Matrix Composites By MISR And Their Electrochemical Properties

Energy storage has been a major problem for humans.In recent years,supercapacitors have become the focus of research.The performance of capacitors were mainly determined by the electrode materials.Therefore,it is very important to develop electrode materials with excellent electrochemical activity.As we know,Ni(OH)2 has a high theoretical capacitance but a poor cycle performance.Therefore,high performance electrode materials were prepared by using their synergistic effects between Ni(OH)2 and RGO.In this work,graphene/nickel matrix composites were prepared by MISR.The main contents are as follows:(1)RGO/Ni(OH)2 composites were prepared by MISR and the optimum process was determined as follows:The mass ratio of RGO:Ni(NO3)2 was 0.1:2.5,reaction pH was 9.5,aging time was 3 h,premixing time was 3 h,impinging flow rate was 7.08 m/s.Under the current density of 1 A/g,the initial specific capacitance of RGO/Ni(OH)2 could reach 2534.8 F/g.After 500 cycles,the capacity retention rate was 51.7%.Under the optimum conditions,we compared the difference of electrochemical performance between both composites prepared with MISR and STR,respectively,and it demonstrated that MISR has noticeable advantages in the preparation of composites.(2)The Ni-Co-Al(OH)n composite material was prepared by doping two kinds of metal ions of Al3+ and Co2+ into Ni(OH)2 within a MISR.The optimum molar ratio of Ni2+ to(Al3+,CO2+)was 3:1,the best molar ratio of Al3+ to CO2+was 3:2,and the optimum concentration of precipitant was 0.25 mol/L.Under the optimum conditions,the initial specific capacitance of the material was 2010.8 F/g with the current density at 1 A/g,after 500 cycles,the capacity retention rate was 80%.We compared the difference of materials prepared by MISR and STR,respectively.It was found that the dispersion of the materials obtained by MISR was much better,the distribution of metal ions was more uniform,and the doping effect was stronger.(3)The RGO/Ni-Co-Al(OH)n composites,which was firstly composed of go and metal hydroxide and then reduced to form the composites,were also prepared by MISR.When the total mass of metal ions is 0.0125 mol and the amount of hydrazine hydrate is 50 ?L,the optimum preparing conditions were determined as follows:the dosage of GO was 50 mg,the premixing time was 3 h,the reduction time was 1 h,and the reduction temperature was 100?.At the current density of 1 A/g,the initial specific capacitance was 2230.9 F/g,and the maximum specific capacitance after full activation could reach 2389.5 F/g.After 500 cycles,the capacity retention rate was 96.5%.After 1000 cycles,the capacity retention rate was still 83.7%.At the current density of 20 A/g,the specific capacitance could reach 1687.5 F/g and the capacity retention rate was 75.6%.It indicated that the composite not only has a very high specific capacitance,but also shows excellent cycling performance and rate capability.