Synthesis And Electrochemical Properties Of Functionalized Graphene/polyaniline Composites

Supercapacitors are one of the most attractive energy storage devices due to their high power density,long cycle life and being environment friendly.Current focuses of the research lie in the development of the electrode materials with excellent electrochemical properties for supercapacitors.Combining with the advantages of graphene and polyaniline,the graphene/polyaniline(with graphene oxide(GO)as the raw material,named RGO/PANI)composites are one of the most promising electrode materials.Due to the strong?-?and van der Waals interaction,graphene sheets are easy to gather and restack in the process of the preparing RGO/PANI composites,which hinders the full utilization of graphene sheets.And so the electrochemical properties of the RGO/PANI composites have not been well embodied.In this project,the composition and structure of RGO/PANI composites were regulated through the functionalization of the graphene and the construction of three-dimensional structure,so as to increase the utilization of graphene sheets and enhance the specific capacitance and cycling stability of the composite s.The preparation parameters of the composites were optimized and the relationship between the microstructure,morphology and electrochemical properties of the composites was also systematically studied to reveal the structure-activity relationship.The detailed specific work was as follows:(1)N-doped graphene/polyaniline(NRGO/PANI)composites were prepared using4-methylaniline as the N source and reducing agent via two-step method.N-doped graphene(NRGO)materials were synthesized by the hydrothermal method with GO as the raw material and 4-methylaniline as the N source and reducing agent first,and then,NRGO/PANI composites were prepared via in-situ chemical oxidative polymerization of aniline(An).The effect of hydrothermal reaction temperature on the microstructure and electrochemical properties of NRGO materials was studied.With the hydrothermal temperature of 180 ^oC,the N content of the NRGO-180 was4.58%and the C/O atomic ratio was 11.86.The specific capacitance of the NRGO-180 reached the maximum value of 238.2 F/g(0.5 A/g).After 1000 cycles,the capacitance retention of the NRGO-180 was 95.5%.The nanometer-sized PANIs were dispersed on the surface of the NRGO-180 sheets in the NRGO/PANI composite that prepared with the ratio of An to GO of 10/1(m/m).The specific capacitance of the NRGO/PANI composite achieved the maximum value of 633.7 F/g(0.5 A/g),which was a great improvement over that of the RGO/PANI composite(479.2 F/g).After1000 cycles,the capacitance retention of the NRGO/PANI composite was 91.2%.(2)Holey graphene/polyaniline(HRGO/PANI)composites were prepared by in situ one-pot synthesis route.First,Zn powder converted GO into holey graphene(HRGO)with the assistance of ultrasound.Then,the HRGO/PANI composite s were prepared by adding An and ammonium persulfate(APS)into the as-prepared HRGO dispersion.The effects of the preparation parameters and nanoholes on the electrochemical properties of the composites were researched,and the relationship between the microstructure,morphology and electrochemical properties of the HRGO/PANI composites was also studied.The HRGO/PANI composite displayed a layer-like structure,and PANI nanoarrays were grown on the surface of the HRGO sheets with the ultrasonic time of 2 min,the ratio of Zn powder to GO of 1.5/1(m/m),and the ratio of An to GO of 30/1(m/m).The HRGO/PANI composite exhibited the maximum specific capacitance of 546.7 F/g at 0.5 A/g,which was a great improvement over that of the composite without nanoholes(530.4 F/g).Moreover,the composite delivered good cycling stability with a high capacitance retention rate of 86.1%after 3000cycles,which was almost the same as that of the composite without nanoholes(87.6%).(3)Three-dimensional N-doped holey graphene/polyaniline(3D-NHRGO/PANI)composites were prepared using H₂O₂ as the hole-forming agent,p-hydroquinone as the reducing agent and ammonia as the N source via three-step method.The preparation parameters were optimized,the effect of N doping on the microstructure,morphology and electrochemical properties of the composites was researched,and the relationship between the microstructure,morphology and electrochemical proper ties of the 3D-NHRGO/PANI composites was also studied.The 3D-NHRGO/PANI composite obtained the best electrochemical properties with the amount of ammonia of 300 u L and the amount of An of 80 u L.In the 3D-NHRGO/PANI composite,PANI nanoarrays were grown uniformly on the surface of the corrugated NHRGO sheets of the 3D-NHRGO frame,while the PANIs were densely coated on the surface of the HRGO sheets of the three-dimensional frame in the non N-doped composite.The3D-NHRGO/PANI composite exhibited a specific capacitance of 615.6 F/g at 1.5m A/cm²,which was a great improvement over that of the non N-doped composite(549.4 F/g).Moreover,the composite delivered good cycling stability with a high capacitance retention rate of 88.7%after 3000 cycles,bu t for the non N-doped composite,the retention rate was 85.4%.(4)Three-dimensional S-doped holey graphene/polyaniline(3D-SHRGO/PANI)composites were prepared using H₂O₂ as the hole-forming agent and Na₂S as the S source and reducing agent via three-step method.The preparation parameters were optimized,the effect of S doping on the microstructure,morphology and electrochemical properties of the composites was researched,and the relationship between the microstructure,morphology and electrochemical properties of the3D-SHRGO/PANI composites was also studied.The 3D-SHRGO/PANI composite obtained the best electrochemical properties with the amount of Na ₂S of 45%(vs.GO)and the amount of An of 100 u L.In the 3D-SHRGO/PANI composite,PANI nanoparticles were grown uniformly on the surface of the corrugated SHRGO sheets of the well-kept 3D-SHRGO frame,while the PANIs were coated on the surface of the HRGO sheets of the three-dimensional frame in the non S-doped composite.The3D-SHRGO/PANI composite exhibited a specific capacitance of 652.2 F/g at 1.5m A/cm²,which was a great improvement over that of the non S-doped composite(549.4 F/g).Moreover,the composite delivered good cycling stability with a high capacitance retention rate of 85.2%after 3000 cycles,bu t for the non S-doped composite,the retention rate was 83.1%.