Study On Structure Regulation And Properties Of Graphene-based Iron Oxide Composites In Supercapacitor

Due to the increasing use of high-tech portable or wearable electronic devices,the development of high-performance energy storage devices has attracted great attention.Supercapacitors are regarded as prospective energy storage devices due to their long cycle of charge-discharge,stability and high power density.Nevertheless,its energy density is too low to satisfy the increasing requirement for high efficiency applications.Consequently,the development of supercapacitors with large power and energy density is considered to be the principal problem that needs to be solved.Transition metal oxides,especially iron oxide,have been widely recognized as potential electrode materials for current commercial supercapacitors,however their lower electronic conductivity limits the specific capacitance and cycle stability of the resulting ultracapacitor devices.Consequently,the application of low-conductivity active materials can be achieved by selecting high-quality current collectors with numerous active sites that allow rapid and efficient charge delivery,which is a key factor in the preparation of high-performance supercapacitors.To date,many carbon materials with large surface areas,such as graphene or carbon nanotubes with conductive polymers,have been proposed as good candidates for supercapacitor active materials.Among them,graphene has been widely attracted by researchers because of its good electrical conductivity and excellent electronic conductivity.This article aims to synthesize high performance active materials for supercapacitors by combining iron oxide with graphene.The effects of graphene content and solvent on the morphology and superelectric properties of materials are discussed,and the formation mechanism of nanocomposites is explored.The main research contents and results are as follows:(1)For the first time,2D nano-circular-like iron oxides coupled reduced graphene oxide composites have been synthesized for the first time via a simple,inexpensive hydrothermal process.and the effects of its morphology and electrochemical performances in the synthesis process were mearsured by adjusting the addition of graphene.The results show that the addition of graphene has no effect on the structure and morphology of the composites,but it can indirectly improve their electrochemical properties by enhancing the conductivity of the composites.In addition,the circular iron oxide nanosheets are uniformly dispersed on the graphene layer,which can provide abundant active sites and effectively buffer the reunion of iron oxide nanocomposites during the electrochemical reactions.At an optimal ratio of 10 wt% GO,the as-prepared sample exhibits electrochemical performance with excellent specific capacitance of 621.3 F g–1 at 5 m V s–1 and 533 F g–1 at 1 A g–1,which is better than that of pure ?-Fe2O3(248.5 F g–1).Most attractively,the specific capacitance is highly retained about 77% after 14000 cycles,revealing superior cycle ability.(2)Iron oxide/graphene nanocomposites were prepared by the same hydrothermal method using anhydrous ethanol,pure water,N,N-dimethylformamide and N-methyl pyrrolidone as solvents,using ferric chloride hexahydrate as iron source.The results show that different solvents have an effect on the morphology and super electric properties of the products.When absolute ethanol was used as solvent,the material showed regular cubes.The morphology of the sample synthesized under N,N-dimethylformamide was regular hexagonal.When the solvent was replaced by N-methyl pyrrolidone and pure water,the material showed irregular morphology.In addition,iron oxide nanoparticles are well distributed on graphene and have excellent electrochemical properties,which mean that the iron oxide nanoparticles have a synergistic effect with the graphene.When the solvent was absolute ethanol,the specific capacitances of the obtained samples were 419 F g-1 at 1A g-1 and 700.98 F g-1 at 5 m V s-1,respectively,which were superior to the other three samples.Because graphene in the regular square structure of the sample synthesized in this solvent has more defects and provides more active sites,which is conducive to the diffusion of electrolyte ions,thus greatly improving the electrochemical properties of the material.