Study On The Preparation And Capacitive Performance Of A Three-dimensional Graphene Material

The fascinating properties of graphene materials make them promising candidates for applications in electrochemical energy storage and conversion devices,wearable electronics,smart textiles,sensors and so forth.When graphene materials serve as electrochemically active substance,close stacking of graphene sheets inevitably causes high-density structural defects,reducing the effective area for charge adsorption and ultimately deteriorating their storage capacity.Three-dimensional graphene materials are composed of physically or chemically cross-linked graphene sheets,which not only overcomes the re-stacking caused by the strong van der Waals interaction between adjacent graphene sheets,but also has a large specific surface area,good electron conductivity and a porous structure.This work aims to explore facile way for the preparation of three-dimensional graphene materials.In this paper,the modified Hummers method is used to prepare graphene oxide,and the liquid crystals and non-liquid crystals of graphene are processed by centrifugation.Three-dimensional graphene spheres?3DGMs?were obtained by dropping graphene oxide?GO?suspension into coagulation bath.Lamellar structures of the graphene oxides with liquid crystal phase and non-liquid crystal phase were studied.Formation mechanism of the graphene spheres in different coagulants was deduced.The capacitive performance of the as-prepared samples was examined.The main research contents are as follows:?i?The GO suspension,whose aqueous solvent was substituted by alcohol,is of a nematic liquid crystal under POM.The 3DGMs with the optimum morphology are produced in the coagulation bath of NaOH: CH₃CH——2OH=1:3 by using 10 mg/ml of GO concentration.The XRD results show that the 3DGMs have a higher extent of graphitization.Its SEM images indicate that the pleated and multilaminar configuration becomes gradually into smooth sheets as the concentration of the GO suspension decreases.At a discharge rate of 1 A/g,the sample has a specific capacitance of 201 F/g.?ii?The ammonia-modified GO suspension is of non-liquid crystal under POM.The droplets turn from dark yellow to black,eventually becoming non-flowing microsphere.SEM images reveals that sheets in the samples prepared in the five coagulation baths contain abundant wrinkles,which render the samples larger specific surface areas.The Raman spectrum suggests that the non-liquid crystal phase graphene still has oxygen-containing functional groups and intrinsic defects on its surface.The FT-IR spectrum implies that N atoms are introduced into the samples.The electrochemical results demonstrate that the specific capacitance of the 3DGMs obtained from the alcohol solution is higher than that from acetone and glacial acetic acid coagulation bath.Among them,ethylene glycol has the highest specific capacitance,reaching 217 F/g.