Preparation Of Novel Graphene-based Nanocomposites And Their Applications In Catalytic Hydrogen Evolution And Supercapacitors

Recently,graphene and molybdenum disulfide(MoS2)nanosheets,as two-dimensional nano-materials with various superior performance,have attracted many attentions.They have been widely applied in supercapacitors,catalysis,sensors,photoelectron and many other fields.It is one of the attractive and challenging issues that how to prepare high quality two-dimensional nano-materials with large scale.The common methods are relative to harsh conditions or complex equipment more or less,which can hardly meet the demands of both high quality and large scale.Fortunately,the liquid-phase exfoliation method has provide a new approach.In this paper,MoS2/graphene nano-composites(MG)have been prepared through a one-step salt-assisted liquid-phase co-exfoliation method which improves the exfoliation efficiency.The products have favourable catalytic activity in electrocatalytic hydrogen evolution reaction(HER).The preparation conditions and catalytic mechanism have also been investigated and discussed.On the other hand,in order to avoid the restacking and gathering of the two-dimensional materials during application,the researchers have tried different methods,including formation of hydrogels with three-dimensional structure and preparation of nano-composites.Herein,following these ideas,a graphene hydrogel(GH)was prepared via the ?-? interaction,oxygen-containing functional groups or hydrogen bonds between interlayers of graphene oxide(GO).Then polyaniline(PANI)was added after chemical oxidation in situ polymerization in order to prepare a three-dimensional graphene/polyaniline composite hydrogel(GPH)with properties of both graphene and PANI.This hydrogel with good capacitance has been used as electrode materials of supercapacitors.Besides,the influence of reaction conditions and corresponding synthesis mechanism have been discussed.Moreover,This paper mainly includes the following three parts:(1)From common graphite and MoS2 powder,selecting sodium tartrate as assisted salt and isopropanol(IPA)or N-methyl pyrrolidone(NMP)as exfoliation solvent,high performance MG nanosheets have been synthesis through a one-step ultrasonic co-exfoliation method which is simply operational and low-cost.The MoS2 and graphene nanosheets are believed to be exfoliated into single-or few-layer,and form a combination of MoS2/graphene successfully,according to microstructure characterization and elemental analysis.Besides,the reproducibility has also been confirmed.(2)The MG nanosheets have been further applied in electrocatalytic HER,and the catalytic activity of products from various initial material usage has been investigated.The lowest Tafel slop reaches 61 mV/dec.Moreover,the catalytic mechanism has been discussed in detail.The strategy effects between MoS2 and graphene nanosheets makes the composites have both exposed active sites and outstanding conductivity,which is the key to the good catalytic activity.(3)From natural graphite,GO was first prepared through a modified Hummer method,then GH through a one-step hydrothermal method,finally GPH through in situ polymerization of aniline monomers.The influence of initial material usage and synthesis temperature towards products performance have been investigated.The as-prepared GPH have good capacitance,especially the hydrogels prepared under ice bath,of which the specific capacitance reaches 390.9 F/g.In addition,the effect mechanism of reaction temperature have been discussed.