Graphene Supported Nanocatalyst Prepared By Arc Evaporation And Their Electrochemical Performances

As a novel two-dimensional nanomaterial, graphene has become one of the mostpopular materials and been widely used in electronic science, material science,catalyst carrier and biomedicine etc. since its discovery, due to its outstandingphysical and chemical properties. In this paper, arc discharge method is used to directprepare graphene supported two kinds of nanocatalyst, Pt/graphene composites andMn3O4/graphene composites, respectively, which are applied to direct methanol fuelcells and supercapacitors after that. The morphology, structure and electrochemicalperformance of the samples have been studied. The main details and results are asfollows:(1) Graphene supported platinum nanoparticles and manganese compounds havebeen directly prepared by arc discharge evaporation of carbon electrode including Ptand Mn elements, respectively. The Raman spectroscopy, SEM, and TEM have beenused to characterize the samples. The results show that the as-prepared few-layergraphene have high purity and crystallinity, meanwhile the nanocatalyst, which are inseveral nanometers of average particle size, are well-dispersed on the surface ofgraphene.(2) As-prepared Pt/graphene samples are physically activated to remove thegraphene sheets encapsulating Pt catalyst. Raman spectroscopy, XRD, SEM, EDS,HRTEM show that Pt nanoparticles with face-centered cubic structure exist in thehighly-crystalline graphene samples. For hydrogen-treated samples, it shows that hightemperature treatments below1073K will not lead the Pt NPs to form an obviousaggregation. When the temperature rises up to1173K, the extremely hightemperature will destroy the structure of graphene, leading to the large aggregation ofPt nanoparticles. With the observation of HRTEM, a possible coalescence mannerbetween Pt and graphene is discussed.(3) The electrocatalytic properties of the Pt/graphene samples for methanoloxidation have been evaluated by cyclic voltammetry and chronoamperometry, whichshow that the H1073-Pt/G catalyst displays best electrochemical activity in all samples. Although its Pt loading is just one third of the commercial Pt/C catalyst’s, itexhibits a higher catalytic activity, which about2.8times higher than commercial Pt/Ccatalyst, as well as a better stability and CO poisoning tolerance.(4) To transform the manganese compounds to Mn3O4and remove theamorphous carbon existed in graphene samples, the high-temperature treatment ofmanganese compounds/graphene composites has been carried out to purify andoxidize the samples. A series of characterization results show that manganese exists asMnS2before the high-temperature treatment; during the treatments, MnS2have beentotally oxidized to Mn3O4and it is found that the treatments are effective to removethe amorphous carbon coating MnS2.(5) The supercapacitors with Mn3O4/graphene or pure graphene electrodes inwater system and organic system have been manufactured. With observation ofalternating-current impedance, cyclic voltammetry and constant current’s charge anddischarge curve, it is suggested that all the samples show the obvious capacitancecharacteristics as well as have a low equivalent series resistance and theirelectrochemical properties gradually enhanced with increase of the content related toMn3O4, Furthermore, the doping of Mn3O4not only makes the specific capacitance tobe3times higher than that of pure graphene samples, but also reserves the stability,which is presented in that after3000cycles, the specific capacitance ofMn3O4/graphene electrodes only has a4%decrease.