Modification Of Graphene And Its Application In Anodic Catalyst Of Direct Methanol Fuel Cell

Direct methanol fuel cell(DMFC)as an efficient clean,environmental friendly new energy technologies possesses the wide application prospect in the aerospace,transportation and portable electric power source,etc,due to its small volume,high energy efficiency,easy storage and transportation,low pollution.Pt-based catalysts are still dominated in direct methanol fuel cell anode catalyst.High cost and easy to poisoning are still the key issues hinding the commercial application of DMFC.Using of carbon material with high area as carrier is one important way to improve the efficiency and catalyst activity of Pt-based.Graphene has unique two-dimensional honeycomb structure,large surface area,good electrical conductivity mass transfer and mechanical photoelectric performance,etc.It gets the favour of the researchers.However,these shortcomings of graghene such as easy to gather,poor solubility and wesk intermetallic with catalyst limit its practical application.Therefore,it is necessary to modify graphene for good solubility,obtaining more metal precursor anchor point,improving the catalyst dispersion,enhancing effect between catalyst particles and carrier,and improving the catalyst activity for methanol electro-catalytic oxidation.In this paper,modified graphene by p-aminobenzoic acid,1,3-propanediamine and 1,5-diaminonaphthalene was used as carriers,respectively.Chemical reduction method was applied to preparing Pt-based catalysts.The morphology and structure of catalysts and carriers were characterized by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS)techniques.The electro-catalytic activity and stability of anodic catalysts toward methanol electrooxidation were investigated by fast cyclic voltammetry method(CV),chronoamperometry(CA),Tafel and electrochemical impedance spectroscopy(EIS).The main points of this dissertation are summarized as follows:(1)Graphene oxide(GO)was preared by pre-oxide and scaling with graphite as raw materials.Then,p-aminobenzoic acid(PABA)was diazotized and grafted onto graphene.Benzoic acid groups-modified graphene was obtained.Wet-chemical reduction was used to prepare Pt@PABA-rGO catalyst.SEM,TEM,XRD and XPS characterization show that average diameter of Pt particles in Pt@PABA-rGO is 3.5～4.0 nn.Under the same loading mass of Pt catalyst,the electro-catalytic activity of Pt@PABA-rGO toward methanol electrooxidation is about 1.93 and 3.88 times as high as that of Pt@rGO and pure Pt,respectively.After 500 cycles,the current density retention of Pt@PABA-rGO catalyst is 82.6%,is about 1.37/1.63 times as high as that of Pt@rGO/pure Pt catalyst.These results show that the electro-catalytic oxidation performance of Pt@PABA-rGO catalyst toward methanol electrooxidation is superior to Pt@rGO and pure Pt catalyst.(2)GO was as raw materials,and graphene was grafted by 1,3-propanediamine(1,3-PDA)through acylation amidation reaction.Pt/1,3-PDA-rGO catalyst was prepared with sodium borohydride as reductant.SEM,TEM,XRD and XPS results show that Pt particles distribution of Pt/1,3-PDA-rGO catalyst is more uniform than that of Pt/rGO and its average diameter is about 2.0 nm.CV and CA test results show that the performance of Pt/1,3-PDA-rGO catalyst is better than Pt/rGO and pure Pt catalyst.The peak current density of methanol electrooxidation on Pt/1,3-PDA-rGO catalyst is 17.24 mA cm-2 and is about 1.96 and 3.10 times as high as that on Pt/rGO and pure Pt catalyst,respectively.After 500 cycles the current density retention of Pt/1,3-PDA-rGO toward methanol electrooxidation is 79.3%.These results indicate that the introduction of-NH2 is beneficial to dispersing Pt particles effectively and improving its performance for methanol electro-catalytic oxidation.(3)1,5-Diamino-naphthalene-modified graphene(1,5-DAA-rGO)was synthesized by acylation and amidation reaction with GO as raw materials and thionyl chloride as chloride agent.Pt@1,5-DAA-rGO catalyst was prepared by wet chemical reduction method.SEM,TEM,XRD and XPS results show that Pt@1,5-DAA-rGO catalyst has smaller particle size than Pt@rGO catalyst.These CV and CA results of Pt@1,5-DAA-rGO Pt@rGO and Pure Pt catalyst for methanol electro-catalytic oxidation show that Pt@1,5-DAA-rGO catalyst has better electrocatalytic activity and long-term stability.The peak current density of methanol electrooxidation on Pt@1,5-DAA-rG0 catalyst is 18.30 mA cm-2 and is about 2.50 and 3.35 times as high as that on Pt@rGO and pure Pt catalyst,respectively.The current density retention of Pt@1,5-DAA-rGO toward methanol electrooxidation is 80.4%.(4)With GO as raw materials,PtnRumCu@rGO with different Pt:Ru atomic ratio,PtCu@rGO and Pt@rGO catalysts were prepared by polyols thermal reduction method.The morphology and structure of Pt1Ru1Cu@rGO,PtCu@rGO and their carriers by SEM,TEM,XRD and XPS technology,CV,CA and EIS were applied to investigating the activity and stability of PtnRumCu@rGO catalysts for methanol electro-catalytic oxidation.These experimental results show that Pt1Ru1Cu@rGO catalyst has the best electrochemical activity and long-term stability.