| With the rapid development of world economy,fossil energy is increasingly depleting,and the ecological environment destruction is also becoming more and more serious.In order to solve the energy crisis and environmental problems,human takes an active part in exploring new clean and efficient energy.Direct methanol fuel cell(DMFC)is the most promising power source due to its favorable advantages,such as low operating temperature,quick reflexes,high energy conversion efficiency and less pollution to the environment,and the source of methanol has the advantages of its plenty,cheap cost,and use safety,which is gotten more attention.However,their performance is still limited by the poor kinetics of the anode reaction and the crossover of methanol from then anode to the cathode side through the proton exchange membrane at room temperature,easy to be poisoned by the intermediates formed during methanol oxidation,while Pt catalyst is high cost and limited resource,which are the main obstacles to the commercialization process of DMFC technology.To improve the catalytic activity of anode catalyst,expanded graphite(EG)was used as basic material.Vacuum ion plating,reduction method and electroless plating method were respectively adopted to prepare Pt/EG,Pt-Co/EG and Pd-Co/EG catalysts,and their catalytic performance of methanol were studied in this dissertation.The exploratory research was carried out to solve the main DMFC problems,providing innovative ideas and methods,and the main research and results are as follows:Firstly,expanded graphite was prepared by natural flake graphite,oxidating,intercalating and high-temperature puffing with perchloric acid.Pt/EG catalyst prepared by the vacuum ion sputtering plating technology,and the influence of sputtering Pt deposition time with vacuum ion plating,sulfuric acid concentration,methanol concentration and electric scanning speed were carried out to study the electrocatalysis of Pt/EG catalyst.The results show that it is 110 second of precipitation Pt on expanded graphite,which Pt/EG catalyst has better electrocatalytic activity.Methanol concentration varying from 1.0mol/L to 5.0mol/L,the peak current of positive or negative scanning on Pt/EG electrodes is monotonous increasing,and the peak potential of positive scanning moves to the right.Electric scanning speed from 30 mV/s to 110mV/s,the peak current of positive or negative scanning is linear relationship with v1/2,and 110mV/s is the cut-off point of methanol electrooxidation between diffusion control and electrochemical control.Secondly,Pt/EG and Pt-Co/EG catalysts were prepared by reduction method with sodium borohydride,exploring the influence of the catalytic activity on Pt/EG catalyst by the addition of Co.It was studied that the influence of temperature,sulfuric acid concentration and methanol concentration for the Pt-Co/EG electrocatalytic performance.The results show that the order of the electrocatalytic performance for Pt:Co with different compositions is 1:3>1:2>1:1.Compared with Pt1Co1/EG catalyst,the peak potential of positive and negative scanning for Pt1Co3/EG catalyst have moved to the right 22mV and 31 mV respectively,and the If/Ib value decreases with the increase of the Co content.Temperature varying from 25 ? to 55 ?,the peak potential shifts to the left.It is the best performance for the electrode catalyst is at 45 ?,and the steady-state current at 55? is only 0.82 times than that at 25?.Thirdly,Pd-Co/EG catalyst was prepared by electroless plating method,examining the influence of sulfuric acid concentration,sodium hydroxide concentration for Pd-Co/EG electrocatalytic performance.The results show that peak current and steady-state current of Pd-Co/EG catalyst have increased to 2.59 times and 2.59 times respectively,sulfuric acid concentration varying from O.lmol/L to 0.5mol/L,peak potential moving to the right for 39 mV.Having created the Rs(ReQ1)(Rct5Q2)circuit model,the simulated impedance curve is good anastomotic with the measured experimental data,and the solution resistance Rs and the charge transfer resistance Rct are steady decreasing with the concentration.Sodium hydroxide concentration varying from 0.5mol/L to 2.5mol/L,peak current and peak potential of Pd-Co/EG catalyst are monotone increasing,and the If/Ib value is greater than 1.Finally,It was studied that the influence of the methanol concentration and temperature in the acid or alkaline medium for Pd-Co/EG electrocatalytic performance.The results show that methanol concentration varying from 1.0 mol/L to 2.0mol/L,the slope between the peak current and the methanol concentration is biggest.Temperature varying from 25 ? to 45 ?,the catalytic activity of Pd-Co/EG in acid medium is increasing monotonously with the temperature,and it is the best performance for the electrode catalyst is at 45 C.The peak current of Pd-Co/EG catalyst in alkaline medium at 25 C is 7.46 times than that in acid medium,peak potential lowing 0.18V,and the If/Ib value keeps monotone increasing from 25? to 65 ?. |
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