Effect Of Rt-Ru/C Doping With W,Ni And Sn For Methanol Electro-Calalytic Oxidation In Alkaline Media

Direct methanol fuel cell(DMFC)has been considered as one of the most promising mobile power sources due to the merits of methanol such as the abundance source,the inexpensive price,the low poison,the convenient transportion and storage and the high energy denstity.However,the present proton exchange membrance direct methanol fuel cell(PEM-DMFC)are facing with two main problems of the low anode efficiency and the methanol osmoiss.Benefited from the alkaline media,the electro-catalytic activities of anode and cathodic are greatly improved.The opposive direction of electro-osmosis can depress the methanol crossover from anode to cathodic,cell power may be higher than that of PEM-DMFC.Therefore,AEM-DMFC has been paid more attention gradually by human.At present,Although PtRu alloy catalysts have been used widely as anodic catalysts in DMFC,their performance can not satisfy the applied requirement of DMFC,therefore,developing the new electrocatalytic material is the key to the application of AEM-DMFC.The electronegativity of W,Ni and Sn decreases in turn.After the nano- PtRu doped with them,on the one hand,they can change the valence form of Pt in different degree,on the other hand,their valence form can also make the dissociated adsorption energies of H₂O and the active energies from H₂O or OH- to OH_adschange,the two sides have important influence on activities of catalysts.In this paper,Pt-Ru-M(M=W,Ni and Sn)supporting on carbon were prepared by colloidal method.The crystal structure and valence form of catalysts were characterized by XRD and XPS and the activities of catalysts were by cyclic volyammetry(CV).The results indicated:1.the average particle size of catalysts was about 3nm. 2.the elements of Pt,Ru and M.on the surface of catalyst did not exist completely in the form of zero valence,but exist in the form of zero valence and oxidation.3.in this experiment,with the increasing of methanol concentration, the peak currents of methanol oxidation increased markedly,the activity of catalyst improved;with the increasing of PH of solution,the onset potiential for methanol oxidation shifted negatively,the activity of catalyst improved.In the same concentration of methanol and alkaline,the active order of different catalysts is as follows:Pt₅-Ru₄-Ni_0.7/C＞Pt₅-Ru₄-W_0.7/C＞Pt₅-Ru₅/C＞Pt₅-Ru₄/C≈Pt₅-Ru₄-Sn_0.7/C.About the effect of doping,Ni can improve the activities of Pt-Ru/C for methanol electro-catalytic oxidation markedly,W can improve relatively,but Sn reduced the activities of Pt-Ru/C.Based on the atomic ratio,the doping of Ni,W can improve the activities of catalysts more obviously than that of Ru.The current density on Pt₅-Ru₄-Ni_0.7/C catalyst could reach 842.2mA/mg in 1.0mol/LNaOH+1.0mol/LCH₃OH solution in our experiment.The effect between doping with Ni in different atomic ratio and activities of catalysts is as followed:t₅-Ru₄-Ni_0.7/C＞Pt₅-Ru₅/C＞Pt₅-Ru₄-Ni_0.3/C＞Pt₅-Ru₄/C＞Pt₅-Ru₄-Ni_1.5/C.When the atomic ratio of Pt,Ru and Ni was equal tO 5:4:0.7, the catalyst of Pt-Ru-Ni/C showed the highest activity for methanol oxditation. The relation between the content of Ni and the activities of catalysts appeared volcanic.