Study Of The Influence Of Surface Modification And Support Material On The Electrocatalytic Activity Of Catalysts For Alcohol Oxidation Reaction

Direct alcohol fuel cells（DAFCs）are new low-temperature fuel cells that uses small molecular alcohols such as methanol and ethanol as fuels.Metal composition and carrier are important components of fuel cell catalysts,and are also the main factors affecting catalyst performance.In this study,the following two methods were employed in the preparation of catalysts to improve the activity of catalysts via the synergistic effect between different metals and between metals and support materials for the electrooxidation of alcohol and to reduce the cost of catalysts:one is the electrochemical deposition of a small amount of precious metals on the surface of base metal nanoparticles,and the other one is the use of zeolites as catalyst supports.The details of the work are as follows:1.The decoration of the surface of Ni nanoparticles supported on carbon black with Pd and Au and the electrooxidation of allyl alcohol on the Au/Pd/Ni/C catalysts in alkaline solution have been investigated.The decoration of Ni/C is performed by the electrochemical deposition of a small amount of Pd and then Au on Ni/C,and the Au_x/Pd_y/Ni₁₀₀/C catalysts with the（x+y）:100 atomic ratios of less then 4.5（0.2<x<1.2 and 0.6<y<3.1）are prepared.Characterizations of Au/Pd/Ni/C reveal a uniform dispersion of the metal nanoparticles on carbon black and a low coverage of Au and Pd on the Ni nanoparticle surface.Au/Pd/Ni/C behaves more similar to Pd/C than Au/C in allyl alcohol oxidation,and the catalytic activity of Au/Pd/Ni/C depends on the amounts of Pd and Au,with Au_0.9/Pd_2.2/Ni₁₀₀/C exhibiting the highest activity.Besides Pd and Au,the Ni nanoparticles also play important roles in the activity of Au/Pd/Ni/C,although Ni itself has no catalytic activity.The lack of any one of Pd,Au and Ni leads to low catalytic activity,indicating the synergy among the three metals.The result is helpful for preparing ternary electrocatalysts by the surface decoration.2.The electrocatalytic activity of the Au nanoparticles on carbon black?4A zeolite support（denoted as Au/C?4A-Z）for propane-1,2-diol oxidation has been investigated.Characterizations show that the dispersion of Au nanoparticles on C–4A-Z support is less favorable than on carbon black but is more favorable than on 4A zeolite.The Au/C?4A-Z catalysts,in a wide range of the C:4A-Z mass ratios,show high activity and stability for propane-1,2-diol oxidation in alkaline solution compared to Au/C and Au/4A-Z.For instance,Au/C?4A-Z with a C:4A-Z mass ratio of 2:1 shows a more negative peak potential and about 1.8 and 2.5 times higher peak current density than those on Au/C and Au/4A-Z,respectively.The results indicate that the carbon black?4A zeolite support is very efficient for enhancing the catalytic activity of the Au nanoparticles loaded on it and further suggests potential applications of zeolites as support materials for achieving high activity of catalysts.3.The decoration of the surface of Pd₁Ni₃ nanoparticles supported on carbon black with small amounts of Pt and the electrocatalytic activity of the as-prepared Pt_x/Pd₁Ni₃/C catalysts for the oxidation of ethylene glycol in alkaline solution have been investigated.By tuning the time of the Pt deposition,the Pt_x/Pd₁Ni₃/C catalysts with x=0.01?0.06 were obtained.The catalytic activity of Pd₁Ni₃/C catalyst is significantly enhanced by the decoration wit Pt.The highest activity is obtained by Pt_0.04/Pd₁Ni₃/C,with its peak current density being about 2.7 times that of Pd₁Ni₃/C.The small amount of Pt adatoms and the low content of Pd relative to Ni also means the low cost of catalysts.The results of this study are helpful for the preparation of highly active ternary metal catalysts by modifying bimetallic catalysts with a small amount of another active metal.