Study Of Preparations And Performances Of Alcohol Electro-oxidation Catalysts With Low Noble Metal Loadings

Direct alcohol fuel cells (DAFCs) are devices converting the chemical energydirectly to the electric energy in which small alcohol molecules serves as fuels. DAFCsare promising portable power sources due to their advantages such as high energyconvertion efficiencies, abundant fuel resources, convenient carrying and low costs. Inorder to improve the catalytic activity and the poison resistance of multi-wall carbonnanotube (MWCNT) supported Pd based catalysts toward the electro-oxidation ofalcohols in alkaline media, in this work, Pd/MWCNT was synthesized using an ethyleneglycol reduction method, and the catalyst was modified via the introduction of transitionmetals thus forming PdM/MWCNT (M=Ni, Mo and Ce) binary catalysts. Themorphologies, compositions and structures of catalysts were characterized bytransmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) anddifferential thermal analysis (DTA) analyses. The catalytic activities and poisonresistances of catalysts were evaluated by electrochemical measurements such as cyclicvoltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedancespectra (EIS) and chronoamperometry (CA). The main results are as follows:(1) The Pd/MWCNT and PdNi/MWCNT catalysts were prepared using an ethyleneglycol reduction method. The results show that the addition of Ni leads to a uniformdistribution of Pd nanoparticles over the support surface, with a mean particle size of2.34nm. PdNi/MWCNT displays a high catalytic activity toward the methanolelectro-oxidation in alkaline solutions. Nickel exists mainly in the forms of Ni(OH)2andNiOOH.(2) The addition of Mo and Ce promotes the catalytic activity of PdM/MWCNTcatalysts. The Mo and Ce compounds were calcinated at350℃, and the preparedPdMo/MWCNT (Pd:Mo=1:0.2) and PdCe/MWCNT (Pd:Ce=1:0.1) display highcatalytic activities and poison resistances toward the methanol electro-oxidation and theethanol electro-oxidation, respectively.(3) With the increase in calcination temperature, more metal oxides formed, whichafforded aboundant oxygen species and accelerated the oxidation of adsorbates, thus the poison resistance of the catalyst was improved. On the other hand, a too highcalcination temperature could reduce the conductivity of the catalyst and destroy thecarbon support.(4) Compared with PdCe/MWCNT, PdMo/MWCNT has a smaller particle size anda uniform distribution. Electrochemical measurements show that PdMo/MWCNT has ahigh catalytic activity and poison resistance toward methanol oxidation in alkalinesolutions. As for the ethanol oxidation reaction, PdMo/MWCNT displays a highcatalytic activity, while PdCe/MWCNT has a good poison resistance.