Catalytic activity of Pd-Ag nanoparticles supported on carbon nanotubes for the electro-oxidation of ethanol and propanol

Pd and Pd-Ag nanoparticles supported on multi-walled carbon nanotubes (MWCNT) were prepared by using the NaBH₄ reduction method in a mixed solvent of ethylene glycol and water; their catalytic activity for the electro-oxidation of ethanol, n-propanol and iso-propanol was investigated in alkaline media by the voltammetric method. The results indicate that Pd and Pd-Ag nanoparticles are well-dispersed on the surface of MWCNTs and the average sizes of metal particles on the Pd/MWCNT, Pd₄Ag₁/MWCNT, Pd₂Ag₁/MWCNT and Pd₁Ag₁/MWCNT catalysts are 7, 4, 7 and 11 nm, respectively. Over these catalysts, the electro-oxidation of n-propanol exhibits larger current density than the oxidation of ethanol and iso-propanol. Moreover, the binary Pd_nAg₁/MWCNT catalysts (n=4, 2, 1), especially Pd₄Ag₁/MWCNT, gives higher current density for the oxidation of ethanol and propanols than the Pd/MWCNT catalyst, suggesting that the addition of Ag can enhance the activity of Pd-based catalyst for the electro-oxidation of alcohols. The excellent activity of binary Pd-Ag/MWCNT catalysts is probably attributed to the weak absorption of intermediate species on Pd due to the interaction between Pd and Ag, which may promote the oxidation of alcohols.