Abstract: Nanostructured Pt-on-Au electrocatalysts (coded as Ptm^Au, m shows the atomic Pt/Au ratio) were prepared by deposition of Pt on colloidal Au particles ((10.0±1.2) nm) and then employed for electro-oxidation of formic acid at concentrations of0.2-3.2mol/L by cyclic voltammetry. The electro-oxidation behavior of formic acid was greatly influenced by the morphology and dispersion of Pt deposits on the Au nanoparticles. The electro-oxidation of formic acid occurred mainly in the high potential range(0.6-1.0V vs SCE) when the Pt existed as a shell fully covering the Au particles in the Ptm^Au/C catalysts (m>0.2), which is similar to the electro-catalysis of a Pt/C catalyst. When the state of Pt deposits was varied from a mono-atomic Pt shell (m≈0.2) to very small flecks of Pt clusters or two-dimensional rafts (m<0.2) on the same Au particles, dramatic enhancement in the oxidation current of formic acid was observed in the low potential range(-0.2-0.6V vs SCE). The mass-specific activity of Pt at peak potential (0.38 V) in a Pt0.05^Au/C catalyst with a 100% Pt dispersion (EAS= 236 m2/g-Pt) was as high as about 40 times that of traditional Pt/C catalysts with about 30% Pt dispersion (EAS=74 m2/g-Pt). These results demonstrate that the catalytic activity of Ptm^Au/C catalysts for formic acid electro-oxidation could be dramatically enhanced by decreasing the size of Pt entities or increasing the Pt dispersion on Au particles. On varying the concentration of formic acid, we observed distinct volcano curves by correlating the electro-oxidation current with the concentration of formic acid for both Ptm^Au/C and Pt/C catalysts. Therefore, the determination of an appropriate concentration window for formic acid can be a key factor to the power densities of direct formic acid fuel cells using Pt-based electrocatalysts.

Key words: electrocatalysis, fuel cell, formic acid, nanostructured platinum catalyst, gold nanoparticle