Pronounced synergetic effect of the nano-sized PtSnNi/C catalyst for ethanol oxidation in direct ethanol fuel cell

Carbon supported well-dispersed Pt, Pt₉₀Sn₁₀, Pt₉₀Ni₁₀ and Pt₈₀Sn₁₀Ni₁₀ nanoparticles were synthesized by co-reduction using Bönnemann's colloidal precursor method. X-ray diffraction (XRD) analysis showed that catalysts have the Pt face centred cubic (fcc) structure and their crystallite size are in the range 2-6nm. Regarding the ternary Pt₈₀Sn₁₀Ni₁₀/C catalyst, its lattice parameter is larger than that of Pt₉₀Ni₁₀/C and smaller than that of Pt₉₀Sn₁₀/C. The size of catalyst nanoparticles was observed via Transmission electron microscopy (TEM) and showed an average diameter of 3nm. X-ray photon electron spectroscopy (XPS) results indicate that the surface of Pt₉₀Sn₁₀/C catalyst is enriched in Sn as compared to bulk composition, whereas Pt₈₀Sn₁₀Ni₁₀/C catalyst is Pt-enriched. The onset potentials for ethanol oxidation on Pt₉₀Sn₁₀/C and Pt₈₀Sn₁₀Ni₁₀/C catalysts were significantly lower than that of Pt/C and Pt₉₀Ni₁₀/C. Single direct ethanol fuel cell (DEFC) performances obtained for the Pt₈₀Sn₁₀Ni₁₀/C is promising when compared to that obtained with Pt₉₀Sn₁₀/C catalyst. The effect of Ni by promoting the CC bond cleavage is confirmed by in situ IR measurements. These results suggest the presence of Ni in the Pt₈₀Sn₁₀Ni₁₀/C catalyst can facilitate CC bond cleavage reaction on its Pt-rich surface; however, Sn oxide species activates the adsorbed CO on the surface providing the necessary OH species for oxidation of ethanol at lower potentials.