On the role of Ru and Sn as promotors of methanol electro-oxidation over Pt

Abstract

The role of Ru and Sn on the methanol oxidation over Pt was investigated for three different systems viz. Pt covered with adatom layers of Ru and Sn, electro-codeposited Pt-Ru and carbon supported Pt-Ru. By following the oxide growth on the Pt-promoter metal electrodes with ellipsometry it was found that in the presence of methanol the surface oxides of the promotor metal are no longer present on the surface. This supports the bifunctional model of the promotor action. DEMS measurements at Pt with submonolayer coverage of Ru or Sn revealed that the current efficiency of the methanol oxidation to CO 2 is increased in the presence of Ru or Sn and that the onset potential of the oxidation keeps lowering with increasing amounts of the promoting metal. On electrodeposited Pt-Ru systems the adsorption of methanol already takes place at potentials in the hydrogen range. These results seem to point to an electronic (ligand) effect. This is further corroborated by activity measurements at carbon supported Pt-Ru with very small particles, which show a tenfold higher activity compared with the Ru-free system.It is concluded that the promoting action of Ru and Sn may involve both a bifunctional and an electronic (ligand) effect.

Pt-based anode catalysts for direct ethanol fuel cells

“…Furthermore, as mentioned earlier, -OH species prefers to be adsorbed mostly on Sn than on Pt sites. It is obvious that Sn (or Sn-oxide [30]), Ru and W are able to form oxygen-containing species at lower overpotentials than Pt. These oxygencontaining surface species are necessary for the oxidation of adsorbed CO-like intermediates.…”

Phase diagrams of microemulsions containing reducing agents and metal salts as bases for the synthesis of metallic nanoparticles

“…As was the case for NaOH and NaCl, the wefb at equal -values ( NaOH = 0.02 in Fig.S1 compared to  NaBH4 +  NaOH = 0.02 in Fig.S2(a)) is also slightly affected. The difference, however, is very small as the molecular weights and thus the molar concentrations of NaBH 4 and NaOH are nearly the same (see Tab.1). Looking at Fig.S2(b) one sees that the shift towards lower water and 1-butanol contents is more pronounced due to the larger electrolyte content ( total = 0.11).…”

“…This has proved to be a solution to the problem as it prevents the fast poisoning of the catalyst [1,[3][4][5][6][7][8][9][10]. Different mechanisms were suggested for the role of the added modifying element, namely (a) adsorption of the alcohol molecules on Pt and oxygen derivatives generated from the decomposition of water on the added element (for example Pb, Sn) [11][12][13], (b) "ligand effect" (electronic interaction of the added element with Pt which changes the adsorption energy of the adsorbate on Pt) [14], and (c) homogeneous catalytic reactions which was confirmed by the presence of complexed cations of the added element in the reaction media [12,15].…”

The correlation of electrochemical and fuel cell results for alcohol oxidation in acidic and alkaline media

“…In addition, it has been proposed that the added metal could also have a ligand (electronic) effect on the noble metal [172,173]: the bond between Pt and CO ads is very strong inhibiting the further reaction of the adsorbed molecule, however, when Ru (or Sn) is added to Pt catalyst the energy of the Pt-CO ads bond is decreased and the reaction rate increases. Current knowledge suggests that at least both of these mechanisms apply [174][175][176] indicating that only bimetallic catalysts could increase the reaction rate of alcohol oxidation at low temperatures.…”