This paper reports the results of Hydrogen Oxidation Reaction (HOR) experiments over ordered intermetallic (PtSn and PdSn) nanoparticles under CO-free and CO-covered surface conditions. The activity of PtSn toward the HOR was comparable to the activity of commercially available Pt/C. In addition, PtSn/C presented low susceptibility to CO poisoning. In the case of CO-covered surfaces, it was found that the CO was weakly adsorbed at the surface of the PtSn nanoparticles and it did not inhibit the HOR; in fact, this catalyst performed better than Pt/C under the same experimental conditions. X-Ray Absorption assays conducted in the present work proved that the ability of Sn to donate electrons to the Pt adsorption sites was crucial for the resulting intermetallic catalyst to display high activity in the HOR and low susceptibility to CO poisoning.

This paper describes the synthesis and full characterization of Pt–Sn intermetallics with the same stoichiometry and similar particle size but distinct atomic arrangements (ordered intermetallic, ordinary alloy, and core–shell configuration). We propose that these distinct structures provide different electronic conditions to the noble metal’s surface adsorption site, which could influence the active catalytic species’s electrochemical potential. We prepared ordered intermetallic PtSn, ordinary PtSn alloy, and Sn@PtSn core–shell structures by three different methods. X-ray diffraction (XRD) confirmed the chemical identity of the products, and energy-dispersive X-ray spectrometry attested to a 1:1 Pt/Sn atomic ratio for all the materials. High-resolution transmission electron microscopy showed that the mean particle size ranged from 2 to 3 nm for the ordered intermetallic and alloy structures and was about 4 nm for the core–shell material. Electron diffraction corroborated the chemical identity of the materials that was earlier suggested by the XRD measurements and evidenced the ordered intermetallic character of the shell in Sn@PtSn. In conclusion, the X-ray absorption technique with synchrotron radiation demonstrated that the different Pt–Sn structures afforded distinct electronic conditions for the same Pt surface adsorption site, probably due to changes in the energy of the bond established between Pt and Sn in the investigated materials. The results obtained here will guide the development of (electro)­catalysts and will aid understanding of (electro)­catalytic processes for various purposes.

This work used a rotating disc electrode and quasi-steady state polarization curves to investigate the sodium borohydride electrooxidation of ordered intermetallic PtSn/C in alkaline solution. Under similar experimental conditions, PtSn/C proved to be a better electrocatalyst than Pt in an overall process that involved eight electrons. Assays performed in the presence of thiourea and S 2− species evidenced that a chemical hydrolysis step took place, followed by electrochemical oxidation of the generated H 2. The results presented herein suggest that PtSn/C constitutes a promising electrode material for application in alkaline borohydride fuel cell.

The searching for electrode materials with outstanding performance towards organic fuels electrooxidation reactions often is focused on polymetallic materials since they can exhibit a synergetic action resulting from electronic, geometric and/or bifunctional effects. However, as those effects are correlated, it is a difficult task to ascribe the improvement of the performance to a specific property and so to acquire a better understanding of the electrocatalytic process. It well known that Sn atoms exert a beneficial effect towards noble metal adsorption site that, on its turn, enhanced the kinetic of several organic fuels electrooxidation reactions. The enhancement is often suggested because of the electronic donor action of Sn atom; oxophilic action that provides the removal of intermediate species from the surface sites or a combination of these and other effects. The present work aims to elucidate the influence of the Sn atom present in the matrix of ordered intermetallic and alloy PtSn and PdSn (1:1 atomic ratio) nanoparticle materials towards the glycerol electrooxidation reaction in alkaline medium. Ordered intermetallic PtSn/C and PdSn/C nanoparticles were synthesized via modified polyol method and the same materials as alloys were synthesized via microemulsion route. All materials were obtained with similar particles diameters (~2nm) that assures the comparison of the electrode materials performances excluding the influence of the particle sizes. The materials were fully characterized by means of X-Ray Diffraction (XRD); Energy Dispersive Spectroscopy (EDS); High Resolution Transmission Electron Microscopy (HRTEM) and X-Ray Absorption Spectroscopy (XAS) techniques. Moreover, the electrochemical evaluation was performed by using cyclic voltammetry (CV) and chronoamperometry (CA) techniques and the identification of stable intermediates and products of the reactions were obtained from Mass Spectrometry (MS) technique. The electrochemical experiments were carried out in 0.5 mol.L-1  KOH electrolyte solution and all the potentials cited herein are referred to the Reversible Hydrogen Electrode (RHE). The obtained results have pointed to the best performance of the ordered intermetallic material PtSn/C. This best performance was attributed to the electronic donor effect of the Sn atom towards Pt adsorption site that optimized the adsorption of the glycerol molecule causing the dissociative adsorption of the fuel with the cleavage of the C-C bond. The electronic action of the Sn atom was confirmed by the XAS data. This phenomenon was reinforced by the identification of the following intermediates/products of the electrode reaction: formic acid (higher amount from the reaction taking place at ordered intermetallic PtSn/C); glyceric acid and glyceraldehyde (higher amount from the reaction taking place at alloy PtSn/C); glyceraldehyde/dihydroxyacetone (higher amount for ordered intermetallic PdSn/C) and tartronic acid (higher amount for alloy PdSn/C). The electrode reactions mechanisms were proposed for all systems pointing out to the possibility of using different materials for energy or high aggregate value chemicals production. FAPESP Proc. # 2013/05634-8 Figure 1