No abstract

Platinum nanoparticles have been selectively deposited on composites of titanium oxide-carbon and tungsten oxide-carbon. Selectivity of the deposition made it possible to investigate changes in electronic properties of both platinum and oxide support, induced by the so-called strong metal–support interactions (SMSI). X-ray photoelectron spectroscopy (XPS) was used, and changes in binding energy of Pt 4f, Ti 2p, and W 4f core-levels and Pt 4f peak asymmetry were determined. These parameters allowed us to state the changes in local electron density, when Pt is deposited on oxide support. In all cases the binding energy of the Pt 4f signal for platinum deposited on an oxide support was significantly lower in comparison to samples where Pt was solely supported onto carbon. The increase in Pt 4f XPS signal asymmetry was observed. This suggests an increased electron density on Pt. No electron donor could be identified from the analysis of the oxide supports. To explain the observed data, at least two effects must be considered: (i) alloy formation between Pt and the oxide support and (ii) partial charge transfer from substrate to Pt, which can be correlated to previously observed increased activity toward oxygen reduction reaction.

Vulcan XC-72 carbon-supported Pt−Ni alloy nanoparticle catalysts with different Pt/Ni atomic composition were prepared via the carbonyl complex route and their structure was studied by X-ray diffraction spectroscopy at wide angles (WAXS) and Debye function analysis (DFA). The very good agreement between the WAXS pattern and DFA simulation revealed that all the as-prepared Pt−Ni alloy catalysts have a unique and highly disordered face-centered cubic structure (solid solution) and that the lattice parameter decreases with the increase of the Ni content in the alloys. Transmission electron microscopy (TEM) images indicated that the as-prepared Pt−Ni alloy nanoparticles were well dispersed on the surface of the carbon support with a narrow particle size distribution and that their mean particle size slightly decreased with the increase in Ni content. Energy-dispersive X-ray analysis (EDX) confirmed that the catalyst composition was nearly the same as that of the nominal value. Thus, a comparative study was made for the oxygen reduction reaction (ORR) using the thin-film rotating ring-disk electrode method to the behavior of Pt based catalysts on the same carbon support, having the same metal loading, the same disordered structure, and a similar particle size. As compared to the Pt/C catalyst, the bimetallic catalysts with different Pt/ Ni atomic ratios exhibited an enhancement factor of ca. 1.5 to 3 in the mass activity and of ca. 1.5 to 4 in the specific activity for the ORR and a lower production of hydrogen peroxide in pure perchloric acid solution. The maximum activity of the Pt-based catalysts was found with ca. 30 ∼ 40 at. % Ni content in the alloys, which could originate from the favorable Pt−Pt interatomic distance. The ring-current measurements on all the catalysts showed similar behavior for hydrogen peroxide production. The enhanced electrocatalytic activity of as-prepared Pt−Ni alloy catalysts for the ORR is attributed to the high dispersion of the alloy catalysts, to their disordered structure, and to the favorable Pt−Pt mean interatomic distance caused by alloying.