Platinum nanoparticles supported on porous silicon were synthesized by radiation chemi cal reduction in solutions of reverse micelles. The Pt nanoparticles obtained are electron deficient. The degree of porosity, conductivity type, pore geometry of the silicon matrix, and precursor parameters affect the size, shape, and charge state of the platinum catalysts.Platinum and platinum based composites are consid ered to be the best catalysts of oxygen reduction reactions (ORR) and hydrogen oxidation reactions (HOR) that occur in electrochemical power generators. It was shown in a series of our works 1-4 and other publications 5-8 that nanoparticles of platinum metals and silver supported on porous silicon (PS) and carbon nanotubes are efficient electrocatalysts for fuel cells.Synthesis of metal nanoparticles in solutions of reverse micelles followed by their subsequent adsorption on po rous supports is a promising method for nanoelectrocata lyst formation. 2-4 Reverse micelles are spherical micro droplets of water (pools) stabilized by surfactants (Surf) in an organic solvent. The molar ratio ω 0 = [H 2 O]/[Surf] defined as the solubilization coefficient determines the size of formed metal nanoparticles during the reduction of their ions in water pools. An increase in this ratio favors the formation of larger nanoparticles.There are few published data describing how the elec trocatalytic activity of nanoparticles deposited on the PS surface is influenced by their physicochemical proper ties. 2-6 Therefore, it is of interest to reveal the character of the metal-PS interaction, morphology of supported particles, charge state of the surface, and possibility of formation of new phases and active sites. Information of this kind makes it possible to better understand specific features of the mechanism of electrocatalytic reactions.The formation of catalytic composites involving Pt nanoparticles can result in the appearance of electron deficient Pt δ+ atoms and the electron density redistribu tion at the Pt/semiconductor interface. In addition, chemi sorption of metal nanoparticles on the support will lead, probably, to the formation of chemical compounds be tween the catalyst and supporting matrix. 9,10 On the one hand, it is considered 11 that the adhesion of Pt nanoparti cles on the silicon support is weak because of the low surface energy of interaction between Pt and Si. On the other hand, it is elucidated that new crystalline phases based on Pt, Re, Ru, and Mo are formed 12,13 during the formation of supported metal catalysts with high degree of dispersity. The high electrocatalytic activity of the nano catalyst Pt 3 Sn was shown 14 in the reaction of EtOH oxi dation. Surface intermetallic compounds Pt 3 Co, Pt 3 CoCr, and Pt x Ni are active in the ORR. 15, 16 To solve many controversial questions about the inter action of metal particles with the support, it is important to know the state of these particles on the surface.Measurements of surface potential are usually used to determine the sign of charge of adsorbed ca...
Palladium nanoparticles on the porous silicon were synthesized by radiation chemical reduction in the solution of reversed micelles. The Pd nanoparticles obtained are electron deficient. The porosity, the type of conductivity, the silicon matrix pore geometry, and precur sor parameters influence the size, the shape and the charge state of palladium catalysts. The mechanism of Н 2 and HCOOH electrooxidation on porous silica in the presence of Pd δ+ /Pd redox pair is proposed.The unique properties of the porous silicon (PS) offer the possibility for developing electrocatalytic composites with high surface area (more than 400 m 2 g -1 ) and for preparing specific catalysts in the structure directing porous matrix with the desirable size and shape. 1-4 The low power electric sources of the new generation for elec tronics compatible with the silicon microchips are con structed on the base of catalytically active PS compos ites. 5,6 The use of catalysts in the form of nano sized particles increase their efficiency and decrease their consumption, that is especially important in case of the metals of platinum group. Previously 7,8 we described the results of the synthesis and the application of the palla dium, silver and platinum nanocomposite catalysts for the hydrogen air fuel cells (FC).The development of FC is considered as one of the main breakthrough technologies in the energetics of the 21st century. The efficiency of the direct transforma tion of the chemical energy to the electric energy in the cells achieves 50-70%. The fuel in the PS based FC is hydrogen, methanol, ethanol or formic acid, whereas the oxidant is the oxygen of the air. The reaction products are either H 2 O or H 2 O with СО 2 . In the internal circuit, the ionic electrolyte conductor should provide migration of ions and separation of the fuel reductant and the oxidant. In the modern low temperature FCs the proton exchange membranes are usually utilized as electrolytes. These membranes <0.2 mm thick are prepared from perfluor inated ion exchange polymer permeable to protons. To increase the efficiency of FC operation the development of catalytically active electrodes reactions on anode and cathode is needed.In the development of the novel catalytic systems for the low temperature FC anodes the use of Pd and its composites is at present the most promising option. 2,9The Pd composites possess high catalytic activity in the reactions of oxidation of the widespread fuel types (hydrogen, formic acid, ethanol, etc.) and they are stable toward СО, which is a common catalyst poison in FCs. 9
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