This paper reports the successful preparation of catalytic electrodes based on carbon-fiber paper modified with dendrimer-encapsulated platinum nanoparticles. The metallic nanoparticles were first synthesized from solution within generation-four hydroxyl-terminated PAMAM dendrimers, which serve as a carrier for their subsequent immobilization on the solid substrates. The carbon-fiber surfaces were activated by means of three alternative anodic pretreatments and then loaded with the dendrimermetal nanocomposites by cycling of the carbon-electrode potential. The degree of oxidation of the carbon surface affects the anchoring of the dendritic material, the coverage of which is indicated by the electroactive area of the encapsulated platinum. The modified carbon-fiber surfaces pretreated by cyclic polarization are found to be electrocatalytic for the oxygen reduction reaction, presenting a good exchange-current density at low platinum loading.

This work examines the effect of the degree of surface oxidation of carbon fibers on the anchoring of hydroxyl- terminated dendrimers that encapsulate platinum nanoparticles. Several methods of electrochemical pretreatment were investigated for the preparation of the carbon-fiber surfaces to obtain electrodes with functional groups of varying characteristics. The resulting carbon-fiber surfaces were modified with platinum-encapsulating dendrimers by means of ether linkages. The coverage of active groups on the oxidized carbon surfaces as well as the active area of the dendrimer-encapsulated platinum (G4OHPt) were evaluated with respect to the pretreatment method. The results showed that cyclic voltammetry as the pretreatment method immobilizes a significant amount of dendrimer- encapsulated platinum on the carbon-fiber surface. Accordingly, kinetic parameters obtained for the oxygen-reduction reaction on this surface indicate acceptable catalytic activity.

In this work, we describe the preparation of composites of Pt, Ru and bimetallic Pt-Ru nanoparticles encapsulated in generation-four hydroxyl-terminated dendrimers (PAMAM-G4OH). The absorption of the metal ions and their chemical reduction were followed by UV-vis spectroscopy. Subsequently, the dendrimers encapsulating the Pt, Ru or Pt-Ru particles were immobilized on the oxidized surface of a glassy carbon electrode (GCE). Cyclic voltammetry (CV) and rotating disk electrode (RDE) measurements were used to determine the oxygen reduction reaction (ORR) kinetics on this surface in aqueous sulfuric acid media and in sulfuric acid solution containing methanol. Preliminary results show that the nanoelectrocatalyst exhibits good stability in these media and good electrocatalytic activity for the ORR in the presence of methanol.