This work reports the use of polythiophene films as supporting matrix for Pt particles. The polymer film hosts were prepared using a strong acid aqueous solution, impregnated with Pt particles, and then tested for electrocatalytic properties for the oxygen reduction reaction ͑ORR͒. Cyclic voltammetry shows that the redox behavior of polythiophene in 12.5 M H 2 SO 4 presents a general feature equivalent to that of several other conducting polymers, especially polypyrrole. Features of the UV-visible spectra obtained during the redox process are consistent with the polaron/bipolaron model. Scanning electron microscopy measurements show that a very homogeneous film layer is obtained with the Pt deposited as very fine particles. Polarization measurements have shown that the ORR occurs through a mechanism involving four electrons with Tafel slopes of ca. 0.12 V dec Ϫ1 for potentials below 0.85 V vs. RHE ͑reference hydrogen electrode͒, in agreement with previous results for other types of dispersed Pt electrocatalysts.

Pd particles were inserted into polythiophene ͑PT͒ films and studied for the activity for the hydrogen oxidation reaction ͑HOR͒ and oxygen reduction reaction ͑ORR͒ in acid media. In situ X-ray absorption spectroscopy ͑XAS͒ was employed for the characterization of the Pd particles and the results confirmed that they possess metallic character. At low potentials, hydrogen is incorporated into the Pd lattice resulting in an increase in both the average Pd-Pd bond distance as well as the structural disorder. XAS results also indicated that a considerable fraction of the total Pd atoms is located in the surface of the electrodeposit, as expected for such a high surface area material. No activity for the HOR is seen for the PT films in the absence of catalysts. For the catalyzed PT films, a chemical reaction involving atomic adsorbed hydrogen atoms on Pt or Pd and the carbon radical in the polaronic PT species may occur causing a progressive degradation of the film properties during HOR. The Pd-modified electrode exhibits a considerable catalytic activity for ORR. Above 0.3 V, only formation of hydrogen peroxide occurs, leading to a two electron ORR mechanism. For smaller potentials, further reduction of H 2 O 2 to water occurs, resulting in a four electron global process.

No abstract

X-ray absorption spectroscopy ͑XAS͒ was used to study the electrochemical incorporation of perrhenate anion, from a 0.1 M NH 4 ReO 4 solution, into poly͑vinylferrocene͒ ͑PVFc͒ and a modified PVFc ͑a copolymer of 30% t-butyl acetylferrocene and 70% t-butyl divinyl ferrocene͒. The polymers were deposited on a carbon cloth current collector from a solution of the polymers in CH 2 Cl 2 . In situ XAS measurements were done at the Fe K edge on the reduced polymers and at 0.9 V vs. Ag/AgCl. Ex situ XAS was done at the Re L 3 edge after oxidation of the polymers at 0.9 V. The oxidized electrodes were washed in water to remove dissolved NH 4 ReO 4 in the electrode pores. XAS was done both on wet-washed electrodes and on electrodes that were dried. XAS showed that at 0.9 V the Fe was oxidized from a ferrocene to a ferrocenium moiety and the FeuC bond distance increased from 2.05 to 2.08 Å. Both the X-ray absorption near-edge spectroscopy and extended X-ray absorption fine structure ͑EXAFS͒ results are consistent with having Ͼ75% of the ferrocene moieties in the polymer oxidized at 0.9 V. The Fe K-edge EXAFS showed no direct indication of interaction of Fe with ReO 4Ϫ . At the Re L 3 edge the only indication of interaction of ReO 4 Ϫ with the polymers was a slight change in the XANES features.Many industrial contaminants exist as anions. These include high-priority pollutants such as chromate, pertechnetate, and nitrate ions. Technetium is an important and difficult pollutant in nuclear waste. Because of its half-life of 213,000 years, technetium ( 99 Tc) presents a long-term hazard for waste disposal. Much of the 99 Tc in the tank wastes is present as pertechnetate (TcO 4 Ϫ ), accounting for its high solubility and mobility in aqueous systems. Conventional sorbents such as commercial ion exchange resins can be used to extract TcO 4Ϫ . However chemical elution of the ion exchange resin generates unwanted secondary wastes. An attractive alternative is to use an electrically conducting polymer ͑e.g., polyvinyl ferrocene, PVFc͒ to separate technetium from nitrate in high-level liquid nuclear waste. Absorption and elution can be done electrochemically without the generation of secondary wastes. The work reported here involves the use of in situ X-ray absorption spectroscopy ͑XAS͒ to study the interaction of anions with conductive polymer poly͑vinyl-ferrocene͒ electrodes. XAS investigation on pure ferrocene and related compounds has been reported earlier by others. [1][2][3][4] In this study perrhenate salts were used as nonradioactive surrogates for pertechnetate. The chemistry and electrochemistry of rhenium and technetium are rather similar. 5 The incorporation of anions in poly͑vinylferrocene͒ ͑PVFc͒ has been extensively studied. This work has been summarized in recent publications. 6,7 Until now the most effective in situ tool has been the electrochemical quartz crystal microbalance ͑EQCM͒. The technique is very effective in studies of anion intercalation and cointercalation of solvent. 6,7 However, EQCM does not yield chem...

By the application of short voltage pulses to a tool electrode in close proximity to a substrate electrode, the electro-polymerization of pyrrole in aqueous solution was locally confined with down to micrometer precision. Depending on the pulse parameters polypyrrole towers with up to 100 microm height and about 50 microm diameter were fabricated on the substrate. The spatial confinement of the electro-polymerization reaction is explained by the local charging behavior of the double layer capacitance during voltage pulses of only 100 ns to 10 micros duration. Additionally, the 3D morphology of the polymer patterns is influenced by the diffusion of the educts and intermediate reaction products in the gap between the tool electrode and the substrate. Proper choice of the tool substrate distance and the pulse to pause ratio of the pulse trains allows the deposition of structures whose morphologies vary from fiber-like to cauliflower-like and compact.