We have investigated the potential-dependent assembly of 2,2′-bipyridine molecules on both Au(100) and Au(111) surfaces using a newly developed Shell-Isolated Nanoparticle Enhanced-Raman Spectroscopy (SHINERS) technique. We present potential-dependent SHINERS spectra of 2,2′-bipyridine adsorbed on both surfaces collected under anodic as well as cathodic polarization. A series of processes were characterized by the analysis of the data set with Perturbation Correlation Moving Window Two-Dimensional Spectroscopy (PCMW2D) and Two-Dimensional Correlation Spectroscopy (2DCOS). Exquisite spectral detail was achieved and allowed for the characterization of the complicated ring breathing mode and C–C inter-ring stretching modes that are diagnostic of molecular orientation on the surfaces. Detection of several occluded vibration peaks was also made possible with SHINERS. Analysis reveals that in very negative potentials 2,2′-bipyridine adsorbs in a disordered, mixed state with both π-flat cis and several different vertically N-bound cis orientations, in contrast to previously published reports. Our findings provide insight into 2,2′-bipyridine adsorption on Au single crystals and also powerfully combine SHINERS with two-dimensional correlation analysis to yield a more detailed view of spectral transitions.

This work reports the results of a study on the effect of electroless surface deposition of Co on physical and electrochemical properties of a metal hydride alloy. Discharge curves obtained for the Co-covered alloy indicate an additional contribution of the Co redox process on the overall discharge capacity of the electrode. There is an increase on the cycle life of the metal hydride alloy on electrodes cycled until a cutoff potential of −800 normalmV (vs. Hg/HgO KOH 6 mol L−1false), although for electrodes cycled until −700 normalmV, there is an increase on the degree of the degradation processes. In situ X-ray absorption near-edge structure and extended X-ray absorption fine structure studies conducted at the K-edges of Co and Ni of the coated alloy have shown that there is some metal oxidation after the electrode cycling. There was no significant change in the cobalt environment with the alloy charging, except by an increase on the coordination number. This indicates the presence of a more ordered Co phase in the charged alloy. © 2003 The Electrochemical Society. All rights reserved.

Surface-enhanced Raman scattering (SERS) spectra were collected continuously during cyclic voltammetric measurements on silver electrodes in alkaline aqueous solution at room temperature. Three water librational modes as well as the bending mode peak were observed in cathodic potential range. The 2D-COS analysis of spectra collected in LiOH and KOH solutions showed that the librational bands appear prior to the bending band on the cathodic scan, while in CsOH solution the potential dependence of these bands was identical. A comparison of librational band frequencies revealed that the water molecules around Cs(+) cations arranged on the electrode surface were poorly hydrogen bonded in contrast to Li(+) and K(+). The water bending band of spectra collected in LiOH solution was found to be the convolution of two contributions, consistent with a two state model of water arranged on an electrode surface.

The behavior of the CO interaction with gold in an electrochemical environment is presented in this work by means of the SERS technique. The results show spectroscopic evidence that the adsorbed CO promotes the formation of oxidic species even at potentials where it is not thermodynamically favorable (lower than 0.6 V vs RHE), explaining the low-overpotential CO electrooxidation reaction onset (@ ca. 0.2 V). At high potentials (<1.3 V), the CO displays an anomalous behavior, persisting adsorbed on the surface at the high coverage oxide film, which allows us to use the CO molecule as a probe and get information about the electrode surface on the course of the reaction as well as suggests gold oxide to be an active catalyst in small organic alcohol oxidation.

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Recebido em 26/4/00; aceito em 9/8/00 NICKEL-METAL HYDRIDE BATTERIES, AN ALTERNATIVE FOR THE NICKEL-CADMIUM BATTERIES. Nickel metal hydride (Ni-MH) batteries have emerged as an alternative for replacement of nickel-cadmium batteries, because of their more environmental compatibility and high energy capacity. In this article, we described the properties and applications for Ni-MH batteries, giving some emphasis on the metal-hydride electrode, including the description of composition, the charge storage capacity and the discharge profile. The key component of the nickel-metal hydride electrode is a hydrogen storage alloy whose composition is formulated to obtain a high stable material over a large number of charge-discharge cycles.Keywords: metal-hydride batteries; hydrogen storage alloys; environmental protection. Quim. Nova, Vol. 24, No. 2, 243-246, 2001. Divulgação INTRODUÇÃOA necessidade de se desenvolver baterias de alta densidade de energia tem aumentado nos últimos anos. Com o advento dos veículos elétricos, micro computadores, telefones celulares e outros aparelhos portáteis, esta necessidade tornase mais urgente. Embora o "design" das baterias convencionais baseadas nos sistemas níquel-cádmio e chumbo-ácido, tenha sido aperfeiçoado nos últimos anos, adequando-as para o uso em aparelhos portáteis, problemas com o descarte de baterias contendo cádmio e chumbo demonstram a necessidade de desenvolvimento de novos sistemas de armazenamento de energia. As baterias de níquel-hidreto metálico (Ni-MH) podem ser consideradas como as sucessoras das baterias de níquel-cádmio, com a vantagem de não conterem metais pesados tóxicos em sua composição, e de possuírem maior densidade de energia 1 . Além disso são consideradas ecologicamente mais corretas pois podem reduzir os problemas associados com o descarte de baterias de níquel recarregáveis.A bateria de níquel-hidreto metálico (Ni-MH) é uma tecnologia relativamente nova que apresenta características operacionais similares às da bateria de níquel-cádmio 2 . Sua principal diferença consiste no uso de hidrogênio absorvido em uma liga, na forma de hidreto metálico, como material ativo no eletrodo negativo, ao invés de cádmio utilizado nas baterias de níquel-cádmio 2 . O eletrodo de hidreto metálico apresenta uma maior densidade de energia que um eletrodo de cádmio, portanto a massa de material ativo para o eletrodo negativo usado em uma bateria de níquel-hidreto metáli-co pode ser menor que a usada em baterias de níquel-cádmio 2 . Isto também permite que se possa utilizar uma maior quantidade de material ativo para o eletrodo positivo, o que resulta em uma maior capacidade ou tempo de descarga para esta bateria.A maioria das características operacionais das baterias seladas de níquel-hidreto metálico são similares às das baterias de níquel-cádmio. As similaridades no que diz respeito à voltagem da célula, à pressão característica e aos métodos de controle de carga sugerem que o sistema Ni-MH deverá continuar tomando uma boa fração do mercado de outras células recarregáve...