Neste trabalho rutênio foi depositado em níveis de sub-monocamadas sobre Pt (100) através da deposição espontânea em vários tempos de deposição. As superfícies de Pt(100)/Ru foram analisadas pela técnica de STM ex-situ para visualizar a morfologia dos depósitos de rutênio formados sobre a superfície da Pt (100). Foi observada a formação de aglomerados de rutênio com diâmetros entre 1,0 e 4,5 nm e com espessura biatômica no centro das ilhas. Observou-se que as ilhas de rutênio estão homogeneamente distribuídas sobre os terraços da platina e não ocorre deposição preferencial sobre os degraus ou defeitos superficiais. O grau de recobrimento de rutênio foi avaliado pelo decréscimo das cargas voltamétricas dos picos de adsorção-dessorção de hidrogênio dos eletrodos Pt(100)/Ru. Os eletrodos Pt(100)/Ru com grau de recobrimento de ~ 0,3 mostraram uma alta atividade para a eletrooxidação de etanol. Os resultados eletroquímicos suportam fortemente o mecanismo bifuncional para o aumento na oxidação do etanol.In the present work ruthenium was deposited in submonolayer amounts on Pt(100) by spontaneous deposition at several deposition times. The Pt (100)/Ru surfaces were analyzed using ex-situ STM to image the deposits characteristic of ruthenium on Pt (100). It was observed the formation of ruthenium islands with diameters between 1.0 and 4.5 nm with bi-atomic thickness in the center of the islands. A homogeneous distribution of the ruthenium islands on the platinum terraces was found, with no preferential deposition on steps or surface defect sites. The ruthenium coverage degree had been calculated by the decrease of charge of the hydrogen adsorption-desorption peaks in the cyclic voltammograms of the Pt(100)/Ru electrodes. The Pt(100)/Ru electrodes with a ruthenium coverage degree of ca. 0.3 showed a high activity for the ethanol electrooxidation. The electrochemical experimental results support strongly the bifunctional mechanism for the enhanced ethanol oxidation.Keywords: STM, cyclic voltammetry, Pt(100)/Ru, ethanol oxidation
IntroductionIt is recognized that there are many ways to promote surface modifications in the level of submonolayers or monolayers of metal atoms on a substrate. A very well known way to realize an electrochemical surface modification of a metal substrate is through the called underpotential deposition phenomenon (UPD), where the metal atoms are deposited on a metal substrate that has a higher work function (φ).1 Once formed the film on a substrate, it can be arrayed in two-dimensional surface structure. Some aspects must be taken into account to determine a specific structure, like electrode material, electrode potential, surface crystallography, anion coadsorption and cationic precursor. Generally the films formed on the substrates are dissolved when a sufficiently positive electrode potential is reached.The electrodeposition of sub-monolayers or monolayers is other way of getting metal deposits. In this case, the relationship between the work function of the substrate and that of the deposit is...