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  1. Article ; Online: Quasiperiodic behavior in the electrodeposition of Cu/Sn multilayers: extraction of activation energies and wavelet analysis.

    Menezes, Laura / Parma, Eduardo / Machado, Eduardo G / Nagao, Raphael

    Physical chemistry chemical physics : PCCP

    2019  Volume 21, Issue 37, Page(s) 21057–21063

    Abstract: Living systems are one of the many examples in which self-organizing systems yield more intricate structures than those that can be achieved using a "step-by-step" approach. This phenomenon can be observed in electrochemical organic synthesis, ... ...

    Abstract Living systems are one of the many examples in which self-organizing systems yield more intricate structures than those that can be achieved using a "step-by-step" approach. This phenomenon can be observed in electrochemical organic synthesis, oscillating metal deposition and in chemical clocks. There is a plenitude of temporal instabilities during self-organization, from ordinary period-one oscillations, going through quasiperiodicity, to the onset of chaos. Here, we describe the emergence of quasiperiodic behavior during the oscillatory electro-deposition of Cu/Sn. The time-series were characterized using a continuous wavelet transform in order to extract the oscillation frequency of the process with changes in temperature, and to calculate the apparent activation energies. Two different energy ranges are presented, and these are attributed to an activation barrier (∼50 kJ mol
    Language English
    Publishing date 2019-09-17
    Publishing country England
    Document type Journal Article
    ZDB-ID 1476244-4
    ISSN 1463-9084 ; 1463-9076
    ISSN (online) 1463-9084
    ISSN 1463-9076
    DOI 10.1039/c9cp03605a
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article: Investigation of the Oscillatory Electrodissolution of the Nickel–Iron Alloy

    dos Santos, Caio G. P / Machado, Eduardo G / Kiss, István Z / Nagao, Raphael

    Journal of physical chemistry. 2019 Sept. 05, v. 123, no. 39

    2019  

    Abstract: Among many chemical systems displaying oscillatory behavior, the anodic dissolution of transition metals is considered one of the first, with the reports dating from as early as 1828. Since then, electrochemical oscillators have been studied as single or ...

    Abstract Among many chemical systems displaying oscillatory behavior, the anodic dissolution of transition metals is considered one of the first, with the reports dating from as early as 1828. Since then, electrochemical oscillators have been studied as single or in a multielectrode configuration coupled under different network topologies. The coupling is basically made up of electrical connections between the electrodes, keeping them far apart from each other in such a way that only electric coupling is present. Here, we report experimental studies of the coupling between two electrochemical oscillators, namely, the oscillatory corrosion of Ni and Fe, not as two separated electrodes but as in the form of an alloy. The phenomenon is described in terms of stationary and dynamic electrochemical techniques as well as a bifurcation diagram, depicting the region of a Rₑₓₜ versus E plane in which the oscillations are found. Also, a plot with the rate of the electrode potential change was calculated, which revealed the separation of the activation and passivation processes during an oscillatory cycle. These results suggest that there is a change in the mechanism by which the oscillations are observed when comparing Ni, Ni–Fe, and Fe. It is shown that, for the alloy, at potentials lower than the Flade potential, there is a mixed contribution from both Ni and Fe dissolution on the oscillations. This is a different potential region in comparison to Ni (∼1.2 to 1.5 V vs SCE), which is at the transpassive domain and compared to Fe (∼0.4 to 0.6 V vs SCE), with a mass transport-limited process at the current plateau just before the complete passivation. It is proposed that the oscillations found for the dissolution of the Ni–Fe alloy are produced by a mixed contribution from Fe and Ni in terms of their oxides and salts present in the passivation step, which impacts on the nonlinear dynamics of the system. In conclusion, a small amount of Fe (only 20%) is enough to induce a change in the mechanism by which the oscillations emerge, suggesting that a new process is taking place.
    Keywords alloys ; corrosion ; electrochemistry ; electrodes ; iron ; nickel ; oxides ; physical chemistry ; salts ; topology
    Language English
    Dates of publication 2019-0905
    Size p. 24087-24094.
    Publishing place American Chemical Society
    Document type Article
    ISSN 1932-7455
    DOI 10.1021/acs.jpcc.9b06423
    Database NAL-Catalogue (AGRICOLA)

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  3. Article: The effect of the alkali metal cation on the electrocatalytic oxidation of formate on platinum

    Previdello, Bruno A. F / Machado, Eduardo G / Varela, Hamilton

    RSC advances. 2014 Mar. 25, v. 4, no. 29

    2014  

    Abstract: Non-covalent interactions between hydrated alkali metal cations and adsorbed oxygenated species on platinum might considerably inhibit some electrocatalytic reactions. We report in this communication the effect exerted by electrolyte alkali metal cations ...

    Abstract Non-covalent interactions between hydrated alkali metal cations and adsorbed oxygenated species on platinum might considerably inhibit some electrocatalytic reactions. We report in this communication the effect exerted by electrolyte alkali metal cations on the electro-oxidation of formate ions on platinum. The system was investigated by means of cyclic voltammetry and chronoamperometry in the presence of an electrolyte containing Li+, Na+, or K+. As already observed for other systems, the general activity towards the electro-oxidation of formate ions was found to increase in the sequence Li+ < Na+ < K+. In addition, we observed that the inhibition caused by smaller cations has a peculiar potential dependence because of the multi-peaked current profile of the electro-oxidation of formate on platinum. In this respect, we have also identified a new effect caused by cation inhibition at intermediate potentials, namely a peak splitting towards the use of smaller cations. Results are discussed in connection with mechanistic aspects of this model system.
    Keywords catalytic activity ; cations ; electrochemistry ; formates ; lithium ; metal ions ; models ; oxidation ; platinum ; potassium ; sodium
    Language English
    Dates of publication 2014-0325
    Size p. 15271-15275.
    Publishing place The Royal Society of Chemistry
    Document type Article
    ISSN 2046-2069
    DOI 10.1039/c4ra00769g
    Database NAL-Catalogue (AGRICOLA)

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  4. Article ; Online: Development of a versatile rotating ring-disc electrode for in situ pH measurements.

    Zimer, Alexsandro Mendes / Medina da Silva, Marina / Machado, Eduardo G / Varela, Hamilton / Mascaro, Lucia Helena / Pereira, Ernesto Chaves

    Analytica chimica acta

    2015  Volume 897, Page(s) 17–23

    Abstract: There are some electrocatalytic reactions in which the key parameter explaining their behavior is a local change in pH. Therefore, it is of utter importance to develop an electrode that could quantify this parameter in situ, but also be customizable to ... ...

    Abstract There are some electrocatalytic reactions in which the key parameter explaining their behavior is a local change in pH. Therefore, it is of utter importance to develop an electrode that could quantify this parameter in situ, but also be customizable to be used in different systems. The purpose of this work is to build a versatile rotating ring/disc electrode (RRDE) with IrOx deposited on a glass tube as a ring and any kind of material as disc. As the IrOx is sensitive to pH variation, the reactions promoted on the disc can trigger proportional pH shifts on the ring. In such assembly, the IrOx ring presents a fast response time even during the pH transients due to the small thickness of the ring (approximately 10 μm), which enables the detection of interfacial pH changes. The ring electrode was tested toward the interfacial pH shift observed during the electrolytic reduction of water on the disc and also characterized by acid-base titration to determine the response time. As the main conclusions, fast response and durable RRDE were obtained, and this assembly could be used to revisit many electrocatalytic reactions in order to test the importance of local pH on the process.
    Language English
    Publishing date 2015-10-15
    Publishing country Netherlands
    Document type Journal Article
    ZDB-ID 1483436-4
    ISSN 1873-4324 ; 0003-2670
    ISSN (online) 1873-4324
    ISSN 0003-2670
    DOI 10.1016/j.aca.2015.09.047
    Database MEDical Literature Analysis and Retrieval System OnLINE

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