Evolution of hydrogen at dissolving magnesium surfaces

Frankel, G. S.; Samaniego, Alejandro; Birbilis, Nick

doi:10.1016/j.corsci.2013.01.017

Cited by 357 publications

(260 citation statements)

References 20 publications

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“…[13][14][15][16] However, such high values of the anomalous FE have not been reported yet, to the best of our knowledge. Effect of deposition time on the anodic stripping charge.- Figure 9 shows the charge measured during anodic stripping plotted vs. deposition time.…”

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confidence: 80%

The Initial Stages of Electrodeposition of Re-Ni Alloys

Berkh

Eliaz

Gileadi

2014

J. Electrochem. Soc.

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The early stages of Re-Ni alloy deposition from citrate electrolytes were studied in terms of the apparent faradaic efficiency (FE) of the deposition process, the composition of the deposits and their morphology. The deposition time was varied in the range of 0.05 to 60 seconds. The apparent FE of the deposition process was calculated as the ratio between the charge consumed in electrochemical stripping of the deposit and the charge consumed during electrodeposition. The apparent FE and Re-content in the deposits (measured by energy dispersive X-ray spectroscopy) were shown to decrease with deposition time. Anomalous values of the FE, well above 100%, were observed at short deposition times. Under these conditions, the deposition of material consisting of nanoparticles with diameters of 50-80 nm was observed by scanning electron microscopy studies, supporting the anomalous high deposition rates. This behavior is indicative of chemical reactions taking place at short times in parallel with electrodeposition. The effects of deposition time on the apparent FE and Re-content in the deposits are explained by the changes in catalytic activity of the cathode surface during deposition. Electroplating and electroless plating of Re-based alloys has been investigated in our laboratory in recent years.1-7 Rhenium alone can be deposited, but the faradaic efficiency (FE) is very low and the layer formed is of poor quality and does not adhere well to the substrate. Addition of salts of one of the iron-group metals, (Me = Ni, Co or Fe) leads to high FE and high Re-content of the alloys formed. When alloy deposition is concerned, there are, by definition, at least two reactions occurring in parallel. Moreover, hydrogen evolution is commonly observed. In the particular case of electroplating of Re-Ni alloys, it is common to use citric acid as a complexing agent. This can give rise to several complexes of Ni with the citrate ions, depending on pH, as well as complexes of Re with citrate, and even a triple complex of Re-Ni-Cit. The overall reaction for deposition of Re is given by Eq. 1, in which 7 electrons are involved.Thus, a detailed evaluation of all the steps would be extremely difficult, if at all possible. In several papers in the literature it was shown that this reaction follows the stepwise reduction of the ReO − 4 ion. Deposition of Re from acidic electrolytes was shown to proceed through formation of ReO 2 as an intermediate, followed by the complete reduction to the metal. Possible disproportionation of one of the intermediates has also been suggested as a route for electrodeposition. 8-10The intriguing question is to understand the role of the divalent ion (Me) in inducing the deposition of metallic Re. In our recent papers we proposed the mechanism shown in Eqs. 2 and 3: According to this mechanism, freshly deposited Ni 0 catalytically reduces the perrhenate ion from its complex with citrate to the 5-valent oxidation state in the rhenate ion, ReO

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confidence: 80%

The Initial Stages of Electrodeposition of Re-Ni Alloys

Berkh

Eliaz

Gileadi

2014

J. Electrochem. Soc.

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“…Hydrogen gas collection without external electrolyte convection.-In parallel to the flow cell experiments, additional measurements of the hydrogen evolution on Mg were performed in a setup without external electrolyte convection, 10 which utilized an inverted funnel and burette placed above the working electrode for efficient hydrogen collection. About 1.7 cm 2 of an Mg sample (40 ppm Fe) were exposed to 0.1 M NaCl and various chloride-free buffered solutions, including citric acid solution at pH 3, boric acid solution at pH 7 and carbonate solution at pH 10.5.…”

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confidence: 99%

“…14,16 The notion of incongruent dissolution leading to impurity enrichment is a simple concept, however, not all the characteristics of Mg dissolution or the NDE can be explained simply by such a first order effect. As has been demonstrated and elaborated, 10,17 the hydrogen evolution rate during galvanostatic anodic polarization of Mg is a function of the applied current density, while impurity enrichment effects alone would result in a dependence of HER on the supplied anodic charge for metal dissolution. Consequently, at least one additional factor influencing the HER is mandatory to explain the NDE.…”

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confidence: 99%

“…Furthermore, the cathodic areas grow more rapidly with increasing applied anodic current density, 11 indicating that the copious hydrogen evolution during anodic polarization is induced by an electrochemical reaction. Recent results have also shown that a characteristic of the NDE phenomenon is the accompaniment of enhanced catalytic activity for hydrogen evolution induced by anodic polarization of Mg. [10][11][12] As the exchange current density for the HER is considerably higher on most metals than on Mg, 13 noble metal impurities are thought to play an important role by acting as persistent cathodic sites. Even during extensive dissolution of Mg from anodic polarization, the characteristic potentials realized would not favor the dissolution of noble metals, which would be expected to enrich on the surface with time 14 and in such an instance could enhance the cathodic reaction rate.…”

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confidence: 99%

“…This phenomenon is termed the negative difference effect (NDE), and has been well documented for many decades. [6][7][8][9][10][11] The physical conditions responsible for the NDE remain an important research topic in the context of the complete understanding of Mg as an electrode.…”

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confidence: 99%

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The pH Dependence of Magnesium Dissolution and Hydrogen Evolution during Anodic Polarization

Rossrucker

Samaniego

Grote

et al. 2015

J. Electrochem. Soc.

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The dissolution of magnesium (Mg) has been investigated with an electrochemical flow cell coupled to downstream analysis. The setup allows for polarization experiments and simultaneous determination of the amount of dissolved magnesium ions via inductively coupled plasma -mass spectroscopy (ICP-MS). Additionally, Mg dissolution was compared to hydrogen evolution measurements in the flow cell and also in standard beakers. Experiments were performed in unbuffered NaCl and in buffered solutions of various pH to determine the influence of the pH on surface film stability and Mg dissolution. In borate buffer (pH 10.5), Mg(OH) 2 was found to be more stable than in unbuffered electrolyte. In the flow cell, the negative difference effect (NDE) was absent for low anodic polarization currents in a neutral buffered solution, whilst high anodic polarization currents and unbuffered electrolytes favored its existence. In beaker experiments, strong NDE was observed in a pH 10.5 buffer, and also in pH 7 and 3 buffers, but only at higher applied currents where the buffering capacity was locally overwhelmed. These observations validate the importance of the pH in near surface regions with respect to the stability of Mg-surface films and subsequent NDE.

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Corrosion Performance of Biodegradable Mg–6%Nd–2%Y–0.5%Zr Produced by Melt Spinning Technology**

Hakimi

Aghion

2013

Adv Eng Mater

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Corrosion performance of biodegradable EW62 alloy obtained by melt spinning is evaluated in a simulated physiological electrolyte. The improved corrosion resistance of this alloy is attributed to the formation of a refined microstructure and oxide film both enriched with abnormal content of Nd. The beneficial effect of rapid solidification on the distribution of impurities has minimized their microgalvanic effect, hence contributes the corrosion resistance.

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Evolution of hydrogen at dissolving magnesium surfaces

Cited by 357 publications

References 20 publications

The Initial Stages of Electrodeposition of Re-Ni Alloys

The Initial Stages of Electrodeposition of Re-Ni Alloys

The pH Dependence of Magnesium Dissolution and Hydrogen Evolution during Anodic Polarization

Corrosion Performance of Biodegradable Mg–6%Nd–2%Y–0.5%Zr Produced by Melt Spinning Technology**

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