Correlation of electrochemical and ellipsometric data in relation to the kinetics and mechanism of Cu2O electroformation in alkaline solutions

Chialvo, María R. Gennero de; Zerbino, J. O.; Marchiano, S. L.; Arvía, Alejandro Jorge

doi:10.1007/bf01006847

Cited by 70 publications

(70 citation statements)

References 19 publications

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“…Torto et al also investigated the electrochemical oxidation of mono-and disaccharides at fresh as well as oxidized copper electrodes in alkaline media. [42] From their experimental data and previously reported work [42][43][44][45][46][47][48][49] it is shown that Cu can also oxidize aldohexoses and their acid derivatives electrochemically via a mechanism which proceeds stepwise from aldohexoses to their acid derivatives. [44] In these studies, despite performing exhaustive electrolysis experiments, no concrete evidence for the production of gluconic or glucaric acids was obtained.…”

Section: Introductionmentioning

confidence: 99%

Electrochemical Oxidation of d‐Glucose in Alkaline Medium: Impact of Oxidation Potential and Chemical Side Reactions on the Selectivity to d‐Gluconic and d‐Glucaric Acid

et al. 2019

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The electrocatalytic oxidation of d‐glucose was studied in alkaline medium on copper, platinum, and gold electrodes with particular emphasis on the synthesis of a high value‐added product: glucaric acid. An initial ranking of the three different materials, with respect to their electrochemical activity towards glucose oxidation, was performed utilizing cyclic voltammetry. To determine which functional group can react on which metal, cyclic voltammetry experiments were performed in three different solutions containing 0.04 M gluconic acid, glucuronic acid, or glucaric acid in 0.1 M aqueous NaOH. The observations drawn based on these initial experiments were then verified by analyzing the product solutions (obtained after prolonged electrolysis experiments) with HPLC analysis. The oxidation of glucose on copper at high potentials leads predominantly to C−C cleavage products, mainly formic acid, with a selectivity of 54.2 %; whereas, at lower potentials, the oxidation of the aldehyde group on C1 and of the hydroxymethyl group on C6 produces moderate yields of gluconic and glucaric acid. On platinum, the oxidation of the aldehyde group on C1 is the most relevant process; therefore, the selectivity towards gluconic acid obtained is as high as 78.4 %. Nevertheless, at lower potentials, a higher selectivity to glucaric acid (12.6 %) and a lower selectivity to gluconic acid (68.0 %) are the result of a more effective oxidation of also the hydroxymethyl group on C6. Gold is the most active and selective electrocatalyst of the ones examined in this work. On gold, at lower potentials, the oxidation of the aldehyde group on C1 produces 86.6 % of selectivity to gluconic acid while, at higher potentials, the oxidation of the hydroxymethyl group on C6 also takes place, promoting the further oxidation to glucaric acid (13.5 % of selectivity is reached after 65 h of reaction at 5 °C, with a residual gluconic acid equal to 65.8 %). The demonstrated dependence of the selectivity on the oxidation potential suggests new future perspectives for the electrocatalytic oxidation of d‐glucose to d‐glucaric acid on bare metal electrodes. Moreover, the low selectivity of this process, very often claimed in literature, has been ascribed here for the first time to two chemical processes, which are in competition with the electrochemical one and both consume the reactant and promote the formation of undesired side‐products.

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Section: Introductionmentioning

confidence: 99%

Electrochemical Oxidation of d‐Glucose in Alkaline Medium: Impact of Oxidation Potential and Chemical Side Reactions on the Selectivity to d‐Gluconic and d‐Glucaric Acid

et al. 2019

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“…26,27,[30][31][32] The results of potential scan from 0.2 to Ϫ1.4 V are presented as solid-line curves in Fig. 3 as well.…”

Section: Resultsmentioning

confidence: 98%

Quantitative Characterization of Cu Deposited on Porous Carbon Using Electrochemical Potential Sweep

Cheng

Teng

2004

J. Electrochem. Soc.

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An electrochemical method was developed to analyze the quantity and oxidation state of exposed Cu impregnated in porous carbon. Carbons of different Cu contents were prepared from Cu͑NO 3 ) 2 impregnation followed by heat-treatment at different temperatures. X-ray diffraction has shown the transformation of the deposited Cu from high to low oxidation states upon increasing the treatment temperature. The crystalline size was also found to increase with temperature. A linear potential sweep from the open-circuit potential of the carbons to Ϫ1.4 V vs. SCE in KOH was able to directly estimate the amounts of CuO and Cu in the carbon from the charge consumed in associated reduction peaks. All the Cu species can be oxidized to CuO at 0.2 V vs. SCE, and this was employed to estimate the amounts of total Cu and Cu 2 O. The present work has demonstrated that because of the conductive feature of carbon, electrochemical measurement becomes an important option to quantitatively analyze metals of different oxidation states present in carbon.Qualitative and quantitative characterizations of oxides formed on metals, such as copper, are considered an issue in application of the metals as electric or magnetic wires. 1 The characterizations have been achieved through electrochemical routes 1 because of the conductive feature of the metal substrate. As for carbon materials, carbon surface oxides on carbon substrates have been extensively explored for several decades. 2-7 Characterization of metal oxides on carbon is rather difficult because of the complicated interactions between metal and carbon. Porous carbons deposited with copper have been widely used as catalysts for wastewater or flue gas treatments. [8][9][10][11][12] In our recent studies, 10-12 activated carbons impregnated with copper have proved to be active in catalyzing NO reduction with NH 3 . The activity of the Cu-loaded carbon is a strong function of the treatment temperature. The influence from heattreatment can be attributed to the change of oxidation state and aggregate size of Cu upon heating. 12 Based on this description the chemical and physical states of metal impregnated in carbon are important factors determining the activity of the metal-loaded carbon. Thus, the development of a metal characterization technique is sought in the present work, and copper is used as an example of the metal loaded. To estimate the amounts of copper oxides, some spectroscopic techniques are useful for qualitative analysis but are not necessarily adequate for quantitative measurement, especially for dispersed metals on porous materials. These techniques include X-ray photoelectron spectroscopy, Auger electron spectroscopy, and electron spin resonance spectroscopy, etc. 13-16 As mentioned previously, an electrochemical route becomes an option for quantitative analysis under the condition that the substrate for the oxides is electrically conductive. Potential sweep voltammetry, which is a widely used technique, is able to identify electrochemical reactions of some deposited metal ...

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“…For a chemical dissolution an interaction of the Cu 2 S surface with OHaq , possibly by specific adsorption can be assumed, leading to the intermediate CuOH. [26][27][28][29][30] By taking the binding enthalpies into consideration, 31-33 the following reaction is thermodynamically favored…”

Section: Methodsmentioning

confidence: 99%

Electrochemical Processing of Surface Layers on CuInS[sub 2] Thin Film Solar Cell Absorbers

Aggour

Lewerenz²,

Klaer³

et al. 1999

Electrochem. Solid-State Lett.

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We present a novel method to remove the unwanted covellite (CuS) in Cu-rich prepared CuInS 2 -CdS-ZnO photovoltaic cells by a combined chemical/electrochemical procedure. Our treatment results in a solid-state transformation by electrochemical reduction in an alkaline electrolyte with subsequent chemical dissolution. The reduction is carried out at -0.95 V vs. saturated calomel electrode. The chemical and electrochemical reactions leading to the dissolution are discussed. After completion of the treatment a pronounced photoeffect is observed. X-ray diffraction shows complete removal of CuS. Scanning electron microscopy confirms a distinct change in morphology.Thin film solar cells are subject to intensive research because of their potential for large scale application. 1 They combine the advantage of high performance with low production costs and therefore short energy payback times. Among several other chalcopyrite materials CuInS 2 (CIS) is considered a promising candidate 2 because of its high absorption coefficient and a bandgap energy around the maximum of the solar spectrum. Laboratory solar cells of polycrystalline CuInS 2 with efficiencies up to almost 13% have been fabricated. 3 The further development and the applicability of solar cells made with polycrystalline thin film CuInS 2 is hindered by several problems including (i) the use of a cyanide etch for removal of the notorious covellite phase 4 which is p + degenerate, (ii) the implementation of poisonous CdS as a buffer layer, 5 and (iii) the resulting type II band line up leading to reduced photovoltages. In this paper, we address the first topic by application of a combined electrochemical and chemical procedure to transform the covellite phase into better soluble species, thus replacing the wet cyanide treatment. We present here the first electrochemical experiments on covellite covered CuInS 2 thin film solar cell absorbers.Since the invention of CuInS 2 thin film solar cells, a copper-toindium ratio higher than one has been needed to achieve efficient cell performance. 2,4,6 Whereas earlier cells were made using a coevaporation process, present absorbers are prepared by sequential sputtering of the metals followed by an annealing process in a sulfur atmosphere. 7 During annealing, a segregation of binary copper-sulfur compounds, especially CuS (covellite), occurs at the surface of the absorber, whereas the Cu/In ratio is thought to be stoichiometric in the bulk. Because CuS is a degenerate p + -type semiconductor, it is necessary to remove this phase with a strongly selective etchant that attacks only CuS and does not disadvantageously affect the underlying CuInS 2 . The only chemical etchants which are presently known to fulfill this condition are cyanide containing solutions such as potassium cyanide (KCN) or sodium cyanide (NaCN). 6,8 The chemical reaction starts with the complexation of the Cu atom of CuS and is followed by a dissolution of the compound in the liquid. 9,10 The chemical stability of CuInS 2 is not completely understood but s...

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Correlation of electrochemical and ellipsometric data in relation to the kinetics and mechanism of Cu2O electroformation in alkaline solutions

Cited by 70 publications

References 19 publications

Electrochemical Oxidation of d‐Glucose in Alkaline Medium: Impact of Oxidation Potential and Chemical Side Reactions on the Selectivity to d‐Gluconic and d‐Glucaric Acid

Electrochemical Oxidation of d‐Glucose in Alkaline Medium: Impact of Oxidation Potential and Chemical Side Reactions on the Selectivity to d‐Gluconic and d‐Glucaric Acid

Quantitative Characterization of Cu Deposited on Porous Carbon Using Electrochemical Potential Sweep

Electrochemical Processing of Surface Layers on CuInS[sub 2] Thin Film Solar Cell Absorbers

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