Electrodeposition Of Selenium Research Articles

Electrochemical formation and stability of copper selenide thin films in the choline chloride-urea deep eutectic solvent at gold electrode

The electrodeposition of copper-selenium binary compounds on gold electrode was investigated in the choline chloride – urea (ChCl-U) deep eutectic solvent at 110 °C. Cyclic voltammetry and potentiostatic deposition followed by stripping voltammetries were employed to gain thermodynamic insights pointing to the formation of Cu2Se, which is supported by X-Ray Photoelectron Spectroscopy. The electrochemical stability domain of the compound is about 900 mV (from ≈−0.81 V to ≈+0.07 V vs. a silver quasi-reference electrode) and is consistent with the thermodynamics of induced co-deposition. The domain is limited at positive potentials by the oxidation to Se(0) and at negative potentials by the reduction to Cu(0). While copper is readily deposited on the gold electrode, the electrodeposition of selenium requires a significant overpotential. As a consequence, copper is kinetically favoured in the co-deposition and is present in its pure form at short deposition times. This is circumvented by using longer deposition times or more negative potentials. Photoelectrochemical measurements show that the as-deposited compound behaves as a p-type semiconductor.

Bifunctional Ni–Fe–CoSe2 nanosheets electrodeposited on Ni foam for efficient catalysis of the oxidation of water and urea

Trimetallic selenides as bifunctional electrocatalysts for oxygen evolution reaction (OER) and urea oxidation reaction (UOR) have rarely been reported. Herein, we successfully synthesized nickel-iron-cobalt diselenides on the nickel foam (NiFeCoSe2) by a one-step electrodeposition method. The as-prepared NiFeCoSe2 nanosheets on nickel foam (NF) exhibited significantly improved electrocatalytic performance and stability in a highly alkaline medium (1 M KOH) with and without 0.33 M urea. In particular, the obtained NiFeCoSe2 only requires a potential of 1.52 V (vs. RHE) for OER and 1.37 V (vs. RHE) for UOR to achieve a current density of 50 mA cm−2, along with a stability of 30 h. This was attributed to the unique interconnected nanosheets, binder-free in-situ selenium electrodeposition, synergistic effect, and strong electron interaction of Ni, Fe, Co, and Se elements. This study provides a new avenue for the construction of multimetal selenide electrocatalysts with excellent properties for the oxidation of water and urea.

Phase control in selenium electrodeposition with bath temperature and deposition potential

In the present work selenium films were electrodeposited onto fluorine-doped SnO2 substrates, departing from a Se4+ aqueous electrolyte. The temperature and deposition potential were varied; the structure, morphology and band gap were studied by Atomic Force Microscopy, Raman Spectroscopy and optical absorption. The voltammetry study showed two reduction peaks that shift towards positive potentials as the deposition temperature increases from 25 to 75 °C: the first one shifts between −925 mV and −1120 mV versus Pt and the second between −1060 mV to −1250 mV versus Pt A black/greyish selenium film of a-Se and trigonal Se was deposited at −925 mV@75 °C and a deep red monoclinic Se one at −960 mV@50 °C; in the other conditions the film color indicate a mixture of the red a-Se and trigonal phases confirmed by Raman and optical spectroscopy. Trigonal phase has a calculated band gap of 1.6 eV, red and black a-Se band gap value of 1.83 eV, and monoclinic Se of 2.0 eV, respectively. From Electrochemical Impedance Spectroscopy, the films were found to be n-type, with carrier densities around 1018–1019 cm−3, and Flat Band Potentials between 0.6–1.0 V in dependence of the deposition conditions. The results point out the feasibility of controlling the phase of Se layers using a single aqueous bath and mild temperature conditions.

Effects of Illumination on the Electrochemical Behavior of Selenium Electrodeposition on ITO Substrates

Effects of illumination on the electrochemical behavior of selenium electrodeposition on indium-doped tin oxide(ITO) glass are investigated by linear sweep photovoltammetry, chronoamperometry, electrochemical impedance spectroscopy, and potentiostatic electrodeposition. Linear sweep photovoltammetry results show that the illumination can both enhance the four-electron reduction of Se(IV)/ Se(0) and the six-electron reduction of Se(IV)/ Se(-II). Se(IV)/ Se(-II) and Se(IV)/ Se(0) redox potentials are all positive than the conduction band of selenium, thus the photo-generated electrons which induced from the valence band of selenium can flow to the electrolyte to accelerate the reduction of Se(IV)/ Se(-II) and Se(IV)/ Se(0). Chronoamperometry measurements demonstrate that the electrocrystallization of selenium follows a 3D progressive nucleation model in the dark, while it adheres to a 3D instantaneous nucleation model when under illumination. This is due to the additional driving force (generated by photo-induced electrons) for reduction of SeO32−. Electrochemical impedance spectroscopy proves that the Faraday resistance of Se(IV)/ Se(0) reduction can be greatly reduced by the light. Potentiostatic electrodeposition results indicate that the illumination can accelerate the deposition rate. A denser and larger particle size of selenium thin films can be obtained after applying the photo-assistance.

Electrodeposition of Selenium in a Hydrophobic Room-Temperature Ionic Liquid

Electrodeposition of selenium (Se) in an amide type hydrophobic room temperature ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing SeCl4 as a Se source in the presence of excess chloride on a glassy carbon electrode was studied at 25 and 50°C. Raman spectroscopy showed SeCl4 in BMPTFSA with excess chloride forms an octahedral chlorocomplex of [SeCl6]2–. The reduction of [SeCl6]2– to Se and that of Se to Se(–II) were observed by cyclic voltammetry. Electrodeposits obtained by potentiostatic electrolysis were confirmed to be metallic Se by energy dispersive X-ray, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy.

Electrodeposition of CdSe by ECALD from Citric Buffer

Cadmium selenide thin films were deposited on a gold substrate by the Electrochemical Atomic Layer Deposition (ECALD) method. Detailed investigations of electrodeposition of selenium on gold and cadmium on previously deposited selenium on gold allowed to find the best conditions for CdSe synthesis. The elemental analysis was carried out by stripping voltammetry and energy dispersive spectroscopy (EDS). The analysis of thin films obtained after different number of ECALD cycles suggests stoichiometric ratio very close to the semiconductor compound. Additionally, the analysis were completed by Raman spectroscopy, X-ray diffraction and scanning electron microscopy (SEM) for films obtained after different number of ECALD cycles.

Structure and optical properties of sequentially electrodeposited ZnO/Se bases for ETA solar cells

For a development of base layers for promising solar cells with extremely thin absorbers (ETA) low cost electrodeposition methods for sequential large-scale production of one-dimensional ZnO nanostructures and Se thin films with little material waste were investigated. Research of structure and optical properties of Se and ZnO have allowed us to choose electrolytes and modes in which electrodeposition of selenium was not accompanied by ZnO destruction. It was revealed that annealing of ZnO/Se samples using a halogen lamp provides conversion of amorphous selenious films into suitable for solar cells gray nanocrystalline hexagonal Se without ZnO degradation and thus enables the formation of bases of ETA solar cells.

Study of selenium electrodeposition at gold electrode by voltammetric and rotating disc electrode techniques

The electrodeposition process of selenium has been studied by voltammetry (CV) in connection with a rotating disc electrode (RDE) technique. The paper discusses the mechanism and the rate-determining step of Se deposition. It has been determined that the rate of the Se monolayer-forming process observed at ca. 0.6V vs. NHE is diffusion controlled, not surface activation barrier-dependent. It is proposed that this process is an overpotential deposition process (OPD) and not an underpotential deposition process (UPD). The diffusion coefficient for the reacting species was determined as 2.2×10−5cm2s−1. The reacting species are proposed to be identified with HSeO3− ions. The transfer coefficient, α, for this process was calculated as 0.3, exchange current density, jo, as 1.1×10−6Acm−2, and the rate constant, k, as 9.1×10−7cms−1, respectively.Analysis of RDE data recorded for the Se bulk deposition process taking place at ca. −0.1V vs. NHE and fitting them with either the Levich or the Koutecký–Levich equation indicates that this process is a diffusion-dependent one. The calculated diffusion coefficient was determined as 1.1×10−5cm2s. These data, together with experimental condition (pH) allow one to propose H2SeO3 molecules as those being reduced during the formation of the Se bulk deposited layer. The transfer coefficient, α, for this process was calculated as 0.1, exchange-current density, jo, as 7.7×10−6Acm−2, and the rate constant, k, as 1.6×10−4cms−1, respectively. The comparison of kinetic parameters for six-electron and four-electron processes proves that the reaction responsible for building up the Se film is six-electron reaction.

Microgravimetric Studies of Selenium Electrodeposition Onto Different Substrates

Abstract The mechanism of selenium electrodeposition from sulfuric acid solution on different substrates was studied with the electrochemical techniques. The cyclic voltammetry was combined with the quartz crystal microbalance technique to analyze selenium deposition process. The electrochemical reduction of selenous acid on gold, silver and copper electrodes was investigated. It was found that reduction of selenous acid is a very complex process and it strongly depends from the applied substrate. The voltammetric measurements indicate the range of potentials in which the process of reduction of selenous acids on the applied substrate is possible. Additionally, the microgravimetric data confirm the deposition of selenium and they reveal the mechanism of the deposition process.

Cathodic Electrodeposition of Amorphous Elemental Selenium from an Air- and Water-Stable Ionic Liquid

Electrodeposition of selenium from 1-propyl-1-methylpiperidinium bis(trifluoromethylsulfonyl)imide is reported. In situ UV-vis spectroelectrochemistry was used to investigate the reduction of diethyl selenite to form elemental selenium thin films from an ionic liquid-acetonitrile medium. Three reduction peaks of diethyl selenite were observed via cyclic voltammetry and are attributed to the stepwise reduction of the selenium precursor adsorbed on the electrode. The electrodeposition mechanism is influenced by both potential and time. Electrodeposition at -1.7 V vs Pt QRE resulted in the deposition of elemental selenium nanoparticles that with time coalesced to form a continuous film. At reduction potentials more negative than -1.7 V the morphology of the deposit changed significantly due to the reduction of elemental Se to Se(2-). In addition, p-type photoconductivity of the films was observed during the spectroelectrochemical measurements. X-ray diffraction and Raman spectroscopy confirmed that the deposited selenium films were amorphous. X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy confirm the films consisted of pure selenium with minor residual contamination from the precursor and ionic liquid.

Selenium electrochemistry in choline chloride–urea deep eutectic electrolyte

The electrochemical behaviour of selenium in the deep eutectic solvent made of a 1:2 molar ratio of choline chloride and urea (ChCl–U) has been investigated at a polycrystalline gold electrode by voltammetry and chronoamperometry. In order to favour the deposition of grey selenium, selenium oxide was chosen as the solution precursor and a temperature range from 70 to 110 °C was selected. Cyclic voltammograms recorded in the 1:2 choline chloride–urea liquid containing 10 mM SeO2 are strongly affected by the temperature. At 110 °C, three main cathodic responses are evidenced around −0.075, −0.2 and −0.7 V. These cathodic peaks have been attributed respectively to the underpotential deposition (upd) of Se, the bulk deposition of Se and the cathodic stripping of selenium associated to the formation of Se(−II). Potentiostatic current transients obtained at 110 °C are indicative of a nucleation with diffusion-controlled growth mechanism for the selenium electrodeposition and support the formation of a upd layer preceding the bulk deposition. The dissolution transients triggered by double potential step perturbations could however not be interpreted on the basis of a similar formalism.

Interfacial electrochemistry and electrodeposition from some ionic liquids: In situ scanning tunneling microscopy, plasma electrochemistry, selenium and macroporous materials

In this paper we report on recent results from our group, namely on the interface ionic liquid/electrode, plasma electrochemistry and electrodeposition of selenium and of macroporous structures. Ionic liquids show an interesting and liquid dependent surface chemistry: in some liquids the long range “herringbone” superstructure of Au(1 1 1) is visible, in others it is not. Glow discharge plasmas can be employed as a contact free electrode to make nanoparticles in solutions, e.g. nanoparticles of germanium. Selenium can be electrodeposited from ionic liquids under environmental conditions in an open cell and both the red and the grey phases of selenium are feasible. With the help of self organized opal structures of polystyrene spheres macroporous materials of Ag, Al and conducting polymers can be made. The prospects and limits of ionic liquids in surface electrochemistry and electrodeposition are shortly discussed.

Nucleation and growth of selenium electrodeposition onto tin oxide electrode

Abstract The initial stages of selenium electrodeposition onto SnO2 coated glass substrates are studied using cyclic voltammetry and chronoamperometry. At low overpotential, the deposition of Se proceeds by a four-electron reduction of Se(IV) to Se(0) and a 2D growth under instantaneous nucleation followed by a multilayer spiral growth mode. At high overpotential, the deposition of Se occurs through a comproportionation reaction between Se(IV) and Se(-II) generated from a six-electron reduction of Se(IV), and a 3D growth under progressive nucleation.

Deposition of selenium thin layers on gold surfaces from sulphuric acid media: Studies using electrochemical quartz crystal microbalance, cyclic voltammetry and AFM

In this paper we report here new considerations about the relationship between the mass and charge variations ( m/ z relationship) in underpotential deposition (UPD), bulk deposition and also in the H 2Se formation reaction. Nanogravimetric experiments were able to show the adsorption of H 2SeO 3 on the AuO surface prior to the voltammetric sweep and that, after the AuO reduction, 0.40 monolayer of H 2SeO 3 remains adsorbed on the newly reduced Au surface, which was enough to gives rise to the UPD layer. The UPD results indicate that the maximum coverage with Se ads on polycrystalline gold surface corresponds to approximately 0.40 monolayer, in good agreement with charge density results. The cyclic voltammetry experiments demonstrated that the amount of bulk Se obtained during the potential scan to approximately 2 Se monolayers, which was further confirmed by electrochemical quartz crystal microbalance (EQCM) measurements that pointed out a mass variation corresponding of 3 monolayers of Se. In addition, the Se thin films were obtained by chronoamperometric experiments, where the Au electrode was polarized at +0.10 V during different times in 1.0 M H 2SO 4 + 1.0 mM SeO 2. The topologic aspects of the electrodeposits were observed in Atomic Force Microscope (AFM) measurements. Finally, in highly negative potential polarizations, the H 2Se formation was analyzed by voltammetric and nanogravimetric measurements. These finding brings a new light on the selenium electrodeposition and point up to a proposed electrochemical model for molecule controlled surface engineering.

Electrodeposition of selenium, indium and copper in an air- and water-stable ionic liquid at variable temperatures

The electrochemical behaviour of Au(1 1 1) and highly oriented pyrolytic graphite (HOPG) substrates in the air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([BMP]Tf 2N) was investigated using in situ scanning tunneling microscopy (STM). Furthermore, the electrodeposition of Se, In and Cu in the same ionic liquid was investigated. The high thermal stability as well as the large electrochemical window of this ionic liquid compared with aqueous electrolytes allow the direct electrodeposition of grey selenium, indium and copper at variable temperatures, as the first step in making CIS solar cells electrochemically, in a one pot reaction. The results show that grey selenium can be obtained at temperatures ≥100 °C. XRD patterns of the electrodeposit obtained at 100 °C show the characteristic peaks of crystalline grey selenium. Nanocrystalline indium with grain sizes between 100 and 200 nm was formed in the employed ionic liquid, containing 0.1 M InCl 3, at room temperature. It was also found that copper(I) species can be introduced into the ionic liquid [BMP]Tf 2N by anodic dissolution of a copper electrode and nanocrystalline copper with an average crystallite size of about 50 nm was obtained without additives in the resulting electrolyte.

Preparation and synthesis of Ag2Se nanowires produced by template directed synthesis

We have prepared silver selenide nanowires by a novel synthesis technique. The nanowires were produced through template directed synthesis, in which we used a porous alumina membrane as the template. Silver was deposited on one surface and in the pores close to that surface of the template, followed by electro-deposition of selenium into the pores. Silver selenide nanowires of high quality were produced inside the pores.

Influence of Citrate Ions as Complexing Agent for Electrodeposition of CuInSe2 Thin Films

The preparation of CuInSe 2 thin films by electrodeposition is studied. The effect of sodium citrate (Na 3 C 6 H 5 O 7 ) as complexing agent on the electrodeposition of pure copper, indium, selenium and of their ternary alloy is emphasized. Cathodic shifts of the copper and selenium electrodeposition potentials with increasing citrate concentration are observed. On the contrary, the presence of citrate in the electrolyte does not change the indium electrodeposition potential but improves its crystallinity. The surface morphology and the composition of the deposited films are characterized by scanning electron microscopy (SEM). The texture of the deposits and their compositions are analyzed by X-ray diffraction. The formation of CuInSe 2 films with a chalcopyrite structure and good stoichiometry is observed.

A Comparison of Atomic Layers Formed by Electrodeposition of Selenium and Tellurium Scanning Tunneling Microscopy Studies on Au(100) and Au(111)

Structures formed by the electrodeposition of atomic layers of chalcogenides Se and Te, on Au(100) and Au(111), are described and compared. Each element, on each surface, forms a low coverage structure, consisting of atoms packed simply in high coordinate sites at distances just above their van der Waals diameter. As coverages are increased above this level, structures composed of chalcogenide atom chains or rings are formed. It is proposed that these chains or rings have significant molecular character, involving orbital overlap of adjacent chalcogenide atoms. Mechanisms are described to account for the formation of these chains and rings. Discussion is also presented concerning the appearance of triangular phase boundaries for both chalcogenides on Au(111). In the case of Se, isolated triangles, about 4–6 nm on a side are distributed across the surface, whereas a network of triangular phase boundaries is observed in the deposition of Te. The triangular phase boundaries in Se appear to result from the nucleation of domains in different threefold sites on Au(111). For Te, however, it is proposed that the triangular domains and phase boundaries are the result of Te atoms being too large to form an extended structure. © 1999 The Electrochemical Society. All rights reserved.

Electrochemical synthesis of photoactive In 2Se 3 thin films

In 2Se 3 thin films were grown by alternate electrodeposition of selenium and indium from separate baths onto titanium substrates with subsequent thermal annealing. The influence of annealing temperature on the properties of the obtained films was examined. The results of X-ray diffraction patterns led to the conclusion that films were β-phase when the temperature ranged between 300 and 500°C. At 600°C the thin film loses Se and the ratio Se/In decreases. Only photoanodic response, n-type thin films, was observed when the samples were tested in a photoelectrochemical cell with a sulfite/sulfate redox couple. Values of the photocurrent on the spectra response were increased when the annealing temperature was also increased, showing the best photocurrent values at 500°C, and the films that were annealed at 600°C showed no photoactivity. Spectral responses after chemical etching of the samples showed a significant increase of the photocurrent. Application of Gärtner-Butler's model to the interface semiconductor-eletrolyte makes it possible to obtain the semiconductor energy gap, on samples heated at 500°C, corresponding to a direct allowed band transition.

Electrodeposition of Amorphous Selenium

Amorphous selenium coatings have been electroplated in thicknesses up to 30 µ (1.2 mils) on bright nickel cathodes (and thicker coatings can be prepared). Data are given for studies leading to the selection of the optimum bath and operating conditions for the formation of reproducible, uniform, and adherent deposits. It is shown that the plating baths employed and the amorphous deposits obtained are extremely sensitive to a variety of conditions, thus emphasizing the need for further study of the electrodeposition of selenium in the amorphous form.