Deposition and characterization of copper chalcopyrite based solar cells using electrochemical techniques

Cu(In,Ga)Se2 films were electrodeposited on molybdenum substrates from a single pH buffered bath and annealed in a reducing selenium atmosphere. The opto-electronic properties of the films were characterized using a potentiostatically- controlled three electrode setup and an electrolyte contact. Pulsed illumination was used to determine the carrier type and the speed of photoresponse. Chopped monochromatic illumination was used to measure photocurrent spectra. The electrodeposited copper chalcopyrite films were compared with films prepared by sputtering and spraying techniques

Monitoring Corrosion Products on Metal Artefacts by Linear Sweep Voltammetry (LSV)

Metallic surfaces are highly sensitive to their surroundings, and prone to react with airborne pollutants to form complex layers. Electrochemical techniques have the possibility of simultaneously identifying different electroactive compounds [1]. The high sensitivity of Linear Sweep Voltammetry (LSV) allows the detection of extremely thin surface films before they became visible. LSV leads to reduction peaks, which can identify the compounds within the “tarnishing” layer and also its relative abundance [1, 2]. The potentialities of this and others electrochemical techniques has been well demonstrated in several recent works and they seem to be promising and non-invasive tools, even for in situ investigations on the metallic artifacts from cultural heritage. This communication presents data showing the application of the technique to silver and sterling silver coupons exposed, during periods of 1 and 12 months, in the Treasure Room in the Museum (inside showcases) and near the Holy Altar of the Chapel, of Porto Cathedral (Portugal). The influence of various conditions: the atmosphere (Museum and Chapel), exposure time (1 and 12 months) and season (spring, summer, autumn and winter) have been analysed. The LSV spectra of blank polished samples as well as samples covered with thin films of silver sulphide and of silver chloride, formed under controlled conditions, respectively: (i) H2S, 1000 ppm, RH= 53% ± 2, T= 21 ºC ± 1, over periods of 24, 48 and 72 h) and (ii) 3.5% of NaCl, RH=41% periods of 5 h, have been used as references. Concerning the nature of the products developed on the surface during the exposure, data has revealed that the tarnishing layers have a complex nature and are not composed only by silver sulphide. It happens even that silver sulphide is a relative minor component in the tarnish layer. Peaks corresponding to silver chloride and silver oxides were well visible. Small peaks assigned to silver sulphide were identified on the samples exposed in the Chapel. For the 12 months exposures both peaks have increased in size with the peak assigned to chloride being much higher in the case of the Chapel. The seasonal influence, even for the 1 month exposures, was particularly notable on those samples with exposures started in winter with well visible effects on the chloride peak on the tarnish layer of the samples exposed in the Chapel. Obviously, that to obtain analytical information electrochemical techniques can be complemented with spectroscopic techniques, namely, X- ray photon spectroscopy (XPS), laser induced breakdown spectroscopy (LIBS), x-rays fluorescence spectroscopy, among others. [1] A. Doménech-Carbó, M.T. Doménech-Carbó, V. Costa (2009), Electrochemical Methods in Archaeometry, Conservation and Restoration, Berlin: F. Scholz. [2] V. Costa, M. Dubus (2007), Impact of the environmental conditions on the conservation of metal artifacts: an evaluation using electrochemical techniques, in National Museum of Denmark, Museum Microclimates, Copenhagen: T. Padfield and K. Borchersen, 63-65

Electrochemistry of thorium in LiCl-KCl eutectic melts

This work presents a study of the electrochemical properties of Th chloride ions dissolved in a molten LiCl-KCl eutectic, in a temperature range of 693-823 K. Transient electrochemical techniques such as cyclic voltammetry and chronopotentiommetry have been used in order to investigate the reduction mechanism on a tungsten electrode and the diffusion coefficient of dissolved Th ions. All techniques showed that only one valence state was stable in the melt. The reduction into Th metal was found to occur according to a one-step mechanism, through an irreversible reaction controlled by a nucleation process which requires an overpotential of several 100 mV. At 723 K, the diffusion coefficient is DTh(723K) = 3.7 ± 0.2·10-5 cm2.s-1. EMF measurements indicated that, at 723 K, the standard apparent potential is *0ThCl4 /Th) E (723 K) = - 2.582 V vs. Cl2/Cl-, and the activity coefficient γThCl4(723 K) = 8·10-3 on the mole fraction scale (based on a pure liquid reference state)

Sandia Laboratories in-house activities in support of solar thermal large power applications

The development of thermal energy storage subsystems for solar thermal large power applications is described. The emphasis is on characterizing the behavior of molten nitrate salts with regard to thermal decomposition, environmental interactions, and corrosion. Electrochemical techniques to determine the ionic species in the melt and for use in real time studies of corrosion are also briefly discussed

A knowledge-based system for the automatic chronopotentiometric elucidation of electrode reaction mechanisms

A knowledge-based system for the elucidation of electrode reaction mechanisms based on chronopotentiometric experiments is described. The system runs the diagnostic experiments and uses the results in the reasoning process. New mechanistic knowledge can be added directly to its knowledge base in the form of production rules. The system is fully modular and its domain- specific modules can easily be changed for application to other electrochemical techniques. Correct operation of the system is demonstrated with the familiar reduction mechanisms of cadmium (II), zinc (II), cystamine and cinnamaldehyde

On the use of electrochemical techniques to monitor free oxide content in molten fluoride media

The electrochemical behaviour of oxide ions has been studied in fluoride melts(LiF/NaF eutectic) by cyclic voltammetry, square wave voltammetry and chronopotentiometry. The purpose is to determine whether these techniques can be used for titration of free oxide ions (O2-) in molten fluorides released by lithium oxide additions. Cyclic voltammetry is shown to be unsuitable for this purpose due to oxygen bubbling disturbing the oxidation peak, while square wave voltammetry is far more appropriate because the observed signal is a well defined oxidation peak with a height proportional to the oxide content. Thus, the present work is focused on a strategy of oxide ions titration by square wave voltammetry. In addition, this work allows assessing that the electrochemical reduction of oxide ions proceeds by diffusion of these species, and the O2- diffusion coefficient is estimated by chronopotentiometry

Silicon recovery from silicon-iron alloys by electrorefining in molten fluorides

Electrorefining of a silicon-iron material (Si-4.7at%Fe) in molten NaF-KF at 850°C has been investigated in view of recovering pure Si, using electrochemical techniques, SEM-EDS and ICP-AES analyses. The selective electrochemical dissolution of Si was evidenced. Electrorefining runs led to a maximum Si recovery of 80% of the initial Si contained in the material, in the form of a dense deposit at the cathode, with very high current efficiencies. The Si purity has been examined and no Fe was detected by ICP-AES analysis: the recovered Si purity is thus assumed to be higher than 99.99%

Preliminary results of the comparison of the electrochemical behavior of a thioether and biphenyl

An electrochemical cell was constructed to explore the feasibility of using electrochemical techniques to simulate the tribochemistry of various substances. The electrochemical cell was used to study and compare the behavior of a thioether 1,3-bis(phenylthio) benzene and biphenyl. It is found that under controlled conditions biphenyl undergoes a reversible reduction to a radical anion whereas the thioether undergoes an irreversible reduction yielding several products. The results are discussed in relationship to boundary lubrication

The charge transport process at poly(orthoaminophenol) film electrodes

Poly(o-aminophenol) (POAP) films were deactivated and then reactivated, and dependences of the different charge-transport and charge-transfer parameters on the degree of deactivation (θc ) were obtained by employing Electrochemical Impedance Spectroscopy. While some parameters, such as interfacial metal-film and film-solution resistances the high-frequency capacitance and the redox capacitance exhibit a continuous variation without hysteresis between deactivation and reactivation processes within the whole θc range, others, such as electron and ion diffusion coefficients show not only marked changes of slope from given θc values but also hysteresis between consecutive deactivation and reactivation processes.Fil: Tucceri, Ismael Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentin