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Electrodic surfaces of natural chalcopyrite and natural pyrite minerals (El Teniente mine, Chile) have been studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy including microanalysis (SEM/EDX). For comparison, fractured and polished mineral surfaces were also studied by XPS. In both electrodes, the formation of Fe(III) species containing oxygen were detected and Cu(II) species containing oxygen were additionally detected for chalcopyrite at advanced oxidation states. The presence of Cu(II) species containing oxygen was not detected by XPS for the initial oxidation states of the chalcopyrite. For pyrite, the present results do not allow confirmation of the presence of polysulfurs such as have been previously proposed. In both minerals, the measurements of SEM and EDX show relevant alterations in the respective surfaces when different potential values were applied. The chalcopyrite surface shows the formation of protrusions with a high concentration of oxygen. The pyrite surface shows a layer of modified material with high oxygen content. The modifications detected by XPS, SEM, and EDX allowed the explanation of the complexity of the equivalent circuit used to simulate the experimental EIS data. At high oxidation states, both minerals showed a pseudoinductive loop in the equivalent circuit, which was due to the active electrodissolution of the minerals which takes place through a surface film previously formed.

Cu x S (x → 2) thin films were obtained by sulfidization of copper thin films previously obtained by spin-coating from a dichloromethane solution of [Cu(II)(2-ethyl hexanoate)2(H2O)2] deposited on ITO substrate, irradiated with UV light and electrochemically reduced. Through cyclic voltammetry experiences performed in a 0.05 M Na2B4O7 buffer solution containing 5 mM Na2S, the electroformation mechanism of Cu x S phase is controlled by a first electron transfer, obtaining an initial formation of Cu(HS)ads that evolves to a Cu x S phase. Potentiostatic current transient recorded in the potential range of −0.8 V ≤ E ≤ −0.7 V showed that the nucleation and growth mechanism of the Cu x S phase obeys a two-dimensional instantaneous process with diffusional and charge-transfer contributions. AFM analysis of the deposits shows that Cu x S phase is preferentially deposited in the valleys left by ITO particles. The average size of Cu x S particles is close to 20 nm. Cyclic voltammetry results, electromotive force determination in the Cu/ /Cu x S galvanic cell, EDAX, and UV analysis demonstrate that the stoichiometric factor x in Cu x S is close to 2. The electro-obtained Cu x S phase was unstable and evolved to other nonstoichiometric compounds at open circuit. The processes responsible for the instability were the own oxidation of Cu x S phase and the water reduction that takes place over Cu x S and bare ITO particles. The last process was studied by electrochemical impedance spectroscopy. Photoelectrochemical measurements in the stability potential range of the Cu x S phase shows that the electro-obtained phase presents a p-type conductivity.

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Hematite nanostructures were electrochemically grown by ultrasound-assisted anodization of iron substrates in an ethylene glycol based medium. These hematite nano-architectures can be tuned from a 1-D nanoporous layer to a self-organized nanotube one if the grown is done onto a bare iron foil substrate or onto an electrochemical pretreated one, respectively. Depending upon the pre-treatment conditioning, the self-organized nanotube layer consists of nanotube arrays with a single tube inner diameter of approximately 40-50 nm and wall thickness of 20-30 nm. Their morphological, structural and optoelectronic properties are studied. The photoelectrochemical properties of the resulting hematite nanostructures are studied from the point of view of their application as photoanodes in splitting of water. Through the photocurrent transients for the three nanostructured hematite type electrodes under study, the rate constants k tr and k rec corresponding to the rate constant of charge transfer and recombination processes have been determined. In all cases, the potential value where k tr > k rec was attained at more negative values than the reversible potential of water oxidation, indicating a photocatalytic effect. All samples show a maximum IPCE value between 350 and 375 nm, being the samples pretreated at −1.0 V which shows the highest IPCE value: 45% at 375 nm. In the last years, hydrogen energy has found increased attention as a renewable and clean energy source.1-5 Among many methods, solar hydrogen generation by photoelectrochemical (PEC) water splitting is a particularly attractive one because of the environmental friendless and the abundance of water and solar energy without emission of pollutants. [1][2][3][4][5] Since 1972, when the pioneering work on PEC water splitting was reported by Fujishima and Honda, 6 a wide range of materials has been investigated. In fact, semiconductor materials such as TiO 2 , SrTiO 3 , WO 3 , ZnO, BiVO 4 and Cu(In,Ga)Se 2,3,4,[7][8][9][10] have been used for the development of photoanodes in PEC cells.Compared to these materials, α-Fe 2 O 3 (hematite), has a narrower band-gap (1.9-2.2 eV), which allows to harvest up to 40% of the incident solar radiation. Furthermore, α-Fe 2 O 3 is a promising semiconducting material for photoelectrochemical and photocatalysis applications due to its stability, abundance and environmental compatibility, as well as convenient position of the valence band. 3,[11][12][13][14][15][16][17][18][19][20][21][22][23] In spite of the good properties presented by the α-Fe 2 O 3 , several problems must be solved in order to convert this material in an optimal one for certain applications. For instance, two of these problems correspond to: i) the very short hole diffusion length (20 nm, 24 2-4 nm) 25 compared to the light penetration depth (α −1 = 118 nm at λ = 550 nm), which results in the rapid non-radiative electron-hole recombination inside the semiconductor, and ii) poor electrical conductivity. [26][27][28] Two approaches have been taken to tackle the shor...

This work shows a detailed study of the electrodeposition of Cu2O thin films from DMSO solution employing Cu(ClO4)2 and molecular oxygen as precursors. Through cyclic voltammetry experiences at different temperature, the potential interval where the electrodeposition of Cu2O is carried out was established. The films were obtained potentiostatically and were characterized through different techniques. The films were crystalline with a globular morphology showing a direct bandgap between 2.18 eV – 2.25 eV depending on the temperature of electrodeposition. All the films showed a p-type semiconductor character with a doping level varying between 8.2 × 1018 cm−3 – 2.0 × 1019 cm−3. This difference is attributed to the increase of the stoichiometric defects in the films with the operation temperature.

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