Search

Herein, we propose an approach to three-dimensional (3D) reconstruction of corroded samples to have access to information about the shape, diameter, volume, depth, and spatial distribution of pits. For this purpose, a 304 stainless steel sample, after exposure to controlled corrosion conditions, was submitted to a sequence of polishing, surface image acquisition, and sample thickness measurement. This allows the 3D reconstruction of the sample using computational tomography. The analyses of the two-dimensional and the reconstructed three-dimensional images made it possible to evaluate all the geometric parameters of the pits as well as to compare these data with the electrochemical measurements recorded during the corrosion process.

Copper oxides are considered to be very promising materials for promoting a hydrogen evolution reaction (HER). However, some CuO features, such as the recombination of charge carriers, electron diffusion length, and the chemical stability need to be improved. In this work, NiOx was studied as co-catalyst to FTO/CuO, and the films were physically characterised by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The photo-electrochemical activity and stability toward the HER were evaluated by depositing films on fluorine-tin doped oxide (FTO) substrate. Although, the CuO (− 3.61 eV) and NiOx (− 1.13 eV) conduction band positions, estimated by UV-Vis diffuse reflectance and the Mott–Schottky measurements, did not allow electronic transfer from CuO to NiOx, the formation of a thin layer of NiOx on CuO was beneficial for the activity of this material. The best CuO/NiOx film exhibited a photocurrent density of − 1.02 mA cm−2 at 0 V vs. RHE, which was higher than that for CuO (− 0.92 mA cm−2). A mechanism of electron transfer between CuO and NiOx is proposed. The absorption of visible light by CuO leads to the generation of electron-hole pair. Part of the photogenerated electrons are trapped by the NiOOH present in the NiOx layer, as demonstrated by XPS. The oxy-hydroxide is reduced to metallic Ni, and this species acts as a catalyst for the hydrogen evolution reaction. Due to the increase in interfacial pH caused by the evolution reaction of H2, the formed metallic Ni can be regenerated to NiOx.

The present work outlines a simple and novel approach to obtain nanostructured and heterostructured SnS/Sb2S3 thin films. This material showed enhanced photoelectroactivity in comparison to the individual tin (II) sulphide (SnS) and antimony (III) sulphide (Sb2S3) films. These nanostructured films were grown by electrodeposition of antimony tin (SbSn) compound followed by sulphurisation under a sulphur vapour atmosphere. The optimisation of the growth methodology was systematically performed by evaluating the photoelectroactivity of the films prepared at different deposition potentials as well as by characterisation of the as-deposited binary compound and the films after sulphurisation. In comparison to the individual SnS and Sb2S3 films, the SnS/Sb2S3 one presented a photocurrent response increased 10-fold compared to the former and 48-fold compared to the latter. Further studies carried out by Mott-Schottky analysis and band gap determination confirmed that the band edge positions of the single SnS and Sb2S3 phases are suitably aligned, forming a type II heterostructure which facilitates minority carriers’ separation and transportation and therefore improves the photocurrent density values.

A versatile and low-cost methodology for fabricating free-standing carbon graphite (CG)/SnO2/single-walled carbon nanotube (SWCNT) composites as anode material for lithium-ion batteries is described. CG–SnO2 (1:1) was ball milled and the composite obtained was dispersed with different ratios (wt%) of SWCNT. Then, the flexible composite CG–SnO2–SWCNT was successfully manufactured by a simple vacuum filtration procedure. Electrochemical measurements demonstrated that the anode composite paper with 50 wt% CG–SnO2 and 50 wt% SWCNT showed excellent retention of a high specific capacity (318 mA h g−1) after 30 cycles at current density of 0.08 mA cm−2, which was twice that of SWCNT paper (155 mA h g−1). This SWCNT–CG–SnO2 combination is very promising, since the SWCNT could act as a flexible mechanical support, while CG–SnO2 provides high capacity. This paper presents an inexpensive methodology that may be applied to the design of electrodes and evaluates the interaction between SnO2 and carbon materials as anode in lithium-ion battery systems.

The water photo-oxidation to oxygen on iron oxyhydroxide (FeOOH) deposited on a surface of semiconductor materials play a crucial role in the enhancement of different devices. In order to investigate how FeOOH works to produce O2 from water splitting, we have investigated the role of a deposited layer of FeOOH on the bismuth vanadate (BiVO4) films. The simple-modified method based on polyethylene glycol was applied to produce BiVO4 nanostructures and a FeOOH photoelectrodeposition methodology was used to cover the BiVO4 film surface. The photoelectrochemistry study for FeOOH modified BiVO4 revealed a 3.4 times increase in the photocurrent at 1.23 V vs. RHE. A possible explanation to the FeOOH mechanism is that it is actually a green rust containing a mixture of Fe (II) and Fe (III) that acts as center of charge transfer mediation and not as a catalyst itself. This hypothesis has been supported by a change absence in the onset potential, no photocurrent saturation, and no change in the charge carrier density. Moreover, the FeOOH also passivated the surface states of BiVO4 as the open circuit potential shifted 70 mV vs. RHE to more positive potentials.

Sb2Se3 (SSe) has been highlight as a low-cost, less complex, low toxicity, and earth-abundant photovoltaic (PV) absorber not only because of its excellent properties but also because of its demonstrated 5.6% certified efficiency and decent device stability. An understanding of the effects of intentional dopants on the properties of this material would help to further improve SSe PV devices. In this work, Fe-doped SSe thin film was obtained by electrodeposition at different levels of doping, which is an easy, cheap, and scalable technique. At the studied levels, this dopant caused low influence in band gap and morphologic-structural properties of the films; however, it did impact their electronic properties and photoactivity toward hydrogen gas evolution. The film obtained from a deposition bath composed of 5% of Fe presented a photocurrent similar to that shown by the undoped film, despite showing a carrier density that was three orders of magnitude higher. This behavior makes us believe that, compared to the undoped film, a photovoltaic device made with this 5% Fe-doped film would have a higher fill factor and efficiency.

A novel FTO/WO3 electrode decorated with MoS2 was constructed using two simple and low-cost techniques involving a modified single-step sol-gel method for the WO3 film together with the electrodeposition of amorphous MoS2. The photoelectrocatalytic performance of the material was investigated by monitoring the degradation of Reactive Blue 198 dye under visible-light irradiation. The FTO/WO3/MoS2 electrode exhibited excellent photocatalytic activity and afforded total decolorization of the dye after 90 min at low applied current density (5 mA cm−2). The results described herein support the view that MoS2 acts as a noble metal-free cocatalyst by promoting H2 evolution and assisting in the suppression of electron/hole pair recombination in the photocatalytic material (WO3), thereby improving the process of decolorization of the dye solution. The novel approach of combining of the WO3 and MoS2 materials shows particular promise and may prove to be very effective in the photocatalytic degradation of other hazardous organic compounds.

Nanostructured WO3 films were produced by a simple method using ammonium tungstate dissolved in different solvents: ethanol, PEG 300, and a mixture of ethylene glycol with PEG 300. The suspensions were deposited on an FTO substrate by drop casting method and calcined at 500 °C in air atmosphere. The films were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), UV–Vis diffuse reflectance spectroscopy, and photoelectrochemistry measurements. FTO substrates were fully covered by a thin and adherent WO3 film, which presented a nanostructure with particle diameter of 30–80 nm. XRD confirms the monoclinic structure of WO3. Ethanol samples presented higher photocurrent for water oxidation, compared to other solvents. However, these electrodes showed high fragility and the response did not present repeatability. High adhesion was obtained with PEG as solvent (by itself or mixed with ethylene glycol). In addition, WO3 was applied as a photoelectrochemical sensor to detect dopamine under visible light irradiation. The developed sensor showed photosensitivity to dopamine with reproducibility, stability, wide linear range, and low detection limit (0.30 μM).

One-step deposition of photoelectrochemically active BiVO4 (monoclinic) from a polyethylene glycol (PEG300) precursor paint onto titanium substrates is demonstrated to lead to more complex multioxide phase films. Photocurrents in 0.5 M Na2SO4 remain relatively low when compared to those reported on tin-doped indium oxide (ITO) substrates, possibly due to the effect of detrimental underlying titanium oxide phases or mixed phases. For comparison, the one-step deposition is demonstrated also for the direct formation of V2O5 nanocrystalline films, which also exhibited low photoelectrochemical activity. Impregnation of nanocrystalline V2O5 with aqueous Bi3+ is shown to cause substantial recrystallization with formation of much more photoactive BiVO4. In particular, on low-temperature (high surface area) nano-V2O5 (400 °C) and after further mild annealing at 400 °C much improved photoelectrochemical water oxidation activity (ca. 0.3 mA cm−2 at 1.0 V vs Ag/AgCl (KCl (3 M) at 0.1-W cm−2 xenon lamp radiation) is observed. This opens up a new mild temperature two-step route for BiVO4 photocatalysts on practical titanium substrates.

The main purpose of this work was to evaluate the effect of the silver to mercury ratio on the voltammetric responses of silver solid amalgam electrodes (AgSAE’s). For this, the AgSAE were prepared by mechanical mixing the metals in the following mass ratios of silver to mercury: 30/70, 40/60, 50/50, 60/40, and 70/30. The resulting AgSAE’s were physically characterized by energy dispersive X-ray analysis, X-ray diffraction and scanning electron microscopy, confirming the mass percentages of the silver and mercury, the total absence of liquid mercury and a globular structure of all AgSAE’s. Furthermore, it was observed that the AgSAE 30/70 contained only one single phase (Ag2Hg3), and no metallic silver or mercury oxides. Additionally, the resulting AgSAE’s were chemically characterized with respect to the influence of the electrode composition on the reproducibility and electrochemical signals of a hexamine-ruthenium (III) chloride solution by use of electrochemical impedance spectroscopy and cyclic voltammetry. The separation between anodic and cathodic peaks, and consequently, the charge transfer resistance across the electrode/solution interface, and the electroactive area were calculated demonstrating that the 30/70 composition is the best surface for practical applications. Finally, square-wave voltammetry experiments were performed in 4-nitrophenol solution, with a previous optimization of the experimental and voltammetric parameters. The calculated detection limit shows that the AgSAE 30/70 is suitable for determining any contamination by p-nitrophenol, minimizing the toxic residues in case of using liquid mercury electrodes.

The nucleation process of Pb and Cu onto indium-tin oxide electrodes was studied by single potentiostatic steps using 0.1×10−4 mol L−1 Cu(NO3)2 and 2×10−2 mol L−1 Pb(NO3)2 solutions in aqueous 1.0 mol L−1 NaNO3. The current, I max, and the time, t max, corresponding to the maximum, were evaluated by 3D nucleation with a diffusion-controlled growth model for instantaneous and progressive nucleation. The non-dimensional plots of (I/I max)2 vs. t/t max showed that Cu and Pb nucleation closely followed the response predicted for instantaneous nucleation. Other parameters, such as I vs. t 1/2 and I 2 max t max, as well as nuclei micrographs, were analyzed, corroborating the results obtained.