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Here we investigated the photoelectrodeposition of oxygen-evolving catalysts (OECs) based on oxy-hydroxides-phosphates of Co, Fe, or Ni (CoPi, FePi, and NiPi) on the WO3/BiVO4 heterojunction and their activity in water oxidation. The OECs were deposited by cycles of (i) open-circuit potential (OCP) and (ii) applying a potential positive enough to oxidize the metallic precursor on the WO3/BiVO4. The crystalline and optical properties of the photoanodes were not significantly affected by the OECs deposition. However, there was a remarkable increase in the photocurrent densities (jpc) to water oxidation, where the modification with FePi showed the best result, achieving 2.12 mA cm−2, which corresponds to 2.83 times higher than the heterojunction without the OECs. Furthermore, the OECs deposition changed the morphology of the heterojunction with the deposition of a thin film on its surface. In addition, during the FePi deposition, the BiVO4 layer seems to partially dissolve. Our study shows a facile methodology to boost the activity of photoanodes to the water oxidation by photoelectrodeposition of OECs.

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.

Cu-doped WO3 electrode was fabricated on FTO substrate via one step preparation by modified sol-gel method using a suspension of [(NH4)10H2(W2O7)6] and CuSO4·5H2O in mix of polyethylene glycol 300 and ethylene glycol. Photoelectrocatalytic degradation of bisphenol A (BPA) with Cu-doped WO3 electrode was performed under visible light irradiation and H2O2 as auxiliary oxidizing agent. For monitoring of the photoelectrocatalysis it was used conventional and alternative method (UV–Vis spectrophotometry and electrochemical sensor, respectively). After 8 h of assay, it was verified removal of 80% of BPA and formation of the phenolic intermediates using electrochemical sensor and 75% of total carbon organic removal.

The search for greener energy sources has led to the development of biodiesel. One of its by-product, glycerol, is usually converted into more valuable products by organic synthesis or homogeneous catalysis. There is still room for the research on converting this molecule by means of an electrolytic or fuel cell - for that goal, a deeper understanding of the process and its variables is desirable. This work aims at describing the role of mass transport at the glycerol electro-oxidation on polycrystalline platinum in acidic media. We found that at a proper condition, a new faradaic process is observable in the cyclic voltammetry at ∼0.55 V, regarding the oxidation of glycerol at lower potentials. By means of a numerical experiment it is proposed that a soluble intermediate, namely glyceraldehyde, is the main actor in the inhibition of the process and that its removal, by the electrode rotation, yields a less poisoned surface. The results presented suggest that the aim for electrolytic or fuel cells should be the development of catalysts less active for glyceraldehyde and that the mass transport is a key factor in designing those devices.

In this work, the effect of copper addition on NiMo coating is evaluated in regard to the hydrogen evolution reaction (HER). NiMo and NiMo-NiCu composites are prepared by a simple coelectrodeposition process. The effect of Cu on deposit characters were tested by varying it in the range of 0.06-0.20 molar ratio. Copper addition promotes the growth of a new crystalline phase: NiCu. Also, the copper addition changed the composite surface. NiMo-NiCu0.12 shows a surface roughness 30 times higher than the NiMo material. NiMo-NiCu materials present higher activity toward HER, larger electroactive area, and higher stability in continuous water electrolysis than NiMo catalysts, as demonstrated by Tafel curves, electrochemical impedance spectroscopy measurements, and polarization tests. The combination of the large electroactive area due to the copper addition, the synergism between Ni-Mo, and the presence of Ni and Mo oxides on the surface results in catalyst with excellent features for HER application.

Nitrobenzene, a toxic nitroaromatic, a feedstock compound to the production of many commercially relevant chemicals were photoelectrocatalytically reduced into aniline on a photoelectrode comprised by a bismuth-doped CuGaS2 nanocrystallyne thin films on molybdenum. The activity of the photoelectrodes were compared to the reaction performed on undoped-CuGaS2 films, and they were carried out under illumination with an applied bias potential at 0.9 V. Aniline was highly selectively obtained with 83% of conversion for reaction times of 100 min when using Bi-doped CuGaS2, representing higher conversion of nitrobenzene and yield to aniline than the undoped photoelectrode. The catalytic performance of the doped films remained stable for a set of 5 consecutive experiments. These results indicate Bi-doped CuGaS2 as a promising material to be applied in the photoelectrocatalytic reduction of nitrobenzene into aniline through the direct pathway mechanism, using solar light illumination.

In this work, we present a solvothermal method to prepare bismuth (Bi)-doped CuGaS2 chalcopyrite nanocrystals ink and apply it to an all-solution-processed approach for the preparation of films with a thickness of approximately 730 nm and with enhanced optical properties and lower band gap energy than the undoped semiconductor films. The low-cost deposition method is comprised by spray deposition of the chal-cogenide nanocrystals ink onto the molybdenum substrates, producing microcrystalline films with grains larger than 400 nm originated from coalescence of Bi-doped nanocrystals. Bi-doped CuGaS2 microcrystalline films are a good candidate to be applied as an absorber layer in thin-film solar cells.

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 semiconductor photoanodes play an important role in solar fuel generation, and the design of the semiconductor − aqueous electrolyte interface can be crucial in enhancing the energy conversion efficiency. We have investigated the effects on photoelectrochemical oxygen evolution for monoclinic nanostructured BiVO4 films uncoated and coated with microporous sol-gel Al2O3 “over-layers”. Variation of the thickness of the Al2O3 coating (formed by surface sol-gel deposition and annealing at 435 °C) led to a reduction of pseudo-capacitance and allowed optimization of the quantum efficiency. Exploration of the photocurrent enhancement as a function of applied potential reveals two distinct potential domains/mechanisms: (i) a low bias region enhancement effect (assigned to a lowering of the rate of external recombination of electrons with oxygen) and (ii) a high bias region of enhancement (assigned to higher charge carrier mobility due to less trapping in surface states).

This paper reports a study of the electrodeposition of ZnSe on Pt electrodes in a sulfuric acid solution at pH 2.0 with the purpose of producing stoichiometric films. The film's properties were evaluated for different Zn/Se ratios. The films were deposited at different potentials (− 0.2, − 0.5, − 0.7 and − 0.9 V) and characterized by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), X-ray Fluorescence (XRF) and non-contact 3D optical profilometry (3D-OP). Band gap, photocurrent, carrier number and flat-band potentials were determined. The films with higher photocurrent, carrier number, and crystallinity were obtained at − 0.9 V; these films were p-type and presented 1:1 stoichiometry.

This work reports the electrochemical determination of bisphenol A (BPA), hydroquinone (HQ) and catechol (CC) using glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWCNT) and nickel oxide nanoparticles (NiO). MWCNT were functionalized with sulfonitric solution (3H2SO4:1HNO3) and dispersed in dimethylformamide for the MWCNT/GCE manufacturing. The MWCNT/GCE was modified with NiO using cyclic potential in pH 4 maintained by an acetate buffer solution containing 0.008 mol L−1 of nickel nitrate. The concentration of the nickel solution and the number of cycles in the electrodeposition were studied. Morphological characterization of NiO/MWCNT/GCE was carried out by scanning electron microscopy and the presence of NiO was observed. The electrochemical behavior was evaluated by cyclic voltammetry and electrochemical impedance spectroscopy using BPA solution and the results were compared with those of GCE. The NiO/MWCNT/GCE presented the lowest charge transfer resistance. The electrochemical detection of BPA, HQ and CC was developed using differential pulse voltammetry. The analytical curves showed an excellent linear response and the detection limits for the simultaneous determination of BPA, HQ and CC were 2.8 × 10−8 mol L−1, 2.70 × 10−8 mol L−1 and 5.9 × 10−8 mol L−1, respectively.

Hydrogen is seen as a future energy carrier that will assist the global energy fuel demand. However, it is still necessary to study efficient and inexpensive catalysts that can be used on a large scale to make this technology practical. In this paper the electrodeposition of molybdenum disulfide (MoS2) film on titanium (Ti) substrate was performed by cyclic voltammetry and the film was evaluated for hydrogen evolution reaction (HER). The deposition optimized conditions was 25 cycles and 4 mmol L-1 (NH4)2[MoS4] in 0.1 mol L-1 NaClO4 solution. The film was characterized from X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and they showed an amorphous structure and high catalytic activity for HER. The Tafel slope was 85 mV dec-1 and overpotential at -10 mA cm-2 was -139 mV showing that Ti substrate compared with fluorine-tin doped oxide (FTO) substrate favored the HER and electroactivity of MoS2 films.

The co-electrodeposition of copper, indium, gallium and selenium from a pH 1.5 acid bath onto an FTO substrate in the presence of the additive glycerol (GLR) is studied. The concentration of additive in the bath is evaluated, and conditions are optimised for deposition of Cu(In,Ga)Se2 (CIGSe) thin films. The films are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, ultraviolet-visible-near-infrared spectroscopy (UV-Vis-NIR), Mott–Schottky and photocurrent measurements. Mott–Schottky data, XRD and SEM studies reveal an improvement of the crystalline quality and the reduction the number of surface defects of the CIGSe films electrodeposited in presence of the additive. Photo-electrochemical and UV-Vis-NIR measurements show p-type photoconductivity with band gap of 1.34 eV.

The codeposition of Cu, In, Ga and Se from pH 1.5 at Na 2 SO 4 /H 2 SO 4 solution onto fluorine doped tin oxide (FTO) was studied. The effects of Triton 100-X as a noncomplexing and nonionic additive in the electrodeposition process was evaluated. At optimised experimental conditions was possible to obtain of Ga-doped CuInSe 2 films (CIGSe). The films presented two different morphologies, one layer formed by globular structures and another layer constituted of lamellar clusters. The major phase in the films was CIGSe, but binary phases as InSe and CuSe were also identified. The value of the band gap was at about 1.35 eV for all the films. It was observed that the additive presence in electrolytic bath reduces the number of surface defects and increases the crystallinity and purity of the electrodeposited CIGSe.

An investigation is attempted to highlight the importance of electrode preparation. Graphite carbon (GC), SnO2 and single wall carbon nanotubes (SWCNT) were used as components of anode catalyst for lithium-ion batteries. For mixing these materials, two common processes were performed: ball milling of GC + SnO2+ SWCNT and dispersion of SWCNT in GC-SnO2. The composite electrode prepared from dispersion step presented a superior performance, due the formation of porous and hollow microstructure, which provides more lithium storage sites, shorter Li+ diffusion length and sufficient void space.

Thin film of Cu(InGa)Se2 (CIGSe) is a very promising semiconductor material as absorber layers for solar cell and photoelectrochemical hydrogen production application. The electrodeposition may be one effective alternative to vacuum based techniques of CIGSe fabrication. The use of additives in electrodeposition can to cause interesting effect on the growth and structure of the films. Thus, this work evaluated main effects of non-complexing additives (Glycerol and Triton 100-X) on electrodeposited CIGSe thin films. It was observed changes in the microstructure in the grain size of the deposits and this promotes differences in the carriers density, flat-band potential and others properties of the films.

In this work, the ZnTe thin films were electrodeposited using potentiostatic steps, on Pt substrate. The effect of steps number, the deposition time for each element (Zn or Te) and layer order (Zn/Te or Te/Zn) in the morphology, composition, band gap energy and photocurrent was evaluated. Microanalysis data showed that the ratio Zn/Te ranged from 0.12 and 0.30 and the film was not stoichiometric. However, the band-gap value obtained from in all experimental conditions used in this work was 2.28 eV, indicating film growth of ZnTe. The samples with higher Zn showed higher photocurrent, which was of the order of 2.64 µA cm-2 and dendritic morphology.