The transition from conventional binary tungsten alloys to advanced high-entropy tungsten alloys was investigated to improve hydrogen evolution reaction (HER) performance in highly alkaline media. Namely, electrodeposited FeW, CoW, NiW, CoFeW, CoFeNiW, and CoCuFeNiW alloys were evaluated for catalytic efficiency and corrosion stability in 10 M KOH to assess the influence of iron-group metals and structural characteristics. Corrosion current densities were determined from voltammetric data within a narrow potential range using an original procedure based on the Butler-Volmer equation. The assessed corrosion current density was minimum for NiW alloy and further increased in the order: NiW G CoW G CoCuFeNiW approximate to CoFeNiW G FeW G CoFeW. The corrosion was evaluated using electrochemical impedance data, which involved fitting the spectra to the corresponding equivalent electric circuits and analyzing the behavior of the alloys during anodic polarization. A corrosion mechanism was proposed based on the obtained data, in which the adsorbed intermediate compounds played a significant role. Notably, although the NiW alloy was the most corrosion-resistant, its catalytic activity was rather weak. In contrast, the cobalt-containing alloys catalyzed HER at less negative polarization than the cobalt-free samples and at much lower overpotentials than Pt. In addition, favorable Tafel slopes for HER were observed in materials containing iron. Thus, multi-component alloys such as CoFeNiW and CoCuFeNiW have been shown to exhibit the combined advantages of their constituent metals.

While renewable energy sources supply a progressively larger share of the world’s energetical needs, their non-continuous nature demands coupling with energy storage systems such as batteries or capacitors. Consequently, copper oxide-based materials have emerged as promising candidates due to their affordability, stability, and suitable electrochemical performance. In this study, nanostructured copper oxide-based films were electrochemically synthesized on copper foil and foam electrodes and investigated for their supercapacitive behaviour. The synthesis was carried out via cyclic voltammetry (CV) for up to 1000 cycles in an alkaline electrolyte. By tuning the upper vertex potential (-0.3 V to 0.65 V vs Ag/AgCl), both phase composition (Cu₂O, Cu(OH)₂, CuO) and morphology (grains, nanoneedles, nanoplatelets) were precisely controlled, demonstrating the versatility of this approach. EIS data using foil and foam electrodes shows that various processes occur on the electrode during changing potential from -1,0 to 0,6 V and back. The capacitive properties of the synthesized films were evaluated using CV in the potential range of 0 V–0.65 V, and the optimized CuO film synthesized on Cu foam exhibited a high specific capacitance of 2760 mF cm⁻². Charge-discharge cycling at 100 mV s⁻¹ for 1000 cycles indicated an initial capacitance increase followed by stable retention, highlighting the structural integrity and electrochemical stability of the films. These findings provide valuable insights into the controlled electrochemical synthesis of copper oxide nanostructures and their potential for high-performance capacitor applications.

In this study, nanostructured copper oxide-based films with crystallite size below 10 nm were electrochemically synthesized on copper foil and foam electrodes and investigated for their supercapacitive behaviour. The synthesis was carried out via cyclic voltammetry (CV) for up to 1000 cycles in an alkaline electrolyte. By tuning the upper vertex potential (−0.3 V to 0.65 V vs. Ag/AgCl), both phase composition (Cu2O, Cu(OH)2, CuO) and morphology (grains, nanoneedles, nanoplatelets) were precisely controlled, demonstrating the versatility of this approach. The kinetics of oxide/hydroxide film formation on foil and foam electrodes were analysed based on EIS data that were interpreted in the frame of equivalent electric circuits and their changes with potential. The capacitive properties of the synthesized films were evaluated using CV in the potential range of 0 V–0.65 V, and the optimized CuO film synthesized on Cu foam exhibited a high specific capacitance of 1380 mF cm⁻2. An energy density of 0.061 mWh cm−2 and power density of 1.28 mW cm−2 were obtained at 10 mA cm−2 discharge current. Charge–discharge cycling at 100 mV s−1 for 1000 cycles indicated an initial capacitance increase followed by stable retention, highlighting the structural integrity and electrochemical stability of the films obtained on 3D foam. These findings provide valuable insights into the controlled electrochemical synthesis of copper oxide nanostructures and their potential for high-performance capacitor applications.

There is a growing focus on sustainability, characterized by making changes that anticipate future needs and adapting them to present requirements. Sustainability is reflected in various areas of materials science as well. Thus, more research is focused on the fabrication of advanced materials based on earth-abundant metals. The role of iron and its alloys is particularly significant as iron is the second most abundant metal on our planet. Additionally, the electrochemical method offers an environmentally friendly approach for synthesizing multifunctional alloys. Thus, iron can be successfully codeposited with a targeted metal from complexing electrolytes, opening a large horizon for a smart tuning of properties and enabling various applications. In this review, we discuss the practical aspects of the electrodeposition of iron-based alloys from complexing electrolytes, with a focus on refractory metals as multifunctional materials having magnetic, catalytic, mechanical, and antimicrobial/antibacterial properties with advanced thermal, wear, and corrosion resistance. Peculiarities of electrodeposition from complexing electrolytes are practically significant as they can greatly influence the final structure, composition, and designed properties by adjusting the electroactive complexes in the solution. Moreover, these alloys can be further upgraded into composites, multi-layered, hybrid/recovered materials, or high-entropy alloys.

Nowadays, there is a growing focus on sustainability, characterized by making changes that anticipate future needs and adapting them to present requirements. Sustainability is reflected in various areas of materials science as well. Thus, more research is focused on the fabrication of advanced materials based on earth-abundant metals. The role of iron and its compounds is particularly significant as iron is the second most abundant metal on our planet. Moreover, the electrochemical approach provides a rather eco-friendly way for versatile materials synthesis, including iron-based materials that can be found in various applications, due to a smart tuning of properties by codeposition of appropriate compounds with iron. Thus, highlighting and boosting its magnetic, catalytic, mechanical, antimicrobial/antibacterial properties, thermal, wear, and corrosion resistance. Among iron-based materials, those with refractory metals, including tungsten-based alloys, are widespread research fields with practical possibilities. Special attention in this review is devoted to peculiarities of electrodeposition from complexing electrolytes of such materials as they can meaningfully impact the final structure, content, and design of properties.

Photoelectrochemically active WO3 films were fabricated by electrodeposition from an acidic (pH 2), hydrogen-peroxide-containing electrolyte at −0.5 V vs. SCE. WO3-TiO2 composites were then synthesized under the same conditions, but with 0.2 g/L of anatase TiO2 nanoparticles (⌀ 36 nm), mechanically suspended in the solution by stirring. After synthesis, the films were annealed at 400 °C. Structural characterization by XRD showed that the WO3 films exhibit the crystalline structure of a non-stoichiometric hydrate, whereas, in WO3-TiO2, the WO3 phase was monoclinic. The oxidation of tungsten, as revealed by XPS, was W6+ for both materials. Ti was found to exist mainly as Ti4+ in the composite, with a weak Ti3+ signal. The efficiency of the WO3 films and composites as an oxygen evolution reaction (OER) photo-electrocatalyst was examined. The composite would generate approximately three times larger steady-state photocurrents at 1.2 V vs. SCE in a neutral 0.5 M Na2SO4 electrolyte compared to WO3 alone. The surface recombination of photogenerated electron–hole pairs was characterized by intensity-modulated photocurrent spectroscopy (IMPS). Photogenerated charge transfer efficiencies were calculated from the spectra, and at 1.2 V vs. SCE, were 86.6% for WO3 and 62% for WO3-TiO2. Therefore, the composite films suffered from relatively more surface recombination but generated larger photocurrents, which resulted in overall improved photoactivity.

Electrodeposition of wear-resistant compositions on the surfaces of parts makes it possible to increase the reliability and durability of machines. Studies have been carried out on the process of applying Fe-WC composite galvanic coatings (CGC) from a suspension electrolyte containing 550–600 g/L FeCl2∙H2O and microabrasive tungsten carbide powder. A high incorporation of dispersed phase particles into the coating was obtained. The properties of Fe-WC composite coatings were studied. A relationship has been established between the concentration of tungsten carbide particles in the electrolyte and the current efficiency of the composition as well as the WC content in the coating. Some physical and mechanical properties of CGC have been determined without their mechanical pre-treatment, in particular, microhardness and wear resistance. The roughness of Fe-WC compositions was studied in comparison with Fe-Al2O3 coatings.

The electrospark deposition (ESD) technique is a low-heat-input process that has great potential for coating applications and the restoration of damaged high-value parts. Carbon steels are commonly used as a substrate material for ESD coatings. However, we demonstrated that carbon steels could be used successfully as the electrode tool for the ESD process. Furthermore, ESD coatings commonly have a high as–deposited roughness. In view of this, in order to reduce the roughness of the ESD coatings, electrodeposition as a tool to alter surface morphology was investigated. Hence, the micro-leveling power of several electrolytes for Ni, Fe-W, Fe, and Cr electrodeposition were evaluated. The maximum leveling effect was detected for Ni electroplated from the Watts electrolyte. Thus, the novel hybrid coatings based on an ESD layer and a subsequent layer of electrodeposited Ni were obtained. ESD layers were obtained by using the following electrode tools as anodes: several types of carbon steels (St20, St30, and St45), alloys T15K6 (WC + TiC + Co), CuNiZn; and NiCr. The morphology and structure of the obtained hybrid coatings with an electrodeposited Ni top-layer was analyzed and compared to ESD coatings from the point of view of their wear and corrosion behavior. The wear rate of the novel ESD coatings based on carbon steels was comparable with coatings obtained using the NiCr electrode tool. Moreover, for all the studied cases, the corrosion resistance of the hybrid coatings was higher than for their ESD counterparts and close to electrolytic chromium.

The amount of waste electrical and electronic equipment (WEEE) has been intensely increasing over the recent decades. In this view, the efficient recovery of metals from WEEE will allow a secure supply of raw materials and will contribute to a circular economy. Among many factors currently affecting the contribution of recycling, is the lack of suitable technologies for WEEE treatment in an environmentally friendly way. Current trends in eco-friendly technologies applied for gold, silver, copper, and tin recovery by electrowinning are reviewed in this paper. In addition, a case study on the perspectives of tin electrowinning has been evaluated. Tin can be present in rather high quantities in WEEE; moreover, its price is about three times higher than that for copper. The electrorecovery of tin has been carried out in cooperation with JSC “Elektronikos perdirbimo technologijos”. The eco-friendly process based on electrowinning from citric acid-containing leachates is elaborated. The citrate-based solutions have been chosen because citric acid is considered to be an environmentally friendly component. A high deposition rate and current efficiency have been achieved at a deposition potential −0.85 V at 60 °C. However, additional steps would be beneficial to diminish the interference of metals present in the scraps, such as Pb(II) and Cu(II), on tin electrorecovery.

Photo-/electrochemical water splitting can be a suitable method to produce “green” hydrogen and oxygen by utilizing renewable energy or even direct sunlight. In order to carry out photoelectrochemical (PEC) water splitting, a photoanode based on transition metal oxides, which absorbs photons and produces photoexcited electron–hole pairs, is needed. The positively charged holes can then participate in the water oxidation reaction. Meanwhile, a cathodic hydrogen evolution reaction (HER) can occur more efficiently with electrocatalytic materials that enhance the adsorption of H+, such as MoS2. In this study, it was shown that WO3/MoSx heterostructured materials can be synthesized by an electrochemical method called plasma electrolytic oxidation (PEO). During this process, many micro-breakdowns of the oxide layer occur, causing ionization of the oxide and electrolyte. The ionized mixture then cools and solidifies, resulting in crystalline WO3 with incorporated MoSx. The surface and cross-sectional morphology were characterized by SEM-FIB, and the coatings could reach up to 3.48 μm thickness. Inclusion of MoSx was confirmed by EDX as well as XPS. Synthesis conditions were found to have an influence on the band gap, with the lowest value being 2.38 eV. Scanning electrochemical microscopy was used to map the local HER activity and correlate the activity hotspots to MoSx’s content and surface topography. The bifunctional catalyst based on a WO3/MoSx heterostructure was evaluated for PEC and HER water-splitting activities. As a photoanode, it could reach up to 6% photon conversion efficiency. For HER in acidic media, a Tafel slope of 42.6 mV·dec−1 can be reached.

The scientific school of Alexander Frumkin, a world-renowned electrochemist born in Chisinau, was at the origin of the electrochemical science in the Republic of Moldova. Research directions, such as high-rate anodic dissolution, plasma electrochemical treatment, electrical methods for mass transfer control, identified as “extreme electrochemistry”, and the electrochemical nanostructuring, have been significantly developed at the national level from both fundamental and applicative viewpoints. Moreover, the European cooperation considerably broadened the opportunities for Moldovan electrochemists in the related areas such as materials science and surface engineering. The present review highlights the main scientific contributions of Moldovan researchers to the world information process related to the above mentioned domains and to the academic–industrial collaboration.

In many countries, the textile industry remains the major contributor to environmental pollution. Untreated textile dyes discharged into water negatively impact the performance of aquatic organisms and may cause a variety of serious problems to their predators. Effective wastewater treatment is a key to reducing environmental and human health risks. In this work, the Fe/Cu catalysts were used in heterogeneous Fenton's reaction for the degradation of high concentrations of methyl orange (model azo dye) in aqueous solutions. For the first time, the catalysts were prepared onto commercial copper foams by potentiostatic electrodeposition of iron using an environmentally friendly electrolyte. The influence of electrodeposition conditions, H2O2 concentration, dye concentration and temperature on the model dye degradation was investigated. It was revealed that both the surface area and the catalyst loading play the major role in the effective dye degradation. The experimental results involving spectrophotometric measurements coupled with total carbon and nitrogen quantification suggest that a solution containing up to 100 mg/L of methyl orange can be successfully decolorized within 90 s at 50°C using porous Fe/Cu catalyst in the presence of hydrogen peroxide that largely surpasses the current state-of-the-art performance. Already within the first 10°min, ∼ 30% of total methyl orange concentration is fully mineralized. The described process represents a cost-efficient and environmentally friendly way to treat azo dyes in aqueous solutions.

Selective electrochemical transformations of bismuth interlayers in (Bi 2 ) m (Bi 2 Te 3 ) n superlattices can be of interest as a means of thermoelectric materials design based on bismuth telluride. In this work, the interlayers in the electrodeposited (Bi 2 ) m (Bi 2 Te 3 ) n superlattice structures formed by pulse potential controlled electrodeposition were characterized with electrochemical microgravimetry on quartz crystal electrodes, cyclic voltammetry, potentiodynamic electrochemical impedance spectroscopy (PDEIS), and in situ Raman spectroscopy. The oxidation potential of bismuth in the interlayers is in between the potentials of metallic bismuth and bismuth telluride anodic oxidation, which allows electrochemical detection and selective anodic dissolution of the interlayer bismuth. Microgravimetry and cyclic voltammetry have provided monitoring of bismuth interlayer dissolution and the subsequent underpotential deposition (upd) of bismuth adatoms onto Bi 2 Te 3 layers in the electrochemically created slits. PDEIS provided separate monitoring of the interfacial charge transfer, spatially restricted diffusion, capacitance of faradaic origin, and double-layer capacitance, which disclosed different variations of the electrochemical interface area in the superlattices with initial bismuth content below and above that of Bi 4 Te 3 . In situ Raman spectroscopy has monitored the removal of bismuth interlayers and distinguished different locations of Bi adatoms in two stages of Bi upd. The electrochemically created slits of molecular dimension have a potential of being used as sieves, e.g., to provide selective accessibility of the electrochemically created centers inside them to molecules and ions in multi-component solutions.

The investigation of Fe-W alloys is growing in comparison to other W alloys with iron group metals due to the environmental and health issues linked to Ni and Co materials. The influence of Na2WO4 concentration in the range 0 to 0.5 M on bath chemistry and electrode reactions on Pt in Fe-W alloys’ electrodeposition from citrate electrolyte was investigated by means of rotating disk electrode (RDE) and cyclic voltammetry (CV) synchronized with electrochemical quartz crystal microbalance (EQCM). Depending on species distribution, the formation of Fe-W alloys becomes thermodynamically possible at potentials less than −0.87 V to −0.82 V (vs. Ag/AgCl). The decrease in electrode mass during cathodic current pass in the course of CV recording was detected by EQCM and explained. The overall electrode process involving Fe-W alloy formation may be described using formalities of mixed kinetics. The apparent values of kinetic and diffusion currents linearly depend on the concentration of Na2WO4. Based on the values of partial currents for Fe and W, it was concluded that codeposition of Fe-W alloy is occurring due to an autocatalytic reaction, likely via the formation of mixed adsorbed species containing Fe and W compounds or nucleation clusters containing both metals on the electrode surface.

The magnetic properties of Fe are exploited in variety of different nanotechnological applications. The electrodeposition conditions have strong influence on resulting properties of Fe films. In this study different methods were used to identify and characterise the morphology and the magnetic properties of Fe films of various thickness electrodeposited at different temperatures. The studied electrodeposited Fe films had elongated structural components orientated mostly perpendicularly to the surface, which caused the magnetisation tilt from the surface of the film. The electrodeposition at 20 degrees C led to more fine and disordered structure compared to the structure obtained at higher electrodeposition temperature, i.e. 65 degrees C. . By applying magnetic field perpendicular to the surface, the minor hysteresis loops of the sample electrodeposited at 20 degrees C changed significantly with repeated measurements. The loop shape depended on initial conditions, probably on the variable magnetic state left after previous magnetisation or on the changes in sample position caused by small angle differences. The analysis of first order reversal curves showed that the magnetisation switching field (pseudo-coercivity) depended on magnetisation at reversal magnetic field, considerably only for 20 degrees C thin film. The magnetic peculiarities of thin film grown at 20 degrees C can be explained by the competing influence of the dipolar interactions and shape anisotropy of vertically elongated grains, and the presence of intergranular soft magnetic material.

Underpotential deposition, i.e. the cathodic deposition above reversible potential E(Men+/Me), produces an atomic layer of a metal on a semiconductor electrode, such as e.g. bismuth telluride. This phenomenon allows electrodeposition of superlattices formed of building blocks of a layered semiconductor structure joined by biatomic metal interlayer. This work outlines the optimized pulse potential controlled electrodeposition of (Bi2)m(Bi2Te3)n films produced under mentioned above technique. The influence on the morphology of the electrodeposited films of key-parameters as applied pulse frequency, duty cycle, a routine of sodium dodecyl sulfate introduction in the electrolyte is discussed. The optimized procedure comprises a short (about 10 s) cathodic pre-treatment at high overpotential of the cathodic reaction, the subsequent periodic switching for 120 min between potentials of electrodeposition and refinement at 0.1 Hz and 5% duty cycle with addition of surfactant 60 min after the start of the electrodeposition.

WO3 photoanodes are widely used in photoelectrochemical catalysis, but typically the as-synthesized material is annealed before application. It is therefore desirable to explore less energy-intensive treatments. In this study, WO3 films of up to 3.9 μm thickness were obtained by galvanostatic anodization of tungsten foil in a neutral-pH Na2SO4 and NaF electrolyte, also containing a NaH2PO2 additive (to suppress O2 accumulation on the pore walls). Additionally, the WO3 photoanodes were modified by applying a cathodic reduction (H+ intercalation) and anodic activation treatment in-situ. XPS spectra revealed that intercalation modifies WO3 films; the amount of W5+-O and O-vacancy bonds was increased. Furthermore, subsequent activation leads to a decrease of the W5+ signal, but the amount of O-vacancy bonds remains elevated. The as-prepared and reduced (intercalated & activated) films were tested as OER photoanodes in acidic 0.1 M Na2SO4 media, under illumination with a 365 nm wavelength LED. It was observed that thinner films generated larger photocurrents. The peculiarities detected by XPS for reduced films correlate well with their improved photocatalytic activity. Photo-electrochemical impedance and intensity modulated photocurrent spectroscopies were combined with steady-state measurements in order to elucidate the effects of H+ intercalation on photoelectrochemical performance. The reduction results in films with enhanced photoexcited charge carrier generation/separation, improved conductivity, and possibly even suppressed bulk recombination. Thus, the intercalation & activation adopted in this study can be reliably used to improve the overall activity of as-synthesized WO3 photoanodes, and particularly of those that are initially poorly photoactive.

Magnetostriction, known as the ability of magnetic materials to expand or contract in response to magnetic field, is a key property of Fe-Ga alloys exploited in various types of transducers. Usually, thin films of Fe-Ga deposited on rigid substrates suffer from a clamping effect that hinders the propagation of strain. Herein, Fe-Ga films with macroporous, not fully constrained, geometry are prepared by electrodeposition on metallized silicon substrates templated with sub-micrometer-sized polystyrene spheres. For comparison, fully-dense and inherently nanoporous films are prepared by sputtering and electrodeposition, respectively. The electrodeposition mechanism is discussed in terms of electrochemically active species distribution and partial current densities. The composition of the Fe-Ga films has been tuned (2–40 at.% Ga) by varying the electrodeposition parameters. A complete assessment of the nanomechanical and magnetic properties of the films with variable composition and porosity has been performed for an optimized performance. The magnetostriction has been studied by X-ray diffraction applying an in-situ magnetic field. The results demonstrate a larger magnetic-field-induced crystal deformation in templated (macroporous) films compared to the non-templated and fully-dense counterparts. The observed effects in porous Fe-Ga films are very appealing for the design of various strain-engineered nanomaterials, e.g., energy transducers or magnetoelectric composites.

The geometry of porous materials is complex, and the determination of the true surface area is important because it affects current density, how certain reactions will progress, their rates, etc. In this work, we have investigated the dependence of the electrochemical deposition of copper coatings on the geometry of the copper substrate (flat plates or 3D foams). Chronoamperometric measurements show that copper deposition occurs 3 times faster on copper foams than on a flat electrode with the same geometric area in the same potential range, making metal foams great electrodes for electrowinning. Using electrochemical impedance spectroscopy (EIS), the mechanism of copper deposition was determined at various concentrations and potentials, and the capacities of the double electric layer (DL) for both types of electrodes were calculated. The DL capacity on the foam electrodes is up to 14 times higher than that on the plates. From EIS data, it was determined that the charge transfer resistance on the Cu foam electrode is 1.5–1.7 times lower than that on the Cu plate electrode. Therefore, metal foam electrodes are great candidates to be used for processes that are controlled by activation polarization or by the adsorption of intermediate compounds (heterogeneous catalysis) and processes occurring on the entire surface of the electrode.

The possibility to use highly saturated acetate bath to electrodeposit the mixed-phase materials containing Mo oxides has been investigated. The XRD characterization revealed that the as-deposited coatings are amorphous and consist only of MoO2 and MoO3 phases without traces of metallic Mo phase. This statement has been supported by XPS measurements, which reveal the presence of three different molybdenum oxidations states in electrodeposits: Mo4+, Mo5+ and Mo6+. It was found that the Mo6+ state prevails with 41% of total contribution, whilst Mo5+ and Mo4+ contribute to 28 and 31%, respectively. The deposits retain an amorphous structure up to 800°C; while molybdenum at this temperature is predominantly oxidized to the Mo6+ state (91%). These results, coupled to those of SEM and EDS, revealed that concentrated acetate bath could be used mainly for the formation of the mixed valence molybdenum oxide film unlike to the deposition of the metallic Mo phase.