M. DAKHOUCHE Achour

This work focuses on the photoelectrochemical and semicondictrise study ofthe corrosion layer formed in the dark on Lead and lead-tin alloys in a 0.5Msulfuric acid solution: Electrochemical Impedance Spectroscopy (EIS), LinearSweeping Voltage (LSV), Mott-Schottky plots and photocurrent measurements.The composition was determined respectively by XRD diffraction and SEMelectron microscopy. The findings indicate that the incorporation of tin leads toa reduction in the corrosion layer thickness while significantly enhancing itselectrical conductivity. This effect is attributed to the formation of conductive,non-photoactive tin oxides and the development of a compact interfacial thelayer separating the grid from the positive active material.

The presence of various organic pollutants in wastewater, surface water, and groundwater can be attributed to sources such as contaminated soil, agricultural runoff, industrial wastewater, and leaks from the storage of hazardous compounds. These pollutants, which include dyes, volatile phenols, benzene, and benzene derivatives, are
highly toxic and difficult to biodegrade. Conventional treatment methods, such as biological processes, may not be effective in removing these substances. Therefore, advanced treatment techniques are necessary to enhance water quality by eliminating dyes. Layered Double Hydroxides (HDLs), particularly NiFeCO3 HDLs, also known as nickel-iron carbonate, are complex mineral compounds that have attracted considerable interest in materials science, energy storage, and wastewater treatment. Composed of nickel, iron, and carbonate ions, these compounds possess unique structures and properties. In this study, NiFeCO3 HDL was synthesized using a co precipitation method. The physicochemical characterization was conducted through various analytical techniques, including X-ray diffraction (XRD), differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and surface characterization using BET analysis. The physicochemical analysis, alongside assessments of the material's electrochemical and catalytic properties, demonstrated that NiFeCO3 HDLs possess significant potential as anode materials for lithium-ion batteries. They exhibit high capacity, excellent rate capability, and
remarkable cycling stability. Additionally, the inclusion of iron in the structure enhances the material's catalytic properties. The combination of nickel and iron within the HDL structure results in unique activity, making it suitable for applications in water purification.

Water is essential for life, yet many aquatic environments face imperilment by noxious contaminants. Valuable waterways are compromised by an array of pollutants stemming from human activities and waste disposal. A wealth of recent scientific work has focused on the potency of layered double hydroxides to sequester an alarming group of toxic chemicals commonly found in effluent. These alkaline compounds show aptitude for withdrawing harmful dyes, pharmaceutical residues, and additional man-made toxins that jeopardize the purity of rivers and oceans. Further research on maximizing the adsorptive properties of LDHs may help safeguard water quality and supply. Suitable remediation tactics are urgently needed to curb the accumulation of destructive pollutants in crucial water sources.
Double layer hydroxides showcase a laminated architecture composed of sheets displaying alternating planes containing divalent and trivalent cations. Numerous techniques have been created for synthesizing the HDL phase with the aim of improving certain characteristics, such as crystallite dimensions (which can fluctuate from a handful of nanometers to several microns), morphology, specific surface region, and crystallinity. Of these approaches, three are generally utilized: co-precipitation, anion substitution, and
reformation. Heavy metals and dyes are highly hazardous industrial pollutants that pose significant risks both to the environment as well as to human health. Therefore, there is aurgent need for remediation methods that are simple, cost-effective as well as scalable. Layered double hydroxides, also known as LDHs, have emerged as very promising candidates due to their unique blend of characteristics. These include structures that can be easily adjusted, synthesis procedures that are straightforward to execute, as well as stability,
large surface areas and the capability to form various nanocomposites. Due to their adjustable structures, large surface areas and ability to form nanocomposites, LDHs are particularly potent in adsorbing an extensive assortment of pollutants from wastewater. This article will focus on the diverse synthesis techniques employed for generating LDH-based materials, examining their structural features thoroughly, outlining techniques for thorough physicochemical characterization, and exploring their diverse applications in eco-friendly pollutant remediation.

Water is a scarce resource and is considered a fundamental pillar of sustainable development. The modern development of society requires more and more drinking water. For this cleaner wastewater, treatments are key factors. Among those that exist, Layered Double Hydroxides (HDLs). NiFeCO3 HDLs, also known as nickel iron carbonate, is a complex mineral compound that has gained significant attention in the fields of materials science and energy storage and wastewater treatments. This compound is composed of nickel, iron, and carbonate ions, and its unique structure and properties have made The synthesis of NiFeCO3 HDLs has been extensively studied, and various methods have been employed, such as co precipitation, hydrothermal, and sol-gel techniques.
In this work, NiFeCO3 HDL was synthesized using co-Wastewater Treatment by nickel–iron layered double hydroxide (LDH). precipitation method. Physicochemical characterization was carried out using analytical methods: X-ray diffraction (DRX), differential thermal analysis (ATG), Scanning electron microscopy (SEM).

Freshwater resources are being threatened by the activities of a growing population and the escalating rate of overuse. Water pollution, caused by effluents from industrial, agricultural, and domestic sources, is detrimental to the environment. Consequently, reducing pollution through the adoption of eco-friendly technologies has become extremely important. Synthetic dyes, commonly utilized in various industries such as textiles, leather tanning, printing, and food processing, are one of the harmful effluents that need to be addressed. The treatment of effluents from textile industries typically involves using physico-chemical techniques and biological methods to remove organic matter, nitrogen, phosphorus, and metals. However, these traditional approaches have been found to be inefficient. Currently, there is a high priority among the scientific community to develop environmentally-friendly and cost-effective technologies for removing dyes from textile effluents.
Layered double hydroxides (LDH) with adsorption properties have been found to be promising in water treatment due to their ease of adsorption and recyclability. The LDH, also known as hydrotalcite like compounds or anionic clays, are 2-D nano-materialsthat can be used as storage matrix (hosting), and control the release of different anionic species, LDH present a great number of properties due to their varied compositions and methods of synthesis. In this study, the preparation and characterization of LDHs will be discussed through the following methods and techniques: DRX, MEB, ATG, BET.
Layered double hydroxides (LDHs) have proven to be good candidates for removing anionic dyes from aqueous solutions and waste treatment in water. These materials, which are endowed with high anionic exchange capacity and good adsorptive ability.

Industrialization is the primary cause of water and environmental pollution. The release of various pollutants, such as heavy metals, anions, dyes, organic compounds, pharmaceutical drugs, and pesticides, into the water has detrimental effects on the environment, human health, and wildlife. Therefore, it is crucial to develop technologies that can effectively remove toxic pollutants from water and wastewater in order to ensure its safety for human consumption. Many efforts have been made to remove dissolved organic dyes from wastewater, culminating in the development of materials such as double layer hydroxide (HDL). Hydrotalcite materials (HDL) are a type of layered compounds that are easily synthesized, non-toxic,
and inexpensive. They also have a wide range of physical and chemical properties. Layered compounds are a class of compounds with a lamellar structure, allowing for ion exchange between the layers and possessing cationic characteristics. In this article, we will focus on the synthesis methods of LDH-based materials, their structural features, techniques for physicochemical characterization, and their applications in pollutant remediation. Layered double hydroxides (LDHs) have emerged as promising candidates due to their unique
characteristics, such as adjustable structure, straight forward synthesis procedures, stability, large surface area, and the ability to form various nano-composites. These properties make LDHs highly effective in adsorbing a wide range of pollutants from wastewater.

L'eau est une ressource rare et un pilier essentiel du développement durable. La croissance de la société moderne exige un approvisionnement croissant en eau potable. Le traitement des eaux usées joue un rôle essentiel pour relever ce défi. Parmi les diverses méthodes de traitement disponibles, les hydroxydes doubles stratifiés sont étudiés en tant que solution durable. L'objectif principal de ce manuscrit est de présenter les avancées scientifiques dans ce domaine. Les hydroxydes doubles (HDL) ont une structure bidimensionnelle composée de couches alternées de lamelles contenant des cations divalents et trivalents. Diverses méthodes de synthèse de la phase HDL ont été mises au point pour améliorer des propriétés spécifiques, notamment la taille des cristallites (qui peut varier de quelques nanomatériaux à plusieurs microns), la morphologie, la surface spécifique et la cristallinité. Parmi ces méthodes, trois sont les plus couramment employées : la co-précipitation,échange ;anions et la reconstruction. Les métaux lourds et les colorants sont des polluants industriels très dangereux qui présentent des risques significatifs pour ;environnement et la santé humaine. Il est donc urgent de trouver des méthodes assainissement simples et rentables. Les hydroxydes doubles stratifiés (LDH) sont apparus comme des candidats prometteurs en raison de leurs caractéristiques uniques, notamment leurs structures ajustables, leurs procédures de synthèse simples, leur stabilité, leurs grandes surfaces et leur capacité à former divers nanocomposites. Ces propriétés rendent les LDH particulièrement efficaces pour adsorber une large gamme de polluants dans les eaux usées. Cet article se concentre sur les méthodes de synthèse des matériaux à base de LDH, leurs caractéristiques structurelles, les techniques de caractérisation physicochimique et leurs applications dans la remédiation des polluants. Les Ni-Fe HDL constituent une option fiable pour les applications de traitement de l'eau, car ils présentent une bonne stabilité dans diverses conditions environnementales, telles que le pH et la température.

Novel materials are designed by exploring the nano scale properties of the matter. Nano and biomaterials can be combined together and further used as efficient tools in engineering, biomedicine, electronics and biotechnology. Layered Double Hydroxides (LDHs) are an important class of inorganic lamellar nanomaterials that have attracted considerable interest in life science applications due to their controllable synthesis and excellent biocompatibility. Layered double hydroxides, also known as anionic clays, are a type of hydrotalcite nanocomposite that holds significant potential for applications in nanotechnology and biotechnology. Layered double hydroxides (LDHs) have attracted considerable attention in biomedical applications because of their outstanding properties, such as excellent biocompatibility, degradability, interlayer ion exchangeability, high loading capacity, pH-responsive release, and a large specific surface area. Additionally, their structural composition is flexible, and surface modification is straightforward, allowing for the creation of specifically functionalized LDHs designed to address the diverse needs of various applications. The aim of this study was to synthesise NiFeCO3 nanoparticles using the co-precipitation method, characterise them and determine their effectiveness in the biomedical and biotechnological fields. These materials are studied for their unique properties and technological significance in various fields, including catalysis, drug delivery, medical science, cosmetics, biosensing, and nanocomposite material engineering. This paper provides an overview of the most recent applications of layered double hydroxides (LDHs) in biomedicine and biosensing.

The synthesis of spinel ferrite nanoparticles is rapidly gaining popularity as a research field, driven by technological interests and their appealing magnetic properties. Spinel ferrites have the general formula MFe2O4, with M representing a divalent metal ion. These compounds exhibit a cubic structure and are utilized across a variety of technological applications. Over the past decade, ferrite nanoparticles have attracted considerable interest due to their high permeability, electrical resistivity, and advantageous electromagnetic properties. Consequently, they are well-suited for numerous applications, including magnetic storage, microwave devices, biosensors, drug delivery, disease diagnosis, gas sensors, energy conversion, photocatalysis, and magnetic separation. Several studies have been conducted on the preparation of this type of ferrite using various chemical methods. In this study, NiFe2O4 spinel nickel ferrite was synthesized using the coprecipitation method. The physicochemical properties were characterized through various analytical techniques, including X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR).
Nickel ferrite (NiFe2O4) is a significant soft ferrite utilized in various industries, appreciated for its qualities that make it ideal for soft magnetic core materials in power transformers and as a photocatalyst. It possesses low coercivity and high electrochemical stability. Ferrites produced using this method display smaller particle sizes, smooth surfaces, stability, and a homogeneous structure.

In recent years, nanostructured magnetic nanocomposites have received increasing attention due to their unique chemical and physical properties and their inexpensive nature and their wide range of applications in several fields such as pharmaceuticals, energy, water treatment and catalysts. Many nanomaterials have been prepared and the most effective is the layered double hydroxide (LDH) recognized as anionic clays or brucite-like compounds, these two subclasses are significant types of ionic layered materials. The primary components of LDHs are the charged layers, which offer a variety of chemical compounds with versatile applications, such as biocompatibility,
adsorption, intercalation, and ion exchange, these are the foundations of the diverse technological applications of LDHs across various fields, including medicine, polymer industries,
electrochemistry, food, catalysis, and drug delivery. Compared to other drug delivery mechanisms, which often suffer from low circulation stability, poor bioavailability, and drug degradation, LDHs serve as exceptional drug nano-carriers. They are relatively cost-effective, exhibit low toxicity to cells, and demonstrate good biocompatibility.
In this study, NiFeCO3 HDL was synthesized using the coprecipitation method. The physicochemical characterization was performed with various analytical techniques, including X-
ray diffraction (XRD), differential thermal analysis (DTA), Fourier transform infrared spectroscoy (FTIR), scanning electron microscopy (SEM), and surface characterization using the
BET method. Using physicochemical analysis methods and evaluating the electrochemical and catalytic properties of the material,. The integration of nickel and iron into the HDL structure provides unique activity, making it suitable for applications in water purification (specifically for eliminating colorants through advanced oxidation processes), energy conversion, and electrocatalysis.

The evolutions of microstructure and texture and the corrosion behaviour of low light rare-earth containing Mg-1.4Nd and low heavy rare-earth containing Mg-0.6Gd and Mg-0.4Dy (wt.%) were evaluated and compared after processing by high-pressure torsion (HPT) and isochronal annealing at 250 and 450 °C for 1 h using electron backscatter diffraction (EBSD) and electrochemical tests in a 3.5% (wt.%) NaCl solution. The EBSD results show that dynamic recrystallisation (DRX) was restricted in the Mg-1.4Nd alloy which led to a heterogenous deformation microstructure whereas the Mg-0.6Gd and Mg-0.4Dy alloys exhibited a homogenous deformation microstructure formed mostly of equiaxed dynamically recrystallised DRX grains. The HPT processing caused the development of a deviated basal texture in the three alloys. A good thermal stability of the three alloys was noticed after annealing at 250 °C. By contrast, annealing at 450 °C led to a homogenous equiaxed microstructure and weakening of texture for the Mg-1.4Nd alloy and a heterogenous bimodal microstructure with a stable basal texture for the Mg-0.6Gd and Mg-0.4Dy alloys. The HPT-processed Mg–RE alloys exhibited an improved corrosion resistance due to grain refinement. Thereafter, the corrosion resistance of the Mg-0.6Gd and Mg-0.4Dy alloys decreased with increasing annealing temperature due to an increase in grain size while the corrosion resistance of the Mg-1.4Nd alloy was improved after annealing at 450 °C due to precipitation and texture weakening.

The corrosion behaviour of as-cast binary Mg–0.3Ce, Mg–1.44Nd, Mg–0.63Gd and Mg–0.41Dy (wt%) alloys was investigated in
DMEM + 10% FBS solution using electrochemical and weight loss tests. The results revealed that the alloys with heavy RE elements
(Gd and Dy) exhibited the lowest corrosion rate compared to the alloys with light RE elements (Ce and Nd). The cytocompatibility of the
Mg–RE alloys was assessed via live/dead straining after 3 and 7 days. The results show that Mg–0.63Gd alloy is a suitable candidate for
biomedical applications.

The microstructure and texture evolution of an AZ31 alloy were investigated after hot rolling and subsequent
annealing using electron backscatter diffraction (EBSD). First, the alloy was hot-rolled at 350 ◦C up to low,
medium and high strain (20, 50 and 85% of thickness reduction, respectively). The alloy samples where then
annealed at 350 ◦C for 2, 10 and 60 min. The effect of strain level and annealing on corrosion behavior in
seawater was also evaluated using electrochemical tests. At low strain, the microstructure was characterised by
the absence of twinning, mainly due to the prior thermo-mechanical history of the as-received alloy. However,
various modes of twinning were observed at medium strain. At high strain, the dynamic recrystallization process
resulted in a microstructure with a typical basal texture. The results demonstrate that twins are responsible for
the deviation of {0002} basal poles from normal towards the transversal direction. Annealing at 350 ◦C for up to
60 min led to normal grain growth in all the samples. In medium and highly strained samples, the deformation
texture was retained, while the low strain sample underwent noticeable changes due to the absence of dynamic
recrystallization. A synergetic effect of grain refinement and texture weakening was responsible for the alloy’s
enhanced corrosion resistance.

The corrosion behaviour of Mg-0.3Ce, Mg-0.41Dy, Mg-0.63Gd, Mg-1.44Nd and Mg-1.43La (wt.%) alloys in
3.5 wt% NaCl solution was investigated using electrochemical tests. The as-cast microstructures of the
Mg-RE alloys were characterized by the presence of second phases (MgxCe, Mg41Dy5, Mg12Gd, Mg12Nd,
Mg41Nd5, Mg24Nd and Mg12La) with different volume fraction and distribution. Results show that the
corrosion mechanism was altered from uniform to localized corrosion mechanism depending on the
specific RE alloying elements. The corrosion resistance of the Mg-RE alloys is increasing in the following
order: Mg-1.43La, Mg-1.44Nd, Mg-0.3Ce, Mg-0.63Gd and Mg-0.41Dy. Accordingly, the corrosion
morphology in the best resistant Mg-0.41Dy alloy and the worst Mg-1.43La alloy were observed and
compared after 2h and 24 h of immersion using SEM-EDS, XPS and XRD analysis. The formation of the
Dy2O3 oxide prevents the Mg-0.41Dy alloy from pitting corrosion and lead to an excellent corrosion
surface even after 24 h of immersion. Meanwhile, the presence of a high fraction of the Mg12La phase
along the grains boundaries in the Mg-1.43La alloy causes severe pitting corrosion by acting as anodic
phase.

Magnesium and its alloys are increasingly used as lightweight materials in aerospace, automotive and as biomaterials owing to their lower density among all structural materials (ρMg = 1.73 g cm-3). However, Magnesium alloys suffer from poor workability and relative low mechanical strength at ambient temperature due to their hexagonal close packed structure and the associated lack of sufficient independent slip systems which limit their applications as structural materials. Furthermore, their poor corrosion resistance is a serious problem that limits their clinical application. In fact, the control and improvement of mechanical properties of magnesium alloys could be obtained through thermo-mechanical processing such as hot rolling or hot compression. The aim of the present study is to investigate the effect of hot deformation conditions on the corrosion behavior of AZ31 (Mg-3Al-1Zn, % wt.) in 0.9% NaCl solution. The AZ31 alloy was hot rolled at 360 °C to 20 and 50 % of thickness reduction. Electrochimical techniques such as open circuit potential, polarization curves and electrochimical impedance spectroscopy complemented by X-ray diffraction were used. Primary results show that the corrosion rate was strongly affected by the hot rolling level. A lower potential and reduced polarization resistance were observed after hot rolling compared to the as cast AZ31 alloy. Besides the two capacitive loops, all samples exhibited an inductive loop that decreases with increasing thickness reduction which can be associated with the development of more uniform corrosion.

It well known that PbSb alloy has high performance on the charge–discharge for the lead-acid battery. While the demerit of PbSb alloys is that they can increase the water loss in lead acid battery by decreasing the over-potential of hydrogen evolution on the negative plate, andself-discharge of battery and further to the premature loss of the battery capacity. The over-potential of hydrogen evolution on PbCa alloy is higher than that on PbSb alloy for about 200 mV, which result in its lower rate of water consumption and a smaller rate of self-discharge, and then make the PbCa alloy more suitable for maintenance-free applications or valve regulated lead acid battery (VRLA). However, PbCa alloy has an unfavourable factor usually referred to as premature capacity loss (PCL), which is attributed to an high impedance barrier layer composed of PbO, and formed easily at the interface of the positive grid and the active material, which has an undesirable effect of increasing the anode impedance after storage for a certain period of time, and then the capacity of lead acid battery decreasing sharply. In order to improve the conductivity of the passive layer and the charge–discharge performance of the batteries, Sn should be added into the PbCa alloys. According to Giess et al., Sn suppresses the transformation of lead to α-PbO , and inhibits the growth of Pb(II) compound in the film. Although, the passive phenomena of the film cannot be thoroughly eliminated by adding Sn, and excessive Sn content may increase the self- discharge of the lead acid battery but how to promote the maintenance-free property of the battery is still a key problem for developing the novel grid alloy. I well known that during the anodic polarization of a lead electrode dipped in a H2SO4 solution in the lead oxide potential region (-0.40 to + 0.95 V vs. a Hg/Hg2SO4 reference electrode) the electrode system Pb/PbO layer/Pb2SO4 membrane/H2SO4 solution is formed. It was determined by X-ray diffraction that mainly the tetragonal PbO is formed, as well as small amounts of orthorhombic PbO and basic lead sulphates. It was established that the Pb/PbO/Pb2SO4/H2SO4 electrode is photoactive in the visible band (up to 650 nm) of the spectrum. So, the photoeffect is related to the semiconducting properties of the lead monoxide layer (PbO) formed on lead. In this work, the corrosion layer formed in dark on pure Pb and Pb-Sn alloys was photo electrochemically studied using: AC voltammetry, Cyclic voltammetry CV, Electrochemical Impedance Spectroscopy (EIS), Mott-Schottky plots and Photocurrent measurements. The composition was determined by XRD analysis. It was found that tin reduces the thickness and enhances the conductivity of the corrosion layer by formation of conductive and no photoactive tin oxides. A mechanism of action of tin was proposed

Pb–Sn binary alloys with different contents of tin (0–2wt.%) were investigated as the
positive grid of a lead acid battery. The microstructure of Pb–Sn alloys was observed using a
polarizing microscope. The morphology of the corrosion layers and corroded surfaces of Pb
and Pb–Sn alloy electrodes were analyzed by scanning electron microscopy (SEM) following
the corrosion test. The electrochemical properties of Pb–Sn alloys in sulfuric acid solution
were investigated by cyclic voltammetry (CV), open circuit potential (OCP), electrochemical
impedance spectroscopy (EIS), and linear sweeping voltammetry (LSV). The results indicate
that the introduction of tin results in grain refinement, increased corrosion resistance.

Pb–Sn, Pb–Sb and Pb–Ca–Sn alloys are commonly used in the production of positive and negative grids, of both valve-regulated lead–acid (VRLA) and Starting, Lighting and Ignition (SLI) batteries.Pb-Sn binary alloys with different contents of tin (0–2 wt.%) were investigated as the positive grid of a lead acid battery. The microstructure of Pb–Sn alloys was observed using a polarizing microscope. The electrochemical properties of Pb–Sn alloys in sulfuric acid solution were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and linear sweeping voltammetry (LSV). The results indicate that the introduction of tin results in grain large and augmented corrosion resistance.

The effect of three tetrahydroxylated Schiff bases as N,N-bis(2,3-dihydroxybenzyl- idene)-4,4’-diphenylmethane, N,N-bis(2,4-dihydroxybenzyl- idene)-4,4’-diphenylmethane and N,N-bis(2,4-dihydroxybenzylidene)-4,4’-diphenylmethane were studied as inhibitors for mild steel in 1M HCl medium. The experiments were performed using potentiodynamic polarization. This inhibition proved an efficient increase according the position of second hydroxyl of salicylaldehyde suggesting that this inhibition is dependent on concentration and the compound nature. Among these position-isomers, the best inhibition efficiency was obtained with p-hydroxylated (94%) at 1mM. Tafel plots of these inhibitors are the mixed- type, their adsorption is spontaneous obeying to Langmuir’s isotherm. AFM/SEM-EDS characterized metal surface. DFT-calculations and molecular dynamics simulations are correlated to inhibition efficiency obtained.

samples in the 0.5 M H2SO4 solution at 25 C. Electrochemical impedance spectroscopy (EIS) diagrams,
potentiodynamic polarization curves and the equivalent circuit analysis were used to evaluate the electrochemical
corrosion response. It was found that Pb-1 wt.% Sn alloy exhibits a microstructure with large cellular array and
better electrochemical corrosion resistance than that of Pb-1 wt.% Sb.

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at room temperature was studied in an effort to evaluate the effect of applied potential on
the composition limits, corrosion resistance and the electrocatalytic properties of the deposits
towards the hydrogen evolution reaction (HER) in concentrated alkaline solution.
The alloys were potentiostatically electrodeposited onto pure copper sheet substrates. The
electrodeposits were characterized by means of field-emission scanning microscopy
(FESEM) and energy dispersive X-ray analysis (EDXA). In an electrolyte where
MoO2

4 =WO2

4
¼ 1 : 1, at a given deposition potential, there is more Mo than W in the deposits,
indicating an advantageous induced co-deposition of Mo compared to W. The
nucleation mechanism, studied according to Scharifker-Hills theoretical model, revealed
an instantaneous nucleation followed by a three-dimensional growth. On the hand,
increasing MoO2

4 =WO2

4 ratio in the electrolyte under the same deposition potential
reduced both Ni and W content in the deposits. A different trend was observed in an
equimolar solution, when applying more negative potentials, both Mo and W contents
decreased leading to the enhancement of Ni amount. The stability in corrosive media and
the catalytic performances of the coatings depended mainly on the applied overpotentials,
A mechanism of induced co-deposition of molybdenum and tungsten with nickel is proposed
and discussed.

The electrodeposition of NiW alloys from citrate electrolyte was studied in an effort to evaluate the effect of applied potential and solution pH on the composition limit and the properties of the deposits. Electrochemical measurements employing cyclic voltammetry (CV), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to investigate the codeposition process, corrosion resistance and HER electrocatalytic properties of the deposits. The deposits morphology was characterized by scanning electron microscopy (SEM) and the surface composition of coatings was ascertained by Energy dispersive x-ray analysis (EDXA). Possibility of W-rich NiW alloys electrodeposition from ammonia-free citrate electrolyte at room temperature was confirmed. The tungsten content was close to 32 at.% in deposits obtained from a quasi-neutral solution. Structural study revealed that all of NiW coated alloys were amorphous regardless of W content. On the other hand, it was found that Ni-W alloys deposited at -1.4 V/CSE (having about 14 at.% W) are good electrode materials as cathode for HER following the Volmer-Heyrovsky mechanism with substantial surface-adsorbed hydrogen while alloys plated at -1.2 V/SCE (having about 32 wt.% W) were of excellent corrosion resistance in 3.5% NaCl solution.