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Papers by henrikas cesiulis

Research paper thumbnail of Electrochemical Synthesis of a WO3/MoSx Heterostructured Bifunctional Catalyst for Efficient Overall Water Splitting

Coatings

Photo-/electrochemical water splitting can be a suitable method to produce “green” hydrogen and o... more 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 cros...

Research paper thumbnail of The Influence of Sodium Tungstate Concentration on the Electrode Reactions at Iron–Tungsten Alloy Electrodeposition

Coatings, 2021

The investigation of Fe-W alloys is growing in comparison to other W alloys with iron group metal... more 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...

Research paper thumbnail of Coating engineering of cobalt-tungsten alloys and mapping their properties

Research paper thumbnail of Magnetic state instability of disordered electrodeposited nanogranular Fe films

Journal of Magnetism and Magnetic Materials, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Research paper thumbnail of The Characterisation of Electrodeposited MoS2 Thin Films on a Foam-Based Electrode for Hydrogen Evolution

Catalysts, 2020

Molybdenum sulphide is an emerging precious-metal-free catalyst for cathodic water splitting. As ... more Molybdenum sulphide is an emerging precious-metal-free catalyst for cathodic water splitting. As its active sites catalyse the Volmer hydrogen adsorption step, it is particularly active in acidic media. This study focused on the electrochemical deposition of MoS2 on copper foam electrodes and the characterisation of their electrocatalytic properties. In addition, the electrodeposition was modified by adding a reducing agent—sodium hypophosphite—to the electrolyte. To reveal the role of hypophosphite, X-ray photoelectron spectroscopy (XPS) analysis was carried out in addition to scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). MoS2 films, electrodeposited at various charges passed through the cell (catalyst loadings), were tested for their catalytic activity towards hydrogen evolution in 0.5 M H2SO4. Polarisation curves and Tafel slope analysis revealed that the electrodeposited MoS2 films are highly active. Namely, Tafel slopes fell within the 40–50...

Research paper thumbnail of Pulse electrodeposited bismuth-tellurium superlattices with controllable bismuth content

Journal of Power Sources, 2020

Superlattice structures of (Bi 2) m (Bi 2 Te 3) n series with controllable Bi mole fraction from ... more Superlattice structures of (Bi 2) m (Bi 2 Te 3) n series with controllable Bi mole fraction from 0.41 to 0.71 are electrodeposited in pulse potentiostatic mode from acidic electrolytes containing Bi(NO 3) 3 and TeO 2 as precursors. Two valence states of bismuth in superlattices are identified by X-ray photoelectron spectroscopy (XPS). One of those states is attributed to interlayered Bi 0 which is present in (Bi 2) m (Bi 2 Te 3) n superlattice in the form of biatomic layers between bismuth telluride quintuples. X-ray difraction (XRD) analysis and density functional theory (DFT) calculations indicate an increase in subcell parameter a sub and decrease in subcell parameter c sub with the increase of Bi mole fraction. Biatomic layers of Bi 0 are identified with cyclic voltammetry by characteristic anodic peak between potentials of metallic bismuth and Bi 2 Te 3 oxidation. The selective oxidation of Bi-bilayers in (Bi 2) m (Bi 2 Te 3) n superlattice at the potential of the anodic peak results in the product corresponding to Bi 2 Te 3 by stoichiometry, but having an expanded crystal structure. Superlattices with controllable Bi mole fraction and Bi 2 Te 3 with "memory effect" may be of interest for design of new thermoelectric materials with controllable parameters.

Research paper thumbnail of Chemical, electrochemical and tribological study of various olive oils and their behaviour on steel

Chemija, 2018

The influence of different chemical composition and physical properties of olive oils, produced f... more The influence of different chemical composition and physical properties of olive oils, produced from various districts in Morocco with various acidic numbers (from 1.76 to 18.01), on their tribological performance and corrosion protection has been investigated. The chemical composition was determined by means of IR, 1H and 13C NMR spectroscopy. The investigated olive oils show small quantitative and qualitative differences between each other (the amount of free fatty acids and the composition of fatty acids in triglycerides). The spectroscopic data let us unambiguously determine in general that the main fatty acids in oils are saturated palmitic and/or stearic acids, unsaturated oleic and linoleic acids except linolenic acid. The oxidation stability of oils was estimated. The contact angle measurements and electrochemical impedance spectroscopy data show that all films of olive oils on the surfaces of steels are porous; therefore, the values of corrosion inhibition efficiency are re...

Research paper thumbnail of Coupled Electrodeposition of Fe–Co–W Alloys: Thin Films and Nanowires

Frontiers in Chemistry, 2019

The electrodeposition of Fe-CoW alloys was examined using a rotating cylinder Hull (RCH) cell and... more The electrodeposition of Fe-CoW alloys was examined using a rotating cylinder Hull (RCH) cell and conditions were determined to create nanowires. The metal ion reduction mechanism was a combination of induced and anomalous codeposition, with water reduction as a gas evolving side reaction, rending deposition into recesses a challenge. In thin film deposition, under kinetic control, the addition of Fe ions into the electrolyte, greatly reduced the Co partial current density, and thus it's content in the deposit. The change of Co partial current density was attributed to an anomalous codeposition behavior, but it had a minimal effect in changing the W wt% in the deposit, despite the expected inducing characteristic of Fe when codeposited with tungsten. Deposition conditions were determined to electrodeposit Fe-CoW nanowires having similar concentration as the thin films. Nanowires were electrodeposited into polycarbonate membranes under pulsed current at room temperature.

Research paper thumbnail of Modified Electrodeposited Cobalt Foam Coatings as Sensors for Detection of Free Chlorine in Water

Coatings, 2019

Metal foams offer a substantial specific surface area and sturdy frame, which makes them great ca... more Metal foams offer a substantial specific surface area and sturdy frame, which makes them great candidates for various applications such as catalysts, sensors, heat sinks, etc. Cobalt and its various compounds are being considered as a cheaper alternative for precious and rare metal catalysts. The cobalt foams have been electrodeposited under galvanostatic and current pulse modes; the porous surface was created using a dynamic hydrogen bubble template. In order to obtain the highest porosity, four different solutions were tested, as well as a wide current density window (0.6–2.5 A/cm²), in addition many different combinations of pulse durations were applied. The effects of surfactant (isopropanol) on porosity were also investigated. The morphology of obtained foams was examined by SEM coupled with EDS, and XRD spectroscopy. True surface area was estimated based on the values of a double electric layer capacitance that was extracted from EIS data. Cobalt foams were modified using K3[F...

Research paper thumbnail of Nanocrystalline Electrodeposited Fe-W/Al2O3 Composites: Effect of Alumina Sub-microparticles on the Mechanical, Tribological, and Corrosion Properties

Frontiers in Chemistry, 2019

In this study, nanocrystalline FeW alloy and Fe-W/Al 2 O 3 composite coatings with various conten... more In this study, nanocrystalline FeW alloy and Fe-W/Al 2 O 3 composite coatings with various contents of sub-microsized alumina particles have been obtained by electrodeposition from an environmentally friendly Fe(III)-based electrolyte with the aim to produce a novel corrosion and wear resistant material. The increase in volume fraction of Al 2 O 3 in deposits from 2 to 12% leads to the grain refinement effect, so that the structure of the coatings change from nanocrystalline to amorphous-like with grain sizes below 20 nm. Nevertheless, the addition of particles to the FeW matrix does not prevent the development of a columnar structure revealed for all the types of studied coatings. The observed reduction in both hardness and elastic modulus of the Fe-W/Al 2 O 3 composites is attributed to the apparent grain size refinement/amorphization and the nanoporosity surrounding the embedded Al 2 O 3 particles. In the presence of 12 vol% of Al 2 O 3 in deposits, the wear rate decreases by a factor of 10 as compared to FeW alloy tested under dry friction conditions due to the lowering of tribo-oxidation. The addition of alumina particles slightly increases the corrosion resistance of the coatings; however, the corrosion in neutral chloride solution occurs through the preferential dissolution of Fe from the matrix. The obtained results provide a possibility to integrate the nanocrystalline Fe-W/Al 2 O 3 composite coatings into various systems working under dry friction conditions, for example, in high-temperature vacuum systems.

Research paper thumbnail of Electrodeposition of Nanocrystalline Fe-P Coatings: Influence of Bath Temperature and Glycine Concentration on Structure, Mechanical and Corrosion Behavior

Coatings, 2019

A detailed electrochemical study and investigation of a Fe-P glycine bath as a function of the te... more A detailed electrochemical study and investigation of a Fe-P glycine bath as a function of the temperature and glycine concentrations and current density, and their resulting corrosion and mechanical behavior is presented. A low addition of glycine to the electrolyte led to a drastic increase of the P content. At low Fe-P deposition rates, heterogeneous rough deposits with morphological bumps and pores were observed. By increasing the Fe-P deposition rate, the number of pores were reduced drastically, resulting in smooth coatings. Increasing the P content led to the formation of nanocrystalline grains from an “amorphous-like” state. Coatings with higher P contents exhibited better corrosion resistance and hardening, most likely attributed to grain boundary strengthening.

Research paper thumbnail of Design of Highly Active Electrodes for Hydrogen Evolution Reaction Based on Mo-Rich Alloys Electrodeposited from Ammonium Acetate Bath

Coatings, 2019

The given research was driven by prospects to design Mo-rich coatings with iron group metals elec... more The given research was driven by prospects to design Mo-rich coatings with iron group metals electrodeposited from a highly saturated ammonium acetate bath. The obtained coatings could be employed as prominent electrodes for the hydrogen evolution reaction (HER). It was found that the Mo content in Ni–Mo alloys can be tuned from 30 to 78 at.% by decreasing the molar ratio [Ni(II)]:[Mo(VI)] in the electrolyte from 1.0 to 0.25 and increasing the cathodic current density from 30 to 100 mA/cm2. However, dense cracks and pits are formed due to hydrogen evolution at high current densities and that diminishes the catalytic activity of the coating for HER. Accordingly, smoother and crack-free Ni–54 at.% Mo, Co–52 at.% Mo and Fe–54 at.% Mo alloys have been prepared at 30 mA/cm2. Their catalytic behavior for HER has been investigated in a 30 wt.% NaOH solution at temperatures ranging from 25 to 65 °C. A significant improvement of electrocatalytic activity with increasing bath temperature was ...

Research paper thumbnail of Improvement in the Wear Resistance under Dry Friction of Electrodeposited Fe-W Coatings through Heat Treatments

Coatings, 2019

The influence of the microstructural transformations upon heat treatments on the wear resistance ... more The influence of the microstructural transformations upon heat treatments on the wear resistance of Fe-W coatings is studied. The coatings are electrodeposited from a glycolate-citrate plating bath with 24 at.% of W, and the wear resistance is investigated under dry friction conditions using ball-on-disc sliding tests. The samples were annealed in Ar atmosphere at different temperatures up to 800 °C. The microstructural transformations were studied by means of X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Electron Backscattered Diffraction (EBSD) technique. Except for the coating annealed at 800 °C, all the tested coatings suffered severe tribo-oxidation which resulted in the formation of deep cracks, i.e., ~15 μm in depth, within the wear track. The precipitation of the secondary phases, i.e., Fe2W and FeWO4, on the surface of the sample annealed at 800 °C increased the resistance to tribo-oxidation leading to wear tracks with an average depth of ~3 μm. Hence, th...

Research paper thumbnail of In-depth characterization of as-deposited and annealed Fe-W coatings electrodeposited from glycolate-citrate plating bath

Electrochimica Acta, 2018

FeW coatings with 4, 16 and 24 at.% of W were electrodeposited under galvanostatic conditions fro... more FeW coatings with 4, 16 and 24 at.% of W were electrodeposited under galvanostatic conditions from a new environmental friendly Fe(III)-based glycolate-citrate bath. This work aims to find correlations between composition including the light elements, internal structure of the electrodeposited Fe-Walloys and functional properties of material. The obtained alloys were characterized by Glow Discharge Optical Emission Spectrometry (GD-OES), Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDS), Transmission Electron Microscopy (TEM), and X-ray Diffraction (XRD). Compositional depth profiles of 10 mm thick coatings obtained by GD-OES show that the distribution of metals is uniform along the entire film thickness, while SEM imaging depicted the presence of cracks and O-and W-rich areas inside the Fe-Wcoating with 4 at.% W. In the samples with 16 and 24 at.% of W, oxygen and hydrogen are present mostly at the surface about 1 mm from the top while traces of carbon are distributed within the entire coatings. With increasing W content, the structure of the coatings changes from nanocrystalline to amorphous which was shown by XRD and TEM analysis. Also, the surface of coatings becomes smoother and brighter, that was explained based on the local adsorption of intermediates containing iron and tungsten species. Annealing experiments coupled with XRD analysis show that the thermal stability of FeW alloys increases when the W content increases, i.e. the coating with 24 at.% W retains the amorphous structure up to 600 _C, where a partially recrystallized structure was observed. Upon recrystallization of the amorphous samples the following crystalline phases are formed: a-Fe, Fe2W, Fe3W3C, Fe6W6C, and FeWO4. Hence, the FeW coatings with higher W content (>25 at.%) can be considered as suitable material for high temperature applications. Fig. 4. Compositional depth profiles as obtained by GD-OES of FeW samples of different composition: 4 at.% of W (a), 16 at.% of W (b) and 25 at.% of W(c).

Research paper thumbnail of Electrodeposited Co-W alloys and their prospects as effective anode for methanol oxidation in acidic media

Surface and Coatings Technology, 2016

Electrodeposited CoW alloys having different composition and structure were tested as anodes for ... more Electrodeposited CoW alloys having different composition and structure were tested as anodes for methanol electrooxidation. The structure of electrodeposited CoW alloys having various tungsten content is either nanocrystalline (3 and 18 at.% of W) or "amorphous-like" (30 at.% of W). The electrodeposition was performed on the stainless steel substrate from citrate-borate bath at 60°C and a cathodic current density 10 mA•cm −2. Alloys having different compositions were obtained by varying pH from 5 to 8. A well-defined crystalline structure was indicated for CoW having 3 at.% and 18 at.% of W: these deposits have a hexagonal close packed (hpc) structure typical for electrodeposited pure Co. The high content of W in the alloy (~30 at.%) leads to the formation of nanocrystalline structure ("amorphous-like"). The electrocatalytic activity of prepared CoW alloys was examined by means of cyclic voltammetry in the mixture of 1 M CH 3 OH and 0.1 M H 2 SO 4. The electrooxidation of methanol depends on the content of W in the alloy. It was found that the crystalline Co-3 W and Co-18 W alloys are inactive for methanol oxidation, and the electrochemical alloys dissolution occurs in the tested media. Whereas, the high content of W (~30 at.%) in the CoW coating prevents the continuous CoW alloy dissolution and it might be used as anode for the methanol oxidation in the acidic media. The annealing of CoW deposits was performed at 600°C for 1 h in the air and formation of Co 3 O 4 and CoWO 4 compounds with simultaneous decrease of tungsten content in the alloys were detected. The annealed CoW coatings show lower activity toward methanol electroxidation compared to as-deposited Co-30 at.% W.

Research paper thumbnail of A Hybrid Approach to Fabricated Nanowire-Nanoparticle Composites of a Co-W Alloy and Au Nanoparticles

Journal of The Electrochemical Society, 2016

CoW nanowires were fabricated by pulsed electrodeposition from a citrate-glycine electrolyte onto... more CoW nanowires were fabricated by pulsed electrodeposition from a citrate-glycine electrolyte onto rotating cylinder electrodes and into nanoporous polycarbonate membranes. The characterization of the electrodeposition conditions and alloy composition of electrodeposited CoW alloy thin films were determined and used to guide conditions to electrodeposit the nanowires. Gold nanoparticles of 50 nm size were also added to the electrolyte and deposited during electrodeposition of the CoW alloy nanowires, embedded within, and attached to the nanowire tip, introducing a novel procedure to attached nanoparticles onto nanowires.

Research paper thumbnail of Synthesis, electrochemical impedance spectroscopy study and photoelectrochemical behaviour of as-deposited and annealed WO 3 films

Electrochimica Acta, 2017

WO 3 films have been obtained by anodization of tungsten in the different acidic electrolytes (HC... more WO 3 films have been obtained by anodization of tungsten in the different acidic electrolytes (HCl, H 2 SO 4 , H 3 PO 4 , H 3 PO 4 + NH 4 F) and at various applied potentials. Electrochemical impedance spectroscopy was used to investigate film formation and to characterize the obtained oxide films. The equivalent electric circuits modelling reactive and blocking behaviour are provided and discussed. It was found, that oxide film capacitance decreases linearly with increasing anodization potential. The relative permittivity of tungsten oxide films varies from 31 to 56 depending on the acid used. A relatively high rate of the film formation (1.87 nm V-1) and increased resistance against oxide breakdown can be achieved for tungsten oxide obtained from 0.3 M oxalic acid bath. Compact oxide films are formed at the potentials ranged from 10 V to 30 V, whereas increasing of anodization voltage to 60 V resulted in the formation of disordered, porous structures due to surface etching. Semiconductor properties were determined by Mott-Schottky analysis. Photoelectrochemical properties of as-deposited and annealed at 600°C WO 3 films were determined in a Na 2 SO 4 solution under pulsed and constant UV irradiation. It was determined that annealed WO 3 films in comparison to as-deposited films are more stable and generate substantially higher photelectrochemical currents.

Research paper thumbnail of Toward uniform electrodeposition of magnetic Co-W mesowires arrays: direct versus pulse current deposition

Electrochimica Acta, 2016

Template-assisted electrodeposition of Co-rich CoW alloys into mesoporous anodized aluminum oxide... more Template-assisted electrodeposition of Co-rich CoW alloys into mesoporous anodized aluminum oxide from ammonia-free solutions is investigated. The optimum deposition conditions rendering uniform filling of the pores, either by direct current (DC) or pulse current (PC) methods, are established. Contrary to the DC deposition on flat surfaces (which is kinetically controlled), the DC electrodeposition in the mesopores of the template is limited by mass transfer. Conversely, under PC mode, the CoW electrodeposition process is controlled by kinetics at frequencies > 0.3 Hz; and by diffusion at lower frequencies. The obtained mesowires are nanocrystalline and exhibit a hexagonal closed packed (hcp) structure. The magnetic properties of selected CoW mesowires, with variable aspect ratio, are also studied. The arrays of mesowires exhibit a semi-hard ferromagnetic behavior with coercivity values that surpass those of Co mesowires with similar dimensions. The interplay between interwire dipolar interactions, magnetocrystalline anisotropy and shape anisotropy on the overall shape of the hysteresis loops (in particular, on the coercivity and squareness ratio values, as well as on the effective magnetic easy axis direction) is investigated in a semiquantitative manner.

Research paper thumbnail of Anodic Titanium Oxide Films: Photoelectrochemical and Tribocorrosion Behavior

Journal of Nanoelectronics and Optoelectronics, 2014

ABSTRACT Titanium oxide films are fabricated by Ti anodization in orthophosphoric acid-ammonium f... more ABSTRACT Titanium oxide films are fabricated by Ti anodization in orthophosphoric acid-ammonium fluoride electrolytes. On the mechanically polished semi-bright Ti substrates the continuous TiO2 films are formed, whereas ordered nanoporosity is formed on the mirror-like surface of Ti substrate at temperatures of 10–20 °C in the H3PO4 electrolyte with NH4F. The photocurrents and photopotentials are affected by the amount of fluorine in the electrolyte and consequently in the deposit. Tribocorrosion tests were performed in a neutral solution, and changes of open-circuit potential (OCP) as well as electrochemical impedance spectra were recorded with/without 0.4 N load. The rapid changes of OCP can be explained by the passive film abrasion, when oxide film becomes damaged and bare Ti surface is exposed. The wear loss depends on the NH4F concentration in the solution used for TiO2 films fabrication. TiO2 films destroyed during sliding tend to restore within 300–400 s after unloading.

Research paper thumbnail of Tribological behaviour of mineral and rapeseed oils containing iron particles

Industrial Lubrication and Tribology, 2015

Purpose – The purpose of this paper is to investigate the tribological behaviour of commercially ... more Purpose – The purpose of this paper is to investigate the tribological behaviour of commercially available SAE 10 mineral and rapeseed oils containing Fe particles synthesized directly in the oil phase. Design/methodology/approach – Sub-micron Fe particles (50-340 nm) were synthesized by wet chemical reduction reaction of FeSO4 by sodium borohydride in the rapeseed and mineral oils in the presence of surfactant: block copolymer (ENB 90R4) or oxyethylated alcohol (OS-20). A four-ball wear tribometer was used to investigate the tribological properties of mineral and rapeseed oil: coefficient of friction (COF), wear scar diameter and wear loss. Viscosity measurements of oil solutions and determination of synthesized Fe particles size were performed as well. Findings – The presence of Fe particles (0.1 weight per cent) in the rapeseed and mineral oils caused the little change in the COF but resulted in marked improvement of anti-wear property. The oils containing Fe particles with sligh...

Research paper thumbnail of Electrochemical Synthesis of a WO3/MoSx Heterostructured Bifunctional Catalyst for Efficient Overall Water Splitting

Coatings

Photo-/electrochemical water splitting can be a suitable method to produce “green” hydrogen and o... more 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 cros...

Research paper thumbnail of The Influence of Sodium Tungstate Concentration on the Electrode Reactions at Iron–Tungsten Alloy Electrodeposition

Coatings, 2021

The investigation of Fe-W alloys is growing in comparison to other W alloys with iron group metal... more 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...

Research paper thumbnail of Coating engineering of cobalt-tungsten alloys and mapping their properties

Research paper thumbnail of Magnetic state instability of disordered electrodeposited nanogranular Fe films

Journal of Magnetism and Magnetic Materials, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Research paper thumbnail of The Characterisation of Electrodeposited MoS2 Thin Films on a Foam-Based Electrode for Hydrogen Evolution

Catalysts, 2020

Molybdenum sulphide is an emerging precious-metal-free catalyst for cathodic water splitting. As ... more Molybdenum sulphide is an emerging precious-metal-free catalyst for cathodic water splitting. As its active sites catalyse the Volmer hydrogen adsorption step, it is particularly active in acidic media. This study focused on the electrochemical deposition of MoS2 on copper foam electrodes and the characterisation of their electrocatalytic properties. In addition, the electrodeposition was modified by adding a reducing agent—sodium hypophosphite—to the electrolyte. To reveal the role of hypophosphite, X-ray photoelectron spectroscopy (XPS) analysis was carried out in addition to scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). MoS2 films, electrodeposited at various charges passed through the cell (catalyst loadings), were tested for their catalytic activity towards hydrogen evolution in 0.5 M H2SO4. Polarisation curves and Tafel slope analysis revealed that the electrodeposited MoS2 films are highly active. Namely, Tafel slopes fell within the 40–50...

Research paper thumbnail of Pulse electrodeposited bismuth-tellurium superlattices with controllable bismuth content

Journal of Power Sources, 2020

Superlattice structures of (Bi 2) m (Bi 2 Te 3) n series with controllable Bi mole fraction from ... more Superlattice structures of (Bi 2) m (Bi 2 Te 3) n series with controllable Bi mole fraction from 0.41 to 0.71 are electrodeposited in pulse potentiostatic mode from acidic electrolytes containing Bi(NO 3) 3 and TeO 2 as precursors. Two valence states of bismuth in superlattices are identified by X-ray photoelectron spectroscopy (XPS). One of those states is attributed to interlayered Bi 0 which is present in (Bi 2) m (Bi 2 Te 3) n superlattice in the form of biatomic layers between bismuth telluride quintuples. X-ray difraction (XRD) analysis and density functional theory (DFT) calculations indicate an increase in subcell parameter a sub and decrease in subcell parameter c sub with the increase of Bi mole fraction. Biatomic layers of Bi 0 are identified with cyclic voltammetry by characteristic anodic peak between potentials of metallic bismuth and Bi 2 Te 3 oxidation. The selective oxidation of Bi-bilayers in (Bi 2) m (Bi 2 Te 3) n superlattice at the potential of the anodic peak results in the product corresponding to Bi 2 Te 3 by stoichiometry, but having an expanded crystal structure. Superlattices with controllable Bi mole fraction and Bi 2 Te 3 with "memory effect" may be of interest for design of new thermoelectric materials with controllable parameters.

Research paper thumbnail of Chemical, electrochemical and tribological study of various olive oils and their behaviour on steel

Chemija, 2018

The influence of different chemical composition and physical properties of olive oils, produced f... more The influence of different chemical composition and physical properties of olive oils, produced from various districts in Morocco with various acidic numbers (from 1.76 to 18.01), on their tribological performance and corrosion protection has been investigated. The chemical composition was determined by means of IR, 1H and 13C NMR spectroscopy. The investigated olive oils show small quantitative and qualitative differences between each other (the amount of free fatty acids and the composition of fatty acids in triglycerides). The spectroscopic data let us unambiguously determine in general that the main fatty acids in oils are saturated palmitic and/or stearic acids, unsaturated oleic and linoleic acids except linolenic acid. The oxidation stability of oils was estimated. The contact angle measurements and electrochemical impedance spectroscopy data show that all films of olive oils on the surfaces of steels are porous; therefore, the values of corrosion inhibition efficiency are re...

Research paper thumbnail of Coupled Electrodeposition of Fe–Co–W Alloys: Thin Films and Nanowires

Frontiers in Chemistry, 2019

The electrodeposition of Fe-CoW alloys was examined using a rotating cylinder Hull (RCH) cell and... more The electrodeposition of Fe-CoW alloys was examined using a rotating cylinder Hull (RCH) cell and conditions were determined to create nanowires. The metal ion reduction mechanism was a combination of induced and anomalous codeposition, with water reduction as a gas evolving side reaction, rending deposition into recesses a challenge. In thin film deposition, under kinetic control, the addition of Fe ions into the electrolyte, greatly reduced the Co partial current density, and thus it's content in the deposit. The change of Co partial current density was attributed to an anomalous codeposition behavior, but it had a minimal effect in changing the W wt% in the deposit, despite the expected inducing characteristic of Fe when codeposited with tungsten. Deposition conditions were determined to electrodeposit Fe-CoW nanowires having similar concentration as the thin films. Nanowires were electrodeposited into polycarbonate membranes under pulsed current at room temperature.

Research paper thumbnail of Modified Electrodeposited Cobalt Foam Coatings as Sensors for Detection of Free Chlorine in Water

Coatings, 2019

Metal foams offer a substantial specific surface area and sturdy frame, which makes them great ca... more Metal foams offer a substantial specific surface area and sturdy frame, which makes them great candidates for various applications such as catalysts, sensors, heat sinks, etc. Cobalt and its various compounds are being considered as a cheaper alternative for precious and rare metal catalysts. The cobalt foams have been electrodeposited under galvanostatic and current pulse modes; the porous surface was created using a dynamic hydrogen bubble template. In order to obtain the highest porosity, four different solutions were tested, as well as a wide current density window (0.6–2.5 A/cm²), in addition many different combinations of pulse durations were applied. The effects of surfactant (isopropanol) on porosity were also investigated. The morphology of obtained foams was examined by SEM coupled with EDS, and XRD spectroscopy. True surface area was estimated based on the values of a double electric layer capacitance that was extracted from EIS data. Cobalt foams were modified using K3[F...

Research paper thumbnail of Nanocrystalline Electrodeposited Fe-W/Al2O3 Composites: Effect of Alumina Sub-microparticles on the Mechanical, Tribological, and Corrosion Properties

Frontiers in Chemistry, 2019

In this study, nanocrystalline FeW alloy and Fe-W/Al 2 O 3 composite coatings with various conten... more In this study, nanocrystalline FeW alloy and Fe-W/Al 2 O 3 composite coatings with various contents of sub-microsized alumina particles have been obtained by electrodeposition from an environmentally friendly Fe(III)-based electrolyte with the aim to produce a novel corrosion and wear resistant material. The increase in volume fraction of Al 2 O 3 in deposits from 2 to 12% leads to the grain refinement effect, so that the structure of the coatings change from nanocrystalline to amorphous-like with grain sizes below 20 nm. Nevertheless, the addition of particles to the FeW matrix does not prevent the development of a columnar structure revealed for all the types of studied coatings. The observed reduction in both hardness and elastic modulus of the Fe-W/Al 2 O 3 composites is attributed to the apparent grain size refinement/amorphization and the nanoporosity surrounding the embedded Al 2 O 3 particles. In the presence of 12 vol% of Al 2 O 3 in deposits, the wear rate decreases by a factor of 10 as compared to FeW alloy tested under dry friction conditions due to the lowering of tribo-oxidation. The addition of alumina particles slightly increases the corrosion resistance of the coatings; however, the corrosion in neutral chloride solution occurs through the preferential dissolution of Fe from the matrix. The obtained results provide a possibility to integrate the nanocrystalline Fe-W/Al 2 O 3 composite coatings into various systems working under dry friction conditions, for example, in high-temperature vacuum systems.

Research paper thumbnail of Electrodeposition of Nanocrystalline Fe-P Coatings: Influence of Bath Temperature and Glycine Concentration on Structure, Mechanical and Corrosion Behavior

Coatings, 2019

A detailed electrochemical study and investigation of a Fe-P glycine bath as a function of the te... more A detailed electrochemical study and investigation of a Fe-P glycine bath as a function of the temperature and glycine concentrations and current density, and their resulting corrosion and mechanical behavior is presented. A low addition of glycine to the electrolyte led to a drastic increase of the P content. At low Fe-P deposition rates, heterogeneous rough deposits with morphological bumps and pores were observed. By increasing the Fe-P deposition rate, the number of pores were reduced drastically, resulting in smooth coatings. Increasing the P content led to the formation of nanocrystalline grains from an “amorphous-like” state. Coatings with higher P contents exhibited better corrosion resistance and hardening, most likely attributed to grain boundary strengthening.

Research paper thumbnail of Design of Highly Active Electrodes for Hydrogen Evolution Reaction Based on Mo-Rich Alloys Electrodeposited from Ammonium Acetate Bath

Coatings, 2019

The given research was driven by prospects to design Mo-rich coatings with iron group metals elec... more The given research was driven by prospects to design Mo-rich coatings with iron group metals electrodeposited from a highly saturated ammonium acetate bath. The obtained coatings could be employed as prominent electrodes for the hydrogen evolution reaction (HER). It was found that the Mo content in Ni–Mo alloys can be tuned from 30 to 78 at.% by decreasing the molar ratio [Ni(II)]:[Mo(VI)] in the electrolyte from 1.0 to 0.25 and increasing the cathodic current density from 30 to 100 mA/cm2. However, dense cracks and pits are formed due to hydrogen evolution at high current densities and that diminishes the catalytic activity of the coating for HER. Accordingly, smoother and crack-free Ni–54 at.% Mo, Co–52 at.% Mo and Fe–54 at.% Mo alloys have been prepared at 30 mA/cm2. Their catalytic behavior for HER has been investigated in a 30 wt.% NaOH solution at temperatures ranging from 25 to 65 °C. A significant improvement of electrocatalytic activity with increasing bath temperature was ...

Research paper thumbnail of Improvement in the Wear Resistance under Dry Friction of Electrodeposited Fe-W Coatings through Heat Treatments

Coatings, 2019

The influence of the microstructural transformations upon heat treatments on the wear resistance ... more The influence of the microstructural transformations upon heat treatments on the wear resistance of Fe-W coatings is studied. The coatings are electrodeposited from a glycolate-citrate plating bath with 24 at.% of W, and the wear resistance is investigated under dry friction conditions using ball-on-disc sliding tests. The samples were annealed in Ar atmosphere at different temperatures up to 800 °C. The microstructural transformations were studied by means of X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Electron Backscattered Diffraction (EBSD) technique. Except for the coating annealed at 800 °C, all the tested coatings suffered severe tribo-oxidation which resulted in the formation of deep cracks, i.e., ~15 μm in depth, within the wear track. The precipitation of the secondary phases, i.e., Fe2W and FeWO4, on the surface of the sample annealed at 800 °C increased the resistance to tribo-oxidation leading to wear tracks with an average depth of ~3 μm. Hence, th...

Research paper thumbnail of In-depth characterization of as-deposited and annealed Fe-W coatings electrodeposited from glycolate-citrate plating bath

Electrochimica Acta, 2018

FeW coatings with 4, 16 and 24 at.% of W were electrodeposited under galvanostatic conditions fro... more FeW coatings with 4, 16 and 24 at.% of W were electrodeposited under galvanostatic conditions from a new environmental friendly Fe(III)-based glycolate-citrate bath. This work aims to find correlations between composition including the light elements, internal structure of the electrodeposited Fe-Walloys and functional properties of material. The obtained alloys were characterized by Glow Discharge Optical Emission Spectrometry (GD-OES), Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDS), Transmission Electron Microscopy (TEM), and X-ray Diffraction (XRD). Compositional depth profiles of 10 mm thick coatings obtained by GD-OES show that the distribution of metals is uniform along the entire film thickness, while SEM imaging depicted the presence of cracks and O-and W-rich areas inside the Fe-Wcoating with 4 at.% W. In the samples with 16 and 24 at.% of W, oxygen and hydrogen are present mostly at the surface about 1 mm from the top while traces of carbon are distributed within the entire coatings. With increasing W content, the structure of the coatings changes from nanocrystalline to amorphous which was shown by XRD and TEM analysis. Also, the surface of coatings becomes smoother and brighter, that was explained based on the local adsorption of intermediates containing iron and tungsten species. Annealing experiments coupled with XRD analysis show that the thermal stability of FeW alloys increases when the W content increases, i.e. the coating with 24 at.% W retains the amorphous structure up to 600 _C, where a partially recrystallized structure was observed. Upon recrystallization of the amorphous samples the following crystalline phases are formed: a-Fe, Fe2W, Fe3W3C, Fe6W6C, and FeWO4. Hence, the FeW coatings with higher W content (>25 at.%) can be considered as suitable material for high temperature applications. Fig. 4. Compositional depth profiles as obtained by GD-OES of FeW samples of different composition: 4 at.% of W (a), 16 at.% of W (b) and 25 at.% of W(c).

Research paper thumbnail of Electrodeposited Co-W alloys and their prospects as effective anode for methanol oxidation in acidic media

Surface and Coatings Technology, 2016

Electrodeposited CoW alloys having different composition and structure were tested as anodes for ... more Electrodeposited CoW alloys having different composition and structure were tested as anodes for methanol electrooxidation. The structure of electrodeposited CoW alloys having various tungsten content is either nanocrystalline (3 and 18 at.% of W) or "amorphous-like" (30 at.% of W). The electrodeposition was performed on the stainless steel substrate from citrate-borate bath at 60°C and a cathodic current density 10 mA•cm −2. Alloys having different compositions were obtained by varying pH from 5 to 8. A well-defined crystalline structure was indicated for CoW having 3 at.% and 18 at.% of W: these deposits have a hexagonal close packed (hpc) structure typical for electrodeposited pure Co. The high content of W in the alloy (~30 at.%) leads to the formation of nanocrystalline structure ("amorphous-like"). The electrocatalytic activity of prepared CoW alloys was examined by means of cyclic voltammetry in the mixture of 1 M CH 3 OH and 0.1 M H 2 SO 4. The electrooxidation of methanol depends on the content of W in the alloy. It was found that the crystalline Co-3 W and Co-18 W alloys are inactive for methanol oxidation, and the electrochemical alloys dissolution occurs in the tested media. Whereas, the high content of W (~30 at.%) in the CoW coating prevents the continuous CoW alloy dissolution and it might be used as anode for the methanol oxidation in the acidic media. The annealing of CoW deposits was performed at 600°C for 1 h in the air and formation of Co 3 O 4 and CoWO 4 compounds with simultaneous decrease of tungsten content in the alloys were detected. The annealed CoW coatings show lower activity toward methanol electroxidation compared to as-deposited Co-30 at.% W.

Research paper thumbnail of A Hybrid Approach to Fabricated Nanowire-Nanoparticle Composites of a Co-W Alloy and Au Nanoparticles

Journal of The Electrochemical Society, 2016

CoW nanowires were fabricated by pulsed electrodeposition from a citrate-glycine electrolyte onto... more CoW nanowires were fabricated by pulsed electrodeposition from a citrate-glycine electrolyte onto rotating cylinder electrodes and into nanoporous polycarbonate membranes. The characterization of the electrodeposition conditions and alloy composition of electrodeposited CoW alloy thin films were determined and used to guide conditions to electrodeposit the nanowires. Gold nanoparticles of 50 nm size were also added to the electrolyte and deposited during electrodeposition of the CoW alloy nanowires, embedded within, and attached to the nanowire tip, introducing a novel procedure to attached nanoparticles onto nanowires.

Research paper thumbnail of Synthesis, electrochemical impedance spectroscopy study and photoelectrochemical behaviour of as-deposited and annealed WO 3 films

Electrochimica Acta, 2017

WO 3 films have been obtained by anodization of tungsten in the different acidic electrolytes (HC... more WO 3 films have been obtained by anodization of tungsten in the different acidic electrolytes (HCl, H 2 SO 4 , H 3 PO 4 , H 3 PO 4 + NH 4 F) and at various applied potentials. Electrochemical impedance spectroscopy was used to investigate film formation and to characterize the obtained oxide films. The equivalent electric circuits modelling reactive and blocking behaviour are provided and discussed. It was found, that oxide film capacitance decreases linearly with increasing anodization potential. The relative permittivity of tungsten oxide films varies from 31 to 56 depending on the acid used. A relatively high rate of the film formation (1.87 nm V-1) and increased resistance against oxide breakdown can be achieved for tungsten oxide obtained from 0.3 M oxalic acid bath. Compact oxide films are formed at the potentials ranged from 10 V to 30 V, whereas increasing of anodization voltage to 60 V resulted in the formation of disordered, porous structures due to surface etching. Semiconductor properties were determined by Mott-Schottky analysis. Photoelectrochemical properties of as-deposited and annealed at 600°C WO 3 films were determined in a Na 2 SO 4 solution under pulsed and constant UV irradiation. It was determined that annealed WO 3 films in comparison to as-deposited films are more stable and generate substantially higher photelectrochemical currents.

Research paper thumbnail of Toward uniform electrodeposition of magnetic Co-W mesowires arrays: direct versus pulse current deposition

Electrochimica Acta, 2016

Template-assisted electrodeposition of Co-rich CoW alloys into mesoporous anodized aluminum oxide... more Template-assisted electrodeposition of Co-rich CoW alloys into mesoporous anodized aluminum oxide from ammonia-free solutions is investigated. The optimum deposition conditions rendering uniform filling of the pores, either by direct current (DC) or pulse current (PC) methods, are established. Contrary to the DC deposition on flat surfaces (which is kinetically controlled), the DC electrodeposition in the mesopores of the template is limited by mass transfer. Conversely, under PC mode, the CoW electrodeposition process is controlled by kinetics at frequencies > 0.3 Hz; and by diffusion at lower frequencies. The obtained mesowires are nanocrystalline and exhibit a hexagonal closed packed (hcp) structure. The magnetic properties of selected CoW mesowires, with variable aspect ratio, are also studied. The arrays of mesowires exhibit a semi-hard ferromagnetic behavior with coercivity values that surpass those of Co mesowires with similar dimensions. The interplay between interwire dipolar interactions, magnetocrystalline anisotropy and shape anisotropy on the overall shape of the hysteresis loops (in particular, on the coercivity and squareness ratio values, as well as on the effective magnetic easy axis direction) is investigated in a semiquantitative manner.

Research paper thumbnail of Anodic Titanium Oxide Films: Photoelectrochemical and Tribocorrosion Behavior

Journal of Nanoelectronics and Optoelectronics, 2014

ABSTRACT Titanium oxide films are fabricated by Ti anodization in orthophosphoric acid-ammonium f... more ABSTRACT Titanium oxide films are fabricated by Ti anodization in orthophosphoric acid-ammonium fluoride electrolytes. On the mechanically polished semi-bright Ti substrates the continuous TiO2 films are formed, whereas ordered nanoporosity is formed on the mirror-like surface of Ti substrate at temperatures of 10–20 °C in the H3PO4 electrolyte with NH4F. The photocurrents and photopotentials are affected by the amount of fluorine in the electrolyte and consequently in the deposit. Tribocorrosion tests were performed in a neutral solution, and changes of open-circuit potential (OCP) as well as electrochemical impedance spectra were recorded with/without 0.4 N load. The rapid changes of OCP can be explained by the passive film abrasion, when oxide film becomes damaged and bare Ti surface is exposed. The wear loss depends on the NH4F concentration in the solution used for TiO2 films fabrication. TiO2 films destroyed during sliding tend to restore within 300–400 s after unloading.

Research paper thumbnail of Tribological behaviour of mineral and rapeseed oils containing iron particles

Industrial Lubrication and Tribology, 2015

Purpose – The purpose of this paper is to investigate the tribological behaviour of commercially ... more Purpose – The purpose of this paper is to investigate the tribological behaviour of commercially available SAE 10 mineral and rapeseed oils containing Fe particles synthesized directly in the oil phase. Design/methodology/approach – Sub-micron Fe particles (50-340 nm) were synthesized by wet chemical reduction reaction of FeSO4 by sodium borohydride in the rapeseed and mineral oils in the presence of surfactant: block copolymer (ENB 90R4) or oxyethylated alcohol (OS-20). A four-ball wear tribometer was used to investigate the tribological properties of mineral and rapeseed oil: coefficient of friction (COF), wear scar diameter and wear loss. Viscosity measurements of oil solutions and determination of synthesized Fe particles size were performed as well. Findings – The presence of Fe particles (0.1 weight per cent) in the rapeseed and mineral oils caused the little change in the COF but resulted in marked improvement of anti-wear property. The oils containing Fe particles with sligh...