The electrochemical behavior of two single-phase alloys in the Al–Cu–Fe system prepared by mechanical activation is studied in acidic media using potentiodymanic measurements. The first alloy is crystalline and consists of the β-Al(CuFe) phase; the second alloy consists of a quasi-crystalline icosahedral phase. The second alloy with the quasi-crystalline icosahedral structure is more stable. The corrosion stability of samples decreases with a decrease in the solution pH.
This study explores the electrodeposition of Ni–Mn coatings on a copper substrate using a sulfate bath with varying Mn2+ ions concentration ([Mn2+] = 0.05, 0.1, 0.2, and 0.4 M). The effects of [Mn2+] and applied potential (E) on the nucleation mechanism were evaluated using the Scharifker and Hills (S–H) nucleation model. The results indicate that [Mn2+] and E significantly influence the electrochemical behavior of Ni–Mn coatings. The energy dispersive X-ray (EDX) examination confirmed the presence of Ni, Mn and S species in the coatings. Scanning electron microscopy (SEM) micrographs revealed the cauliflower-like morphology, globular shape particles and porous cracked surface. XRD analysis reveals the successful incorporation of Mn atoms into the Ni lattice, resulting in the formation of a face-centered cubic (FCC) substitutional Ni(Mn) solid solution. The linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) analyses demonstrate that the incorporation of a small amount of Mn into Ni significantly improved the corrosion resistance. The obtained Ni96.9Mn1.5 coating shows the highest corrosion resistance. SEM and XRD analyses of the oxide layer confirmed the formation of a porous, non-uniform microstructure composed of MnO2 and Ni(OH)Cl which contributes to the protective properties of the coating.
A novel glassy carbon electrode modified with cerium dioxide (CeO2) nanoparticles and hexadecylpyridinium bromide is developed for the voltammetric determination of propyl gallate. The hexadecylpyridinium acts as a dispersing agent that stabilized the nanomaterial and as a co-modifier of the electrode surface. Modification of the glassy carbon electrode lowered the propyl gallate oxidation peak potential by 20 mV and provided a 2.6-fold increase in the oxidation peak current. The bare and modified glassy carbon electrodes are characterized by scanning electron microscopy, cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. A statistically significant increase in the effective surface area of the modified electrode is shown (32.4 ± 0.5 mm2 as compared with 8.9 ± 0.3 mm2 for the bare glassy carbon electrode). The electrochemical impedance data indicate a 2100-fold decrease in the charge transfer resistance as compared to the bare glassy carbon electrode, which confirms the increase in the electron transfer rate (ket = 1.13 × 10–5 and 2.42 × 10–2 cm/s for glassy carbon electrode and CeO2-nanoparticles/glassy carbon electrode, respectively). Propyl gallate electrooxidation occurred irreversibly with the participation of protons and is controlled by surface processes. The parameters of electrooxidation are calculated and a scheme of the electrode reaction is suggested. The linear dynamic ranges of propyl gallate in the differential pulse voltammetry are 0.10–2.5 and 2.5–50 μM, with a detection limit of 0.022 μM. The selectivity of the electrode response to propyl gallate in the presence of inorganic ions and carbohydrates is demonstrated. Since the propyl gallate is used to prevent oxidation of vegetable oils, α-tocopherol and other antioxidant additives (tert-butylhydroxyanisole and tert-butylhydroxytoluene) used together with propyl gallate are considered as potential interfering agents. A 5-fold excess of α-tocopherol, a 10-fold excess of tert-butylhydroxyanisole and equimolar amounts of tert-butylhydroxytoluene do not interfere with the propyl gallate determination. The method is tested on extracts of sunflower and sesame oils.
Magnesium alloys with rare-earth elements are widely used in industry due to their high specific strength; however, their low corrosion and wear resistance necessitate surface protection. It is studied how the WC and TiC nanoparticles (NPs) used as the dispersed phase in the electrolyte at the plasma-electrolytic oxidation (PEO) of magnesium alloys in the system Mg–Y–Zn–Zr–Nd–Yb containing the long-period staking-ordered (LPSO) phase affect the formation, composition, and properties of oxide layers. The inert incorporation of WC and TiC NPs into the oxide (without their involvement in chemical reactions and phase transitions) is observed as well as the increased productivity of the coating formation for certain concentrations of additives, without commensurate incorporation of nanoparticles into the coating. As compared with WC NPs, the TiC NPs added into the electrolyte induce greater changes in the conditions of coating formation, as reflected in the decrease in the anodic forming voltage of the PEO process up to ~20 V and the increase in the degree of crystallinity of oxide layers to ~80 vol %. The hardness and the adhesion strength of layers increase due to their modification with WC and TiC nanoparticles. The PEO allows reducing the corrosion rate of this alloy by three—four orders of magnitude. The addition of nanoparticles into the electrolyte in concentrations of 2 and 5 g/L WС and 1 g/L TiC makes it possible to additionally increase the charge transfer resistance across the alloy/coating interface by a factor of up to 1.5. At the same time, the high (4–5 g/L) concentration of the dispersed phase in the electrolyte has a negative effect on the long-term corrosion stability of samples. Hence, these coatings are more suitable for articles with limited service life.
Zinc oxide (ZnO) remains a promising candidate in the field of photo(electro)catalytic hydrogen/electricity production from water/biomass and wastewater treatment. However, there has been a need for the development of sustainable, versatile tools for achieving controlled and economically viable production of nano ZnO. This research is aimed at assessing the electrochemical approaches to tune ZnO morphology through electrosynthesis using pulse alternating current (PAC) by varying the average anodic/cathodic current densities ratio (ja : jc) and NaCl electrolyte as one of the most naturally abundant compounds. The composition, morphology, and specific surface area (SSA) of the ZnO synthesized at different ja : jc were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), and low-temperature nitrogen adsorption-desorption (BET) methods. The synthesized ZnO nanopowders were applied as photoelectrocatalytic (PEC) and photocatalytic (PC) materials. PEC performance of ZnO/FTO was investigated using Na2SO3, ethanol, glycerol, ethylene glycol, formic acid, and glucose as inorganic and organic oxygenates. The PC activity of nano ZnO was evaluated using 2,4-dinitrophenol (DNP) as an organic pollutant. The variation in PEC and PC performance depending on the ZnO electrosynthesis conditions was shown.
A modified glassy carbon electrode (GCE) with immobilized nickel manganese oxide nanoparticles (Ni6MnO8 NPs) was developed for the sensitive and selective detection of dopamine (DA) in the presence of serotonin (5-HT). The Ni6MnO8 NPs were synthesized and characterized by using techniques such as powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), elemental mapping, energy dispersive X-ray analysis (EDAX), and High-resolution transmission electron microscopy (HR-TEM). Electrochemical studies of the Ni6MnO8 NPs for detecting DA and 5-HT were conducted using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under optimal conditions, DPV was used for the simultaneous detection of DA and 5-HT at Ni6MnO8 NPs modified surfaces, achieving low detection limits of 0.021 µM for DA and 0.11 µM for 5-HT. The fabricated sensor demonstrated excellent reproducibility and stability, making it suitable for the analysis DA and 5-HT simultaneously. Additionally, the sensor showed satisfactory recovery rates in real sample analyses.
Platinum-free cathodic electrocatalysts of the hydrogen evolution reaction are developed based on iron complexes of sodium pectate. These catalysts are promising for water electrolysis. The catalyst with 25% substitution of iron ions for sodium ions demonstrates the highest efficiency in the hydrogen evolution reaction and can replace platinum with 93% efficiency when used as the cathodic catalyst in water electrolyzers with proton-exchanging membrane at 80°С.
This review is devoted to the examination of modern literature on aluminum batteries developed in recent years, which have already reached the stage of industrial production. Currently, lithium-ion batteries dominate the market. However, they have serious drawbacks: they are explosive and fire hazardous and also contain rare/expensive components (lithium, cobalt, nickel, electrolyte). Aluminum-ion batteries have advantages over lithium-ion batteries, namely: aluminum is cheap because it is the most widespread metal in the Earth’s crust; aluminum batteries are fire- and explosion-proof. As a result of comparing the “specific energy–specific power” combination for different types of aluminum-ion batteries, it is found that the most favorable combination of specific energy (247 W h/kg) and specific power (44.5 kW/kg) is shown by aluminum-ion batteries consisting of a graphite cathode etched with alkali, an aluminum anode, and an aluminum-chloride-based electrolyte. The highest combinations of specific capacity and current density are demonstrated by aluminum-ion batteries with CoSe cathode: 427 mA h/g at 1 A/g, and those based on MoSe2: 753 mA h/g at 0.3 A/g. The highest specific energy (685 W h/kg) is achieved by aluminum-ion batteries with CoMnO-cathode. Aluminum-ion batteries are characterized by a very high charging rate: up to 10 000 C (the discharge time 0.35 s) and also very high cyclability—up to 30 000 cycles.
Comparative investigation of potentiometric characteristics for coatings electropolymerized from phosphate buffer and the 4-(2-hydroxyethyl)-1-piperazineethanesulfonic-acid-based buffer solutions or deep eutectic solvents, such as reline and mixture of citric acid, glucose and water is carried out. Both the effect of media acidity on the sensor potential and the potentiometric response reversibility are evaluated for all the coatings synthesized. The solid-contact potentiometric sensor array is developed for the determination of easily oxidizable organic compounds: hydroquinone, dopamine, quercetin, and ascorbic acid. Analytical characteristics of such easily oxidizable organic compounds are established. According to the media pH, the analytes can perform either as single-charged ions demonstrating the slopes approaching the Nernstian values or as reducing agents affecting polymer redox forms’ ratio in the modifying coatings. The coatings synthesized from deep eutectic solvents showed wider linear ranges of determined concentrations. Also, they had better sensitivity as compared with those electrodeposited from aqueous media. The solid contact potentiometric sensors were tested for analytes’ determination in real samples of cosmetics, pharmaceuticals, and biologically active additives with 92–107% recovery.
The composition of brass metallurgical waste is determined using X-ray fluorescence analysis. The copper content in the slag is shown to reach 15 wt %; the zinc content, 83 wt %. Sulfuric-acid leaching was performed to separate zinc from the metallurgical dust. Optimal process parameters are selected as: leaching duration 60 min, sulfuric acid concentration 0.1 M. After the sulfuric-acid leaching, the acid solution is subjected to electrochemical treatment, in order to recover copper and zinc; the copper cake (copper in unoxidized form), to copper–ammonia leaching for 40 min. The concentration of copper in the copper–ammonia solution reached 35 g/L. At the final stage, solvent extraction of copper from the copper–ammonia leach solution is carried out, for which the most effective extracting agent has been selected. Extracting agents of different nature and classes are studied: D2EHPA (a strong acidic organophosphorus extractant), DХ510А and LIX54 (classified as β-diketones). The concentration of extracting agentnts ranged from 50 to 100%, the diluent is kerosene. Copper stripping from the copper–ammonia extract was performed using 2 M sulfuric acid. The best extractant is found to be LIX54 (50% concentration in kerosene). The final stage is copper electrowinning from the stripping solutions at a current density of 3 A/dm2, with a current efficiency of 65%. Based on the conducted research, a process flow-sheet is developed for the recovery of copper and zinc from the brass metallurgical dust.
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