The electrochemical behavior of as-cast AlxCoCrFeNiM (M = Ti, V, Si, Mn, Cu) high entropy alloys (HEAs) in 1 M NaCl and 0.5 M H2SO4 solutions is studied. Polarization measurements were carried out in a standard three-electrode electrochemical cell with a platinum auxiliary electrode using a P-30J potentiostat device. The potentials were measured relative to a saturated silver chloride reference electrode EVL-1M3 at room temperature (25 °C) with a sweep rate of 5 mV/s. It is shown that despite a wide passivation region, Al0.5CoCrFeNi1.6Ti0.7 HEA undergoes significant corrosion in both sodium chloride and sulfuric acid solutions and exhibits low corrosion potential and current density. Energy-dispersive X-ray spectroscopy (EDS) analysis revealed that Ti-containing eutectic areas are the most susceptible regions to corrosion. Intergranular corrosion was found in Al0.25CoCrFeNiMn and Al0.25CoCrFeNiCu HEAs. Moreover, Al0.25CoCrFeNiCu possesses the smallest passivation interval ΔE among all the investigated HEAs. For samples with Ti, Mn, and Cu, a protective film layer is not formed on the surface of the phases enriched in these elements, or it is brittle and crumbles. For samples with Si and V, a passivating film is formed. Thus, Al0.45CoCrFeNiSi0.45 and Al0.25CoCrFeNiV HEAs exhibited the highest resistance in 1 M NaCl and 0.5 M H2SO4 corrosive environments, respectively.
In this work, studies have been carried out on the electrochemical reduction of hydrogen (hydronium ion) from acidic aqueous solutions in the presence of an organic substance – pyridine. Electrolysis was carried out in an electrolyte with a sulfuric acid content (0.18; 0.36 M) with a pyridine additions of 8.4·10-3 M. Potentiostatic studies were carried out on a Potentiostat P-30Jcom Elins potentiostat using a three-electrode cell. Working electrodes (cathodes) were made of M1 copper with an area (S) of 0.09 cm2; aluminum (AD1) S – 0.125 cm2, zinc (Ts0A) S – 0.35 cm2, lead (Cl) S – 0.20 cm2, auxiliary (anode) – from a platinum plate with an area of 0.20 cm2, reference electrode – silver chloride (AgCl/Ag). In potentiometric measurements, the results are presented according to the average data obtained for 30 s of electrolysis in the potential range (-950 ÷ -1100 mV for AgCl/Ag), and in studies in the galvanostatic mode at current densities from 0 to 110 mV/cm2, the results are presented as average data, obtained in the initial 5 s of the process. The paper presents comparative data on the electrokinetic parameters studied under the same conditions of hydrogen discharge reactions at different cathodes in electrolytes with a sulfuric acid content of 0.36 M. It is shown that the highest discharge current density of the hydronium ion (Н3О+) is achieved at the copper electrode, and the lowest at the lead electrode. With the addition of 8.4∙10-3 M pyridine to the electrolyte, the reduction of hydrogen cations is somewhat reduced on the electrodes used, except for lead. The transfer coefficients of the hydrogen discharge at all electrodes are low, and with the addition of pyridine they decrease even more. The low transfer coefficients indicate that the process of the hydronium ion discharge proceeds in a non-activation mode. The lowest exchange current is recorded at the copper and lead electrode. At the zinc electrode, the exchange of current is one to two orders of magnitude higher than at the other electrodes, so it can be noted that at this electrode the system under consideration is closer to the equilibrium of state. The order of the reaction of the course of electrolysis by the hydronium cation on the copper, aluminum and zinc electrodes is close to unity. The addition of pyridine leads to a slight decrease in the order of the reaction. This is due to the fact that pyridine molecules in acidic solutions exist in the form of pyridinium ion, which is reduced at the cathode. In this case, a significant amount of hydrogen is absorbed, which should explain the decrease in the order of the reaction with respect to the hydronium ion in the presence of pyridine additives. The obtained low values of the transfer coefficients indicate that, during the discharge of hydronium ions, the process is limited to a greater extent by the concentration polarization. The diffusion nature of the reduction of hydronium ions in electrolytes with a sulfuric acid concentration of 0.18 and 0.36 M is also evidenced by data taken in a dynamic mode.
Electrochemical reduction of hydrogen (hydronium ion) was carried out on zinc, aluminum and copper cathodes from acidic aqueous solutions containing sulfuric acid (0.09, 0.18 and 0.36 mol/l) to study the effect of electrolyte acidity, the type of cathodes used and potential values on electrolysis indicators. The studies were carried out on the potentiostat using a three-electrode cell under conditions of intensive electrolyte stirring with a magnetic stirrer. At the initial stage, electrolysis was performed in the following modes: potentiodynamic measurements at a sweep rate of 1 mV/s in the potential range Е = –(700÷850) mV on a copper and aluminum electrode and Е = –(1000÷1150) mV on a zinc electrode. In the indicated potential range, hydronium discharge parameters at each cathode were calculated: Tafel slope, apparent transfer coefficients and exchange currents. Dependences of these parameters on electrolyte acidity were considered. Average values of steady state potentials were obtained, which, similar to the apparent exchange current, significantly depended on the cathode material: –923.1 mV (zinc cathode); +36.1 mV (copper cathode), and –603.7 mV (aluminum cathode) (AgCl/Ag). The effect of surfactants on all the kinetic parameters considered was shown. The order of the reaction with and without surfactant additives was determined. At the next stage, the electrochemical parameters of hydronium discharge on the copper electrode only were compared. It was shown that the electrochemical parameters significantly depend on the cathodic potential range where they are determined, and on the methods used for their calculation. It was noted that the process proceeds in the region of mixed kinetics. As the electrode polarization decreases, the hydrogen discharge mechanism changes, while the proportion of electrochemical kinetics will increase in the region of mixed kinetics. We suppose that the data obtained can also be of practical importance for the zinc electrolysis technology. The data obtained in this research on the electrochemical parameters of hydrogen discharge in a wide range of potentials on cathodes made of different metals as well as on the effect of electrolyte acidity on the behavior of surfactants during electrolysis will expand knowledge about the zinc electrolysis technology.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.