Cathodic Polarization Research Articles

Sulfur poisoning on the La0.75Sr0.25Cr0.5Mn0.5O3-δ-Gd0.1Ce0.9O2-δ fuel electrode for direct electrochemical CO2 reduction in solid oxide electrolysis cells

As a promising energy conversion technology, solid oxide electrolysis cells (SOECs) can efficiently convert CO2 to CO by utilizing renewable energy sources and industrial waste heat. Sulfur poisoning of fuel electrode is a significant drawback to the electrochemical activity and long-term electrolysis performance of SOECs using sulfur-containing fuels. Traditional Ni-based cermet electrodes are susceptible to sulfur poisoning due to the low activation barrier and large enthalpy of the adsorbed sulfur species on the Ni surface. La0.75Sr0.25Cr0.5Mn0.5O3-δ-based materials which exhibit excellent redox stability have been considered as the promising candidates for substitution of Ni-based cermet electrodes. Herein, the sulfur poisoning behavior on the La0.75Sr0.25Cr0.5Mn0.5O3-δ-Gd0.1Ce0.9O2-δ (LSCM-GDC) fuel electrode under CO2–SO2 condition and the mechanism of sulfur poisoning are investigated. The results show that the LSCM-GDC fuel electrode possesses stable electrocatalytic activity as SO2 content up to 10 ppm. With increasing of SO2 content, metallic sulfide, amorphous sulfur and sulfate impurities can be detected on the electrode surface, which decrease the reactive sites and hinder the charge transfer and oxygen ions transport pathway, leading to degradation of the electrolysis performance. The plausible sulfur poisoning mechanism is divided into two categories, namely, thermodynamic and electrochemical processes. For thermodynamic process, SO2 molecules adsorb into oxygen vacancies and couple to coordinated oxygen lattices to form sulfates; for electrochemical process, the formation of amorphous sulfur and metallic sulfide impurities is caused by the binding of SO2 molecules to surface polarons at three phase boundaries under cathodic polarization. This work provides new insights into sulfur poisoning effect on the perovskite oxide electrodes.

Finite Modeling and Simulation of the Effects of Neutral Electrolytic Pickling Process Parameters on EN 1.4404 Steel Strips

Surface treatment via neutral electrolytic pickling (NEP) aims to remove oxide layers and scaling from stainless steel. The objective of this study was to investigate the factors that affect the energy efficiency of the process. This study developed a COMSOL Multiphysics model for the distribution of current across a bipolar steel strip by controlling the following parameters: Na2SO4 concentration, temperature, electrode-to-strip distance, and inter-electrode distance. Full factorial measurements of the electrolyte’s conductivity as well as the steel strip’s and the electrode’s polarization were conducted to provide data for the NEP model. Galvanostatic pulse measurements were performed to calculate transient times during pickling. According to the model, an applied voltage of less than 11 V was insufficient to polarize the steel strip to the potentials needed on both the anodic and cathodic sides. A higher voltage of 11–15 V resulted in anodic current densities of 600–1600 A m−2 and cathodic current densities of 700–2000 A m−2 on the steel strip. These current densities are within the range of previous experimental studies and industrial practices. The model showed that when a steel strip acts as a bipolar electrode, the current’s efficiency decreases, as only a fraction of the strip facing the anodes or cathodes is polarized sufficiently. The galvanostatic tests showed that anodic polarization of the steel strip is easier than cathodic polarization. The slow polarization in the cathodic direction can be improved by using a higher current density. The time needed to polarize stainless steel indicates that the strip’s velocity should be less than 1 m s−1 to give enough time for polarizing the steel strip.

Controlled electrochemical hydridation of Ti surfaces – optimisation and electrochemical properties

Ti is used as a construction material in many applications including electrodes in various electrochemical technologies due to its high corrosion stability provided by the stable oxide layer on the surface. However, this oxide layer is also the reason for its resistivity causing high interfacial resistance between components and energy losses. This problem can be solved by various surface modifications such as acid etching or coating with a layer of precious metals. In this study, we present a novel method for controlled hydridation of Ti materials based on a combination of acid etching and cathodic hydridation aimed primarily for surface modification of Ti components for proton exchange membrane water electrolyser. Cathodic polarisation represents the means to increase the amount of Ti hydride and to tune its properties to obtain a Ti surface with low interfacial resistance and preserved corrosion stability. The study investigated the effects of concentration, temperature, time, and current density on cathodic polarization in H2SO4 electrolytes. The resulting samples were characterized by X-ray diffractometry, X-ray photoelectron spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, Kelvin probe and temperature-programmed desorption. This allowed finding interesting correlations between the surface composition of the Ti samples and their electrochemical properties.

Electrochemical treatment of antibiotic wastewater containing ceftriaxone sodium by porous Ti/Magnéli Ti4O7 nanotube arrays

In this study, porous Ti/Magnéli Ti4O7 nanotube arrays (NTA) was fabricated to pretreat antibiotic wastewater. Characterization of the Ti4O7-NTA illustrated that highly ordered NTA was successfully generated on the porous Ti substrate, which enlarged the specific surface area by 1.67 times. The Ti4O7-NTA has a high oxygen evolution potential (2.60 V) as well as low interfacial charge transfer resistance (4.479 Ω cm−2). Ceftriaxone sodium (CRO) was completely removed from raw antibiotic wastewater after 3 h of treatment by the Ti4O7-NTA, under optimal operation conditions. The biodegradability and toxicity of the wastewater were also significantly enhanced and reduced, as the BOD/COD and EC50,48h values were increased to 0.48 and 57.62 % ± 2.16 %, respectively. The possible degradation pathway of CRO was proposed by LC‒MS. Cathodic polarization was proven to be an effective way to ensure the long-term durability of the Ti4O7-NTA.

Physicochemical and Electrochemical Properties of Materials Based on Titanium Suboxides

The influence of the synthesis conditions on the surface morphology, phase composition, and electrocatalytic activity of materials in oxygen and hydrogen evolution reactions was investigated. For instance, the slopes in the potential vs the logarithm of the current density dependencies during oxygen evolution were 221 and 109 mV/dec for TiO2 nanotubes and platinum-coated layers, respectively. In the latter case, small deviations may be attributed to the structural heterogeneity of the material or the developed surface of the coating. As for pristine TiO2 nanotubes, an atypical Tafel slope was observed, almost twice the theoretical value, indicating the presence of a semiconductor component in the electrode capacitance. Studies showed that the materials are n-type semiconductors. The cathodic polarization stage leads to the formation of titanium suboxides in the nanotube recovery phase, contributing to an increase in the material electrical conductivity. This also allows for the creation of a porous developed surface matrix for the electrodeposition of catalytic metal layers. Tafel slopes were calculated for the investigated materials in the hydrogen evolution reaction. For TiO2 nanotubes, a slope of 175 mV/dec was observed. The material surface was partially blocked by hydroxides, resulting in a low num-ber of active centers for the hydrogen evolution, and the polarization curve had a steep slope. In the case of TiO2 nanotubes coated with a platinum layer, a high number of cationic vacancies in the matrix and a deficit of oxygen ions facilitated the mobility of platinum atoms, leading to the emergence of a large number of active centers for the hydrogen evolution. As a result, the Tafel slope of the polarization curve was found to be 30 mV/dec.

Enhanced stability of electrocatalytic properties against cathodic current polarization for chromium ferrite perovskite-based composite cathodes

The structure, electrical conductivity, thermal expansion and electrocatalytic activity of (100-x) vol% La0.3Sr0.7Fe0.7Cr0.3O3-δ-x vol% Ce0.8Sm0.2O1.9 (x = 10–50) composites were investigated in comparison with single-phase La0.3Sr0.7Fe0.7Cr0.3O3-δ perovskite. The Ce0.8Sm0.2O1.9 component in the composites served to repress the formation of oxygen vacancies on the surface and in the bulk of the La0.3Sr0.7Fe0.7Cr0.3O3-δ component at elevated temperatures, which affected the electrical conductivity, thermal expansion and electrocatalytic activity for oxygen reduction reaction as a result. Moreover, the introduction of Ce0.8Sm0.2O1.9 into La0.3Sr0.7Fe0.7Cr0.3O3-δ resulted in a catalytic spillover effect beneficial to the electrocatalytic activity of the composites. The optimal composition of the composites was determined to be x = 30 based on an overall evaluation of various properties. A porous electrode of the composite with x = 30 achieved a polarization resistance of 0.074 Ω·cm2 at 800 °C in air. In sharp contrast to a porous electrode of La0.3Sr0.7Fe0.7Cr0.3O3-δ, the composite electrode showed appreciably alleviated surface strontium segregation and substantially minimized electrode deactivation after exposure to cathodic current polarization. The enhanced stability of the electrocatalytic activity of the composite electrode against cathodic current polarization was explained with respect to the repression and catalytic spillover effects induced by the Ce0.8Sm0.2O1.9 component.

EIS and relaxation times analysis of the electric double layer construction on Pt cathode surface in MgCl2 molten salt hydrate

The electric double layer on Pt cathode surface in the process of cathodic polarization was analyzed with cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Raman spectroscopy, and Scanning electron microscope (SEM) in magnesium chloride (MgCl2) solution and MgCl2 molten salt hydrate (MSH). The effects of KCl on the structure of MgCl2 molten salt hydrate and electrode reaction were discussed. EIS data were fitted to propose the equivalent electric circuits to simulate the structure of electric double layers on Pt electrodes. Distribution of relaxation times (DRT) analysis was estimated to identify each process for MgCl2 solution and MgCl2 molten salt hydrate on the Pt cathode. The results show that the solution transforms into MSHs as the water content in the solution decreases. The solution and molten salt exhibit different double-layer properties. The movement of hydrated ions has greater resistance in MSHs which leads to the reduction of electrode reaction rate. The DRT and EIS results demonstrate that H+ and hydrated Mg2+ are simultaneously adsorbed on the Pt surface to form a double electric layer in MgCl2 solution or MSHs. In the MgCl2 MSHs, H+, H2O, and compact hydrated Mg2+ on the Pt electrode surface form a double layer. KCl plays an important role in changing the structure of MgCl2 molten salt hydrate, increasing the active H2O, and offering H+ adsorbed on the Pt surface.

Electrodeposition of neodymium from betaine-ethylene glycol deep eutectic solvent using neodymium oxide as a precursor

The electrodeposition of neodymium was investigated in betaine-ethylene glycol (Bet-EG) deep eutectic solvent (DES) containing neodymium oxide (Nd2O3) at different temperatures ranging from 353 K to 373 K. The electrochemical behavior of Nd2O3 dissolved in Bet-EG DES was researched by cyclic voltammetry, potentiodynamic polarization and chronoamperometry methods. Cyclic voltammograms (CVs) manifest that Nd(III) reduction in Bet-EG is an irreversible process with diffusion-controlled, and the reduction overpotential of Nd(III) decreases with the increase of the temperature. The temperature has an impact on the diffusion coefficient of Nd(III) species, obeying the Arrhenius equation. The activation energy is estimated to be 36.78 kJ mol−1. The cathodic polarization analysis shows that the rise of temperature promotes the reduction of Nd(III). The UV–Vis and ESI-MS analyses show that [Nd2(bet)8(H2O)4]6+ complex anions are formed as Nd2O3 is dissolved in Bet-EG DES. Electrodeposited neodymium with various morphologies were characterized and analyzed by EDX, XPS, XRD and SEM. It is found that the electrodeposition temperature has a great effect on the morphology of Nd electrodeposits. Depending on the deposition temperature, metallic Nd with submicron particles or porous structures were obtained.

Exploring B-site high-entropy configuration of spinel oxides for improved cathode performance in solid oxide fuel cells

High-entropy engineering is an emerging strategy to enhance material properties beyond their individual components. In this study, we synthesized a high-entropy spinel oxide cathode material, Ni(Fe0.2Mn0.2Co0.2Cr0.2Ni0.2)2O4, for solid oxide fuel cells (SOFCs) using a solution combustion method. The material exhibits a spinel structure with diverse surface metal valence states and a high concentration of oxygen vacancies. Density functional theory calculations reveal the B-site high-entropy design can significantly improve the oxygen adsorption capability. Electrochemical tests demonstrate that Ni(Fe0.2Mn0.2Co0.2Cr0.2Ni0.2)2O4 has superior conductivity and oxygen reduction activity compared to binary spinel oxides. An anode-supported SOFC with Ni(Fe0.2Mn0.2Co0.2Cr0.2Ni0.2)2O4 cathode achieved a peak power density of 583 mW cm-2 at 800 °C. Impedance and relaxation time distribution (DRT) analyses indicate that the oxygen molecular dissociation and oxygen atom diffusion dominates the cathode polarization. This study demonstrates that high-entropy engineering of the B-site in spinel oxides is a promising strategy to optimize cathode performance for SOFCs.

Effect of pause time on microstructure and corrosion resistance in AZ31 magnesium Alloy's micro-arc oxidation coating

Micro-arc oxidation (MAO) coatings are among the most effective methods for protecting Mg alloys against corrosion. However, the corrosion protection effect of MAO coatings for Mg alloys is unsatisfactory due to the formation of micropores and microcracks in these coatings. Many researchers have improved the microstructure and corrosion resistance through changing the electrical parameters, such as current density, oxidation time, frequency, duty cycle and power modes. This study is one of the first to examine the role of pause time following anodic and cathodic polarization in a MAO process for magnesium alloys. Anodic pause time, as opposed to its cathodic counterpart, augments the corrosion resistance of these alloys, as demonstrated by electrochemical impedance spectroscopy results. Specifically, an MAO-coated specimen subjected solely to anodic pause time exhibits a total impedance six times greater than a specimen undergoing only cathodic pause time, irrespective of identical coating thickness. These findings emphasize the detrimental effect of cathodic pause time on corrosion resistance and demonstrate the beneficial role of anodic pause time.

Super-flat and uni-oriented cobalt film electrodeposited by modulating the crystal nucleation and growth behavior

A precise control of the microstructure of electrodeposited cobalt film is crucial for attaining the desired and reproducible electrical performance in edge nanoelectronic devices. Here we realize the super-flat and uni-oriented cobalt film through a one-step electrodeposition process using benzenesulfinic acid (BNS) as additive. We find that the unsaturated sulfite group in BNS plays a key role in the super-flat cobalt electroplating. Molecular activity analysis and electrochemical test results suggested that the electron donating ability of the sulfite group was higher than that of the sulfonate group, resulting in stronger adsorption of BNS on the cobalt surface and enhanced cathodic polarization. Nucleation model fitting and surface morphology evolution studies revealed that the cobalt nucleation with BNS shifted to progressive nucleation from instantaneous nucleation in the additive-free electrolyte, leading to a more uniform and compact film morphology. Furthermore, equilibrium adsorption calculations indicated that the selective and strong adsorption of BNS on cobalt planes was responsible for the preferential orientation of the (002) crystal plane growth. After annealing, cobalt films prepared with BNS exhibited substantial grain growth and impurity diffusion, which further improved the electrical performance.

Preparation of Ti4O7 Reactive Electrochemical Membrane for Electrochemical Oxidation of Coking Wastewater

The effluent of coking wastewater comprises hundreds of refractory organics and is characterized by high toxicity and non-biodegradation. Electrochemical advanced oxidation processes (EAOPs) have been widely applied in the field of water purification. In this study, a Ti4O7 reactive electrochemical membrane (REM) was prepared using the plasma spraying method for the electro-oxidation of coking wastewater. The composition and surface morphology of the Ti4O7 REM were characterized via X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The computational fluid dynamics (CFD) simulation was used to compare the mass transfer performance of the Ti4O7 REM in traditional batch (TB) mode and flow-through (FT) mode. In the FT mode, the effects of current density and anode–cathode distance on the treatment efficiency were investigated, and the electrocatalytic performance of the anode on coking wastewater was analyzed. The results showed that the COD removal efficiency reached 76.2% with an energy consumption of 110.5 kWh kg−1 COD under the optimal condition. In addition, cathodic polarization provides an effective technique for maintaining the long-term activity of the Ti4O7 REM. The three-dimensional fluorescence results and UV-vis spectrum showed that the aromatic compounds could be effectively degraded using the Ti4O7 REM. The Ti4O7 REM demonstrated excellent performance of electrochemical oxidation and satisfactory stability, which had a strong potential for application in the field of practical wastewater and engineering practices that respond to the concept of sustainable development.

Electro-assisted reduction of chalcopyrite using acetic acid. The feasibility to use weak and less aggressive acids

This work presents for the first time an electrochemical study of the electro-assisted reduction of chalcopyrite using an organic weak acid. The chalcopyrite reduction was assessed at the microelectrolysis level using different electrochemical and characterization techniques. The voltamperometric and FESEM/EDS results revealed that chalcopyrite can be reduced to bornite at more cathodic potentials than −0.25 V vs SHE. When the acetic acid concentration was increased from 0.5 to 3 M, the chalcopyrite reduction kinetics was favored liberating a higher amount of chalcopyritic iron into the bulk solution. The Tafelarian analysis of the system showed that the exchange current density of the chalcopyrite reduction was increased from 1.72x10-7 to 9.71x10-7 A/mm2 at 0.5 and 3 M acetic acid, respectively. A constant Tafel slope of −0.2 V/dec was found in the range of 0.5–3 M acetic acid, which revealed that the same rate determining step (rds) controlled the chalcopyrite reduction. The calculation of the reaction order confirmed that the formation of monoatomic hydrogen from undissociated acetic acid molecules is the rds.The effect of multiple cathodic polarizations was also evaluated on the solid products formed during the chalcopyrite reduction. The X-ray diffraction analysis revealed the formation of less refractory phases. The effect of agitation was studied in the acetic acid system, the results showed that the chalcopyrite reduction kinetics was considerably increased producing metallic copper.

Influence of AC-DC-AC Cycling with Hydrostatic Pressure on Accelerated Protective Performance Test of Glass Flake Epoxy Coating

To achieve fast testing of the barrier properties of organic coatings, immersion tests, AC-DC-AC tests, and coupled tests of AC-DC-AC with hydrostatic pressure were conducted in seawater for a glass flake epoxy coating. Electrochemical impedance spectroscopy (EIS) was used to characterize the degradation processes of the coating during the tests, and the surface of the coating was analyzed using an optical microscope, scanning electron microscope (SEM), and a Fourier transform infrared spectrometer (FTIR). The results showed that periodic cathodic polarization coupled with high hydrostatic pressure can accelerate the degradation of a coating by facilitating the diffusion and uptake of electrolyte and the delamination of the coating. The coupled test method has the largest acceleration due to the synergetic effect of AC-DC-AC and hydrostatic pressure.

High temperature electrochemical reaction parameters affecting electrochemical corrosion potential of stainless steels in hydrogen peroxide environment

ABSTRACT High-temperature electrochemical reaction parameters for stainless steels have been determined based on data measured in pure water at high temperatures to realize an analytical model that can predict electrochemical corrosion potential (ECP) of stainless steels in a hydrogen peroxide (H2O2) environment without using any adjustment parameters based on ECP data. Behaviors of measured cathodic polarization curves for H2O2 were explained well with the determined parameters. Calculated ECPs of stainless steels agreed with measured values in the cases that it was acceptable for the model to have an error range of ±0.1 V in a range from the deaerated condition to 1000 ppb (= μ g kg−1) H2O2 concentration. It is expected that the ECP model in the H2O2 environment with the determined electrochemical reaction parameters will have greater validity for, and better interpretability of, the ECPs of stainless steels determined in a boiling water reactor environment than previous models.

Development of conducting Bi0.5Sr0.5FeO3–δ-Gd0.1Ce0.9O2–δ composite cathodes for IT-SOFCs

Decreasing the working temperature of solid oxide fuel cells (SOFCs) to 400 °C–600 °C is a primary concern for current fuel cell research. Unfortunately decrease in operating temperatures leads to increase in cathode polarization, which deteriorates electrochemical activity of the cathode for oxygen reduction reaction (ORR). Consequently, the search of new cathode materialsis one of the critical bottle-neck towards the development of intermediate-temperature SOFCs (IT-SOFCs). In this study, we have successfully synthesized Bi0.5Sr0.5FeO3-δ and Bi0.5Sr0.5FeO3-δ-Gd0.1Ce0.9O2-δ((1-x) BSFO-xGDC) composite cathodes with varying compositions (x = 50, 40, 30, and 20wt%). The crystal structure, microstructure, electrochemical properties and performance stability of these composite cathodes have been comprehensively evaluated using techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Our results demonstrate that the introduction of Gd0.1Ce0.9O2-δ( GDC) has a significant impact on the electrochemical performance of the composite cathodes. Among the different compositions studied, the cathode with a composition of x = 70 wt% exhibits particularly promising electrochemical properties. The electrode resistance polarization of 70BiSFO-30GDC is 0.39 Ωcm2 and 0.8 Ωcm2 for symmetrical and half-cell at 600 °C. The preliminary results of this study reveal that the 70BiSFO-30GDC composite cathode demonstrates remarkable ORR activity. Further investigations and comprehensive analyses are warranted to validate and explore the full potential of the 70BiSFO-30GDC composite cathode in the context of SOFC applications.

Long-Term Stability of Ni–Sn–Fe-Based Coatings Prepared by Electrodeposition for the Oxygen Evolution Reaction

A coating comprising Ni, Sn, and Fe was deposited on a Ni mesh by cathodic polarization from a bath containing Ni2+, Sn2+, and Fe3+ salts in solution, and the oxygen evolution reaction properties of the thus obtained electrode were investigated. The lattice volume of the Ni–Sn–Fe-based coating was estimated to be 77.1 Å3, a much larger value than that (44.0 Å3) of the Ni–Fe-based coating obtained in the absence of Sn2+. The Ni–Sn–Fe-coated electrode manufactured by cathodic polarization at a current density of −120 mA cm−2 afforded a current density of 10 mA cm−2 at an overpotential of 276 mV in 1 M KOH. The said electrode’s Tafel slope was estimated to be 37 mV dec−1. When electrolyzed at constant current density (+50 mA cm−2 to +800 mA cm−2), it exhibited a stable potential for at least 162 h. The Ni–Sn–Fe-coated electrode was also used as the anode in a two-electrode cell (80 °C; 30 wt% KOH) and electrolyzed for 3 d. Evidence indicated a low cell voltage of 1.81 V at a current density of +600 mA cm−2, which is at an industrial level.

Robust cobalt-free perovskite type electrospun nanofiber cathode for efficient electrochemical carbon dioxide reduction reaction

Solid oxide electrolysis cell (SOEC) is a very competent device for cleanly and efficiently electrochemical carbon dioxide reduction reaction (CO2RR) to high-value added carbon monoxide (CO). However, the low specific surface area and the three-phase boundary (TPB) as the disadvantages of traditional powdery cathode hinder the development of SOEC. Herein, a cobalt-free perovskite oxide Sr2Fe1.5Mo0.5O6-δ nanofiber (SFM-NF), synthesized by the electrospinning technique, is explored as the cathode for CO2RR. The cathode polarization resistance measured by the symmetric cell is reduced from 2.01 Ω cm2 for nanoparticle (SFM-NP) cathode to 1.61 Ω cm2 for SFM-NF cathode at 800 °C in CO:CO2 (2:1) atmosphere. In addition, the corresponding current density of the single cell is greatly increased from 0.732 to 1.173 A cm−2 under 2.0 V and 800 °C. These results all indicate the enhancement of CO2RR catalytic activity. The distribution relaxation of times analysis results for the electrochemical impedance spectra reveal that the increase of surface oxygen species at the interface for SFM-NF cathode allows for a more rapid oxygen ion transport path, and accelerates the CO2RR in a SOEC. This work provids an insightful way for the optimization mechanism of electrode, guiding the development of robust and efficient CO2RR device.

Influence of Cathodic Polarization on Plasma Electrolytic Oxidation of Magnesium and AZ31 and AZ91 Magnesium Alloys

In this study, the influence of cathodic polarization on the plasma electrolytic oxidation (PEO) behaviors of pure magnesium and AZ31 and AZ91 magnesium alloys with varied Al alloying contents was systematically examined in a dilute alkaline silicate electrolyte by adjusting the cathodic-to-anodic current density ratio (R = jc/ja) from 0 to 3.2. The results show that moderate cathodic polarization (R = 0.6) led to the thickest coatings on the Mg and Mg alloys, and the coatings grew in an outward-and-inward mode compared with the inward growth at R = 0. Excessive cathodic polarization (high R ratios) differently influenced the PEO behaviors of the magnesium alloys. For the pure magnesium and AZ31 alloy, the coatings blistered or peeled off when the R ≥ 0.9. However, the tolerance to cathodic polarization was significantly improved for the AZ91 Mg alloy. The coatings were undamaged even with the highest R ratio of 3.2, and their compactness was further improved as the R ratio increased to 0.9 and 1.2. An increase in cathodic polarization led to a reduction in the anodic potential and spark softening but did not result in an improvement in the coating quality. Optical emission spectroscopy identified two spectral lines at 559.79 and 570.11 nm, which are assigned to the Mg species but not found in databases or the literature. The corrosion and wear resistance of the PEO coatings were also investigated. The coating formed on the AZ91 magnesium alloy at R = 1.2 displayed the narrowest wear track due to its high compactness.

Electrolyte-Plasma Nitriding of Austenitic Stainless Steel under Cathodic and Anodic Polarity

Electrolyte-Plasma Nitriding of Austenitic Stainless Steel under Cathodic and Anodic Polarity