Cyclic Polarization Curves Research Articles

An ammonia electrolytic cell with NiCu/C as anode catalyst for hydrogen production

An ammonia electrolytic cell with NiCu/C as anode catalyst for hydrogen production is presented. The electrochemical oxidation of ammonia was investigated on NiCu/C catalyst prepared by a chemical reduction method. It was found that current response of ammonia is strongly dependent on the mass ratio of Ni and Cu. Cyclic voltammetry and polarization curves of cell showed that 50 wt. % Ni50Cu50/C electrode catalyst was energy-effective. The electrolyzer can operate under low cell voltage to save energy in hydrogen production.

Study of stainless steels corrosion in a strong acid mixture. Part 1: cyclic potentiodynamic polarization curves examined by means of an analytical method

The corrosion resistance of AISI 316L, AISI 904L, Sanicro 28, SAF 2205, SAF 2507 and SAF 2707 was studied in an acid mixture containing tartaric acid saturated solution, H2SO4 and HCl, as a function of temperature (22–60°C) and alloys composition. The stainless steels were examined through anodic polarization curves; an analytical method is proposed to obtain the characteristic parameters from these curves. The results indicate that Cr and Mo play the most important role on the active-passive transition of the tested alloys. AISI 904L, Sanicro 28 and SAF 2707 showed the best anodic characteristics among the examined stainless steels.

Mechanical Properties and Corrosion Behavior of Hot Extruded Mg 99.2 Ca 0.6 Mn 0.2 Alloy in SBF Solution

Abstract The tensile and compression properties of hot extruded Mg99.2Ca0.6Mn0.2 (at%) alloy were tested, and the cyclic polarization curves and impedance spectroscopy of the alloy soaked in SBF solutions with various pH values were measured by electrochemical method so that the corrosion behavior of the alloy can be evaluated and the experimental foundation for preparation of magnesium implant materials was provided. The results show that the tensile failure of the alloy appears to be characteristic of quasi-cleavage fracture. The tensile strength, yield strength, compressive strength and elongation are 279 MPa, 251 MPa, 330 MPa and 11% at room temperature, respectively. The pH value of the solution has prominent effect on corrosion behavior. As the pH value increases, the arc radius of impedance spectroscopy and corrosion potential increase remarkably, whereas the corrosion current density decreases, and thus the corrosion resistance of the alloy is strengthened. There is only one time constant which appears at low frequency in phase angle plot. The corrosion rate can be significantly reduced by increasing pH value of the solution. The instantaneous corrosion rates of the alloy immersed in the solutions with pH value of 7.2 and 10.0 are 4.1 mm/a and 0.2 mm/a, respectively.

(Invited) Electrochemical Deposition of Carbon Materials in Molten Salts

Molten salt CO2 capture and electrochemical transformation (MSCC-ET process) into carbon and oxygen [1] is a promising way for effectively capturing and utilizing the greenhouse gas. In the process, CO2 is first absorbed by the molten salt to form carbonate ions and then they are reduced to carbon on the cathode. There are several advantages of the process over others: (1) high current density; (2) high selectivity and current efficiency; (3) lower decomposition potential and overpotential for both anode and cathode reaction; (4) value-added product of functional carbon; (5) simple and cost-affordable electrodes; (6) scalability; (7) environmental friendly and etc. Although electrodeposition of carbon in molten carbonates was first reported in 1960s [2], it is very recent that it becomes a research focus due to the great concern of global warming. There is some new advancement in the field either on the fundamental aspects or practical applications in recent years. Herein, we report the absorption kinetics and thermodynamics of CO2 by molten salt under different temperature and partial pressure of CO2 using a home-made CO2 absorption testing system [3]. The absorption capacity of dissolved Li2O was 0.835 molCO2/molLi2O at 723 K in Li2O containing ternary eutectic carbonate. The mass transfer of carbonates was the dominating factor governing the rate of static absorption. The reduction mechanism of cathode and anode was evaluated by in-situ gas analyzing. There was no CO was detected at 723K over a wide potential range. The reduction kinetics of carbonate was further investigated by cyclic voltammetry and steady-state polarization curve measurements under different temperature and the rate-limiting step was determined. Furthermore, carbon materials with different morphology and composition were obtained under different electrolysis temperature, cell voltage or in different molten salts. It was found that the MSCC-ET process can not only capture CO2 but also absorb SO2 in flue gas. Sulfur doped carbon was obtained by using flue gas as raw material and zero SO2 emission was realized in the process. The obtained carbons show very high specific capacitance and specific capacity as electrode materials for supercapacitor and lithium ion battery, respectively [4].

One-pot liquid phase synthesis of (100−x)Li3PS4–xLiI solid electrolytes

(100−x)Li3PS4–xLiI solid electrolytes are successfully prepared using a simple process proposed in this study. The results show that the heat-treatment process plays a crucial role in the formation of the final product. In the case of x = 33.3%, 2Li3PS4–1LiI, a nearly pure crystalline phase of Li7P2S8I (LPSI), is obtained. The cyclic voltammogram result and DC polarization curves indicate that the interfacial layer between LPSI and the Li metal is stable. Li2S, LiI, Li5P, Li4P2S6, and some unknown substances were detected in the interfacial layer by XRD.

Pyrite oxidation under simulated acid rain weathering conditions.

We investigated the electrochemical corrosion behavior of pyrite in simulated acid rain with different acidities and at different temperatures. The cyclic voltammetry, polarization curve, and electrochemical impedance spectroscopy results showed that pyrite has the same electrochemical interaction mechanism under different simulated acid rain conditions, regardless of acidity or environmental temperature. Either stronger acid rain acidity or higher environmental temperature can accelerate pyrite corrosion. Compared with acid rain having a pH of 5.6 at 25°C, the prompt efficiency of pyrite weathering reached 104.29% as the acid rain pH decreased to 3.6, and it reached 125.31% as environmental temperature increased to 45°C. Increasing acidity dramatically decreases the charge transfer resistance, and increasing temperature dramatically decreases the passivation film resistance, when other conditions are held constant. Acid rain always causes lower acidity mine drainage, and stronger acidity or high environmental temperatures cause serious acid drainage. The natural parameters of latitude, elevation, and season have considerable influence on pyrite weathering, because temperature is an important influencing factor. These experimental results are of direct significance for the assessment and management of sulfide mineral acid drainage in regions receiving acid rain.

Effect of Cu content on exfoliation corrosion and electrochemical corrosion of A7N01 aluminum alloy in EXCO solution

The exfoliation corrosion (EXCO) sensitivities and electrochemical corrosions of A7N01 aluminum (Al) alloys with 0.074% and 0.136% Cu contents were investigated in EXCO solution. The exfoliation corrosion developed more rapidly for the alloy with 0.136% Cu by expressing higher exfoliation rate and deeper corrosion pits as observed by SEM and laser confocal scanning microscopy (LCSM). In EXCO solution, the alloy with 0.136% Cu content showed lower open-circuit potential (OCP) than the alloy with 0.074% Cu content. The alloy with 0.136% Cu content had bigger “hysteresis loop” in cyclic polarization curve which meant lower self-passivation ability. In electrochemical impedance spectroscopy plot, its curvature radius and capacitance index were lower. The electrochemical test results revealed that the alloy with 0.136% Cu content showed more severe electrochemical corrosion than the alloy with 0.074% Cu content, consistent with the exfoliation corrosion results. The microstructures of two alloys were observed through optical microscopy (OM) and transmission electron microscopy (TEM). The continuous distribution of the equilibrium precipitate [Formula: see text]-MgZn2 on grain boundaries, the decreasing of the width of precipitate-free zone (PFZ) and the coarse Cu–Fe–Si–rich phase were responsible for the higher corrosion sensitivity of the Al alloy with 0.136% Cu than that of Al alloy with 0.074% Cu content in EXCO solution.

Enhanced activity and durability of the oxygen reduction catalysts supported on the surface expanded tubular-type carbon nanofiber

Tubular type carbon nanofibers (TCNFs) are prepared and used as a catalyst support material for a cathode electrode of low temperature fuel cells through structural modification. The pristine TCNF is treated by graphitization and makes partially torn-tube shape through the surface expansion by rapid thermal treatment of the oxidized graphitized TCNF. Physical properties of the TCNF group are examined, and it is confirmed that the unique ripped texture along fiber axis with graphitic structure is obtained by the surface expansion. Platinum catalysts supported on these TCNF group are prepared and evaluated. Electrochemical properties are examined via cyclic voltammograms and polarization curves for oxygen reduction reaction activity. The platinum catalyst on the surface expanded TCNF has the enhanced activity at initial and the stable performance even after accelerated durability test due to their unique structure.

The Stress Corrosion Cracking Susceptibility in Ethanol-Gasoline Blends

The interest in terms of fuels who are based on ethanol, as a total or partial substitute for fossil fuels. In this research, three concentrations of water (0.5%, 5% and 10%) by volume were evaluated, in ethanol-gasoline blends at 95% by volume of ethanol, using cyclic polarization curves (CPC) on API-5L X52. As a complementary technique, weight loss (WL) was monitored with exposures of 30, 60 and 90 days of immersion. The objective of this investigation is to determine the mechanism of corrosion and the measurement of the effect of the water related to the WL of steel, regardless to the ethanolic mixtures. The result obtained from the mass loss was increased when the water concentration was less than 5% by volume. The CPC showed that blends with low water content there is a tendency to the formation of corrosion by pitting, which was corroborated by scanning electron microscope (SEM).

Corrosion performance of Al2CrFeCoxCuNiTi high-entropy alloy coatings in acid liquids

Abstract The Al 2 CrFeCo x CuNiTi high-entropy alloy coatings were prepared by laser cladding on Q235 steel surface. The microstructure was characterized by scanning electron microscopy with spectroscopy (SEM/EDS). Electrochemical workstation was used to test the corrosion resistance of Al 2 CrFeCo x CuNiTi high-entropy alloy coatings and Q235 steel in H 2 SO 4 and HCl solutions. Experimental results show that the coating and its substrate are well combined. The cladding zone is mainly composed of equiaxed grains, as well as “cat foot shaped” grains and “snowflake” grains distributed in the matrix grains. Cracks appear in the coatings due to thermal stress. The corrosion resistance of Al 2 Co x CrCuFeNiTi coatings is excellent in H 2 SO 4 and HCl solutions, which can be attributed to three factors: the formability of Co element, passivation film formed on the alloy surface and the microstructure of the alloy. Increasing Co content can lead to an enhancement of the corrosion resistance of high-entropy alloy coatings in 0.5 mol/L HCl solution. Cyclic polarization curve shows no pitting corrosion in the 0.5 mol/L H 2 SO 4 solution for the Co 2.0 high-entropy alloy coating, but slight pitting corrosion in 0.5 mol/L HCl solution for the Co 0.5 high-entropy alloy coating due to the Cl − in the medium.

Mathematical modeling of nonlinear reaction–diffusion processes in enzymatic biofuel cells

Enzymatic biofuel cells convert the chemical energy of biofuels into electrical energy by employing oxidoreductase enzymes as catalysts. They have attracted considerable attention due to their potential use as a promising alternative to traditional power sources. Also, enzyme-modified electrodes have important applications in electrochemical biosensors, bioreactors, implantable medical devices as well as in biochemistry as a source of information on the action of enzymes. Among the different electrochemical techniques available, enzymatic biofuel cells and electrodes are generally studied via cyclic voltammetry, chronoamperometry, polarization curves and impedance measurements to gain better insight into the enzymatic system. The main aim is to assess the influence of the mediator species and its diffusivity, the loading of biocatalysts, the amount of substrates, mediators and inhibitors, the strategy of enzyme immobilization, etc. as well as to study the enzymatic kinetic mechanism. Within this context, mathematical models must be used to understand, predict and optimize the performance of enzymatic biofuel cells and electrodes as a function of the chief experimental parameters above mentioned. In this review article, major recent research activity concerning the mathematical modeling of enzymatic electrodes and fuel cells is discussed, highlighting the main contributions as well as current problems and challenges.

Synthesis and electrocatalytic properties of La<sub>0.8</sub>Sr<sub>0.2</sub>FeO<sub>3−δ</sub> perovskite oxide for oxygen reactions

Perovskites are important alternatives for precious metals as catalysts for bifunctional oxygen electrodes, involving oxygen evolution (OER) and reduction (ORR) reactions as is the case of regenerative fuel cells. In this work, strontium doped lanthanum ferrite La1−xSrxFeO3−δ (x = 0; 0.1; 0.2; 0.3; 0.4; 0.6 and 1.0) powders were prepared by a self-combustion route. The oxides, in the form of carbon paste electrodes, were characterised by cyclic voltammetry in alkaline solutions. Data analyses lead to the selection of La0.8Sr0.2FeO3−δ to prepare gas diffusion electrodes (GDEs). Cyclic voltammetry and steady state polarization curves were used, respectively, to assess the electrochemical behaviour of GDEs and to obtain kinetic data for both OER and ORR. It is concluded that the oxide preparation conditions/electrode configuration determine the electrode performance. The bifunctionality of the electrodes was assessed, under galvanostatic control, using a cycling protocol within the potential domains for OER and ORR. The potential window, i.e., the total combined overpotential between OER and ORR was found to be of ≈770 mV, value which compares well with that obtained under potentiostatic control. Even though the potential window keeps constant during 140 cycles, the increase in cycling time and/or current density (≥2.5 mA·cm−2) led to a gradual metallization of the GDE surface, as confirmed by Scanning Electron Microscopy and X-ray diffraction analysis.

Effect of Carbonitriding in a Salt Bath by a QPQ Scheme on Stainless Steel 321 Microstructure and Service Properties

Wear resistance, corrosion properties and structure of reinforced layers deposited on steel AISI 321 with carbonitriding by the quench-polish-quench (QPQ) Tennifer® process with subsequent oxidation are studied. The structure of the layers is investigated by scanning electron microscopy with energy dispersive local analysis and x-ray diffractometry. Steel wear resistance is determined by a pin-on disk test, and oxide layer adhesion is determined by a scratch method. Pitting corrosion resistance is determined by plotting cyclic polarization curves.

Corrosion resistance of laser patterned ultrahydrophobic aluminium surface

Ultrahydrophobic aluminum surface is fabricated by laser direct writing technique. Corrosion resistance was investigated using cyclic polarization curves and open circuit potential (OCP) measurements. The superhydrophobic surfaces exhibited improvement in corrosion rate and polarization resistance due to an oxide layer formed during the laser processing as well as by the small volume of air trapped in µ-cavities which resist the penetration of corrosive species and reduce the area of solid – liquid interface.

Preparation and Analysis of Complex Barrier Layer of Heterocyclic and Long-Chain Organosilane on Copper Alloy Surface

A single electrodeposited film of 6-(3-triethoxysilylpropyl)amino-1,3,5-triazine-2,4-dithiol monosodium (TES) on a copper alloy surface was prepared by the galvanostatic method, then octyl-triethoxysilane (OTES) or hexadecyl-trimethoxysilane (HDTMS) was used to modify the electrodeposited film by the self-assembled technique to fabricate the complex film. The electrodeposition process was inferred by cyclic voltammetry. The single and complex films were characterized by means of contact angle, cyclic voltammetry, Fourier transform infrared spectroscopy (FT-IR), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM). The results showed that the contact angle of the complex film covering the copper alloy surface was up to 118.1° compared with 89.4° of the bare copper alloy. The cyclic voltammogram, polarization curves and EIS indicated that the anti-corrosion performance of complex film was better than that of single electrodeposited TES film, and the protection efficiency was up to 90.2%.

Comportamiento a la Corrosión del Acero API X70 Soldado por el Proceso de Doble Arco Sumergido Inmerso en Diferentes Medios Corrosivos

Resumen Los aceros API X70 son aplicados en fabricación y construcción de tuberías para el transporte de hidrocarburos, sin embargo, a un lapso de tiempo se degradan debido al medio ambiente al cual están expuestos; influyendo en la velocidad y tipo de corrosión sobre las superficies del metal base (MB), zona afectada por el calor (ZAC) y zona de fusión (ZF). A fin de conocer y evaluar la susceptibilidad a la corrosión en uniones del acero API X70 sometido a diferentes medios corrosivos, varias pruebas se llevaron a cabo por el proceso de soldadura de doble arco sumergido (DSAW, por sus siglas en inglés), las cuales fueron inmersas en diferentes electrolitos: Cloruro de Sodio (NaCl al 3,5%) y Agua (H2O) a temperatura ambiente para conocer su comportamiento. Se utilizaron técnicas electroquímicas de ruido electroquímico (RE) y curvas de polarización cíclica (CPC) para obtener velocidad y tipo de corrosión producida en cada una de las muestras analizadas, incluyendo las tres zonas: MB, ZAC y ZF. Además, se utilizaron técnicas de caracterización como microscopía óptica (MO) y microscopía electrónica de barrido (MEB) para el análisis superficial. La mayoría de las soldaduras presentan corrosión mixta, con mayores velocidades de corrosión en 3,5% de NaCl.

Study of the pitting corrosion of superduplex stainless steel and X-65 carbon steel during erosion–corrosion by cyclic polarisation technique

Erosion-enhanced corrosion behaviour of X-65 carbon steel and UNS S32750 superduplex stainless steel was investigated by electrochemical cyclic polarisation. The tests were performed using a jet slurry device coupled with a potentio-galvanostat at various jet velocities of 4, 6.5 and 9 m s−1 and impingement angles of 30 and 90˚ in a 3.5 wt-% NaCl water containing 6 wt-% silica sand particles. The results showed that increasing the jet velocity and impingement angle increased the corrosion rate of both alloys. Negative hysteresis and greater Erp than OCP were observed for superduplex stainless steel in all erosion–corrosion conditions that indicated the pitting resistance of the alloy. However, the low resistance of carbon steel against pitting during erosion–corrosion was demonstrated by positive hysteresis in the cyclic polarisation curves as well as SEM images of the eroded surfaces.

Treatment of Amaranth dye in aqueous solution by using one cell or two cells in series with active and non-active anodes

The anodic oxidation of Amaranth dye has been studied by electrochemical measurements (cyclic voltammetry and polarisation curves) and bulk electrolysis employing a single or two cells in a serial mode system using active and non-active anodes (Ti/IrO2-Ta2O5 and Nb/BDD) as electrode materials. The results of electrochemical measurements showed that, Nb/BDD had a significant oxidation power to mineralise Amaranth dye than Ti/IrO2-Ta2O5 anode. Single cells were tested at different current densities (30, 60 and 80mAcm−2). At Nb/BDD anode, total colour elimination and 49.1% of COD removal were achieved by applying 30mAcm−2 after 60min of treatment. Conversely, 98.5% of colour removal and 43.2% of COD decay were accomplished at 60mAcm−2 with Ti/IrO2-Ta2O5 electrode, after 360min of electrolysis time. Supported on the obtained results with single cells, a system in a serial mode was further evaluated for the first time. The arrangement with Ti/IrO2-Ta2O5 electrode at 30mAcm−2 in the first cell followed by Nb/BDD anode at 30mAcm−2 revealed the most interesting results. Complete decolourisation and 75.1% of COD abatement were achieved after 60min with lower energy requirements of about 25.4kWhm−3 (0.2kWhgCOD−1). This study demonstrates the potential of a serial system to be applied as a wastewater pre-treatment approach.

Corrosion resistances of passive films on low‐Cr steel and carbon steel in simulated concrete pore solution

AbstractThe passive ranges of carbon steel rebar and 3Cr steel rebar in saturated Ca(OH)2‐simulated concrete pore solution with pH 12.6 were determined by means of cyclic voltammetry and potentiodynamic polarization curves. Chronopotentiometry was used to obtain steady‐state conditions for the formation of passive films on rebar samples at different anodic potentials. Electrochemical impedance spectroscopy, Mott–Schottky and X‐ray photoelectron spectrometer curves were employed to compare the formed passive films at different potentials. Additionally, cyclic polarization curves were used to compare the corrosion resistances of formed passive films on the two rebars in saturated Ca(OH)2‐simulated concrete pore solution with different concentration of Cl−. The results show that the passive ranges of the two rebars are all between −0.15 and +0.6 V, and more stable passive films can be formed on both rebars at the anodic potential of +0.3 V. In the absence of Cl−, the stability and corrosion resistance of the passive film formed on the 3Cr rebar are better than those of CS rebar. The passive film of 3Cr steel has the relatively better pitting corrosion resistance than carbon steel in saturated Ca(OH)2‐simulated concrete pore solution that contains different concentration of Cl−. Copyright © 2016 John Wiley & Sons, Ltd.

Study on the electrocatalytic degradation of 4-chlorophenol on PbO2–ZrO2 composite electrode and its electrochemical property

PbO2–ZrO2 composite electrodes were prepared by anodic electrodeposition in the lead nitrate solution. The electrochemical property of this electrode was studied by cyclic voltammetry, polarization curves and open-circuit potential–time curves. The results show that PbO2–ZrO2 composite electrodes possess higher oxygen evolution overpotential and better anti-corrosion performance than traditional PbO2 electrodes. Electrocatalytic oxidation of 4-chlorophenol (4-CPs) in aqueous solution was studied to evaluate the applications of this electrode in environmental protection. The influence of experimental parameters on the COD removal efficiency was studied on PbO2–ZrO2 composite electrodes as a function of the current density, initial concentration of the 4-CPs, initial pH, supporting electrolyte concentration and electrolysis time. The results show that the 4-CPs removal efficiency in 0.1 mol L–1 Na2SO4 solution containing 8 mmol L–1 4-CPs could reach 89.2% with the current density at 200 mA cm–2 and pH value at 6.5 after 4 h. Compared with traditional PbO2 anodes, the PbO2–ZrO2 composite electrodes show higher instantaneous current efficiency with degradation of 4-CPs. The experimental results demonstrate that the PbO2–ZrO2 composite electrodes possess the excellent electrocatalytic activity in refractory pollutants degradation.