Galvanostatic Polarization Curves Research Articles

Electrochemical properties of powder-pressed Pb–Ag–PbO2 anodes

Abstract Pb–Ag–PbO2 composite anodes with different mass fractions (1%, 2%, 3%, 4% and 5%) of β-PbO2 were prepared by powder-pressed (PP) method. The galvanostatic polarization curves, Tafel curves and anodic polarization curves were tested in sulfuric acid solution. The morphologies and phase compositions of the anodic layers formed after galvanostatic polarization were investigated by using scanning electron microscope (SEM) and X-ray diffractometer (XRD), respectively. The results showed that β-PbO2 can improve the electrocatalytic activity of anodic oxide. The anode containing 3% β-PbO2 had the lowest overpotential of oxygen evolution reaction (OER) and the best corrosion resistance. The morphologies of the anode surfaces were gradually transformed from regular crystals to amorphous ones as the content of β-PbO2 increased in anodes.

Influence of manganese on the electrochemical behavior of an aluminum cathode used in zinc electrowinning

Pure aluminum is commonly used as the cathode electrode in the traditional hydrometallurgy applications of zinc electrowinning. However, with the decrease of zinc concentrate grade and increase of the impurity ions in the electrolyte, the corrosion consumption of the cathode material increases gradually. To further improve the corrosion resistance and electrocatalytic activity of the aluminum cathode, the electrochemical behavior of manganese as an additive for pure Al cathode material, such as Al-Mn alloy, was studied herein. Using the analysis methods of electrochemical impedance spectroscopy, cathodic polarization, galvanostatic polarization, and Tafel curves, the effect of Mn content on the electrochemical behavior of Al-Mn alloy in 40℃ constant temperature conditions and a solution containing Zn2+ at 65 g·L-1 and H2SO4 at 150 g·L-1 was investigated. The results show that the corrosion resistance of Al alloy containing Mn increases obviously compared to that of pure Al electrodes, and the increase of the Mn content could decrease the corrosion current. Moreover, the corrosion potential and the Mn content do not exhibit obvious change trends. When the Mn content reaches 1.5%, the corrosion current reaches the lowest value of 1.11 mA·cm-2 and the corrosion potential reaches the minimum of -1.0954 V. When the electrical potential of cathode becomes zero, the exchange current density is influenced by the Mn content and the exchange current density i0 exhibits an initial increasing trend and then declines with the increase of the Mn content. When the Mn content is 1.5%, the exchange current density of the Al alloy cathode reaches the maximum of 3.7462×10-16 mA·cm-2; this value is much higher than that of the pure Al electrode (4.8027×10-33 mA·cm-2). The overall change amplitude is obvious, and the electrocatalytic activity of the Al-Mn electrodes is much improved compared with a pure Al electrode. The electrochemical process is controlled by the electrochemical mass transfer. Considering the corrosion resistance and electrocatalytic activity of the electrode material, the Al-Mn alloy containing 1.5% of Mn can be used as an ideal electrolytic zinc cathode.

Solvent Free Glycolysis of Plastic Waste as Green Corrosion Inhibitor for Carbon Steel in Sulfuric Acid

Solvent free efficient green glycolysis of Polyethylene terephthalate waste, PET, in this respect, PET waste was subjected to depolymerization with propylene glycol in the presence of manganese acetate as a catalyst, the product is Bis-(3-hydroxy-propyl)-terephthalate, BHPT, as non-ionic surfactant was separated, characterized by FT-IR and 1HNMR, BHPT was evaluated as corrosion inhibitor for steel in the presence of 1.0 M sulfuric acid by chemical and electrochemical methods, the corrosion inhibition efficiency increase with inhibitor concentration and decrease with temperatures, the galvanostatic polarization curves indicate that the BHPT, compound act as mixed inhibitor, the impedance of the inhibited solution has increased with the increase in the concentration of the inhibitor. the inhibition due to adsorption of the inhibitor molecules on the steel surface, the adsorption obey Langmuir adsorption isotherm. Thermodynamic parameters were computed and discussed, Scanning electron microscope (SEM) was used to study the surface morphology of steel in absence and presence of the used inhibitor, hydrogen evolution techniques was used to evaluate the inhibition efficiency of the BHPT inhibitor compound. the data obtained from different techniques are in good agreement to each other and show the BHPT, surfactant derived from PET, waste considered as good corrosion inhibitor for steel in sulfuric acid.

Phase Transfer Synthesis of Novel Based Surfactants: Role of Biocorrosion Inhibition

Two types of corroded medium, acid and SRB, could be evaluate novel aziridinium, pyrrolium and azepanium quaternary ammonium salts as corrosion inhibitors at the concentration range of 500 - 100 ppm in 1M HCl. Quaternization of a series of heterocyclic amines with 4-nonyl phenol in the presence of aqueous sodium hydroxide under phase transfer conditions in chloroform as a solvent was performed (Scheme 1). Active ingredients of those inhibitors included long chain hydrocarbon heterocyclic amines were confirmed using FTIR, 1H NMR, and elemental analyses. The results, which include the corrosion and electrochemical testing data, showed that tested corrosion inhibitors In1 - In4 are effective in studied range of concentration and the corrosion effectiveness of tested quats increases toward In1- In3 with increase the number of member rings. The galvanostatic polarization curves showed that, the inhibitor behaves as mixed type. The observed corrosion data indicate that, the inhibition of carbon steel corrosion is due to the adsorption of the inhibitor molecules on the surface, which follow Langmuir adsorption isotherm. By fitting the obtained experimental data with Langmuir adsorption model, some thermodynamic and kinetic parameters such as adsorption free energy, Gads, equilibrium constant, Kads, were estimated. Apparently, the polar group makes it possible to lengthen the hydrophobic fragment of the inhibitor without significantly disturbing its hydrophilic–lipophilic balance and thus make the inhibitor not only more hydrophobic but also more soluble in water, which enhances its technological properties. For evaluation of SRB inhibition efficacy, microbial activity was monitored and cell counts were determined. All inhibitors were able to reduce microbial activity. The growth of the reference SRB (Desulfomonas pigra) was shown to be completely inhibited by In1- In3. In contrast, In4 had only a slight effect as being due to the presence of pyrrolium cation which may also be achieved due to decreasing the protective effect process. In this work, the thermodynamic parameters for adsorption and activation processes were determined; the following formulation properties are considered: the surface tension at cmc (?cmc), critical micelle concentration (cmc) of the surfactants in aqueous solutions, saturated adsorption amount of the surfactant (G8) and the minimum average area per surfactant molecule (Amin) at the air–water interface. On the bases of the result of small saturated adsorption amount and the large minimum average area per surfactant molecule, it is indicated that the minimum average area of surfactant decreases with the enhanced hydrophilic character of the molecule. A direct relationship has found between the corrosion efficacy (% IE) and G8.

Phase transfer synthesis of novel based surfactants: Role of biocorrosion inhibition and corrosion of steel

Four novel aziridinium, pyrrolium and azepanium bis-quaternary ammonium salts joined within similarly aromatic spacer have been synthesized. The phase transfer synthesized cycloadduct as a selective and startreaction material is a positive indicator for the corrosion inhibition process. The structures of the desired heterocyclic surfactants were confirmed by using elemental analysis, FT-IR and 1H NMR spectral analysis. The adsorption of these compounds on the metal surface is found to obey Tafel adsorption isotherm. Furtheron, the dilution method need to be included to evaluate their biocorrosion inhibition. This study explores the corrosion resistance of the prepared bisquats in 1 M HCl and SRB corroded medium. The growth of the reference SRB (Desulfomonas pigra) was shown to be completely inhibited by bisquaternary ammonium surfactants, In1- In3, and also the inhibition efficiency was found to increase with increasing inhibitor concentration and decreased with increasing surface tension which is due to the fact, that the rate of corrosion of carbon steel is higher than the rate of adsorption and therefore indicates that the joint adsorption of these compounds and chloride ions by the addition of HCl is due to the increase of the surface coverage. On the other hand, opposite cases were found where the presence of certain cations decreased the protective effect, for example, towards the corrosion of In4. Additionally, the thermodynamic parameters for adsorption and activation processes were determined; the following formulation properties are considered: the surface tension at cmc (γcmc), critical micelle concentration (cmc) of the surfactants in aqueous solutions, saturated adsorption amount of the surfactant (Г∞) and the minimum average area per surfactant molecule (Amin) at the air–water interface. On the bases of the result of small saturated adsorption amount and the large minimum average area per surfactant molecule, it is indicated that the minimum average area of surfactant decreases with the enhanced hydrophilic character of the molecule. A direct relationship has found between the corrosion efficacy (% IE) and Г∞. The galvanostatic polarization curves showed that, the inhibitor behaves as mixed type. The observed corrosion data indicate that, the inhibition of carbon steel corrosion is due to the adsorption of the inhibitor molecules on the surface, which follow Langmuir adsorption isotherm. By fitting the obtained experimental data with Langmuir adsorption model, some thermodynamic and kinetic parameters such as adsorption free energy, Gads, equilibrium constant, Kads, were estimated.

Suppression of Oxide Growth on Ti Substrate of Ir1-XSnxO2/Ti Anodes in Electrolytic Oxygen Evolution

INTRODUCTION In order to prevent global warming and to supply renewable energy in the form of methane, Hashimoto et al. have been proposing global CO2 recycling and have tailored the necessary key materials, that is, the anodes and cathodes for seawater electrolysis and catalysts for CO2 methanation by the reaction with hydrogen. The most difficult was the anode for seawater electrolysis, because the anode should evolve only oxygen without forming chlorine even in seawater electrolysis. Titanium is generally used as the electroconductive substrate. We usually covered the titanium substrate with IrO2 for prevention of oxidation of titanium. In chloride containing electrolytes, chlorine evolution occurs preferentially on the IrO2-covered titanium. Thus, we needed to prepare g-MnO2-type electrocatalysts covering the IrO2 layer for exclusive oxygen evolution in seawater electrolysis. We revealed that the Ir1-xSnxO2 double oxides have better protectiveness against oxidation of titanium than IrO2. The Mn1-x-yMoxSnyO2+x/Ir1-xSnxO2/Ti anode showed more than 99.9% oxygen evolution efficiency for 4200 h in the electrolysis of 0.5 M NaCl solution of pH 1 at 1000 Am-2. Although the oxygen evolution efficiency was close to 100%, the oxide growth on the titanium substrate was unavoidable due to the inward diffusion of oxygen through electrocatalyst and intermediate layers during oxygen evolution. The present work aimed to improve the protectiveness of Ir1-xSnxO2 double oxide. Since the Ir1-xSnxO2/Ti anodes themselves are oxygen evolution anodes in chloride free aqueous solutions, the protectiveness of Ir1-xSnxO2 double oxide during oxygen evolution at high current densities was examined using the Ir1-xSnxO2/Ti anodes in H2SO4 solutions. EXPERIMENTAL After surface roughening by immersion in 11.5 M H2SO4 the titanium substrate was coated with butanol solutions of H2IrCl6 and SnCl4, in which the sum of metallic cations was 0.1, 0.26 or 0.52 M. The specimens were dried at 80oC for 10 min and calcined at 250-450oC for 10 min. This procedure was repeated three times and the final calcination was continued for 0.5-24 h. The anodes were previously used for the electrolysis at 13,333 Am-2 in 3 M H2SO4 solution at room temperature for various periods of time, and then characterization of the used anodes was carried out by electrochemical measurements in 1 M H2SO4 solution at 25°C. Galvanostatic polarization curves were measured by the current density rise every 1 min. The potential rise due to the solution resistance at high current densities was corrected by the ordinary current interruption technique. Two more different current interruption techniques were applied at higher current densities using a digital oscilloscope for the measurement of the potential decays at every 0.0625 ms and 0.4 ms, respectively. RESULTS AND DISCUSSION The oxide growth on the titanium substrate occurred during electrolysis at high current densities for long periods. The oxide growth rate was estimated with anodic polarization curves and current interruption technique by the assumption of equivalent circuit of oxide covered metal electrode. When the sum of Ir4+ and Sn4+ was 0.52 M, the solely IrO2-coated anode showed the lowest rate of resistance growth. However, when the sum of Ir4+ and Sn4+ was 0.26 M, an increase in Ir4+ higher than 0.13 M was not effective to decrease the oxide growth. When the sum of Ir4+ and Sn4+ was 0.1 M, the minimum oxide growth rate appeared at 0.04 M Ir4+, where the oxide growth rate was similar to that of the anode prepared in 0.13 M Ir4+ - 0.13 M Sn4+ solution. Consequently, in order to save iridium, lower concentrations of Ir4+ and Sn4+ will be useful. On the other hand, an increase in calcination temperature led to incorporation of oxidized titanium in Ir1-xSnxO2. This also led to a resistance increase. Furthermore, the increase in calcination temperature resulted in potential increase at low current densities. This implied a decrease in the oxygen evolution activity due to inclusion of Ti2+ in Ir1-xSnxO2. However, the formation of triple oxide of Ir1-x-ySnxTiyO2 was not always detrimental for the elongation of the life of the anode. The growth rate of titanium oxide during anodic polarization at 13,333 Am-2 in 3 M H2SO4 solution was lowest when the anode was formed by calcination at 450°C. Consequently, the protectiveness of Ir1-x-ySnxTiyO2 formed by calcination at 450°C was highest even if oxidized titanium was included in the active anode for oxygen evolution. Consequently, the optimum preparation condition of Ir1-xSnxO2/Ti anodes was coating of Ti substrate with butanol solution of 0.13 M Ir4+ and 0.13 M Sn4+ and calcination at 450°C for 1 hour.

Durability of Electrodeposited Ni-Fe-Co-C Anodes for Alkaline Water Electrolysis

IntroductionWe have been studying more than a quarter of century for supply of renewable energy in the form of methane via electrolytic hydrogen generation using carbon dioxide as the feedstock. Although we created cathodes and anodes for direct seawater electrolysis, the energy efficiency was not sufficient. For immediate industrialization, we are concentrating our current effort on alkaline water electrolysis, creating efficient cathodes and anodes. The present work aimed to determine the composition of active Ni-Fe-Co-C alloy anodes prepared by electrodeposition and to examine the durability for continuous electrolysis at a high current density of 6000 Am-2 in 4.5 M KOH at 90°C. Experimental Procedures The substrate for electrodeposition was a chemically etched Ni plate. Electrodeposition was carried out at a current density of 300 Am-2 for 10 min in 1.14 M NiSO4-0.189 M NiCl2-0.49 M H3BO3-0.104 mM CH3(CH2)11OSO3Na solutions containing various concentrations of FeSO4, CoSO4 and lysine, the pH of which was adjusted at 1.5 by the addition of 18 M H2SO4. Lysine was added as the carbon source. The composition of metallic elements in the electrodes was analyzed by electron probe microanalysis, and carbon was chemically analyzed by combustion infrared absorption method. The solution used for oxygen evolution was 4.5 M KOH at 90oC. The activity of the anodes was evaluated from galvanostatic polarization curves measured by the current density rise every 1 min. The potential rise due to the solution resistance at high current densities was corrected by the current interruption technique. Potentiodynamic polarization curves were also measured at a potential sweep rate of 0.52mV-1 for comparison. Results and Discussion As-deposited alloys were used for examination of oxygen evolution activity. Ni was a stable anode but less active for industrial electrolysis. The addition of Co ion and lysine to the deposition electrolyte containing Ni ion enhanced the oxygen evolution activity, but the activity of Ni-Co-C alloys was not yet sufficiently high. Ni-Fe-Co-C alloys deposited showed significantly high activity for oxygen evolution. An increase in Fe content in the alloy was more effective than the increase in Co content for enhancement of oxygen evolution activity. Thus, an increase in Co concentration in deposition electrolytes did not largely change the activity because the increase in Co content in the alloy resulted in the decrease in the content of Fe. The addition of lysine to the deposition electrolytes containing Ni, Fe and Co ions enhanced the oxygen evolution activity. The highest activity was attained at 0.2 M lysine in the deposition solution, but further increase in lysine concentration was not effective. An increase in lysine concentration led to asymptotic increase in the C content in the Ni-Fe-Co-C alloys up to about 6 at%. The deposition electrolyte to form the most active Ni-Fe-Co-C alloy for oxygen evolution was 1.33M Ni-0.072M Fe-0.018M Co-0.2M lysine solution. When the Ni-Fe-Co-C alloy prepared from this electrolyte was used for oxygen evolution at a current density of 6000 Am-2 for 800 h, the mass loss was about 5 % of the original mass. The galvanostatic polarization potential of as-deposited Ni-Fe-Co-C alloy measured by the current density rise every 1 min was in the active region at lower current densities, but the potential shifed to the oxygen evolution region at higher current densities. Once the specimen was polarized in the oxygen evolution region, the potential was stayed in the oxygen evolution region even when the current density was lowered. After oxygen evolution at 6000 Am-2 for long period of time, the potential stayed in the oxygen evolution region regardless of current densities. In fact, the dissolution current density estimated from the mass loss by polarization at 6000 Am-2 for 800 h even on the assumption of Fe dissolution in the form of Fe6+ as FeO4 2- was only 4.5 x 10-3 Am-2 that is less than one-millionth of oxygen evolution current. Consequently, the active Ni-Fe-Co-C alloy anode thus prepared is sufficiently stable maintaining the passive state in the severe environment for oxygen evolution at 6000 Am-2 in a concentrated KOH solution at 90°C for long period of time. Conclusion The active oxygen evolution anode in alkaline water electrolysis for hydrogen production was created. The addition of Fe, Co and C to Ni enhanced the oxygen evolution efficiency in 4.5 M KOH solution at 90°C. The Ni-Fe-Co-C alloy thus prepared kept the passive state during electrolytic oxygen evolution at 6000 Am-2 for a long period of time.

Electrochemical characterization of degradation of oxygen evolution anode for seawater electrolysis

The electrolysis at a high current density, such as 2000 A m−2 for hydrogen production in 0.5M NaCl of pH 1 using the oxygen evolution anode consisting of three layers of Mn0.929Mo0.067Sn0.004O2.067/Ir0.84Sn0.16O2/Ti led to a gradual increase in the cell voltage due to the oxide growth on the titanium substrate of the anode. The potential decay curves of the anode measured every 0.1μsec and 0.4 msec after the interruption of a high polarization current density differentiated discharges of the oxide condenser and the electrochemical double layer. The potential measured by galvanostatic polarization was the sum of the potential drop based on the solution resistance, the overpotential for the electrochemical reaction, the equilibrium potential of the reaction and the potential drop based on the oxide resistance. The potential difference, ΔEj, at individual current density, j, between galvanostatic polarization curves of an anode after and before electrolysis showed a linear increase beginning from the origin of the coordinate axes with current density, j, the gradient, ∂ΔEj/∂j, of which corresponded to the difference in the oxide resistance after and before electrolysis at the high current density. The linear increase of the potential difference after and before electrolysis with current density of galvanostatic polarization and the gradient increase with time of electrolysis indicated the electric resistance increase by electrolysis at the high current density without change in the electrochemical properties of the anode surface. The oxide resistance for the anode examined became about 0.8 mΩ m2 after oxygen evolution for 430h at 2000 A m−2.

Electrochemical Study of the Corrosion Behavior of Zinc Surface Treated with a New Organic Chelating Inhibitor

The effect of a new organic compound (N-[(1E)-(4 methoxy phenyl)methylene]hydrazinecarbothioamide), called ATSC, with chelating groups, on the corrosion behavior of zinc was investigated. Electrochemical study of the zinc specimens was carried out in aqueous electrolyte containing 0.2 M Na2SO4 and 0.2 M NaCl maintained at pH 5 using galvanostatic polarization curves. The surface treatment of zinc was achieved by immersion in solutions of different concentrations of ATSC and for different immersion time and bath temperatures. The zinc metal treated with ATSC at 5% has showed good corrosion resistance and maximum protection efficiency of about 84% at 300 K. Moreover, the treatment induced a basic modification of the cathodic nature of zinc and controls the corrosion by decreasing the electron transfer rate. The corrosion protection could be explained by the formation of a protective organometallic layer on the zinc surface due to the chelation reaction between zinc and inhibitor molecules. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) were applied to study the protective layer.

An electro-kinetic study of oxygen reduction in polymer electrolyte fuel cells at intermediate temperatures

The oxygen reduction process in polymer electrolyte fuel cells (PEMFCs) was in-situ investigated at intermediate temperatures (80°–130 °C) by using a carbon supported PtCo catalyst and Nafion membrane as electrolyte. To overcome the Nafion dehydration above 100 °C, the experiments were carried out under pressurized conditions. Electro-kinetic parameters such as reaction order and activation energy were determined from the steady-state galvanostatic polarization curves obtained for the PEM single cell. Negative activation energies of 40 kJ mol−1 and 18 kJ mol−1 were observed at 0.9 V and 0.65 V, respectively, in the temperature range 100°–130 °C. This was a consequence of ionomer and membrane dry-out. The ionomer dry-out effect appears to depress reaction kinetics as the temperature increases above 100 °C since the availability of protons at the catalyst–electrolyte interface is linked to the presence of proper water contents. An oxygen reduction reaction of the first order with respect to the oxygen partial pressure was determined at low current densities. Maximum power densities of 990 mW cm−2 and 780 mW cm−2 at 100 °C and 110 °C (H2–O2) with 100% R.H., were achieved at 3 bars abs.

Galvanostatic Anodic Polarization Curves and Galvanic Corrosion of AZ31B in 0.01 M Na2SO4 Saturated with Mg(OH)2

AbstractMeasured polarization curves were used in a BEM model of the galvanic corrosion of the Mg alloy AZ31B. The AZ31B galvanostatic anodic polarization curves indicated: (i) the existence of the uni‐positive Mg+ ion, (ii) some hydrogen dissolved in the AZ31B metal, and (iii) self corrosion was more important than the applied current density in causing weight loss. Galvanic corrosion of the AZ31B consisted of: (i) corrosion that decreased in depth from the 2024–AZ31B interface, and (ii) heterogeneous corrosion that was denser closer to the 2024–AZ31B interface. There was good agreement between the BEM model and the experimental measurements.

Direct bio-electrocatalysis by multi-copper oxidases: Gas-diffusion laccase-catalyzed cathodes for biofuel cells

We have studied the bio-electroreduction of oxygen based on direct electron transfer (DET) between laccase and the electrode. Laccase enzymes from two different sources, namely, tree laccase from Rhus vernicifera, and fungal laccase from Trametes hirsuta were used in the study. The gas-diffusion cathode was made using a mixture of teflonized carbon and untreated carbon black, with a nickel mesh that served as a current collector, sandwiched between a hydrophobic gas diffusion layer, and a hydrophilic biocatalytic layer with physically adsorbed laccase enzyme. High current densities: up to 1 mA cm −2 under oxygen (for bio-electrocatalytic oxygen reduction) and increased stability (up to 30 days) has been achieved using teflonized carbon blacks at gas–electrode interface, high surface area carbon black for loading the enzyme. Gas diffusion laccase-catalyzed cathode demonstrates a number of advantageous properties including good adhesion, biocompatibility and high bio-electrocatalytic properties. An open circuit potential (OCP) of 600 mV at pH 7 for tree laccase ( R. vernicifera) and 725 mV at pH 5 for fungal laccase ( T. hirsuta) at zero current densities were obtained with respect to SHE reference electrode. Tafel plots obtained confirmed different DET characteristics for the two sources of laccase enzymes, which could suggest different mechanism of charge transfer: 4-electron electroreduction of oxygen using fungal laccase and 2-electron electroreduction using tree laccase. The performance of the cathode was studied in galvanostatic mode and polarization curves at various conditions are reported including those obtained under air and neat oxygen feed from the gas phase.

Enhancement of oxygen reduction by incorporation of heteropolytungstate into the electrocatalytic ink of carbon supported platinum nanoparticles

Nafion stabilized inks of Vulcan XC-72 supported platinum (20 wt.%) nanoparticles (Pt/XC-72) were utilized to produce electrocatalytic films on glassy carbon. The catalysts were modified (activated) with phosphododecatungstic acid H 3PW 12O 40 (PW 12). Comparison was made to bare (PW 12-free) electrocatalytic films. Electroreduction of dioxygen was studied at 25 °C in 0.5 mol dm −3 H 2SO 4 electrolyte using rotating disk voltammetry. For the same loading of platinum (≈95 μg cm −2) and for the approximately identical distribution of the catalyst, the reduction of oxygen at a glassy carbon electrode modified with the ink containing PW 12 proceeded at ca. 30–60 mV more positive potential (depending on the PW 12 content), and the system was characterized by a higher kinetic parameter (rate of heterogeneous electron transfer), when compared to the PW 12-free electrocatalyst. Gas diffusion electrodes with Pt/XC-72 supported on carbon paper (Pt loading 1 mg cm −2) were also tested. Under the same experimental conditions, while the exchange current density and the total resistance contribution to polarization components, computed from the galvanostatic polarization curves were found to be clearly higher and lower, respectively, for the ink modified with PW 12 relative to the unmodified system. The results demonstrate that addition of heteropolytungstatic acid (together with Nafion) enhances the electrocatalytic activity of platinum towards reduction of oxygen.

Electrochemical Behavior of Copper in Alkaline-Sulfide Solutions

Abstract Cyclic voltammograms and galvanostatic polarization curves were traced for the copper electrode in alkaline and alkaline-sulfide solutions. In sulfide-free sodium hydroxide (NaOH) solution...

Chloroanilines as corrosion inhibitors for zinc in nitric acid

The Inhibition by chloro-substltuted anilines on corrosion of zinc in nitric acid has been studied in relation to acid concentration, Inhibitors concentration and temperature. The corrosion increases with acid concentration and with increase of temperature. The . mode of the inhibition appears to be chemisorption. Zinc in 0.05 M HNO 3 shows a corrosion potential as -920 mV. Galvanostatic polarization curves shows both anodic and cathodic polarization.

Corrosion inhibition of mild steel in 1 M sulfuric acid solution using anionic surfactant

The anionic surfactant [ p-myristyloxy carbonyl methoxy- p′-sodium carboxylate-azobenzene] was prepared. The surface tension at 298 K was measured, the critical micelle concentration (cmc) and some surface active parameters were calculated. The inhibition efficiency ( η%) of this surfactant has been studied by both chemical and electrochemical techniques at 25 °C. A significant decrease in the corrosion rate was observed in presence of the investigated inhibitor. The galvanostatic polarization curves showed that, the inhibitor behaves as mixed type but the cathodic effect is more pronounced. Tafel slopes are approximately constant and independent on the inhibitor concentration. The observed corrosion data indicate that, the inhibition of mild steel corrosion is due to the adsorption of the inhibitor molecules on the surface, which follow Langmuir adsorption isotherm. The surface morphology of mild steel samples in absence and presence of the inhibitor was examined using scanning electron microscopy.

Corrosion and passivation behaviors of some stainless steel alloys in molten alkali carbonates

The corrosion and passivation behaviors of two types of stainless steel alloys (ferritic and austenitic steels) in ternary molten Li 2CO 3–Na 2CO 3–K 2CO 3 mixture at different temperatures (475–550 °C) were studied using galvanostatic polarization and cyclic voltammetry. The galvanostatic polarization curves of the investigated alloys illustrate the passivation and passivity breakdown of the alloys. The passivation potential range for the three investigated steel alloys is about 1.15–1.3 V. During this potential range different oxide and spinels are formed, the nature of which depends on the type of alloy and the anodization potential. At high anodic potentials the decomposition of carbonate takes place, leading to passivity breakdown and oxygen evolution. The values of corrosion parameters ( R p, i o and i corr) were calculated. The calculated values indicate that the corrosion resistance of the austenitic stainless steel is higher than that of the ferritic steel. The activation energy of the corrosion process was found to be equal to about 70 kJ mol −1. The results of the cyclic voltammetric investigations indicate that the behavior of the austenitic steels is about the same and differs from that of ferritic steel. The corrosion tests in 0.2 M HCl solutions have shown that the oxide scales formed on the surface of the austenitic stainless steels are multilayered, whereas those formed on the ferritic alloy are uniform.

Electrochemical hydrogen evolution on solid oxides RuO2, Ru0.7Rh0.3O2 and IrO2 from acidic water

In contrast to traditional research with pure metals and intermetallic electrocatalysts for evolving hydrogen from acidic water, solid oxide catalytic electrode materials have been investigated recently. RuO2, Ru0.7Rh0.3O2 and IrO2 pellet electrodes have been prepared and the occurrence of the hydrogen evolution reaction on these oxides has been characterised by cyclic voltammetric and galvanostatic polarization curves in 2.5 M H2SO4 solution at room temperature. Measurements of thepH dependence of the surface charge densities on oxide particles have been carried out to correlate surface oxide properties with electrochemical properties. Reaction mechanistic pathways on metals and intermetallic compounds have incorporated the adsorption of hydrogen atoms on metal sites. It is suggested from the correlation of surface acid/base properties of oxides with their electrochemical properties that the sites of reaction are the surface oxygen atoms covalently bonded to suitable cations and possessing the appropriate energetics in the oxides.

Kinetics and Mechanism of Electroless Deposition of Copper

This paper describes investigations on the role of electrolyte composition on the mechanism of the electroless copper deposition process. Both potentiostatic and galvanostatic polarization curves as well as steady‐state plots are used in these investigations. Actual deposition rates are also measured through gravimetrically determined weight gain for comparison. The observation indicates that the two‐compartment cell gives the mixed potential, Em, values closer to that of the actual plating, whereas the deposition rate determined from the mixed current, im, value is lower than that of the actual one. The mechanism of electroless copper deposition changes from anodic to cathodic control as well as from diffusion to activation control depending on the concentration of and HCHO. The mechanism in each case could be determined through the application of the Butler‐Volmer equation to the half‐cell reactions depending on the position of Em in the polarization plots of the individual half‐cell reactions.

The Effect of the Molecular Structure of Cyanine Dye on the Corrosion of Low-Carbon Steel in Hydrochloric Acid Solution

The effect of two different cyanine dyes 2-(2-hydroxystyryl)quinolinium-1-ethyl iodide (I) and 4-(2-hydroxystyryl)quinolinium-1-ethyl iodide (II) on the electrochemical corrosion behaviour of low-carbon steel (0.05% C, 0.04% Si, 0.023% S, 0.004% Cu) in HCl solution has been studied. Weight loss measurements, galvanostatic polarization curves, open-circuit potential variation of steel electrode with time and the cathodic protective current values show that the investigated cyanine dyes have an anticorrosive character. The inhibition effect depends mainly on the structure of the studied dye molecules, and is more pronounced in case of pretreated carbon steel with the dye solution before immersion in the corrosion medium than that obtained by addition of the dye to the corrosive medium.