Electrochemical reduction of nitrate in weakly alkaline solutions

The electrocatalytic activity of several materials for the nitrate reduction reaction was studied by cyclic voltammetry on a rotating ring disc electrode in solutions with different concentrations of sodium bicarbonate. Copper exhibited highest catalytic activity among the materials studied. Nitrate reduction on copper was characterized by two cathodic shoulders on the polarization curve in the potential region of the commencement of hydrogen evolution. In this potential range an anodic current response was observed on the Pt ring electrode identified as nitrite to nitrate oxidation. This indicates that nitrite is an intermediate product during nitrate reduction. These conclusions were verified by batch electrolysis using a plate electrode electrochemical cell. Copper and nickel, materials representing the opposite ends of the electrocatalytic activity spectra, were used in batch electrolysis testing.     

Electrode kinetics of antimony in alkaline solutions

The kinetics of the electro-oxidation and electro-reduction of Sb in alkaline solutions as well as the electrodeposition of Sb(III) on Sb have been studied. The rest potential follows the relation,E ₀=0.152–0.059 pHV is SHE which is the equation for the equilibrium potential for the redox reaction, 2Sb+60H^–=Sb₂O₃+3H₂O+6e^– The rates of anodic dissolution and electro-reduction can be expressed by the following empirical kinetic equations,i _a=6F¯k _a[OH^–]² exp 0.59FE/RT and ¦i _c=6F¯k _cexp–1.31FE/RT The empirical kinetic equation for electrodeposition of Sb (III) is ¦i_c¦=3F¯k_c[SbO ₂ ^– ] exp–0.454FE/RT Mechanisms are proposed to interpret the experimental results.Nomenclature b _a Anodic Tafel slope - b _c Cathodic Tafel slope - b _c Tafel slope for electrodeposition reaction - E Electrode potential - E ^e Equilibrium potential - E ₀ Rest potential - i _a Anodic current density - i _c Cathodic current density - i ₀ Exchange current density for Sb/Sb(III) reaction - i _{c, 28a} Sb(III) electrodeposition current density for Step 28a - i _c,21e Cathodic current density for Step 21 e - i_c Current density for Sb(III) electrodeposition - i₀ Exchange current density for Sb(III) electrodeposition - ¯k _a Anodic rate constant - ¯k _c Cathodic rate constant - ¯k _c,28a Electrodeposition rate constant for Step 28a - k _a,21e Anodic rate constant in Equation 22 - k _c,21e Cathodic rate constant in Equation 25 - ¯k_c Electrodeposition rate constant - ¯k_a,21e Anodic rate constant in Equation 23 - ¯k_c,21e Cathodic rate constant in Equation 26 - R Gas constant - T Absolute temperature - _a Anodic charge transfer coefficient - _c Cathodic charge transfer coefficient - _c Charge transfer coefficient for Sb (III) electrodeposition reaction - Symmetry factor     

Corrosion protection performance of novel hybrid polyaniline/sol–gel coatings on an aluminium 2024 alloy in neutral, alkaline and acidic solutions

In this study the corrosion performance of a novel coating, consisting of a combination of silica sol–gel and conductive polymer, in 3.5% NaCl at different pH levels is presented. Electrochemical Impedance Spectroscopy showed the impedance of the coating remained stable for up to 24 months in neutral 3.5% NaCl solution. No corrosion or delamination was observed after 500 h in salt spray tests and Scanning Vibrating Electrode Technique tests showed the coating exhibited a “self healing” property. The surface morphology was characterised by Scanning Electron Microscopy and the mechanical properties, notably adhesion, were studied using pull off and cross cut techniques.     

Pt-decorated nanoporous gold for glucose electrooxidation in neutral and alkaline solutions

Exploiting electrocatalysts with high activity for glucose oxidation is of central importance for practical applications such as glucose fuel cell. Pt-decorated nanoporous gold (NPG-Pt), created by depositing a thin layer of Pt on NPG surface, was proposed as an active electrode for glucose electrooxidation in neutral and alkaline solutions. The structure and surface properties of NPG-Pt were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and cyclic voltammetry (CV). The electrocatalytic activity toward glucose oxidation in neutral and alkaline solutions was evaluated, which was found to depend strongly on the surface structure of NPG-Pt. A direct glucose fuel cell (DGFC) was performed based on the novel membrane electrode materials. With a low precious metal load of less than 0.3 mg cm^-2 Au and 60 μg cm^-2 Pt in anode and commercial Pt/C in cathode, the performance of DGFC in alkaline is much better than that in neutral condition.     

Membraneless laminar flow-based micro fuel cells operating in alkaline, acidic, and acidic/alkaline media

The lack of a polymer electrolyte membrane (PEM, e.g. Nafion) in membraneless, laminar flow-based micro fuel cells (LF-FCs) eliminates several PEM-related issues such as fuel crossover, cathode flooding, and anode dry-out, as we reported previously. This paper explores the media flexibility of LF-FCs by working in acidic and alkaline media, as well under “mixed-media” conditions in which the anode is in acidic media while the cathode is in alkali, or vice versa. Operating a fuel cell under alkaline conditions has positive effects on the reaction kinetics, both at the anode and cathode, while the cell performance under “mixed-media” conditions offers an opportunity to increase the maximum achievable open cell potential (OCP). The lack of media-related constraints and the simplicity of the LF-FC design allow for these experiments to be performed consecutively in a single LF-FC without changing the system, except for altering the composition/pH of the fuel and oxidant stream. The performance of LF-FCs operated with different media is described and compared.     

The performance of epoxy coatings containing polyaniline (PANI) nanowires in neutral salt,alkaline, and acidic aqueous media

PANI/epoxy coatings have great promise applications in the industry as the metal corrosion protection coating, and their performance directly determines the life span of the coating and equipment durability. In this study, the performance of epoxy coatings with and without PANI nanowires immersed in 12 wt% NaCl, 5 wt% HCl, and 5 wt% NaOH solutions at different temperature were investigated for the first time. The performance and the degradation reactions of the coating cooperated with PANI nanowires were characterized by the variety of techniques and methods, including ultraviolet–visible spectrophotometry (UV–vis), field emission scanning electron microscopy (SEM), Attenuated Total Reflectance-Fourier transform Infrared spectroscopy (ATR-FTIR), and thermogravimetric analysis (TGA). The experiment results indicated that the failure mechanism of the different coatings varied with the different temperatures and solutions. Electrochemical impedance spectra (EIS) results showed that an appropriate content of PANI nanowires improve the protection performance of epoxy coatings in 12 wt% NaCl, 5 wt% HCl, and 5 wt% NaOH solutions, which is attributed to the passivation ability and shielding effect of PANI nanowires.     

Anodic processes in plasma electrolytic oxidation of aluminium in alkaline solutions

In this paper, basic electrochemical processes (such as oxide film growth, anodic dissolution and oxygen liberation) on an aluminium anode in a model alkaline solution are considered under conditions of galvanostatic DC plasma electrolytic oxidation (PEO). The experiments performed include: (i) recording and analysis of the main electrical characteristics of the process; (ii) determination of the oxide layer thickness; (iii) anodic gas collection and composition analysis and (iv) electrolyte analysis to determine dissolved aluminium. Four different stages of the PEO process have been identified, characterised by various rate proportions of the partial anodic processes. Overall current efficiency of the oxide film formation has been estimated to be in the 10-30% range. The film growth rate decreases significantly with increasing electrolyte concentration from 0.5 to 2 g l⁻¹ KOH, since the rate of anodic dissolution increases. Oxygen evolution is shown to be the main electrochemical process at the potentials corresponding to the plasma stages of the electrolysis. The overall rate of oxygen liberation at the anode exceeds the Faraday yield, which is probably due to the radiolytic effect of the plasma discharge on the adjacent electrolyte volume.     

Electrochemical study of benzene on Pt of various surface structures in alkaline and acidic solutions

The electrochemical behaviour of benzene on platinum electrodes (polycrystalline and single-crystal electrodes) has been studied in acidic and alkaline solutions. In acid solutions the reduction of benzene to cyclohexane takes place in all the platinum surface structure employed, however it does not occur in alkaline media (0.1 M NaOH). In this case, the hydrogen adsorption-desorption processes displace the adsorbed benzene from the electrode surface. The oxidation of benzene is also affected by the pH of the electrolyte and also by the surface structure of the platinum electrode used. In acid solutions, this oxidation at higher potentials (1.4 V vs. RHE) yields CO₂, benzoquinone and α,β-unsaturated esters or lactones, however in alkaline media carbonate anions coming from CO₂ and salts of carboxylic acids have been detected by in situ FTIR spectroscopy using a platinum polycrystalline electrode. Bulk electrolysis of benzene solutions using a platinum electrode in acid and alkaline media was performed in order to confirm the results obtained by spectroscopic measurements.     

A comparative study of the electrocatalytic oxidation of ethylene glycol on PtAu nanocomposite catalysts in alkaline, neutral and acidic media

Electrocatalytic oxidation of ethylene glycol on platinum-gold nanocomposite catalysts is investigated by cyclic voltammetry. Platinum-gold nanoparticles are prepared by chemical reduction, and cyclic voltammograms of carbon-supported platinum-gold nanocomposite catalysts show significant differences in alkaline, neutral and acidic solutions. The catalysts exhibit high electrocatalytic activity and stability in alkaline solution, showing oxidation peaks at low potentials with high current densities. Oxidation peaks at higher potentials with significant current declines are observed in neutral solution, and further positive shifts in peak potential are observed in acidic solution. The concentrations of ethylene glycol and the supporting electrolytes also affect the reaction. A higher alkaline concentration is favorable for oxidation at low potential with high current density. Increased phosphate concentration in neutral buffer solution yields a negative shift in peak potential and minor enhancement in peak current density. Changes in the sulfuric acid concentration mainly affect peak current density. Factors such as the synergic catalysis effect and increased active surface area are thought to be responsible for the reactivity of the platinum-gold nanocomposite catalysts.     

Evaluation of cysteine as environmentally friendly corrosion inhibitor for copper in neutral and acidic chloride solutions

The efficiency of cysteine as a non-toxic corrosion inhibitor for copper metal in 0.6 M NaCl and 1.0 M HCl has been investigated by electrochemical studies. Potentiodynamic polarization measurements and electrochemical impedance spectroscopy “EIS” were used to study the effect of cysteine on the corrosion inhibition of copper. Inhibition efficiency of about 84% could be achieved in chloride solutions. The presence of Cu²⁺ ions increases the inhibition efficiency to 90%. Potentiodynamic polarization measurements showed that the presence of cysteine in acidic and neutral chloride solutions affects mainly the cathodic process and decreases the corrosion current to a great extent and shifts the corrosion potential towards more negative values. The experimental impedance data were analyzed according to a proposed equivalent circuit model for the electrode/electrolyte interface. Results obtained from potentiodynamic polarization and impedance measurements are in good agreement. Adsorption of cysteine on the surface of Cu, in neutral and acidic chloride solutions, follows the Langmuir adsorption isotherm. The adsorption free energy of cysteine on Cu (−25 kJ mol⁻¹) reveals a strong physical adsorption of the inhibitor on the metal surface.     

Redox processes at iron hydroxide layers formed on platinum substrates in alkaline solutions

Redox processes taking place at precipitated hydrous iron hydroxide layers chemically formed on platinum substrates in sodium hydroxide solutions are investigated at 25°C. The electrochemical behaviour of these layers depends considerably on the electroreduction level reached in chargedischarge cycles. The accumulation of Fe₃O₄ during oxidation-reduction cycles can produce an increasing irreversibility of the Fe(II)/Fe(III) redox couple. Data are compared to results obtained with iron hydroxide layers formed by electrochemical and chemical methods on massive iron electrodes. Results are discussed in terms of a composite structure for the iron hydroxide layers.     

Corrosion and passive behaviour of aluminium in weakly alkaline solution

The title subject has been studied by stationary and transient polarization measurements on high-purity aluminium electrodes in acetate solutions of pH 7–10 at 25°C and by Auger electron spectroscopic investigations of oxide films formed. In such deoxygenated solutions, aluminium corrodes under hydrogen evolution and is in some state of active/passive transition, or close to it. Oxygen (when added) acts as a passivator and mostly lowers the corrosion rate. The stationary passive current is potential independent, but varies with pH. It goes through a minimum at a pH of about 8. Oxide films formed have a thin inner barrier layer and an outer non-barrier layer whose thickness increases with increasing pH. Transients yield information on the barrier layer and on charge transfer reactions occurring.     

The voltammetric detection of intermediate electrochemical processes related to iron in alkaline aqueous solutions

The application of the triangularly modulated triangular potential sweep technique (TMTPS) to the Fe/alkaline solution interface yields information about the various reactions involving Fe(II) and Fe(III) film-forming species. Qualitative conclusions are derived about the chemical reactions of both Fe(OH)₂ and FeOOH with regard to the corresponding ageing processes of these species. The ageing processes appear to be coupled to the overall electrochemical reaction through a composite reaction pattern which, in its simplest form, approaches the square reaction pathway postulated earlier to explain the electrochemical behaviour of the Ni/alkaline solution interface.     

BSn-500弱酸性镀锡工艺

针对陶瓷和玻璃电子元件,开发了BSn-500弱酸性镀锡工艺。介绍了工艺的操作条件、流程和重点工序,讨论了镀液中配位剂、导电盐、甲基磺酸亚锡和添加剂等物质的作用,检测了镀液和镀层的性能。结果表明,该镀液性能稳定,分散能力、覆盖能力较好;镀层附着强度高,抗变色能力强,可焊性符合GB/T16745-1997要求。     

Applicability of four recent models to the discharge behaviour of different phases of MnO2 in alkaline and acidic/neutral electrolytes

Manganese dioxides belonging to different crystalline phases were discharged in 9 M KOH and 5 M NH₄Cl+2 M ZnCl₂ at a constant current of 1 mA 0.1 g. These phases were characterized by X-ray diffractometry and chemical analysis. Four different models were tried for their applicability to the discharge behaviour of these phases. Almost all the four models successfully predict the values of the oxyhydroxides in the first half of the reduction range 0<r<0.5, but fail to do so in the secon half i.e. 0.5<r<1. The only exception to this is the model (Model 2) of Maskell, Shaw and Tye. This model yields, by far, the best match with the experimental data in acidic/neutral electrolyte. In alkaline electrolyte, however, even this model fails to account satisfactorily for the observed potentials in the lower half of the reduction. This failure could perhaps be explained as due to the formation of a new phase at about MnO_1.6 (r0.8). The cation vacancy model of Ruetschi predicts most of the physical properties rather well but the match of the theoretical potentials with the experimental values is poor, specially in the lower half.     

羧甲基壳聚糖在酸性溶液中缓蚀性能

采用失重及电化学方法（EIS 和 Tafel曲线）研究了羧甲基壳聚糖（CM-chitosan）作为一种绿色缓蚀剂,在1 mol·L-1 HCl 和0.5 mol·L-1 H2SO4溶液中对碳钢的缓蚀作用。结果表明,CM-chitosan是一种良好的缓蚀剂,且在1 mol·L-1 HCl 溶液中的缓蚀作用要优于在0.5 mol·L-1 H2SO4溶液中的缓蚀作用。在HCl和H2SO4两种酸性溶液中,CM-chitosan在碳钢表面的吸附都遵循修正的Langmuir吸附等温式。