Showing papers in "Journal of Applied Electrochemistry in 2011"

Redox flow batteries: a review

Abstract: Redox flow batteries (RFBs) are enjoying a renaissance due to their ability to store large amounts of electrical energy relatively cheaply and efficiently. In this review, we examine the components of RFBs with a focus on understanding the underlying physical processes. The various transport and kinetic phenomena are discussed along with the most common redox couples.

Polarization curve analysis of all-vanadium redox flow batteries

Abstract: We outline the analysis of performance of redox flow batteries (RFBs) using polarization curves. This method allows the researcher immediate access to sources of performance losses in flow batteries operating at steady state. We provide guidance on ‘best practices’ for use of this tool, illustrated using examples from single cells operating as vanadium redox batteries.

Electrodeposition: a versatile and inexpensive tool for the synthesis of nanoparticles, nanorods, nanowires, and nanoclusters of metals

Abstract: The synthesis of various nanoscale materials, such as nanoparticles, nanowires of Au, Pt, Ni Co, Fe, Ag etc., by electrodeposition techniques have been demonstrated in this article. Both potentiostatic and galvanostatic methods were employed to carry out the electrodeposition process under different potential ranges, time durations, and current densities. The electrochemical behavior of the deposited nanoparticles on various substrates was investigated by cyclic voltammetric and chronoamperometric techniques. The synthesis of mono-dispersed gold (Au) nanoparticles on indium tin oxide (ITO) coated glass, preparation of Au nanorods on nanoporous anodic alumina oxide (AAO), formation of Au nanoclusters on polypyrrole-modified glassy carbon electrode and one-step electrodeposition of nickel nanoparticle chains embedded in TiO2 etc. have been highlighted in this article. The potential applications of synthesized nanoparticles such as the role of maghemite (Fe2O3) in arsenic remediation, higher electrocatalytic activity of Ag nanoclusters for the reduction of benzyl chloride, and the role of C60 nanoparticle-doped carbon film in fabrication processes are also presented in this article.

Electrochemical simultaneous determination of nitrophenol isomers at nano-gold modified glassy carbon electrode

Abstract: A novel method for simultaneous determination of nitrophenol isomers at nano-gold modified glassy carbon electrode has been developed. The gold nanoparticles were directly electrodeposited onto the glassy carbon electrode via a constant potential −0.2 V (vs. SCE) for 60 s from 0.1 mol L−1 KNO3 containing 0.4 g L−1 HAuCl4. The resulting electrode (nano-Au/GCE) was characterized with scanning electron microscopy (SEM). The electrochemistry response of nitrophenol isomers at the nano-Au/GCE was studied. The result indicated that o-, m-, and p- nitrophenol are separated entirely at nano-Au/GCE, and a semi-derivative voltammetric technology was adopted to enhance the determination sensitivity. This modified electrode could be applied to direct simultaneous voltammetric determination of nitrophenol isomers in water samples without preseparation with higher sensitivity.

Chemical and mechanical degradation of sulfonated poly(sulfone) membranes in vanadium redox flow batteries

Abstract: A sulfonated poly(sulfone) (S-Radel®) membrane with high proton conductivity and low vanadium ion permeability showed high initial performance in a vanadium redox flow battery (VRFB) but suffered mechanical and chemical degradation during charge/discharge cycling. The S-Radel membrane showed different degradation behavior in flow cell cycling and ex-situ vanadium ion immersion tests. When the membrane was immersed in aqueous V5+ solution, the sample cracked into small pieces, but did not degrade to any measurable extent in V4+ solution. During charge/discharge cycling in the VRFB cell, the membrane underwent internal delamination, preferentially on the side of the membrane that faced the positive electrode. A vanadium-rich region was observed near the membrane surface that experienced delamination and Raman spectroscopic analysis of the degraded surface indicated a slightly depressed 1026 cm−1 band corresponding to a loss in the sulfonate SO2 stretch intensity. Even though the S-Radel membrane underwent severe mechanical damage during the flow cell cycling, significant chemical degradation was not obvious from the spectroscopic analyses. For the VRFB containing an S-Radel membrane, an increase in membrane resistance caused an abnormal voltage depression during the discharge cycle. The reversible increase in membrane resistance and severe mechanical degradation of the membrane during cycling may be attributed to repeated formation and dissolution of particles inside the membrane. The mechanical stresses imposed by the particles coupled with a small amount of chemical degradation of the polymer by V5+ ions, are likely degradation mechanisms of the S-Radel membrane in VRFBs under high state-of-charge conditions.

Effects of additives on the stability of electrolytes for all-vanadium redox flow batteries

Abstract: The stability of the electrolytes for all-vanadium redox flow battery was investigated with ex-situ heating/cooling treatment and in situ flow-battery testing methods. The effects of inorganic and organic additives have been studied. The additives containing the ions of potassium, phosphate, and polyphosphate are not suitable stabilizing agents because of their reactions with V(V) ions, forming precipitates of KVSO6 or VOPO4. Of the chemicals studied, polyacrylic acid and its mixture with CH3SO3H are the most promising stabilizing candidates which can stabilize all the four vanadium ions (V2+, V3+, VO2+, and VO2+) in electrolyte solutions up to 1.8 M. However, further effort is needed to obtain a stable electrolyte solution with >1.8 M V5+ at temperatures higher than 40 °C.

Bench-scale electrochemical system for generation of CO and syn-gas

Abstract: A flow cell based, bench-scale electrochemical system for generation of synthesis-gas (syn-gas) is reported. Sensitivity to operating conditions such as CO2 flow, current density, and elevated temperature are described. By increasing the temperature of the cell the kinetic overpotential for the reduction of CO2 was lowered with the cathode voltage at 70 mA cm−2 decreased by 0.32 V and the overall cell voltage dropping by 1.57 V. This equates to an 18% increase in cell efficiency. By closely monitoring the products it was found that at room temperature and 70 °C the primary products are CO and H2. By controlling the current density and the flow of CO2 it was possible to control the H2:CO product ratio between 1:4 and 9:1. The reproducibility of performing experiments at elevated temperature and the ability to generate syn-gas for extended periods of time is also discussed.

Electrochemical sensor for bisphenol A detection based on molecularly imprinted polymers and gold nanoparticles

Abstract: A novel bisphenol A (BPA) sensor based on amperometric detection has been developed by using molecularly imprinted polymers (MIPs) and gold nanoparticles. The sensitive layer was prepared by electropolymerization of 2-aminothiophenol on a gold nanoparticles-modified glassy carbon electrode in the presence of BPA as a template. Cyclic voltammetry was used to monitor the process of electropolymerization. The properties of the layer were studied in the presence of Fe(CN)6 3−/Fe(CN)6 4− redox couples. The template and the non-binding molecules were removed by washing with H2SO4 (0.65 mol L−1) solution. The linear response range of the sensor was between 8.0 × 10−6–6.0 × 10−2 mol L−1, with a detection limit of 1.38 × 10−7 mol L−1 (S/N = 3). The proposed MIPs sensor exhibited good selectivity for BPA. The stability and repeatability of the MIPs senor were found to be satisfactory. The results from real sample analysis confirmed the applicability of the MIPs sensor to quantitative analysis.

Performance of vanadium-oxygen redox fuel cell

Abstract: A promising approach to improving the energy density of the all-vanadium redox flow battery while also saving on raw materials costs, is to eliminate the positive half-cell electrolyte and replace it with an air electrode to produce a hybrid vanadium–oxygen redox fuel cell (VOFC). This concept was initially proposed by Kaneko et al. in 1992 and first evaluated at the University of New South Wales by Menictas and Skyllas-Kazacos in 1997. In this project the performance of the VOFC over a range of temperatures and using different types of membranes and air electrode assemblies was evaluated. Despite early problems with the membrane electrode assemblies that saw separation of the membrane due to swelling and expansion during hydration, with improved fabrication techniques, this problem was minimized and it was possible to operate a 5-cell VOFC system for a total of over 100 h without any deterioration in its performance.

Acceleration of the redox kinetics of VO2+/VO2 + and V3+/V2+ couples on carbon paper

Abstract: The redox kinetics of VO2+/VO2 + and V3+/V2+ couples on a carbon paper (CP, HCP030 N, Shanghai Hesen, Ltd., China) electrode were investigated in terms of their standard rate constant (k 0) and reaction mechanism. The values determined for k 0 for VO2+ → VO2 + and V3+ → V2+ using the CP electrode are 1.0 × 10−3 and 1.1 × 10−3 cm s−1, respectively. The value of k 0 increases by one or two order(s) of magnitude compared with values obtained using electrodes composed of pyrolytic graphite and glassy carbon. The acceleration of the redox kinetics of vanadium ions is a result of the large surface area of the CP electrode. An inner-sphere mechanism for the reaction on the surface of the electrode is proposed. The kinetic features of vanadium redox reactions on the CP electrode reveal that CP is suitable for use as the electrodes in vanadium redox-flow batteries.

Electrode kinetics in non-aqueous vanadium acetylacetonate redox flow batteries

Abstract: Three electrode materials (glassy carbon, gold, and platinum) were investigated for application in a non-aqueous single-metal redox flow battery based on vanadium (III) acetylacetonate, supported by tetraethylammonium tetrafluoroborate in acetonitrile. Redox couples associated with the one-electron disproportionation of V(acac)3 were observed in voltammetry for each metal tested. An elementary kinetic model was created and used to determine rates for oxidation or reduction of the vanadium complex. The oxidation rates for V(acac)3 were mass-transfer limited on all electrode materials, suggesting reversible kinetics. For the V(acac)3 reduction reaction, exchange-current densities of 1.3, 3.8, and 8.4 A m−2 were observed on glassy carbon, platinum, and gold electrodes, respectively.

Preparation and characterisation of carbon-supported palladium nanoparticles for oxygen reduction in low temperature PEM fuel cells

Abstract: Pd nanoparticles have been synthesised using different reducing agents, including ethylene glycol (EG), formaldehyde and sodium borohydride and their activity for the oxygen reduction reaction (ORR) evaluated. The use of EG led to the best morphology for the ORR and this synthetic method was optimised by adjusting the system pH. Carbon-supported Pd nanoparticles of approximately 7 nm diameter were obtained when reduction took place in the alkaline region. Pd synthesised by EG reduction at pH 11 presented the highest mass activity 20 A g−2 and active surface area 15 m2 g−1. These synthetic conditions were used in further synthesis. The effect of heat treatment in H2 atmosphere was also studied; and increased size of the palladium nanoparticles was observed in every case. The Pd/C catalyst synthesised by reduction with EG at pH 11 was tested in a low temperature H2/O2 (air) PEMFC with a Nafion® 112 membrane, at 20 and 40 °C. Current densities at 0.5 V, with O2 fed to the cathode, at 40 °C were 1.40 A cm−2 and peak power densities 0.79 W cm−2, approximately; which compared with 1.74 A cm−2 and 0.91 W cm−2, respectively for a commercial Pt/C.

Effect of sodium chloride on corrosion of mild steel in CO2-saturated brines

Abstract: Corrosion rates of mild steel were measured in oxygen-free, CO2-saturated brines as a function of NaCl concentration employing electrochemical techniques. Decreased corrosion rates were observed as salt concentration increased. However, at high salt concentration (≥20 wt% NaCl), corrosion rates were independent of the flow rate of CO2-saturated brine. To understand this phenomenon, corrosion surfaces were analyzed by scanning electron microscopy and X-ray diffraction and showed only residual iron carbide for salt concentrations of 0.5–5 wt%. However, at 20 wt% NaCl, a porous corrosion scale with embedded crystals, possibly magnetite, was observed. No iron carbonate was observed and water chemistry showed it was 10,000 times below saturation. A numerical model of corrosion in CO2–NaCl systems was able to predict the reduced corrosion rates with salt concentration increase as a consequence of reduced solubility of CO2 (“salting-out”). However, the model did not predict that corrosion rates were flow-independent at high salt concentration. These results demonstrate that flow-independent corrosion is a consequence of a diffusion barrier created by magnetite scale, present only at high salt concentrations.

Voltammetric behavior and the determination of quercetin at a flowerlike Co3O4 nanoparticles modified glassy carbon electrode

Abstract: Flowerlike Co3O4 nanoparticles were used as a modifier on the glassy carbon electrode to fabricate a quercetin (Qu) sensor. The morphology and crystallinity of the prepared Co3O4 material were investigated by scanning electron microscopy and X-ray diffraction. Electrochemical behavior of Qu at the sensor was studied by cyclic voltammetry and semi-derivative voltammetry. Results suggested that the modified electrode exhibited a strong electrocatalytic activity toward the redox of Qu. The electron transfer coefficient (α), the number of electron transfer (n), and the diffusion coefficient (D) of Qu at the sensor were calculated. Under the optimum conditions, the catalytic peak currents of Qu were linearly dependent on the concentrations of Qu in the range from 5.0 × 10−7 to 3.3 × 10−4 M, with a detection limit of 1.0 × 10−7 M. This proposed method was successfully applied to determine the quercetin concentration in Ginkgo leaf tablet and human urine samples.

Study of electrochemical bleaching of p -nitrosodimethylaniline and its role as hydroxyl radical probe compound

Abstract: In the present paper, research on the electrochemical bleaching of p-nitrosodimethylaniline (RNO) in different electrolyte systems is presented with special attention to the role of RNO as a selective hydroxyl radical probe compound. At a Ti/Pt90–Ir10 anode, RNO was found to be bleached in 0.050 M sodium sulphate electrolyte due to lattice active oxygen without hydroxyl radicals being intermediately present. In 0.050 M sodium chloride, the bleaching rate was greatly enhanced due to indirect bulk oxidation by active chlorine species, again without the presence of hydroxyl radicals in the oxidation mechanisms. Under galvanostatic electrolysis, a linear relationship was found between the concentration of added chloride to a supporting sodium sulphate electrolyte and the first order rate constant of the bleaching reaction, showing the importance of the indirect bulk chlorine bleaching in chloride electrolyte systems. In this fashion both the chemically bonded active oxygen and the chemical bulk oxidation by active chlorine species proved to be valid bleaching pathways of RNO that according to these findings cannot be regarded as a fully selective hydroxyl radical probe compound. In addition, the difference in the mechanisms of chloride electrolysis at Ti/Pt90–Ir10 and Si–BDD anodes was clearly demonstrated using t-BuOH as hydroxyl radical scavenger.

Electro-organic reactions. Part 60[1]. The electro-oxidative conversion at laboratory scale of a lignosulfonate into vanillin in an FM01 filter press flow reactor: preparative and mechanistic aspects

Abstract: The electrochemical conversion of a spruce lignosulfonate into vanillin, at nickel anodes, was explored in previously unobtainable detail. A flow reactor (FM01), in a rig that permitted considerable variation of electrolysis conditions, allowed up to 150 g to be electrolysed at up to12 A at a variety of electrode configurations. Samples taken during electrolysis gave detailed reaction profiles. The electrolyser operated at 145 °C/500 kPa/3 M NaOH and yields of vanillin were similar to those obtained industrially using chemical oxidants (about 5–7% w/w). Vanillin production was favoured by low current density and low initial concentration of lignosulfonate. Vanillin, alone, was consumed in a 2.7 F process under the above conditions. Historically, yields in chemical and electrochemical conversions of lignins into vanillin do not exceed 10%; the results herein explain this apparent limit as equilibrium between formation of vanillin, its concomitant oxidative destruction and further condensation of lignins.

Characterization of the performance and failure mechanisms of boron-doped ultrananocrystalline diamond electrodes

Abstract: This research investigated the anodic stability of boron-doped ultrananocrystalline diamond (BD-UNCD) film electrodes on a variety of substrates (Si, Ta, Nb, W, and Ti) at a current density of 1 A cm -2 . At an applied charge of 100 A h cm -2 , measurable BD-UNCD film wear was not observed using SEM cross-sectional measure- ments. However, anodic treatment of the electrodes resul- ted in surface oxidation and film delamination, which caused substantial changes to the electrochemical proper- ties of the electrodes. The substrate roughness, substrate electroactivity, and compactness of the substrate oxide were key parameters that affected film adhesion, and the primary mechanism of electrode failure was delamination of the BD-UNCD film. Substrate materials whose oxides had a larger coefficient of thermal expansion relative to the reduced metal substrates resulted in film delamination. The approximate substrate stability followed the order of: Ta ( Si ( Nb ( WTi.

Adsorption properties and inhibition of mild steel corrosion in hydrochloric acid solution by ceftobiprole

Abstract: The inhibition effect of ceftobiprole against the corrosion of mild steel in 1 M HCl solution was studied by weight loss, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and atomic force microscopy techniques. Inhibition efficiency increased with inhibitor concentration where as decreased with acid concentration. Data obtained from EIS studies were analyzed to model the corrosion inhibition process through appropriate equivalent circuit models. The adsorption of ceftobiprole obeyed Langmuir adsorption isotherm. Both thermodynamic and activation parameters were calculated and discussed. Polarization curves indicated that they are mixed type of inhibitors. Polarization curves showed that ceftobiprole act as mixed-type inhibitor. The results obtained from weight loss, EIS and Potentiodynamic polarization are in good agreement.

A simple two-step electrochemical synthesis of graphene sheets film on the ITO electrode as supercapacitors

Abstract: In this study, a simple and controllable two-step electrochemical process is described for the synthesis of graphene sheets (GS) film on a cleaned indium tin oxide (ITO) sheet electrode. Namely, the main procedures involve the electrophoretic deposition (EPD) of graphene oxide (GO) film onto ITO electrode and the subsequent in situ electrochemical reduction (ECR) of GO to generate GS film. X-ray photoelectron spectroscopy (XPS) measurement demonstrates that most of the oxygen-containing functional groups in GO film have been removed after ECR. By electrochemical measurements, the maximum specific capacitance of the prepared GS film electrode was calculated to be 156 F g−1, besides, the capacitance retention of the material remained 78% after 400 times of cycling, showing a promising prospect as supercapacitor materials.

Electrochemical reforming of an acidic aqueous glycerol solution on Pt electrodes

Abstract: The feasibility of the electrochemical conversion of glycerol to alternative, more valuable compounds was evaluated with platinum electrode under galvanostatic conditions. The results indicated a potentially good feasibility of reforming glycerol by electrolysis, particularly under strong acidic conditions (pH 1). Indeed, under controlled conditions at pH 1, various commercially valuable compounds, such as propanediol, glycidol, and 2-propenol, amongst others, were produced. The mechanism for the generation of the key compounds is proposed.

3,4-Dimethoxybenzaldehydethiosemicarbazone as corrosion inhibitor for aged 18 Ni 250 grade maraging steel in 0.5 M sulfuric acid

Abstract: The corrosion inhibition of the aged 18 Ni 250 grade maraging steel in 0.5 M sulfuric acid by 3,4-dimethoxybenzaldehydethiosemicarbazone(DMBTSC) has been investigated by potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) techniques. The inhibition efficiency increased with the increase in inhibitor concentration and decreased with the increase in temperature. Polarization curves indicated mixed type inhibition behavior affecting both cathodic and anodic corrosion currents. The thermodynamic parameters of corrosion and adsorption processes were evaluated. The adsorption of DMBTSC on the aged maraging steel surface was found to obey the Langmuir adsorption isotherm model, and the calculated Gibb’s free energy values confirm the spontaneous adsorption. The results obtained by the two techniques were in good agreement.

Electrochemistry and voltammetric determination of furazolidone with a multi-walled nanotube composite film-glassy carbon electrode

Abstract: This study describes the electrochemical properties of furazolidone (Fu) at a glassy carbon electrode (GCE) modified with a multi-walled carbon nanotube (MWCNT) composite film. Cyclic voltammetry and chronoamperometry techniques were used for diagnostic purposes. The electrode (MWCNT-film-modified GCE) exhibited excellent electrocatalytic behavior for the reduction of Fu as evidenced by the enhancement of the 4e-reduction peak current and the shift in the reduction potential to more positive potential (by 50 mV) in comparison with a bare GCE. The formal potential, E0′, of Fu is pH dependent with a slope of 54.4 mV per unit of pH, close to the anticipated Nernestian value of −59 mV for a four-electron and four-proton processes. The transfer coefficient (α), standard rate constant of the surface reaction (ks), diffusion coefficient (D), and surface concentration (Γ) for the MWCNT-film-modified GCE were calculated. On the other hand, Fu can be accumulated effectively on the MWCNT-film-modified GCE. Under the selected experimental conditions, i.e., solution pH 6, accumulation time 10 min, and accumulation potential −0.30 V, the peak current shows a dynamic linear range 3–800 μM with detection limit 2.30 μM. The method was successfully applied to analyze pharmaceutical formulations. The method used in this study was further applied for the determination of Fu.

Synergistic effect of additives on bright nanocrystalline zinc electrodeposition

Abstract: The influence of additives like cetyltrimethylammonium bromide (CTAB) and Ethyl vanillin (EV) on zinc electrodeposition from acid sulfate bath was systematically investigated by scanning electron microscopy, X-ray diffraction, and voltammetric techniques. The result shows the existence of interaction between CTAB and EV. They exhibited synergistic effect to produce bright nanocrystalline zinc coating on steel surface. The combined effects of these two compounds on deposition overpotential, hydrogen evolution, zinc ion diffusion, and surface coverage were discussed. The morphological and orientational changes occurred in electrodeposit were presented. Also the nucleation mechanism exhibited by zinc during electrodeposition in the presence of additive was examined.

Synergistic effect of polyethylene glycol 600 and polysorbate 20 on corrosion inhibition of zinc anode in alkaline batteries

Abstract: Polyethylene glycol 600 (PEG 600) and polysorbate 20 (Tween 20) were used as a composite corrosion inhibitor of zinc in alkaline solution for the first time. The effects of the composite and individual inhibitors on corrosion inhibition of zinc were evaluated by weight-loss analysis and electrochemical methods including potentiodynamic, potentiostatic, and electrochemical impedance spectroscopic measurements. It was found that there was a synergistic effect between PEG 600 and Tween 20 on corrosion inhibition of zinc. The corrosion inhibition efficiency of the composite inhibitor, 500 ppm PEG 600 + 500 ppm Tween 20, was 89%, much higher than that of the individual inhibitor, 1000 ppm Tween 20 (71%) or 1000 ppm PEG 600 (55%). The battery (Zn/MnO2) discharge performance tests showed that the composite inhibitor reduced the self-discharge of zinc anode more effectively than the individual inhibitor. The synergistic mechanism between PEG 600 and Tween 20 was discussed.

Gas diffusion electrodes for high temperature PEM-type fuel cells: role of a polymer binder and method of the catalyst layer deposition

Abstract: The topic of this study is the optimization of the preparation procedure and chemical composition of a gas diffusion electrode (GDE) for utilization in high-temperature PEM fuel cells. A phosphoric acid-doped polybenzimidazole derivative membrane was used as a polymer electrolyte. The following parameters were studied: nature and content of the polymeric binder (PTFE—hydrophobic, PBI—hydrophilic) in the catalytic layer (CL) and concentration of platinum in catalytic powder (affecting the thickness of the CL). Brushing and spraying were selected as the most suitable techniques of CL deposition. Surprisingly, both polymeric binders investigated in the framework of this study were found to provide a similar GDE performance for CL deposited on the gas diffusion layer surface by spraying.

Electrochemical recycling of cobalt from spent cathodes of lithium–ion batteries: its application as coating on SOFC interconnects

Abstract: In this work the metallic cobalt was electrodeposited on 430 steel in order to obtain a low electrical resistance film made to Co3O4 Pure cobalt was obtained by acidic dissolution of lithium cobalt oxide (LiCoO2) present in exhausted Li-ion battery cathode The electrodeposition was performed with a 96% efficiency at a potential of 150 V versus Ag/AgCl The electrodeposited cobalt showed the face-centered cubic (23%) and hexagonal centered (77%) phases After oxidation at 850 °C for 1000 h in air, the cobalt layer was transformed into the Co3O4 phase On the other hand, a sample without cobalt showed the usual Cr2O3 and FeCr2O4 phases After 1000 h at 850 °C, in air the area specific resistance of the sample with the cobalt oxide layer was 0038 Ω cm−2, while it was 130 Ω cm−2 for the bare sample

Pulse current electrodeposition and corrosion properties of Ni–W alloy coatings

Abstract: Ni–W alloy coatings were prepared on a mild steel substrate by means of pulse current (PC) and compared to the coatings electrodeposited by direct current (DC). In particular the study dealt with the influence of the frequency using pulse current on the surface morphology while maintaining a constant duty cycle. A constant charge for DC and PC electrodeposition of Ni–W alloy coatings was used. The morphology of the coatings was explored by scanning electron microscopy and the composition of the coatings was analysed by X-ray powder diffraction and energy dispersive X-ray analysis. Corrosion resistance of Ni–W alloy coatings was investigated by potentiodynamic polarization in a chloride medium. The corrosion products were analysed by Raman spectroscopy. It was found that the temperature of the electrolysis affects current efficiency of the DC and PC electrodeposition. The frequency of pulse electrodeposition alters the morphology of the Ni–W alloy coatings. There was evidence of the positive influence of increased tungstate concentration in the electrolyte on corrosion resistance of the Ni–W alloy coatings.

The occurrence of bromate and perbromate on BDD anodes during electrolysis of aqueous systems containing bromide: first systematic experimental studies

Abstract: Bromide electrolysis was carried out on laboratory-scale cells in the range of 1–1,005 mg [Br−] dm−3 using boron-doped diamond (BDD) anodes. These studies were part of fundamental research activities on drinking water electrolysis for disinfection. Synthetic water systems were mostly used in the experiments, which varied the temperature between 5 and 30 °C, the current density between 50 and 700 A m−2, and the rotation rate of the rotating anode between 100 and 500 rpm (laminar regime). Hypobromite and bromate were found as by-products, as expected. Bromite was not detected. Higher bromate levels were formed at higher current density, but no clear relationship was observed between bromate concentration and the rotation rate or temperatures between 5 and 30 °C. Bromate yields higher than 90% were found at higher charge passed. Perbromate was found as a new potential synthesis or disinfection by-product (DBP), but no perbromate was detected at the lowest bromide concentrations and under drinking water conditions. The perbromate yield was about 1%, and somewhat lower when bromate was used as a starting material instead of bromide. At a temperature of 5 °C more perbromate was detected compared with experiments at 20°. Approximately 20 times more perchlorate was formed compared with perbromate formation in the presence of chloride ions of equimolar concentration. State of mechanistic considerations is presented and a mechanism for perbromate formation is proposed. The reaction from bromate to perbromate was found to be limited that is in contrast to the earlier studied chlorate-to-perchlorate conversion. In the measured concentration range, reduction processes at the mixed oxide cathode showed a much higher impact on the resulting concentration for perbromate than for bromate.

Characterisation of a electrochemical hydrogen pump using electrochemical impedance spectroscopy

Abstract: Electrochemical hydrogen pumps are electrochemical devices which are used for hydrogen purification and pressurization purposes. In such cells, gaseous hydrogen is oxidized at the anode and released at the cathode. Results presented in this paper are related to the characterization and optimization of a proton-exchange membrane (PEM) hydrogen pump using electrochemical impedance spectroscopy (EIS). Only the case of hydrogen purification is considered here. Current–voltage characteristics have been measured. The kinetics and efficiency of the cell have been investigated using EIS. The roles played by the cell structure (in particular by the ion-exchange polymer content in the electro-catalytic layers) and by different operating parameters (the cell temperature, the relative humidity and the partial pressure of hydrogen) on the overall process efficiency have been evaluated and are discussed.

Electrochemical treatment of water containing chlorides under non-ideal flow conditions with BDD anodes

Abstract: In this work a undivided parallel plate cell equipped with boron doped diamond (BDD) anode was tested as electrochemical reactor for disinfection of water. Two configurations were adopted: a single pass configuration (SPC) and a recirculated configuration (RC) in which also a reservoir was inserted in the hydraulic circuit. In both the experimental configurations the system worked in continuous mode with a flow rate ranging from 0.05 to 0.42 dm3 min−1; in the RC the recirculating flow rate ranged from 0.45 to 6 dm3 min−1. Thermostated (25 °C) galvanostatic electrolyses were carried out with aqueous solutions containing 100 mg dm−3 of chloride ions: values of current density from 2.5 to 5.0 mA cm−2 were used. Steady state data revealed that active chlorine and chlorate ions were the main oxidation products. Particular attention was paid to the hydrodynamics both for SPC and RC: pulse-response curves were experimentally obtained with an inert tracer, and the behaviour of the system was interpreted by models based on a combination of ideal flow reactors, bypass flow elements, and dead zones. The hydrodynamic models were utilized to predict the outlet concentration of the electrolysis products. A good agreement between model predicted and experimental data was obtained for a wide range of experimental conditions. Preliminary disinfection tests were then performed using Escherichia coli as model microorganism. Results were discussed in terms of both disinfection efficiency and by-products formation.