Rotating Cylinder Electrode Research Articles

Electrodeposition of Cu-Sn alloys from a methanesulfonic acid electrolyte containing benzyl alcohol

Deposition of Cu-Sn alloys from a methanesulfonic acid electrolyte containing small amounts of benzyl alcohol was investigated. Polarisation experiments (cylic and linear sweep voltammetry) were carried out using a rotating disc electrode to identify the reduction and dissolution processes that take place in the system and to determine the effect of the solution constituents on them. Potentiostatic deposition was performed onto a rotating cylinder electrode and the resulting deposits were charactised using SEM and XRD. The results showed that co-deposition of copper and tin is possible even at potentials less cathodic than tin discharge potential. The latter was attributed to the underpotential deposition of Sn2+ on a copper substrate. Smooth and compact deposits were obtained at various deposition potentials and Cu2+ concentrations, with Sn contents between 1.6 - 62.4 wt.%. Several stable phases, such as pure copper, α-CuSn, ϵ-Cu3Sn and η′-Cu6Sn5 phase, were detected at different operating conditions. Finally, it was found that BA increases the amount of tin in the deposit when Cu2+ concentrations in the solution is kept low, especially at high overpotentials. This additive also inhibits the formation of dendrites and reduces surface roughness.

(Keynote) Experimental Considerations for Electrocatalytic CO2 Reduction

Electrocatalytic reduction of CO2 has the potential to convert CO2 into carbon-based fuels by using renewable energy. While a wide range of electrocatalytic materials have been investigated, the process is still limited by poor reaction selectivity or large overpotentials. Hence many have studied the effects of surface oxides, crystal facets, and nanoparticles on the activity and selectivity of CO2 reduction. Others have also shown that the reaction is sensitive to conditions such as temperature, CO2 pressure, electrolyte buffer concentration and electrode porosity. These effects mean that it can be challenging to determine the underlying cause for differences in intrinsic catalytic behaviour [1,2], and thus it is important to understand the effect of experimental conditions on CO2reduction. Firstly, we will review the literature and our own experimental work which clearly highlight the importance of interfacial pH on the reaction [2-4]. It is well known that in weak buffers such as KHCO3, the pH at the surface of the cathode is significantly higher than the bulk due to the hydrogen evolution and CO2 reduction reactions. By conducting experiments over a range of KHCO3 concentrations (and thus different interfacial pH values), it is clear that this alters the selectivity and activity of CO2 reduction. As the hydrodynamics at the cathode surface will also alter interfacial pH, we have examined the effect of hydrodynamics on the CO2 reduction reaction using a Cu rotating cylinder electrode [5]. Given that the enhanced mass transport will also increase the CO2 concentration at the electrode surface [6], it seems clear that mass transfer effects should influence the reaction selectivity. We confirm that this is indeed an important factor and suggest that increasing mass transport not only decreases the interfacial pH (closer to bulk values) but also decreases the surface coverage of CO on the cathode (a key immediate during CO2 reduction), which ultimately lowers the current going to the CO2reduction reaction. As these experiments revealed the importance of both KHCO3 concentration and mass transport, we developed a numerical model to predict how the bulk electrolyte composition changes during long term electrolysis experiments. This model was validated against experiment data and shows that changes in the bulk electrolyte (ionic resistance, pH, CO2-electrolyte equilibria) can occur over the course of long-term electrolysis experiments. These changes can complicate the interpretation of long-term electrode behaviour as well as the control of the electrochemical process. From these findings, we suggest a range of strategies to improve the experimental aspects of electrochemical CO2reduction investigations. [1] A.S. Hall, Y. Yoon, A. Wuttig, Y. Surendranath, Mesostructure-Induced Selectivity in CO2Reduction Catalysis, Journal of the American Chemical Society 137 (2015) 14834-14837. [2] R. Kas, R. Kortlever, H. Yılmaz, M.T.M. Koper, G. Mul, Manipulating the Hydrocarbon Selectivity of Copper Nanoparticles in CO2Electroreduction by Process Conditions, ChemElectroChem 2 (2015) 354-358. [3] K.J.P. Schouten, E. Pérez Gallent, M.T.M. Koper, The influence of pH on the reduction of CO and to hydrocarbons on copper electrodes, Journal of Electroanalytical Chemistry 716 (2014) 53-57. [4] A.S. Varela, M. Kroschel, T. Reier, P. Strasser, Controlling the selectivity of CO2electroreduction on copper: The effect of the electrolyte concentration and the importance of the local pH, Catalysis Today 260 (2016) 8-13. [5] C.F.C. Lim, D.A. Harrington, A.T. Marshall, Effects of mass transfer on the electrocatalytic CO2 reduction on Cu, Electrochimica Acta (2017) in press. [6] N. Gupta, M. Gattrell, B. MacDougall, Calculation for the cathode surface concentrations in the electrochemical reduction of CO2 in KHCO3solutions, Journal of Applied Electrochemistry 36 (2006) 161-172. [7] K. Hara, A. Tsuneto, A. Kudo, T. Sakata, Electrochemical Reduction of CO2 on a Cu Electrode under High Pressure: Factors that Determine the Product Selectivity, Journal of The Electrochemical Society 141 (1994) 2097-2103.

Role of turbulent flow seawater in the corrosion enhancement of an Al–Zn–Mg alloy: an electrochemical impedance spectroscopy (EIS) analysis of oxygen reduction reaction (ORR)

The effect of flow on the corrosion of Al–14wt% Zn–8wt% Mg alloy in aerated synthetic seawater at ambient temperature was studied using a rotating cylinder electrode (RCE) under turbulent regime conditions by means of electrochemical impedance spectroscopy (EIS). The overall electrochemical corrosion process was found to be strongly influenced by the oxygen mass transfer process under turbulent flow conditions on the cathodic kinetics, driving to a significant increase in corrosion rate.At corrosion potential, Ecorr value, contributions from the anodic and cathodic processes involved were observed in the impedance diagrams. Instead, at a cathodic potential of −1.2V (sce), impedance measurements proved the predominance of the mass-transfer process for oxygen. A primary analysis of the impedance plots allowed to confirm such situation.

Luminescent electrospun nanofibers doped with organic dye: Toward a disentangled deposition

Luminescent organic nanofibers were fabricated by electrospinning the mixture of polar polymer polyacrylonitrile and rhodamine 6G dissolved in polar solvent dimethylformamide. SEM observations revealed that large volumes of nanofibers were successfully fabricated at the line velocity of 8 m s−1 with constant diameter along the whole length of nanofibers. Fluorescence optical microscopy revealed that homogeneously luminescent nanofibers were deposited on a rotating cylinder electrode with reduced entanglement, opening a novel usage as detached separate nanofibers: when intentionally embedded in commercial textiles, they will function as, for example, forensic tracking owing to the invisibility to naked eyes.

Electrochemical production of colloidal sulphur by oxidation of sulphide ion at lead coated-2- and -3-dimensional rotating cylinder anode surfaces

An electrochemical reactor with a rotating cylinder electrode is analysed for the production of colloidal sulphur by oxidation of sulphide ions with a concentration of 2gdm−3 in alkaline solutions at 80°C. The anode, coated with lead, was either a smooth cylinder or a three-dimensional one. The formation of polysulphides takes place in a wide range of potential of 0 to 1.2V, against saturated calomel electrode (SCE), at a constant current density, which is independent on the rotation speed for values higher than 100rpm. For the smooth anode the space time yield was 0.4kgm−3h−1. However, this parameter was increased 5 times in the potential range of 0.8V to 1.2V, vs. SCE, by using a three-dimensional structure with a bed depth of 8mm. The specific energy consumption was 11.7kWhkg−1 with a current efficiency near 100%. When the sulphide ions were replenished by dissolution of hydrogen sulphide from a gas stream a further increase of the space time yield to 3.6kgm−3h−1 was achieved. At the end of the experiments the solution was acidified forming colloidal sulphur particles of different shapes with an average size of 5μm.

Effect of dissolved copper ions on erosion–corrosion synergy of X65 steel in simulated copper tailing slurry

Erosion-corrosion is studied in the context of carbon steel pipelines transporting copper tailings with focus on the influence of dissolved copper ions present in the slurry. API 5L X65 steel is exposed to flow of slurry in rotating cylinder electrode (RCE) simulating flow conditions typical of a slurry pipe. Degradation is evaluated by means of electrochemical and gravimetric techniques, and the worn surfaces are analyzed by scanning electron microscope equipped with focused ion beam. It is found that 500ppm of dissolved copper ions increases the total weight loss by at least 30% and the increase is attributed to the combined contributions of corrosion and the erosion-corrosion synergy, with the underlying mechanism being galvanic coupling of steel with the reduced copper ions deposited on steel surface.

Corrosion Analysis of Super Duplex Stainless Steel Immersed in Seawater under Different Rotation Speeds

This work presents the influence of the turbulent flow in the corrosion of super duplex stainless steel (SDSS) samples immersed in synthetic seawater at room temperature and atmospheric pressure. In order to control the turbulent flow conditions, a rotating cylinder electrode (RCE) was used. Five different rotation rates were studied: 0 (or static conditions), 1000, 2000, 3000, 5000 and 7000 rpm. The electrochemical technique used in the corrosion study was potentiodynamic polarization curve. In addition, Eisenberg equation and analysis of dimensionless numbers were used to determine the limiting current density generated by the cathodic reaction. The results show that of the turbulent flow just has influence in the first rotational speeds of rotating cylinder electrode with an increment in Reynolds number. Cathodic current density obtained at static conditions is higher than densities obtained at 4000, 5000 and 7000 rpm. It is important to point out that at those last rotation speeds; the turbulent flow has not influence on the cathodic current density.

Electrochemical Study of Super Duplex Stainless Steel in Synthetic Seawater under Turbulent Flow Conditions

This work presents the study of the effects that the electrolyte and the turbulent flow have on the electrochemical kinetic of the super duplex stainless steel (SDSS) immersed in synthetic seawater at room temperature, atmospheric pressure under static and turbulent flow conditions. In order to control the hydrodynamic conditions, a rotating cylinder electrode was used (RCE) at four rotation rate (1000, 3000, 5000 y 7000 rpm). A typical three-electrode electrochemical cell was used. Cylindrical working electrodes made of SDSS were used in all experiments as working electrode, sintered graphite bar as auxiliary electrode and a saturated calomel electrode as reference. In order to analysis the corrosion phenomenon, the technique electrochemical impedance spectroscopy was used during 24 hours of the exposure time. According to the impedance technique, the corrosion rate decreased as the exposure time in seawater increased. In addition, the effect of the turbulent flow on corrosion process was really negligible. On the other hand, it is important to point out that the oxygen diffusion was the limiting process in the SDSS corrosion.

Effects of mass transfer on the electrocatalytic CO2 reduction on Cu

The effects of mass transfer on the electrocatalytic reduction of CO2 on a polycrystalline Cu rotating cylinder electrode were investigated. When the rotation rate was increased, the current efficiency toward CO2 reduction products decreased while that for the hydrogen evolution reaction increased. Furthermore, the product selectivity switched from CH4 to CO as the rotation rate was increased. This observation is generally inconsistent with the widely reported dependence of the electrocatalytic CO2 reduction on interfacial pH and CO2 concentration. As increasing the rotation rate improves mass transfer of species to and from the electrode surface, the interfacial pH becomes closer to the bulk pH while the interfacial concentration of CO2 at the electrode surface increases. However, increasing the rotation rate significantly decreased the CO2 reduction activity for constant current electrochemical CO2 reduction despite the increased availability of CO2 at the electrode surface. As the changes in interfacial pH and CO2 concentration with rotation rate cannot adequately explain the results, it is instead suggested that the enhanced mass transfer of dissolved CO away from the electrode surface at high rotation rates is the main reason behind the observed effects. We propose that this enhanced mass transfer of CO away from the electrode surface decreases the surface coverage of COads (due to the equilibrium between COads and dissolved CO at the electrode-electrolyte interface) and limits the further reduction of COads to hydrocarbons.

Application of the rotating cylinder electrode in molten LiCl-KCl eutectic containing uranium(III)- and magnesium(II)-chloride

The application of the rotating cylinder electrode (RCE) to molten LiCl-KCl eutectic mixtures for electroanalytical measurements is presented. This enabled the measurement of the limiting current which was observed to follow a linear trend with the rotational rate raised to 0.64–0.65 power on average, which closely agrees with existing RCE mass-transfer correlations. This is the first publication of electroanalytical RCE measurements in LiCl-KCl eutectic based molten salt mixtures, to our knowledge. These measurements were made in mixtures of molten LiCl-KCl eutectic containing UCl3 and MgCl2. Kinetic parameters were calculated for Mg2+ in LiCl-KCl eutectic. The exchange current density (io) of Mg2+ deposition varied with mole fraction (x) according to io(A cm−2) = 1.64x0.689. The parameters from RCE measurements were also applied in an electrochemical co-deposition model entitled DREP to detect and predict the deposition rate of U and Mg. DREP succeeded in detecting the co-deposition of U and Mg, even when Mg constituted less than 0.5 wt% of the deposit.

Erosion–corrosion behaviour of spark plasma sintered WC - 12Co in aggressive media

Erosion-corrosion is a complex degradation mechanism prevalent in multiphase system and material selection is a strategy to mitigate the destructive process. This study evaluates the candidature of spark plasma sintered WC-12Co in aggressive media and with sand particles via rotating cylinder electrode. Corrosion and hardness tests were carried out, and the cermets surface morphology was examined. General corrosion results from total mass loss showed the least degradation resistance in sulphuric acid which informed the recommendation of the alloy for industrial applications in simulated mine water and seawater. Localised attack parameters from cyclic potentiodynamic polarization and the micrographs were well correlated.

Electropolishing Behaviour of 73 Brass in a 70 vol % H3PO4 Solution by Using a Rotating Cylinder Electrode (RCE)

The electropolishing behaviour of 73 brass was studied by means of a rotating cylinder electrode (RCE) in a 70 vol % H3PO4 solution at 27 °C. Owing to the formation of a blue Cu2+-rich layer on the brass-RCE, an obvious transition peak was detected from kinetic- to diffusion-controlled dissolution in the anodic polarisation curve. Electropolishing was conducted at the potentials located at the transition peak, the start, the middle, and the end positions in the limiting-current plateau corresponding to the anodic polarisation curve of the brass-RCE. A well-polished surface can be obtained after potentiostatic electropolishing at the middle position in the limiting-current plateau. During potentiostatic etching in the limiting-current plateau, a blue Cu2+-rich layer was formed on the brass-RCE, reducing its anodic dissolution rate and obtaining a levelled and brightened brass-RCE. Moreover, a rod climbing phenomenon of the blue Cu2+-rich layer was observed on the rotating brass-RCE. This enhances the coverage of the Cu2+-rich layer on the brass-RCE and improves its electropolishing effect obviously.

Erosion-corrosion characteristics of spark plasma sintered pure nickel in simulated mine water

This study estimates the impact of shear stress and solid particles on the erosion-corrosion behaviour of spark plasma sintered pure nickel in simulated mine water. Rotating cylinder electrode system was employed to carry out the erosion-corrosion tests by weight-loss and electrochemical measurements. Corroded coupons were examined with the aid of microscope to assess the surface morphology. The gravimetry data was inconsistent with both weight gain and weight loss recorded. The impact of the hydrodynamic parameters was correlated with the pitting resistance and re-passivation behaviour of the sintered nickel, while the morphology results showed minimal general attack and severe localised corrosion.

Editors' Choice—A Methodology to Electrochemically Fabricate Fe-Ni-Co Nanotips

Fe-Ni-Co nanotips at the end of nanowires are fabricated at the interface of two Fe-Ni-Co regions via a combination of pulse electrodeposition, anodization and chemical etching. The conditions to electrodeposit and anodize the Fe-Ni-Co nanowires in polycarbonate templates were investigated with a rotating cylinder electrode (RCE) to inspect the polarization behavior of the thin film deposition. The wires were fabricated with three, consecutive electrochemical conditions, where first an Fe-Ni-Co wire segment is deposited, followed by an anodic potential to induce growth of an iron oxide thin film, and then followed by an applied, pulse cathodic current density to reduce the oxide and deposit another layer of Fe-Ni-Co. Upon etching, tips formed at the end of the last Fe-Ni-Co region, as evidenced by SEM. Potential transients during the last applied cathodic pulse current step, suggests that both the reduction of the oxide and metal occur, and that TEM/SAED confirm changes in the crystalline Fe-Ni-Co structure at the interfacial region between steps that contributes to the tip formation.

Electrochemical Removal of Nitrite Using an Activated Copper Rotating Cylinder Electrode

An undivided electrochemical reactor with a rotating cylinder electrode was examined for the removal of nitrite from a synthetic effluent, 30 mmol dm−3 NaNO2 in 0.1 mol dm−3 Na2SO4 as supporting electrolyte. Nitrite was reduced to ammonia at a copper cathode activated by a film of copper oxides, which was anodically produced at a potential of 18 mV against saturated calomel electrode, SCE, in the supporting electrolyte. The deactivation of the cathode was avoided by application of a periodic potential reversal, PPR, technique making the rotating electrode work 5 min as a cathode and 5 min in reactivation. The reactor performance was improved applying both strategies, cathode activation and use of a PPR procedure. The best results were obtained at a cathodic potential of −1.3 V vs. SCE, ammonia being the main product of the reduction of nitrite, obtaining a molar yield of 94% and a current efficiency of 59% with a nitrite conversion of 92% in an experiment of 1 h.

Simulations of Turbulent Flow, Mass Transport, and Tertiary Current Distribution on the Cathode of a Rotating Cylinder Electrode Reactor in Continuous Operation Mode during Silver Deposition

This work presents numerical simulations of turbulent flow, mass transport and tertiary current distribution on the cathode of a rotating cylinder electrode reactor (RCE) in a continuous operation mode. A configuration of a RCE with electrolyte inlet at the bottom and the electrolyte exit at the top was employed. Silver electrodeposition (12.15 mol m−3 (1300 ppm) Ag(I), 883.5 mol m−3 (23000 ppm) CN−, pH 13 and 150 mS cm−1 conductivity) was used as a test system. Bulk electrolysis in the RCE was performed at a constant potential of − 1.2 V vs. SCE, which ensured complete mass transport control. A constant volumetric inflow rate of 0.1 L min−1 at the RCE inlet was employed. CFD simulations were obtained solving the RANS equations with the standard k − ε turbulence model. For mass transport simulations, the averaged diffusion-convection equation was solved. For the simulations of tertiary current distribution, wall functions were employed. The tertiary current distribution on the RCE interface along the z-coordinate presented one border effect close to the electrolyte inlet, afterwards, even current distribution was obtained. The border effect is created by the abruptly silver concentration depletion at the electrolyte inlet. Good agreement between mass transport correlation and current distribution simulations with experimental data were attained.

Recovery of lead from simulated wastewater by using stainless steel rotating cylinder electrode electrochemical reactor

Recovery of lead from simulated wastewater by using stainless steel rotating cylinder electrode electrochemical reactor

Indirect Electrochemical Oxidation of Phenol Using Rotating Cylinder Reactor

Indirect electrochemical oxidation of phenol and its derivatives was investigated by using MnO2 rotating cylinder electrode. Taguchi experimental design method was employed to find the best conditions for the removal efficiency of phenol and its derivatives generated during the process. Two main parameters were investigated, current density (C.D.) and electrolysis time. The removal efficiency was considered as a response for the phenol and other organics removal. An orthogonal array L16, the signal to noise (S/N) ratio, and the analysis of variance were used to test the effect of designated process factors and their levels on the performance of phenol and other organics removal efficiency. The results showed that the current density has the higher influence on performance of organics removal while the electrolysis time has the lower impact on the removal performance. Multiple regressions was utilized to acquire the equation that describes the process and the predicted equation has a correlation coefficient (R2) equal to 98.77%. The best conditions were found to get higher removal efficiency. Removal efficiency higher than 95% can be obtained in the range of C.D. of 96-100 mA/cm2 and electrolysis time of 3.2 to 5 h. The behavior of the chemical oxygen demand (COD) mineralization denotes to a zero order reaction and the rate of reaction controlled by active chlorine reaction not by mass transfer of phenol towards the anode.

Electrodeposition of Ag-Ni-W Alloys

The induced codeposition of tungstate has been widely examined in the presence of nickel, cobalt and iron ions.1 On the other hand, more noble elements, such as Ag, can also induce the reduction of tungstate ions, but to a lesser extent, resulting in silver-rich alloys, by either electrodeposition2 or electroless deposition.3,4 Since both nickel and silver species can induce tungstate, the combined effect is investigated here. Electrodeposited Ag-Ni-W alloys from a stable, thiourea-citrate electrolyte, is examined using rotating cylinder electrodes. The deposit composition was determined with x-ray fluorescence, and used to calculate partial current densities. The increase of nickel ions to a Ag-W electrolyte did not further induce the reduction of tungstate ions, but inhibited it. To probe if the type of nickel species were responsible for affecting the tungsten rate, citrate concentration in the electrolyte was also varied. A significant factor in inducing tungsten was attributed to the presence of silver species compared to nickel species suggesting a thermodynamic control for tungstate reduction. Acknowledgements The authors wish to thank the AESF foundation and Tyco Electronics Connectivity Ltd. for partial support of this project.

Cathode depassivation using ultrasound for the production of colloidal sulphur by reduction of sulphur dioxide

The effect of ultrasound is analysed in order to avoid the passivation of the cathode as a result of blocking the electrode surface area by the sulphur produced from sulphur dioxide reduction. The experiments were carried out with a rotating cylinder electrode using either a single phase electrolyte which contained 5gdm−3 sulphur dioxide, or in a biphasic system processing a gas phase with 5% of sulphur dioxide in nitrogen. In both cases the supporting electrolyte was a 0.5moldm−3 H2SO4 solution. It was found that the application of ultrasound is very effective to detach the sulphur from the cathode surface and also to improve the reactor performance in comparison with a silent system. The best working conditions were achieved at cathodic potentials in the range of −0.6 to −0.7V. vs. SCE. Representative values for the figures of merit of the process are as follows: the space time yield was 1.4kgm−3h−1 and 0.7kgm−3h−1 for the biphasic and single phase systems, respectively. The current efficiency was 70%, 23kWhkg−1 the specific energy consumption and 91% the molar yield towards the sulphur production in the biphasic system at −0.7V. The volumetric mass-transfer coefficient was calculated from experimental data and compared with the theoretical prediction for a rotating cylinder electrode under silent condition, corroborating the beneficial effect of ultrasound for the production of colloidal sulphur. The particles have high purity and a spheroidal shape with an average diameter of 1.84μm, similar to those obtained without the application of ultrasound.