Electrolytic preparation of magnesium perchlorate

The electrochemical preparation of magnesium perchlorate from magnesium chlorate employing a platinum anode and a rotating stainless steel cathode is described. The effect of electrolyte concentration, cathode and anode current densities, pH and temperature of the electrolyte and cathode rotation on current efficiency for the preparation of magnesium perchlorate was studied. A maximum current efficiency of 65–72% was achieved. Based on the results obtained on the laboratory scale, a 100 A cell was designed, fabricated and operated.     

In‐situ Preparation of a Porous Copper Based Nano‐Energetic Composite and Its Electrical Ignition Properties

In this paper, the in‐situ preparation and characterization of a porous copper‐sodium perchlorate energetic nano‐composite (PCu/NaClO₄) and its electrical ignition properties are presented. Porous copper was in‐situ produced by electro‐deposition on a Ni/Cr alloy wire, which acts as a cathode during the electro‐deposition. The PCu/NaClO₄ nano‐composite was produced by dipping the bridge with porous copper into a saturated sodium perchlorate acetone solution. SEM, EDS, and XRD were used to characterize the composite and DSC was used to study the thermal decomposition of the composite. The copper grain size was reduced by using additives such as CTAB in the electrolyte. The PCu/NaClO₄ nano‐composite on the bridge can be ignited by feeding a current through the bridge and the ignition delay time and electrical ignition sensitivity were measured.     

Performance characteristics of organic–inorganic composite electrodes in magnesium reserve batteries

Electrochemical characteristics of m-dinitrobenzene (m-DNB) based composite cathode materials involving compounds such as AgCl, TiO₂, HgO and CuCl have been investigated and (Mg AZ31 alloy anode) as an activated battery system using 2 M magnesium perchlorate aqueous electrolyte. The concentration of the composites has been optimized so as to obtain high electrochemical performance of Mg/m-DNB reserve batteries through constant current discharge studies. Mg/m-DNB cells containing 5-wt % of HgO when discharged at current density of 2.1 mA cm⁻² delivered 5.3 Ah capacity corresponds to a columbic efficiency of 97% as compared to the cells without composite.     

Electrodeposition of chromium from Cr (III) electrolytes in the presence of formic acid

Chromium coatings deposited from sulphate, chloride and perchlorate electrolytes based on the [Cr(H₂O)₄(HCOO)]²⁺ complex ion were investigated. The current efficiency reached 30% in the case of chloride electrolyte for various current densities in the range 4–10 A dm^-2 depending on pH. Such a large current efficiency is due to the catalytic effect of the chloride ions on the electroreduction of the chromium complex to metallic chromium. Deposition of chromium from sulphate electrolyte took place with a current efficiency of 16% which rose for higher pH and lower current densities. Semi-bright and bright coatings with thickness of approximately 10m of good adhesion to a copper electrode were deposited from chloride and sulphate electrolytes.     

A new magnesium — air cell for long-life applications

A novel type of magnesium-air primary cell has been evolved which employs non-polluting and abundantly available materials. The cell is based on the scheme Mg/Mg(NO₃)₂, NaNO₂, H₂O/O₂(C). The magnesium anode utilization is about 90% at a current density of 20 mA cm^–2. The anode has been shown to exhibit a low open-circuit corrosion, a relatively uniform pattern of corrosion and a low negative difference effect in the electrolyte developed above as compared to the conventional halide or perchlorate electrolytes. In the usual air-depolarized mode of operation, the cell has been found to be capable of continuous discharge over several months at a constant cell voltage of about 1 V and a current density of 1 mA cm^–2 at the cathode. The long service-life capability arises from the formation of a protective film on the porous carbon cathode and fast sedimentation of the anodic product (magnesium hydroxide) in the electrolyte. The cell has a shelf-life in the activated state of about a year due to the low open-circuit corrosion of the anode. These favourable features suggest the practical feasibility of developing economical, long-life, non-reserve magnesium-air cells for diverse applications using magnesium anodes with a high surface area and porous carbon-air electrodes.     

Electrocatalytic reduction ofo andm-nitroanilines at a Ti/ceramic TiO2 cathode

Galvanostatic reduction ofo andm-nitroanilines to the corresponding phenylenediamines has been carried out in aqueous H₂SO₄ medium at a Ti/ceramic TiO₂ cathode under varying conditions of acid strength, current density and temperature. The best conditions for obtaining maximum yields of the corresponding diamines have been established. Results show higher current efficiency for diamine formation at a Ti/ceramic TiO₂ cathode in comparison with those obtained at a copper cathode under identical conditions, thus indicating the electrocatalytic nature of the former. Experiments on the re-use of the electrolyte have also been carried out, the results of which show that the yields of the corresponding diamines are not affected up to the fourth re-use of the electrolyte. Cyclic voltammetric studies on the reduction of these compounds confirm that the reduction of the nitro group is catalysed by Ti⁴⁺/Ti³⁺ redox species at the electrode.     

Electrochemical characteristics of LSCF-SDC composite cathode for intermediate temperature SOFC

A kind of composite cathode, La_0.58Sr_0.4Co_0.2Fe_0.8O_3−δ-Ce_0.8Sm_0.2O_2−δ (LSCF-SDC), was presented in this paper. The electrochemical performance of the cathode on the electrolyte of SDC and YSZ coated with a thin SDC (YSZ/SDC) layer was studied by electrochemical impedance spectroscopy (EIS) and cathodic polarization techniques for their potential utilization in the intermediate temperature solid oxide fuel cell (IT-SOFC). Also studied was the relationship between the electro-catalytic characteristics and the electrode microstructure. Results showed that the LSCF-SDC composite electrode performed better on the SDC electrolyte than on the electrolyte of YSZ/SDC. The polarization resistance, R_p, of the cathode on the SDC electrolyte was 0.23 Ω cm² at 700 °C and 0.067 Ω cm² at 750 °C, much lower than the corresponding R_p of the same cathode on the YSZ/SDC electrolyte. At 750 °C, the cathodic overpotential of the composite cathode on the SDC electrolyte was 99.7 mV at the current density of 1.0 A cm⁻².     

Role of Mo<Superscript>6+</Superscript> during nickel electrodeposition from sulfate solutions

The effect of Mo⁶⁺ on the current efficiency, deposit quality, surface morphology, crystallographic orientations and polarisation behaviour of the cathode during electrodeposition of nickel from sulfate solutions was investigated. Mo⁶⁺ did not have a significant effect on current efficiency over the concentration range 2–100 mg dm⁻³. However; a decrease in current efficiency by a magnitude of more than 20% was seen at 500 mg dm⁻³. The quality of the nickel deposit with reference to the visual appearance and contamination level varied with varying concentration of Mo⁶⁺; this was also reflected in the morphology and crystallographic orientations of the deposits. Addition of Mo⁶⁺ to the electrolyte introduced two new crystal planes i.e., (220) and (311). Depolarisation of the cathode was noted at lower concentrations of Mo⁶⁺ (2–40 mg dm⁻³) whereas polarisation of the cathode was observed at Mo⁶⁺ concentration >40 mg dm⁻³ .The effect of Mo⁶⁺ on parameters such as Tafel slope (b), transfer coefficient (α) and exchange current density (i ₀) were also determined.     

Behavior of diffusing elements from an integrated cathode of an electrochemical reduction process

The electrochemical reduction process for spent oxide fuel is operated in a molten salt bath and adopts an integrated cathode in which the oxides to be reduced act as a reactive cathode in the molten salt electrolyte cell. Heat-generating radioisotopes in the spent oxide fuel such as cesium and strontium are dissolved in the molten salt and diffuse from the integrated cathode. However, the behavior of the dissolved cations has not been clarified under an electrochemical reduction condition. In this work, the reduction potentials of cesium, strontium, and barium were measured in a molten LiCl-3 wt% Li₂O salt and their mass transfer behavior was compared with two current conditions on the cell. The concentration changes of the cations in the molten salt phase were measured and no significant differences on the dissolution behavior were found with respect to the current. However, under a continued current condition, the removal of the high heat-generating elements requires more time than the complete reduction of metal oxide due to the slow rate of diffusion.     

Conduction in Bi2O3-based oxide ion conductors under low oxygen pressure. I. Current blackening of the Bi2O3-Y2O3 electrolyte

The cathodic current blackening of Bi₂O₃-based oxide ion conductors was examined for the Bi₂O₃-Y₂O₃ electrolyte at low oxygen pressure. In air, more than 500 mA cm^–2 d.c. could be passed at 600° C without causing changes in the electrolyte itself. However, in argon gas, a limiting current of 3 mA cm^–2 was observed and the electrolyte was blackened at the cathode side. The limiting current was ascribed to control by the diffusion of oxygen gas at the cathode. The blackened oxide was found to consist of a mixture of Bi metal and Bi₂O₃-Y₂O₃ solid solution and to exhibit the equilibrium oxygen partial pressure almost corresponding to that of the Bi, Bi₂O₃ mixture.     

Study on energy consumption of Al2O3 coating prepared by cathode plasma electrolytic deposition

Al₂O₃ coatings with large specific surface were prepared on cast nickel-based superalloy K418 by cathode plasma electrolytic deposition (CPED) in aqueous solutions at different concentrations. The significance of energy consumption and a simple calculation method during CPED were proposed, and the influence of electrolyte concentration on current density-voltage curve, energy consumption, and microstructure of coatings were studied. It was found that increasing the concentration of electrolyte can effectively reduce the current density at the initial stage while prolonging the deposition time and stepping up the energy consumption of whole coating preparation. The morphology observation results showed that the pore size of Al₂O₃ coatings enlarges with the increase of the concentration, and the optimum electrolyte concentration is 0.5–1 mol L^?1. Under this condition, the new method of oxidation pretreatment at 950 ℃ on samples for 30 min can efficiently decrease the current density during the early stage of preparation, which is beneficial to the deposition of complex-shaped samples with large size.     

Effect of GDC interlayer thickness on durability of solid oxide fuel cell cathode

Long-term performance degradation of solid oxide fuel cell (SOFC) cathode as a function of gadolinium doped ceria (GDC) interlayer thickness has been studied under accelerated operating conditions. For this purpose, SOFC half-cells with GDC interlayer thicknesses of 2.4, 3.4 and 6.0 µm were fabricated and tested for 1000 h at 900 °C under constant current density of 1 A/cm². The half-cells consisted of lanthanum strontium cobalt ferrite (LSCF)/GDC composite cathode, GDC interlayer, scandia-ceria stabilized zirconia electrolyte and platinum anode as a counter electrode. Area specific resistance (ASR) of the half-cells was continuously measured over time. Higher increase in ASR was observed for the half-cells with GDC interlayer thickness of 2.4 and 6.0 µm, which is attributed to higher strontium (Sr) diffusion towards electrolyte and to cathode/GDC interface delamination coupled with small Sr diffusion, respectively. However, half-cell with GDC interlayer thickness of 3.4 µm showed smaller degradation rate due to highly dense GDC interlayer which had less interfacial resistance and suppressed Sr diffusion towards electrolyte.     

Power Generation and Electrochemical Analysis of Biocathode Microbial Fuel Cell Using Graphite Fibre Brush as Cathode Material

To improve cathodic efficiency and sustainability of microbial fuel cell (MFC), graphite fibre brush (GFB) was examined as cathode material for power production in biocatalysed‐cathode MFC. Following 133‐h mixed culturing of electricity‐producing bacteria, the MFC could generate a reproducible voltage of 0.4 V at external resistance (R_EX) of 100 Ω. Maximum volumetric power density of 68.4 W m^–3 was obtained at a current density of 178.6 A m^–3. Upon aerobic inoculation of electrochemically active bacteria, charge transfer resistance of the cathode was decreased from 188 to 17 Ω as indicated by electrochemical impedance spectroscopy (EIS) analysis. Comparing investigations of different cathode materials demonstrated that biocatalysed GFB had better performance in terms of half‐cell polarisation, power and Coulombic efficiency (CE) over other tested materials. Additionally, pH deviation of electrolyte in anode and cathode was also observed. This study provides a demonstration of GFB used as biocathode material in MFC for more efficient and sustainable electricity recovery from organic substances.     

Synthesis of hydrogen peroxide in microbial fuel cell

BACKGROUND: Hydrogen peroxide (H₂O₂) is an important chemical product, and this study investigated its synthesis at the cathode of a microbial fuel cell (MFC) system using spectrographically pure graphite (SPG) rods as cathode electrode. RESULTS: Electrochemical methods showed that oxygen reduction reaction (ORR) on SPG mainly followed the two‐electron pathway yielding H₂O₂, while, the optimal condition for H₂O₂ production was in 0.1 mol L^?1 Na₂SO₄ electrolyte. When SPG was used as the cathodic electrode in the MFC system, H₂O₂ concentration reached 78.85 mg L^?1 after 12 h operation with an external resistance of 20 Ω (H₂O₂ production rate was 6.57 mg L^?1 h^?1). Coulombic efficiency, current efficiency and COD conversion efficiency were 12.26%, 69.47% and 8.51%, respectively. Repeated experiments proved this system had a stable operating performance. CONCLUSIONS: H₂O₂ was synthesized at the cathode of an MFC, and this study provides a proof‐of‐concept demonstration to realize the process of synthesizing H₂O₂ with wastewater. Copyright © 2010 Society of Chemical Industry     

Solid-state ionics-solid electrolyte cells with copper ion conductors

A solid electrolyte cell has been developed using a high copper ion conductivity solid electrolyte, 7CuBr·C₆H₁₂N₄CH₃Br, a copper anode, and a chalcogen cathode. The open-circuit voltages of the cells with sulphur, selenium, and tellurium as cathode materials were 0·448, 0·373, and 0·258 V, respectively, at 25° C. These cells yielded a current of several tens of microamperes at room temperature and several milliamperes at 114° C without appreciable polarization. An energy density of 4.5 Wh kg^–1 at room temperature was evaluated from the weights of the electrolyte and electrode materials for the cell using a selenium cathode in the discharge current density range 60–150A cm^–2.     

Electrochemical regeneration of ceric sulphate in an undivided cell

Ceric sulphate (0–0.5 m) was generated electrochemically from cerous sulphate slurries (0.5–0.8 m total cerium) in 1.61 m sulphuric acid, at 50 °C, using a bench scale differential area undivided electrochemical cell with an anode to cathode ratio of eleven. A cell current efficiency for Ce(IV) of 90% was obtained at an anode current density of 0.25 A cm^–2. An empirical model illustrates an increase in overall current efficiency for Ce(IV) with an increase in electrolyte velocity, an increase in total cerium concentration, and a decrease in the cell current. From separate kinetic studies on rotating electrodes, both, anode and cathode kinetics were found to be affected by cerium sulphate adsorption processes. Anode adsorption of cerous sulphate species leads to inhibited mass transfer and negatively affected current efficiencies for Ce(IV). Cathode adsorption of cerium sulphate is thought to be responsible for high cathode current efficiencies for hydrogen (93–100%). The dissolved cerous sulphate concentration increased with increasing ceric sulphate and total cerium sulphate concentrations resulting in slurries with a stable dissolved cerous sulphate concentration of as high as 0.851 m in 1.6 m H₂SO₄ at room temperature.     

Mineralization of the Pharmaceutical β-Blocker Atenolol by Means of Indirect Electrochemical Advanced Oxidation Process: Parametric and Kinetic Study

Atenolol is a β-blocker that can be found in urban wastewaters and which is not removed efficiently by conventional wastewater treatments. In the present study, electro-Fenton (EF) process was used to assess the degradation and mineralization of pharmaceutical atenolol in aqueous solutions. Electrolyses of 250 mL of atenolol solution (0.17 mM), at initial pH 3, were carried out in an undivided electrolytic cell in galvanostatic mode. Influence of material cathode (graphite, stainless steel, and platinized titanium), applied current (100–500 mA), sulfate dosage (0.01–0.5 M), and catalyst ferrous ions concentration (1–10 mM), on the oxidation efficiency was studied. Atenolol mineralization was monitored by COD dosage. Kinetic analysis indicated that atenolol mineralization followed a pseudo-first order model and the rate constant increased with rising current, ferrous ions concentration (up to 5 mM) and electrolyte concentration. Results showed that graphite cathode, 0.5 M Na₂SO₄ electrolyte, 0.3 A and 5 mM FeSO₄ catalyst were the best conditions for atenolol mineralization. In these optimal conditions, after 240 min more than 87% of the initial COD was removed. The corresponding current efficiency (CE) and specific energy consumption (SEC) were 22.33% and 0.194 kWh/kg COD, respectively. This latter corresponds to 0.078 kWh/m³ of treated wastewater.     

The recovery of chlorine from by-product hydrogen chloride Part 2: Molten metal cathode method

A new method of recovering chlorine from by-product hydrogen chloride is proposed and developed. According to the reaction Me+2HC1 = MeCl₂+H_o (Me = Metal) hydrogen chloride is reduced to give hydrogen and metal chloride. Gaseous hydrogen was drawn out from the reaction system and the metal chloride dissolved in the electrolyte, where it was electrolysed to give chlorine and metal using molten metal as a cathode. The metal was recovered on the cathode in a molten state and reused for the former reaction. Bench scale tests were also carried out, where zinc was used as a molten metal cathode and the cell capacity was about 50 A. The cell voltage was 6.5 V at 50 A (working temperature 560°C, distance between anode and cathode 5 mm) and in this case, the ohmic loss was about 70%. The current efficiency was about 90% (anodic current density 200 A/dm²) when the working temperature was 500°C and electrode distance between anode and cathode was 18 mm.This method seems very promising on the basis of the above-mentioned data.     

Performance and cycling of the iron-ion/hydrogen redox flow cell with various catholyte salts

A redox flow cell utilizing the Fe²⁺/Fe³⁺ and H₂/H⁺ couples is investigated as an energy storage device. A conventional polymer electrolyte fuel cell anode and membrane design is employed, with a cathode chamber containing a carbon felt flooded with aqueous acidic solution of iron salt. The maximum power densities achieved for iron sulfate, iron chloride, and iron nitrate are 148, 207, and 234 mW cm^?2, respectively. It is found that the capacity of the iron nitrate solution decreases rapidly during cycling. Stable cycling is observed for more than 100 h with iron chloride and iron sulfate solutions. Both iron sulfate and iron chloride solutions display moderate discharge polarization and poor charge polarization; therefore, voltage efficiency decreases dramatically with increasing current density. A small self-discharge current occurs when catholyte is circulating through the cathode chamber. As a result, a current density above 100 mA cm^?2 is required to achieve high Coulombic efficiency (>0.9).     

Electrochemical reduction of CO2 to formate at high current density using gas diffusion electrodes

The electrochemical reduction of carbon dioxide into formate was studied using gas diffusion electrodes (GDE) with Sn as electrocatalyst in order to overcome mass transport limitations and to achieve high current densities. For this purpose, a dry pressing method was developed for GDE preparation and optimized with respect to mechanical stability and the performance in the reduction of CO₂. Using this approach, GDEs can be obtained with a high reproducibility in a very simple, fast, and straightforward manner. The influence of the metal loading on current density and product distribution was investigated. Furthermore, the effect of changing the electrolyte pH was evaluated. Under optimized conditions, the GDE allowed current densities up to 200 mA cm^?2 to be achieved with a Faradaic efficiency of around 90 % toward formate and a substantial suppression of hydrogen production (<3 %) at ambient pressure. At higher current densities mass transport issues come into effect and hydrogen is increasingly produced. The corresponding cathode potential was found to be 1.57 V vs. SHE.