The Bromine Electrode. Part I: Adsorption Phenomena at Polycrystalline Platinum Electrodes

A cyclic voltammetric study of the behaviour of Br^– and Br^– ₃ at Pt electrodes, in the potential range between hydrogen and oxygen evolution, is described. Different experiments were carried out, in the presence of Br^– and Br^– ₃, in which the ratio between the species has been kept constant and equal to 1. The halide concentration was varied between 4 × 10^–6 and 1 × 10^–3 and mol dm^–3, at constant ionic strength, in 1 M HclO₄ as well as in 1 M NaClO₄ adjusted to a pH of 2. Underpotential deposition of Br is observed at potentials as low as –0.125 V vs SCE. The adsorption parameters of Br species were determined from the adsorption/desorption peak pair in the hydrogen adsorption/desorption region, and from the oxide reduction peak data. In the absence of oxygen adsorption, a relatively high coverage of the electrode surface is attained. A Langmuir-type adsorption is observed under the different experimental conditions.     

Kinetic investigation of the chlorine reduction reaction on electrochemically oxidised ruthenium

The rate and mechanism of the electroreduction of chlorine on electrooxidised ruthenium has been investigated with focus on the effect of solution pH. Current/potential curves for the reduction process in solutions with constant chloride concentration of 1.0 mol dm⁻³ and varying H⁺ concentration have been obtained with the use of the rotating disk electrode technique (RDE). It was found that the chlorine reduction rate is highly inhibited in solutions with high H⁺ concentrations and that it can be satisfactorily described by the Erenburg mechanism, previously suggested for the chlorine evolution on RuO₂ and RTO. The expression of the kinetic current as a function of chlorine and H⁺ concentration was obtained by solving the elementary rate equations of the kinetic mechanism. The kinetic constants obtained from the correlation of the kinetic current expression to the experimental data were used to simulate the dependence of the surface coverages and elementary reaction rates on overpotential.     

Synthesis and electrode performance of layered nickel dioxide containing alkaline ions

Several polymorphs of layered nickel dioxide were prepared by using the chemical insertion of alkaline ions into Li_0.10NiO₂. We used aqueous AOH (A = Li, Na, K) solutions as reducing agents. Sodium and potassium insertion resulted in hydrated layered compounds that can be classified as γ-NiOOH with high crystallinity, while lithium insertion occurred without hydration. We discuss the coordination environment around the A⁺ ions for these inserted compounds. The thermal behavior, analyzed using high temperature (HT) X-ray diffraction (XRD) and thermogravimetric (TG) measurements, indicated that heating the hydrate at 150 °C yielded its dehydrate. The electrode performance of the nickelate was studied in lithium cells. We discuss the effect of interlayer water on cell rechargeability and the similarity between these nickelate and hydrated manganese dioxide (birnessite).     

Electrochemical study of a hydrogen diffusion anode-membrane assembly for membrane electrolysis

The membrane electrode assembly (MEA) studied was constituted with a gas diffusion electrode (E-TEK) impregnated with Nafion^® solution which was assembled with a Nafion^® 117 cation exchange membrane under heat and pressure. The MEA was used as anode in a membrane electrolysis (ME) cell with the objective to regenerate HCl and NaOH from NaCl. Current efficiency for hydrogen oxidation was determined and its value is 100%, which indicates that the only reaction occurring at the anode is the oxidation of hydrogen. Current-potential curves, recorded in different conditions, showed a linear variation in the range 0-3000 A m⁻² when hydrochloric acid concentration is below 2 mol dm⁻³. In this case, the overvoltage was shown to be mainly due to the ohmic drop in the membrane and in the layer where Nafion^® impregnation was performed. MEA overvoltage necessary to reach 3000 A m⁻² current density was about 0.12 V. For high HCl concentration (6-8 mol dm⁻³), the MEA overvoltage increased sharply with current density due to the adsorption of chloride anions on platinum catalyst.     

A glue method for fabricating membrane electrode assemblies for direct methanol fuel cells

We present a simple glue method for fabricating membrane electrode assemblies (MEA) for direct methanol fuel cells (DMFC). Rather than the conventional “dry” hot-pressing method that relies solely on hot-pressing at a high pressure and temperature to form a MEA, the “wet” method developed in this work introduces a binding agent, consisting of Nafion^® solution, between a polymer electrolyte membrane (PEM) and an anode/cathode. The introduced binding agent can provide a better adhesion and stronger binding force between a membrane and an electrode, thereby facilitating a better interfacial contact between the electrode and the Nafion^® membrane, which has been proved by scanning electron microscopy (SEM) analyses to the cross-sectional morphology of the MEA after long-term operation. The cell performance characterization showed the MEA fabricated by the glue method was more stable in cell performance than that fabricated by the conventional hot-pressing method. Cyclic voltammetry (CV) results also demonstrated the MEA fabricated by the glue method exhibited a higher electrochemical surface area (ESA) as a result of the improved interfacial contact between the Nafion^® membrane and the electrodes. Finally, the DMFC with the MEA fabricated by the glue method was characterized by the electrochemical impedance spectroscopy (EIS).     

Glass Furnace Boost Technology-Series/Parallel Switch

In the paper, the characters and fields were introduced for utilizing the Series/Parallel Switch (SPS). The circuit principle of the SPS technology was analyzed in detailed, explained and illuminated. We understood clearly the difference between SPS and single-phase transformator by the figure and table. Finally, it summarized that the main characters of SPS.     

Modification of glassy carbon electrode with multi-walled carbon nanotubes and iron(III)-porphyrin film: Application to chlorate, bromate and iodate detection

In this study, multi-wall carbon nanotubes (MWCTs) is evaluated as a transducer, stabilizer and immobilization matrix for the construction of amperometric sensor based on iron-porphyrin. 5,10,15,20-Tetraphenyl-21H,23H-porphine iron(III) chloride (Fe(III)P) adsorbed on MWCNTs immobilized on the surface of glassy carbon electrode. Cyclic voltammograms of the Fe(III)P-incorporated-MWCNTs indicate a pair of well-defined and nearly reversible redox couple with surface confined characteristics at wide pH range (2-12). The surface coverage (Γ) and charge transfer rate constant (k_s) of Fe(III)P immobilized on MWCNTs were 7.68 × 10⁻⁹ mol cm⁻² and 1.8 s⁻¹, respectively, indicating high loading ability of MWCNTs for Fe(III)P and great facilitation of the electron transfer between Fe(III)P and carbon nanotubes immobilized on the electrode surface. Modified electrodes exhibit excellent electrocatalytic activity toward reduction of ClO₃⁻, IO₃⁻ and BrO₃⁻ in acidic solutions. The catalytic rate constants for catalytic reduction of bromate, chlorate and iodate were 6.8 × 10³, 7.4 × 10³ and 4.8 × 10² M⁻¹ s⁻¹, respectively. The hydrodynamic amperometry of rotating-modified electrode at constant potential versus reference electrode was used for detection of bromate, chlorate and iodate. The detection limit, linear calibration range and sensitivity for chlorate, bromate and iodate detections were 0.5 μM, 2 μM to 1 mM, 8.4 nA/μM, 0.6 μM, 2 μM to 0.15 mM, 11 nA/μM, and 2.5 μM, 10 μM to 4 mM and 1.5 nA/μM, respectively. Excellent electrochemical reversibility of the redox couple, good reproducibility, high stability, low detection limit, long life time, fast amperometric response time, wide linear concentration range, technical simplicity and possibility of rapid preparation are great advantages of this sensor. The obtained results show promising practical application of the Fe(III)P-MWCNTs-modified electrode as an amperometric sensor for chlorate, iodate and bromate detections.     

Characterization of boron-doped diamond electrodes by electrochemical impedance spectroscopy

Charge transfer on boron doped diamond (BDD) electrodes was studied by cyclic voltammetry and electrochemical impedance spectroscopy. The diamond films of 5 μm thickness and boron content between 200 ppm and 3000 ppm were prepared by the hot filament CVD technique on niobium substrate and mounted in a Teflon holder as rotating disk electrodes. The electrochemical measurements were carried out in aqueous electrolyte solutions of 0.5 M Na₂ SO ₄ + 5 mM K₃[Fe(CN)₆]/K₄[Fe(CN)₆]. Significant deviation in the redox behaviour of BDD and active Pt electrodes was indicated by a shift of the peak potentials in the cyclic voltammograms with increasing sweep rate and lower limiting diffusion current densities under rotating disk conditions. In the impedance spectra an additional capacitive element appeared at high frequencies. The potential and rotation dependence of the impedance spectra can be described quantitatively in terms of a model based on diffusion controlled charge transfer on partially blocked electrode surfaces. Direct evidence for the non-homogeneous current distribution on the diamond surface was obtained by SECM measurements.     

Air electrode supported manganese electrocatalysts for neutral electrolyte magnesium air cell

The catalysts of air electrode were prepared by sintering the active carbon loaded with manganese nitrate and potassium permanganate at 360 °C The air electrode was made up of a catalyst layer, a waterproof and gas-permeable layer, a current collecting substrate and a second waterproof and gas-permeable layer. The cell was assembled by the air electrode, pure magnesium anode and 10% NaCl solution used as electrolyte. The microstructures of air electrodes before and after discharging were characterized by SEM. The electrochemical behaviors of the air electrodes were determined by means of polarization curves, volt-ampere curves and constant current discharge curves. The polarization voltage of air electrode is—173 mV (vs SCE) at the current density of 50 mA/cm². The air electrodes exhibits good activity and stability in neutral electrolyte. The magnesium-air cell could work at 5 W for more than 7 h.     

复合掺杂Nd（III）和Zn（II）非晶态Ni（OH）2电极活性材料的制备及其表征

以NiSO4、ZnSO4和Nd（NO3）3为原料,采用共沉淀快速冷冻法制备出了复合掺杂稀土Nd（III）和Zn（II）的非晶态氢氧化镍粉体材料。测试发现：样品材料微结构无序性强,结晶水含量较高。将样品材料制备成镍电极并组装成MH—Ni电池,在80mA／g恒电流充电5．5h、40mA／g恒电流放电、终止电压为1．0V的充放电制度下,复合掺杂6％Nd（III）和6％Zn（II）样品材料电池的放电平台为1．2624V,放电比容量为343．12mAh／g,远高于目前应用的B-Ni（OH）2电极活性材料的放电比容量。