Electrocatalytic oxidation of cyclohexanol on a nickel oxyhydroxide modified nickel electrode in alkaline solutions

Electrocatalytic oxidation of cyclohexanol was investigated with cyclic voltammograms, linear galvanic voltammograms and chronoamperometric responses on a nickel oxyhydroxide modified nickel (NOMN) electrode prepared by cycling the potential of a nickel electrode in the potential range of 0.1 V to 0.6 V (vs SCE) in alkaline solutions. It was found that cyclohexanol was oxidized by NiOOH generated with further electrochemical oxidation of nickel hydroxide during the anodic potential sweep. One of the products of the reaction between cyclohexanol and NiOOH was Ni(OH)₂ which was subsequently oxidized to NiOOH on the anode. This resulted in the appearance of a new anodic peak in cyclic voltammograms compared with the absence of cyclohexanol and this anodic peak strongly depends upon potential scan rates and cyclohexanol concentrations. In addition, the presence of cyclohexanol in NaOH solutions also lead to the decrease of anodic potentials in linear galvanic voltammetric responses and the increase of current densities in chronoamperometric curves. Results showed that the oxidation of cyclohexanol on the NOMN electrode follows the catalytic reaction mechanism.     

Ball milled cobalt oxyhydroxide coat on the surface of nickel hydroxide

Cobalt oxyhydroxide coat on the surface of nickel hydroxide particles is finished employing a simple ball milling process. The structure, morphology, and surface composition of the coated Ni(OH)₂ particles is characterized by using X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy tests. The results show that numerous strip-like particles of a mixture of Ni(OH)₂ and CoOOH aggregate on the surface of the Ni(OH)₂ particles, and a structure of β-Ni(OH)₂ is preserved. Compared to the Ni(OH)₂ electrodes with a mixed CoO additive, the electrochemical activity of the electrodes with ball milled CoOOH coat can be improved as shown by using electrochemical impedance spectroscopy test, thus resulting in charge–discharge and cycle life performance improvement of the electrodes.     

The cycling behaviour of zinc electrodes in a nickel oxide-zinc accumulator

The behaviour of porous zinc electrodes was investigated by monitoring the potential distribution along the surface of the electrode during charging and discharging in a nickel oxide-zinc battery. Impedance measurements of the zinc electrode were taken as a function of state-of-charge and of the cycle number. The composition of the electrode was varied with HgO and PbO additives. Shape change was observed for all electrodes. The observed potential distribution has led to the tentative explanation that the shape change phenomenon is caused by diffusion of zincate along the surface.     

Leaching of Raney nickel composite-coated electrodes

The changes in the morphology and the composition of Raney Ni composite-coated electrodes was investigated during leaching in concentrated NaOH aqueous solutions. The rate of hydrogen generated during leaching is increased by stirring the solution, raising the temperature and increasing the NaOH concentration to 6.09 M. The depletion of Al from the Raney Ni particles results in phase transformations and the metal/solution interfacial area increases with time. It is suggested that the electrodeposited nickel has a dominant influence on the hydrogen discharge since the electrocatalytic activity is practically independent of the leaching time.     

The electrochemical behaviour of polycrystalline nickel electrodes in different carbonate-bicarbonate ion-containing solutions

The dissolution and passivation of polycrystalline nickel in carbonate-bicarbonate ion-containing solutions covering wide ranges of pH and electrolyte concentration were investigated by employing voltammetric, galvanostatic and potentiostatic transient techniques. Results obtained with a rotating disc electrode allow the competing reactions related to the active-passive transition to be distinguished through the influence of the potential sweep rate and the rotation speed on the electrochemical behaviour of the system at fixed concentrations of either carbonate or bicarbonate ion. The first oxidation level of nickel corresponds mainly to Ni(OH)₂ formation, the chemical dissolution of the surface layer and the precipitation of NiCO₃ and Ni(OH)₂. The partial removal of the prepassive layer is predominantly assisted by both the bicarbonate ion concentration and the electrode rotation. In the presence of chloride ions the formation of soluble Ni(II) species and NiCo₃ in the potential range of the first oxidation level appears to be enhanced. This effect can be interpreted by taking into account competitive adsorption processes at the base metal between Cl^– and OH^– ions.     

Direct electrochemical detection of pyruvic acid by cobalt oxyhydroxide modified indium tin oxide electrodes

An enzyme-free electrode was fabricated by anodic electrodeposition of cobalt oxyhydroxide film on an ITO electrode (CoO_x(OH)_y/ITO) for direct electrochemical detection of pyruvic acid (PA) in solution. Scanning electron microscopy (SEM) and atom force microscopy (AFM) were employed to characterize the morphology of CoO_x(OH)_y film. Cyclic voltammetry (CV) was used to investigate the electrochemical properties of PA on CoO_x(OH)_y/ITO in order to select the optimal potential for the chronoamperometric detection of PA. It was found that the CoO_x(OH)_y/ITO electrode served as an excellent PA sensor with a linear detection range of 1.00 μM to 1.91 mM, a detection limit of 0.55 μM, and a high sensitivity of 417.1 μA mM⁻¹ cm⁻². Moreover, the response time of CoO_x(OH)_y/ITO to PA is less than 10 s, which is the shortest for PA detection reported in literature using electrochemical method. These properties and the high stability of CoO_x(OH)_y/ITO made it a good candidate for developing electrochemical enzyme-free PA sensing device.     

Discharge behaviour of plane nickel hydroxide electrodes

Plane nickel oxide electrodes were prepared by electrochemical deposition of nickel hydroxide on flexible nickel strips. Compact and adherent deposits were obtained, with thickness up to 4 × 10^?3 cm. They were cycled in 6 M KOH solution, and owing to the flexibility of the supporting nickel strips, did not show detaching. The results obtained from galvanostatic discharge curves fit the Peukert equation iⁿt = constant, giving an n value of 1.23 for the 1 × 10^?3 cm thick film and a value of 1.10 for the 4 × 10^?3 cm think film. The diffusion coefficients of moving species are in the order of magnitude of 10^?5 ?10^?6 cm²s^?1; the rate of discharge does not seem to be limited by proton diffusion. The proton diffusion in solid phase is not the only factor to be taken into account in the discharge process; diffusion and migration OH^? and H₂O species play an important role in plane thick nickel oxide film discharge.     

Theory of porous electrodes—XVI. The nickel hydroxide electrode

A model of the positive plate of a nickel—cadmium accumulator is proposed, based on the known electrochemical behaviour of hydrated nickel oxides and on transport equations similar to those used previously for the cadmium electrode. The mathematical treatment of this model allows to predict the theoretical discharge characteristics, which are compared with those measured on a real electrode. A comparison of the calculated and measured discharge time suggests that the composition of the oxidised form is intermediate between NiO_1.5 and NiO_1.8.     

The preparation of high surface area nickel oxide electrodes for synthesis

A study of the electrodeposition of nickel onto copper and graphite is described; the objective was to prepare high surface area, i.e. microrough, but stable deposits which could be used as nickel oxide anodes in aqueous base. It is shown that such electrodes may be prepared by electrodeposition at a high current density (200 mA cm^–2) from a Watts bath and that they give useful apparent current densities for a model synthetic reaction, the oxidation of ethanol to acetic acid.     

The potentiodynamic response of polycrystalline nickel electrodes in 0.5mK2CO3

The electrochemical behaviour of nickel in 0.5 M K₂CO₃ is investigated by applying simple and combined potentiodynamic techniques in the potential regions of the Ni(OH)₂/Ni and Ni(III)/Ni(II) redox couples. The diffusion controlled hydrated NiCO₃ precipitation interferes with the electroformation of the Ni(OH)₂ prepassive layer. Both anodic and cathodic peak multiplicities are observed in the potential range of the Ni(III)/Ni(II) electrode. The presence of CO ₃ ^2– ions is tentatively associated with a change in the hydration of the composite Ni(OH)₂/NiOOH layer and eventually with HCOc ions coming out from the CO ₃ ^2– /HCO ₃ ^– equilibrium, which depends on the local change in pH produced during the corresponding anodic and cathodic reactions.     

Prediction of residual capacity in thin adsorbers

A simple reliable method to measure Residual Adsorption Capacity (RAC) of charcoal adsorbers on which a gas is physisorbed has been developed. The method consists of passing a pulse of weakly adsorbed gas(es) through the adsorption filter(s) and measuring the retention time. This retention time is then correlated to the residual adsorption capacity. In order to predict the retention time-RAC relationship for filters with various configurations and bulk densities, this pulse test was mathematically modeled. The numerical solution of the model involved estimating the transport rate parameters, using existing correlations and the moment technique. A perturbation analysis indicated that the accuracy of the model is closely associated with the estimates of adsorption equilibrium constant and the intraparticle diffusion coefficient of the test gas. The model is shown to be accurate in predicting the RAC of an adsorber under dry and humid conditions from a limited data set.     

The impedance of 23 Ah Ni-Cd cells with sintered electrodes: measurements in the range 10 kHz-0.001 Hz as an indication of residual capacity

Impedance measurements on 23 Ah Ni-Cd cells at various residual capacity levels are described. These have been made using non-inductive connections coupled directly to a potentiostat and a frequency response analyser. The capacitive reactance at 0.39 Hz provided the best residual capacity indicator.     

Degradation mechanisms of nickel oxide electrodes in zinc/nickel oxide cells with low-zinc-solubility electrolytes

Nickel oxide electrodes that suffered capacity degradation during extended cycling in zinc/nickel oxide cells were examined by a variety of chemical and physical techniques. Nickel hydroxyzincates, which have been speculated to cause such capacity degradation, were also examined. Powder X-ray diffraction experiments indicated that the intersheet distance between layers of turbostratic nickel hydroxide increased when zinc was incorporated. Photoelectron spectra (XPS) showed that this material is probably a mixture of NiOH)₂ and ZnO or Zn(OH)₂. Raman spectroscopy data also supported this conclusion. XPS indicated that the form of zinc in degraded nickel oxide electrodes is probably ZnO or Zn(OH)₂. Significant increases in resistivity were found in cycled nickel oxide electrodes, and optical microscopy provided visible evidence of mechanical damage during cycling. These results suggest that the observed capacity degradation was largely mechanical in nature, and not due to the formation of nickel-zinc double hydroxides, as had been reported by others. Cell-cycling experiments indicated that the mechanical degradation is largely irreversible.     

Photocurrents at irradiated mercury electrodes in solutions of nickel ions

The influence of concentration and potential on photocurrents produced at mercury electrodes in solutions of nickel ions have been investigated using a pulsed xenon lamp. It is concluded that the mechanism involves scavenging of hydrated electrons by the nickel ions followed by an oxidative regeneration, rather than the reduction of excited nickel ions.     

Performance improvement of pasted nickel electrodes with an addition of ball-milled nickel hydroxide powder

Spherical β-Ni(OH)₂ was modified by a low-cost method of normal ball milling (NBM), and the physical properties of both ball-milled and un-milled Ni(OH)₂ were characterized by transmission electron microscopy, specific surface area, particle size distribution and X-ray diffraction. It was found that NBM could obviously increase the surface area, decrease the particle and crystallite size, and reduce the crystallinity of β-Ni(OH)₂, which were advantageous to the improvement of the electrochemical activity of Ni(OH)₂. NBM also lowered the packing density and flowability of Ni(OH)₂, as revealed by the measurements of tapping density and angle of repose. Electrochemical performances of pasted nickel electrodes with an addition of ball-milled Ni(OH)₂ to spherical Ni(OH)₂ as the active material were investigated, and were compared with those of the pure spherical Ni(OH)₂ electrodes. Charge/discharge tests showed that ball-milled Ni(OH)₂ addition could enhance the charging efficiency, specific discharge capacity, discharge voltage and high-rate capability of the electrodes. This performance improvement could be attributed to a more compact electrode microstructure, better reaction reversibility and lower electrochemical impedance, as indicated by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. Thus, it was an effective method to modify the microstructure and improve the electrochemical properties of pasted nickel electrodes by adding an appropriate amount of ball-milled Ni(OH)₂ to spherical Ni(OH)₂ as the active material.     

Performance improvement of pasted nickel electrodes with multi-wall carbon nanotubes for rechargeable nickel batteries

Carbon nanotubes (CNTs) were employed as a functional additive to improve the electrochemical performance of pasted nickel-foam electrodes for rechargeable nickel-based batteries. The nickel electrodes were prepared with spherical β-Ni(OH)₂ powder as the active material and various amounts of CNTs as additives. Galvanostatic charge/discharge cycling tests showed that in comparison with the electrode without CNTs, the pasted nickel electrode with added CNTs exhibited better electrochemical properties in the chargeability, specific discharge capacity, active material utilization, discharge voltage, high-rate capability and cycling stability. Meanwhile, the CNT addition also lowered the packing density of Ni(OH)₂ particles in the three-dimensional porous nickel-foam substrate, which could lead to the decrease in the active material loading and discharge capacity of the electrode. Hence, the amount of CNTs added to Ni(OH)₂ should be optimized to obtain a high-performance nickel electrode, and an optimum amount of CNT addition was found to be 3 wt.%. The superior electrochemical performance of the nickel electrode with CNTs could be attributed to lower electrochemical impedance and less γ-NiOOH formed during charge/discharge cycling, as indicated by electrochemical impedance spectroscopy and X-ray diffraction analyses. Thus, it was an effective method to improve the electrochemical properties of pasted nickel electrodes by adding an appropriate amount of CNTs to spherical Ni(OH)₂ as the active material.     

Electrodeposition of copper and nickel on InBi alloy electrodes

Electrodeposition of copper and nickel was investigated on the 67–33 w/w InBi soft alloy, which has a low melting point (72°C). The electrochemical behaviour of this alloy was found to be similar to that of pure indium in a Watt's type bath. Direct and pulsed current techniques were compared. For copper, a current density ranging from 500 to 1000Am–2 was found to be suitable to obtain regular and shiny deposits at 25°C. For nickel, at 45°C, the current density range used was 500 to 1250Am–2 to obtain good deposits, that were not affected by hydrogen evolution. Pulsed and direct currents were found to be equally efficient. The main interest of electrodeposition on InBi alloy was the ease of removal of the alloy by simple melting, and consequently to make electrodes of unusual shapes which are normally difficult to produce industrially. Only a small amount of InBi alloy remained in the inner part of the deposit.     

DSA-泡沫镍电极电解法处理印染废水

采用泡沫镍材料作电解废水装置的阴极以提高单位电化学反应器体积的电流,使电极与废水界面之间的作用可在低电流密度下进行.用新型电极构成的电化学装置处理印染废水,研究过程的停留时间、施加的电流强度以及不同pH值对废水中的CODcr、汞和浊度去除效果的影响.结果表明电流强度增大,CODCr、汞和浊度的去除率均增加,最佳电流强度为1.0～1.2A;废水停留时间增加,各污染物的去除率增大,最佳停留时间约为20 min.     

Studies concerning charged nickel hydroxide electrodes. VI. Voltammetric behaviour for pre-cycled electrodes

In this study cyclic voltammetry/coulometry has been combined with oxygen volume measurements to identify the species giving the multiple anodic and cathodic peaks for a pre-cycled -Ni(OH)₂ starting material. A complex sequence of 1 and 2 electron transfer reactions involving several U/V and U/V coexisting phase pairs has been identified. This system is complicated by overlap of the various processes in some cases and also the chemical transformation of unstable -phases. As many as six anodic and four cathodic processes can be encountered depending on the charging history.     

Rhodium electrodeposition on nickel electrodes used for urea electrolysis

A procedure for the constant potential electrodeposition of rhodium onto nickel electrodes, the subsequent surface characterizations, and electrochemical evaluation is presented. The resulting Ni/Rh electrodes were evaluated for their activity as anode catalysts for the electro-oxidation of urea. A detailed procedure for the electrodeposition of Rh onto Ni foil is provided. It is shown that the electrocatalytic performance of Ni/Rh electrodes on the oxidation of urea in alkaline medium is primarily influenced by two electrodeposition parameters: the applied electrodeposition potential and the loading of Rh (mg?cm^?2). An optimization for electrocatalytic performance based on the electrodeposition potential and Rh loading is demonstrated. The effect of these parameters on visual finish, surface morphology, and crystal structure was also studied.