Study of the performance of secondary alkaline pasted zinc electrodes

Calcium zincate was prepared by a chemical coprecipitation method and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The electrochemical performance of pasted zinc electrodes with bismuth and calcium additives was investigated by the charge–discharge method. The addition of metallic bismuth powder improves the discharge performance of zinc electrodes due to the formation of an electronic conduction matrix. The calcium-containing zinc electrodes showed higher discharge capacity, less shape change and longer cycle lifetime. Moreover, zinc electrodes using calcium zincate as active material show better electrochemical performance than those with the physical mixture of zinc oxide and calcium hydroxide.     

The electrochemistry of Magnéli phase titanium oxide ceramic electrodes Part I. The deposition and properties of metal coatings

The electrodeposition of copper, gold, nickel, palladium and platinum onto Ebonex^® ceramic cathodes has been studied. It is demonstrated that good quality deposits may be obtained and that the kinetics of the deposition and dissolution of metals are similar at Ebonex^® to other common substrates (for example, Pt, C). In addition, the kinetics of some simple redox couples at coated and bare Ebonex^® ceramic electrodes are compared; it is confirmed that such electron transfer reactions are very slow on the bare Ebonex^® ceramic but when the surface is coated with a metal, the kinetics are similar to those on the bulk metal.This paper is dedicated to Professor Dr Fritz Beck on the occasion of his 60th birthday.     

Cyclic voltammetric study of zinc and zinc oxide electrodes in 5.3 M KOH

The behaviour of zinc and zinc oxide in 5.3 M KOH in the presence of alkaline earth oxides, SnO, Ni(OH)₂ and Co(OH)₂ was examined by cyclic voltammetry. The influence of the alkaline earth oxides was compared with additives of established effects (Bi₂O₃, LiOH, Na₂CO₃ and CdO). The alkaline earth oxide each exhibits a distinct behaviour towards zincate. Whereas, a single process of interaction with zincate was shown by CaO; two modes of reaction were obtained with SrO and BaO. Solid solution formation was noticed with BeO and MgO. The other additives forming solid solution with ZnO were CdO, SnO. The ionic sizes of Ni(OH)₂ and Co(OH)₂ allow solid solution formation with Zn(OH)₂. Both Bi₂O₃ and Na₂CO₃ enter into complexation with zincate. LiOH forms two distinct zincates, of which one is an oxo zincate leaching the `hydroxyl' functionality. Cyclic voltammetry revealed the deposition of the oxide/hydroxide additives as metal prior to the onset of zinc deposition and the potential range for this additive metal deposition is almost the same for different additives (SnO, CdO, Ni(OH)₂). The beneficial action of these additives to zinc alkaline cells is associated with a substrate effect. The implication of this electrocatalytic deposition of metals on a zinc oxide electrode is also discussed.     

The electrochemistry of partially discharged Planté electrodes

The electrochemistry of partially discharged Planté electrodes has been investigated. The reduction of partially discharged electrodes continues in the manner expected for a crystallization and growth limited electrode process. The oxidation of partially discharged Planté electrodes is less well defined and it appears that the effects due to nucleation of lead sulphate are removed by the initial discharge from the fully charged condition.Nomenclature i current - Z number of electrons transferred - F Faraday - M molecular weight - density - h height of nucleus - t time - A rate of nucleation - k chemical rate constant - N ₀ initial number of nuclei - i _m current maximum - t _m time at current maximum All potentials in this paper are referred to this reference electrode system.     

Microwave-electrochemical formation of colloidal zinc oxide at fluorine doped tin oxide electrodes

Colloidal ZnO is obtained during microwave-enhanced electrochemical deposition experiments from an aqueous solution containing 0.1 M Zn(NO₃)₂ and 0.02 M H₂O₂ via repetitive negative going potential cycles from 0.3 to −0.8 V vs. SCE. The effects of temperature and temperature gradients on ZnO electro-formation at fluorine doped tin oxide (FTO) electrodes are investigated with both a conventional thermostated bath system (isothermal) and an in situ microwave electrochemistry system (non-isothermal). Mainly electrodeposition of ZnO is observed in uniformly heated stagnant solution and predominantly the electro-formation of ZnO colloid is observed in the presence of microwave-induced temperature gradients in a flowing solution. For the ZnO colloid prepared via microwave activation, SAXS data suggests an average particle radius of ca. 18 nm. The increase of ZnO nanoparticle concentration during repetitive potential scans is followed by photoluminescence spectroscopy. A possible mechanism for ZnO colloid formation during electrochemical reduction of H₂O₂ is suggested.     

The electrochemistry of gases at metallized membrane electrodes

The electrochemistry of four gases, hydrogen, nitric oxide, nitrogen dioxide and sulphur dioxide at metallized membrane electrodes is reported. It is shown that, as was the case with oxygen and carbon monoxide, it is possible by suitable choice of electrode potential, electrode metal and electrolyte to find conditions where the currents are determined by the rate of diffusion of the electroactive species through the membrane. The experimental data are used to estimate values for the diffusion coefficient and solubility of the gases in the membrane material and the relevance to the design of environmental monitors of these experiments with high partial pressures of gases is discussed.     

Electrochemical cycling of pasted antimonial lead electrodes (positives)

The behaviour of Pb-5% Sb positives during electrochemical cycling experiments is followed using a combination of linear sweep voltammetry and potentiostatic pulse experiments. The poor charge acceptance of antimonial lead is discussed in terms of the morphology of the lead sulphate crystals. A comparison is made between unpasted and pasted Pb-Sb electrodes.     

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.     

The influence of different factors on the kinetics of potentiostatic forming of pasted positive lead electrodes

The influence of such factors are the surface active material, H₃BO₃ and mixing of H₂SO₄ on the potentiostatic forming of positive lead electrodes with the production paste was investigated. The potentiostatic forming of pasted positive plates with 4PbO.PbSO₄ has been examined.     

Dry sliding wear of zirconia-toughened alumina with different metal oxide additives

Tribological behaviour of zirconia-toughened alumina (ZTA) with different metal oxide additives was studied. Solid oxide lubricants (MO_x; M = Cu, Ti, Mg, Zn, Mn) were added in small quantities (∼8–11 wt%) to provide a self-lubrication action and thereby to decrease the coefficient of dry friction. Dry mixed ceramic composites powders were compacted and pressureless sintered at different temperatures. Densification studies show that near full densities (>97%) were obtained for ZTA ceramic containing both TiO₂–CuO and TiO₂–MnO₂ at 1450 °C. Phase and qualitative compositional analysis was done using X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS). Tribological behaviour of the various ZTA composites was tested by dry sliding the different specimens against SiC abrasive grit paper at a load of 50 N. The lowest specific wear rate of 9.2 × 10⁻⁵ mm³/N m and coefficient of friction of 0.35 were observed for the ZTA ceramic composite with TiO₂–MnO₂. The basic wear mechanisms were abrasion and grain pullout as corroborated from scanning electron microscopy (SEM) images.     

Functionalizing nanocrystalline metal oxide electrodes with robust synthetic redox proteins

De novo designed synthetic redox proteins (maquettes) are structurally simpler, working counterparts of natural redox proteins. The robustness and adaptability of the maquette protein scaffold are ideal for functionalizing electrodes. A positive amino acid patch has been designed into a maquette surface for strong electrostatic anchoring to the negatively charged surfaces of nanocrystalline, mesoporous TiO(2) and SnO(2) films. Such mesoporous metal oxide electrodes offer a major advantage over conventional planar gold electrodes by facilitating formation of high optical density, spectroelectrochemically active thin films with protein loading orders of magnitude greater (up to 8 nmol cm(-2)) than that achieved with gold electrodes. The films are stable for weeks, essentially all immobilized-protein display rapid, reversible electrochemistry. Furthermore, carbon monoxide ligand binding to the reduced heme group of the protein is maintained, can be sensed optically and reversed electrochemically. Pulsed UV excitation of the metal oxide results in microsecond or faster photoreduction of an immobilized cytochrome and millisecond reoxidation. Upon substitution of the heme-group Fe by Zn, the light-activated maquette injects electrons from the singlet excited state of the Zn protoporphyrin IX into the metal oxide conduction band. The kinetics of cytochrome/metal oxide interfacial electron transfer obtained from the electrochemical and photochemical data obtained are discussed in terms of the free energies of the observed reactions and the electronic coupling between the protein heme group and the metal oxide surface.     

Experimental study of combustion characteristics of nanoscale metal and metal oxide additives in biofuel (ethanol)

An experimental investigation of the combustion behavior of nano-aluminum (n-Al) and nano-aluminum oxide (n-Al₂O₃) particles stably suspended in biofuel (ethanol) as a secondary energy carrier was conducted. The heat of combustion (HoC) was studied using a modified static bomb calorimeter system. Combustion element composition and surface morphology were evaluated using a SEM/EDS system. N-Al and n-Al₂O₃ particles of 50- and 36-nm diameters, respectively, were utilized in this investigation. Combustion experiments were performed with volume fractions of 1, 3, 5, 7, and 10% for n-Al, and 0.5, 1, 3, and 5% for n-Al₂O₃. The results indicate that the amount of heat released from ethanol combustion increases almost linearly with n-Al concentration. N-Al volume fractions of 1 and 3% did not show enhancement in the average volumetric HoC, but higher volume fractions of 5, 7, and 10% increased the volumetric HoC by 5.82, 8.65, and 15.31%, respectively. N-Al₂O₃ and heavily passivated n-Al additives did not participate in combustion reactively, and there was no contribution from Al₂O₃ to the HoC in the tests. A combustion model that utilized Chemical Equilibrium with Applications was conducted as well and was shown to be in good agreement with the experimental results.     

Effects of different additives on bimetallic Au-Pt nanoparticles electrodeposited onto indium tin oxide electrodes

Bimetallic Au-Pt nanoparticles (Au-Pt_NPs) have been synthesized using an electrochemical reduction approach. The effects of the addition of different additives in the electrodeposition bath namely KI, 1-nonanesulfonic acid sodium salt and Triton X-100 have been investigated. The structural characterization of the bimetallic nanoparticles has been carried out using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), UV-vis spectroscopy, X-ray diffraction (XRD) and cyclic voltammetry (CV). The Au-Pt_NPs prepared in the presence of KI and Triton X-100 characterized by a relatively narrow size distribution as well as a higher particle density and surface coverage whereas no changes in the morphology were observed. These results suggest a dependence of the size and distribution of the bimetallic nanoparticles from the type and concentration of the additives employed.     

一种替代含铅助熔剂制备大尺寸氧化锌晶须方法的研究

以工业氧化锌(ZnO)粉为原料,助剂以四钛酸钾(K_2Ti_4O_9)为主,采用助熔剂法制备大尺寸针状ZnO晶须,并对其生长条件及影响因素进行了研究。主要采用X粉末衍射仪,能谱仪和超景深显微镜机等分析手段对ZnO晶须的结构和形貌进行了表征并进行了简单的探讨。结果表明,当物料配比为C∶ZnO(5%Na_2B_4O_9·10H_2O)∶K_2Ti_4-O_9=0.60g∶0.50g∶3.00g,其中K_2Ti_4O_9粒径为10目,反应温度为900℃,恒温时间120min,坩埚容量30mL时,便得到纯度高、颜色白、形貌均一、针体长度约20mm的ZnO晶须。     

一种替代含铅助熔剂制备大尺寸氧化锌晶须方法的研究

以工业氧化锌(ZnO)粉为原料,助剂以四钛酸钾(K_2Ti_4O_9)为主,采用助熔剂法制备大尺寸针状ZnO晶须,并对其生长条件及影响因素进行了研究。主要采用X粉末衍射仪,能谱仪和超景深显微镜机等分析手段对ZnO晶须的结构和形貌进行了表征并进行了简单的探讨。结果表明,当物料配比为C∶ZnO(5%Na_2B_4O_9·10H_2O)∶K_2Ti_4-O_9=0.60g∶0.50g∶3.00g,其中K_2Ti_4O_9粒径为10目,反应温度为900℃,恒温时间120min,坩埚容量30mL时,便得到纯度高、颜色白、形貌均一、针体长度约20mm的ZnO晶须。     

The anodic behaviour of porous zinc electrodes

The passivation of horizontal and vertical porous zinc (unamalgamated) electrodes in aqueous KOH solutions has been studied. The results are interpreted in terms of the formation of a soluble anodic product which decomposes within the electrode forming an insoluble deposit. The ohmic resistance of the insoluble anodic product provides the major component of the electrode polarization and determines the useful duration of discharge of the electrode.