Structure and electrochemical properties of nickel hydroxide electrodes with cobalt additives

In this article,cobalt additives are introduced into nickel hydroxide electrodes by two incorporation methods—co-precipitated cobalt hydroxide during the nickel hydroxide synthesis or post-added CoO with nickel hydroxide. The results of X-ray diffraction, cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge tests indicate that (i) the diffraction peaks show a decrease in intensity and increase in the half peak breadths for Ni(OH)₂ with co-precipitated cobalt hydroxide; (ii) the electrochemical activity of nickel hydroxide can be improved by both incorporated cobalt and the effects of post-added CoO are more notable; (iii) CoOOH derived from post-added CoO is not stable in the KOH electrolyte when the potential of the Ni(OH)₂ electrode is lowered and its reduction product may be inactive, thus results in an irreversible capacity loss of nickel-metal-hydride battery after over-discharge-state storage.     

Studies concerning charged nickel hydroxide electrodes. II. Thermodynamic considerations of the reversible potentials

In this paper the thermodynamics of mixing are applied to account for the independence of the discharge potential of the nickel hydroxide electrode as a function of nickel oxidation state. The constant potential region is considered to arise from the formation of a pair of co-existing solid solutions having a composition predetermined by the magnitude of the interactions between the oxidized and reduced species. From considerations of the excess-energy terms, it can be shown for a symmetrical potential/ composition profile, that the constant potential region is identical with the standard potentialE ₀. The influence of asymmetry on the changes inE ₀ are discussed. Consideration has also been made of the influence of dissociation of oxidized and/or reduced species on the potential determining equations. The removal of n-type defects from the nickel(II)-rich phase on discharge is considered to be responsible for the observed secondary discharge plateau at potentials 300 mV more cathodic than normal. This non-equilibrium behaviour can be explained in terms of a mixed pn-semiconducting material.List of symbols E electrode potential at constant pH(V) - E ₀ standard electrode potential (V) - R the gas constant (J K^–1 mole^–1) - F the Faraday constant (C g-equiv^–1) - T the absolute temperature (K) - ^aH⁺ proton activity in the electrolyte - a _z activity of oxidized species z - a _y activity of reduced species y - _H+ chemical potential of the proton - _e chemical potential of the electron - _z ^o standard chemical potential of species z - _z chemical potential of species z - _y ^o standard chemical potential of species y - _y chemical potential of species y - _H,e chemical potential of the proton/electron pair - x _y orx mole fraction of reduced species y - x _z mole fraction of oxidized species z - G _M total free energy of mixing (J mole^–1) - G _R free energy of reaction (J mole^–1) - G _I free energy of mixing under ideality (J mole^–1) - G _E excess free energy (J mole^–1) - A,A _i andB _i interaction energy parameters (J mole^–1) - x _u mole fraction of y in co-existing phase u - x _v mole fraction of y in co-existing phase v - _y activity coefficient of undissociated reduced species y - _z activity coefficient of undissociated oxidized species z - _y ^± mean ionic activity coefficient of y - _z ^± mean ionic activity coefficient of z - _y activity coefficient of y in phase u - _z ^u activity coefficient of z in phase u - _y ^v activity coefficient of y in phase v - _z ^v activity coefficient of z in phase v - I current (A) - S cross-sectional area (cm²) - L conductor length (cm)     

Studies on the lithium and potassium uptake of nickel hydroxide electrodes

The extent of lithium and potassium uptake by both- and-Ni(OH)₂ electrodes has been studied by atomic absorption/emission spectroscopy. It was found that lithium ions are preferentially taken up into the bulk of the electrodes. The increase in the end-of-charge potential on constant current charging in lithiated electrolyte compared with pure potassium hydroxide is attributed to the bulk incorporation of lithium into the Ni(OH)₂ electrodes. X-ray studies have indicated no change in the phases present in the lithiated electrolytes either in the charged or discharged states. Cyclic voltametric measurements to 100 cycles showed no significant benefit due to lithium ions in terms of charge retention.     

纳米级氢氧化镍制备及电化学性能研究

介绍了一种通过合成草酸镍,进而生成β型纳米氢氧化镍的新的合成路线,从而达到大幅度提高镍氢电池正极放电容量的目的。使用X射线衍射（XRD）分析产品的晶型结构。从产品谱图中可以得知：由于特征衍射峰的出现可以判定该产品为β型,且由于（001）峰的宽化可以初步判定其为纳米级。通过透射电镜（TEM）可以看出产品粒径和形貌的具体特征,即产品为针状,长度为100～200 nm,直径为10～20 nm。将纳米级氢氧化镍制成电极,经过充放电测试可以发现电容量约为400 mA.h/g,远远高于球形微米级氢氧化镍的放电容量。     

Studies concerning charged nickel hydroxide electrodes. VII. Influence of alkali concentration on anodic peak positions

After repetitive potential cycling employing a high positive potential limit (>700 mV wrt Hg/HgO/ KOH) three anodic and one cathodic peak can be observed using aβ-Ni(OH)₂ starting material. Anodic peaks found at 425, 470 and 555 mV in 5 mol dm^?3 KOH shift to less positive potentials as the alkali concentration is increased appearing at 365, 410 and 455 mV respectively in 12.5 mol dm^?3 KOH. Four anodic processes involving various pairs of coexisting phases within both theβ andα-/γ-phase system can be identified as summarized below in order of increasing positive potential: Peak A $$\begin{gathered} Peak A{\text{ }}U_\alpha ^A \to {\text{ }}V_\gamma ^A \hfill \\ Peak B{\text{ }}U_\beta ^B \to {\text{ }}V_\beta ^B \hfill \\ {\text{ }}\mathop C\limits^ + {\text{ }}U_\alpha ^C \to {\text{ }}V_\gamma ^C \hfill \\ Peak E{\text{ }}V_\beta ^B \to {\text{ }}V_\gamma ^E \hfill \\ \end{gathered} $$ Observed shifts in anodic and cathodic peak potentials are consistent with the known influence of alkali and water activity on the reversible potentials for the above processes.     

An electrochemical DNA biosensor developed on novel multinuclear nickel(II) salicylaldimine metallodendrimer platform

An electrochemical DNA biosensor (EDB) was prepared using an oligonucleotide of 21 bases with sequence NH₂-5′-GAGGAGTTGGGGGAGCACATT-3′ (probe DNA) immobilized on a novel multinuclear nickel(II) salicylaldimine metallodendrimer on glassy carbon electrode (GCE). The metallodendrimer was synthesized from amino functionalized polypropylene imine dendrimer, DAB-(NH₂)₈. The EDB was prepared by depositing probe DNA on a dendrimer-modified GCE surface and left to immobilize for 1 h. Voltammetric and electrochemical impedance spectroscopic (EIS) studies were carried out to characterize the novel metallodendrimer, the EDB and its hybridization response in PBS using [Fe(CN)₆]^3−/4− as a redox probe at pH 7.2. The metallodendrimer was electroactive in PBS with two reversible redox couples at E°′ = +200 mV and E°′ = +434 mV; catalytic by reducing the E_pa of [Fe(CN)₆]^3−/4− by 22 mV; conducting and has diffusion coefficient of 8.597 × 10⁻⁸ cm² s⁻¹. From the EIS circuit fitting results, the EDB responded to 5 nM target DNA by exhibiting a decrease in charge transfer resistance (R_ct) in PBS and increase in R_ct in [Fe(CN)₆]^3−/4− redox probe; while in voltammetry, increase in peak anodic current was observed in PBS after hybridization, thus giving the EDB a dual probe advantage.     

Morphological and structural studies of nanoporous nickel oxide films fabricated by anodic electrochemical deposition techniques

Porous nickel oxide films are directly deposited onto conducting indium tin oxide coated glass substrates by cyclic voltammetric (CV), galvanostatic, and potentiostatic strategies in a plating bath of sodium acetate, nickel sulfate, and sodium sulfate. By tuning the deposition parameters, it is possible to prepare nickel oxide films with various morphologies and structures. Film formation relies on the oxidation of dissolved Ni²⁺ to Ni³⁺, which further reacts with the available hydroxide ions from a slightly alkaline electrolyte to form insoluble nickel oxide/hydroxide deposits on the substrate. A compact film with particularly small pores is obtained by CV deposition in a potential range of 0.7-1.1 V. A galvanostatically deposited film is structurally denser near the surface of the substrate, and becomes less dense further away from the surface. Interestingly, a potentiostatically deposited film has pores distributed uniformly throughout the entire film. Therefore, for obtaining a uniform film with suitable pore size for electrolyte penetration, potentiostatic deposition technique is suggested. In addition, except for CV deposition, the deposited films resemble closely to cubic NiO when the annealing temperature exceeds 200 °C.     

Effects of ball milling on the physical and electrochemical characteristics of nickel hydroxide powder

Nickel hydroxide powder was modified by the method of ball milling, and the physical properties of both the ball-milled and un-milled nickel hydroxide were characterized by scanning electron microscopy, specific surface area, particle size distribution and X-ray diffraction. It was found that the ball milling processing could obviously increase the surface area, decrease the particle and crystallite size, and reduce the crystallinity of β-Ni(OH)₂, which was advantageous to the improvement of the electrochemical activity of nickel hydroxide powder. Electrochemical performances of pasted nickel electrodes using the ball-milled nickel hydroxide as an active material were investigated, and were compared with those of the electrodes prepared with the un-milled nickel hydroxide. Charge/discharge tests showed that the ball-milled nickel hydroxide electrodes exhibited better performances in the charging efficiency, specific discharge capacity, active material utilization and discharge voltage. The improvement of the performances of β-Ni(OH)₂ through ball milling could be attributed to the better reaction reversibility, higher coulombic efficiency, higher oxygen evolution potential and lower electrochemical impedance, as indicated by the cyclic voltammetry and electrochemical impedance spectroscopy studies. Thus, ball milling was an effective method to modify the physical properties and enhance the electrochemical performances of nickel hydroxide powder for the active material of rechargeable alkaline nickel batteries.     

Copper(II) and nickel(II) complexes of pyridylamido hexadentate ligands: chemical speciation and spectroscopic studies

Two novel potentially hexadentate ligands, 1,10-(2-bis picolinamide)-4,7-diazadecane (pycdpnen) and 1,8-bis(2-picolinamide)-3,6-dioxaoctane (pycdado) have been synthesised as their hydrochloride salt; its protonation constants and the stability constants of the copper(II) and nickel(II) chelates have been determined by potentiometry. Amide groups deprotonation permits the formation of [MLH₋₁]⁺ species in all cases, while only pycdado gives [MLH₋₂] species. The solid complexes of copper and nickel with the neutral and the deprotonated ligands have been synthesised and characterised by IR, UV–Vis and ESR spectroscopy. The amidic groups are coordinated through the oxygen atoms in all solid complexes [ML](ClO₄)₂ (M=Cu²⁺ and Ni²⁺). The complexes obtained with the deprotonated forms of the ligands imply the coordination through the nitrogen atoms of the amidic groups.     

Structural modifications and electrochemical behaviour of the β(II)-Ni(OH)2/β(III)-NiOOH redox couple upon galvanostatic charging/discharging cycling

Among the various crystallographic phases of nickel hydroxide, the β-form is the most widely used as the active mass of the positive electrode of nickel-based secondary cells. However, the exact electrochemical and structural behaviour of the β(II)/β(III) redox system upon cycling and ageing remains to be clarified. This work reports the electrochemical behaviour under galvanostatic conditions of two non-doped Ni(OH)₂ samples having different initial crystallography and morphology. The evolution of these features is investigated as a function of the cycling conditions and more particularly as a function of the reduction state achieved on discharge. Electrodes cycled at the 1st discharge plateau show that charged/discharged active materials are very similar. However, when discharge is continued down to the so-called ‘second discharge plateau’, drastic changes are observed as an increase of the crystallisation degree and of the compactness of the Ni(OH)₂ powder. Some insights into the nickel electrode redox behaviour are given. It appears that the nickel electrode operates, upon charge, as a single-phase or as a mixed-phase system depending on the depth of discharge.     

Synthesis and characterizations of nanosized iron(II) hydroxide and iron(II) hydroxide/poly(vinyl alcohol) nanocomposite

Nanosized Fe(OH)₂ was synthesized by a coprecipitation method. Peaks between 500 and 1250 cm^?1 in Fourier transform infrared (FTIR) spectroscopy confirmed the presence of metal hydroxide stretching. X‐ray diffraction showed the suppressed crystalline system of Fe(OH)₂/aniline (ANI) due to the presence of a higher weight percentage of the dispersing agent, ANI. Thermogravimetric analysis implied that 75.5 wt % of residue remained up to 800°C. High resolution transmission electron microscope (HRTEM) analysis of Fe(OH)₂/ANI revealed that its size ranged from 10 to 50 nm with a rodlike morphology. Scanning electron microscopy implied that pristine Fe(OH)₂ had a nanotriangular platelet morphology, and a higher weight percentage of dispersing agent intercalated with Fe(OH)₂ had a spheroid with an agglomerated structure. The (UV–visible) spectrum implied the presence of Fe²⁺ ions at 326 nm and the existence of an amino group intercalated with Fe(OH)₂ showed a sharp peak at 195 nm, the intensity of which increased with increasing intercalated dispersing agent weight percentage. Photoluminescence showed that ANI‐intercalated Fe(OH)₂ showed a lesser intensity than the pristine Fe(OH)₂. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Study of the effects of nanometer β-Ni(OH)2 in nickel hydroxide electrodes

Nanometer β-Ni(OH)₂, showed by XRD, was prepared by our supersonic coordination-precipitation method, with an average grain size of about 50 nm by TEM. Proton diffusion coefficient of nanometer Ni(OH)₂ and spherical Ni(OH)₂ were 1.93 × 10⁻¹¹, and 5.50 × 10⁻¹³ cm²/s, respectively, with combination of chronocoulometry and cyclic voltammetry. Charge-discharge test of simulated batteries at 0.2 °C showed that addition of 8 mass% of our prepared nanometer Ni(OH)₂ in nickel hydroxide electrodes led to increases in cathode discharge specific capacity (CDSC) by nearly 10% and the chargeability of the electrode by about 50 mAh/g, and a decrease in polarization. Cycle life test of AA-type MH-Ni batteries discovered that effect of nanometer Ni(OH)₂ in increasing CDSC was more apparent for the first 100 cycles and not much difference was found after 350 cycles. XAS demonstrated a higher oxidation state of Ni in fully charged nanometer Ni(OH)₂ composite electrode (Nano-E) and a lower one in discharged Nano-E, compared with micrometer Ni(OH)₂ spherical electrodes (Micro-E). A larger structure distortion was found in Nano-E, offering more vacancies for proton diffusion. Thus conversion between Ni²⁺ and Ni³⁺ was promoted during the charge-discharge process, which was assumed to be one explanation of increasing CDSC with the addition of nanometer Ni(OH)₂.     

Synthesis, electrochemical, and photophysical studies of hexadecachlorinatedphthalocyaninato zinc(II)

Synthesis of a new symmetrical 1,4,8,11,15,18,22,25-octahexyloxy-2,3,9,10,16,17,23,24-octa-(3,5-dichlorophenyl)phthalocyaninato zinc(II), ZnPc, has been described and characterized by ¹H NMR, ¹³C NMR, MS, UV-Vis, and IR spectrometry. The newly prepared ZnPc is soluble in organic solvents and is not aggregated in solution. The photophysical properties were studied by steady-state absorption and emission, cyclic voltammetry, and nanosecond transient absorption techniques. The prepared ZnPc absorbs and emits at longer wavelengths compared to that of reported phthalocyanine derivatives. The electron-donating properties of the ZnPc have been examined by mixing it with the electron-accepting dicyanoperylene-3,4,9,10-bis(dicarboximide), PDICN₂. The recorded nanosecond transient spectra in the visible/near-IR region showed clearly the electron-transfer from the triplet-excited state of the ZnPc to PDICN₂ with a rate of 3.40 × 10⁸ M⁻¹ s⁻¹. Light absorption in a wide section of the solar spectrum, favorable redox properties, and the electron-transfer properties suggest usefulness of the ZnPc in light-energy harvesting and developing optoelectronic devices.     

Metal chelates with some cellulose derivatives. Part III. Synthesis and structural chemistry of nickel (II) and copper (II) complexes with carboxymethyl cellulose

Cu(II) and Ni(II) complexes with three grades of carboxymethyl cellulose (CMC) with different degrees of substitution have been synthesized and characterized. Probable structures of the metal complexes are inferred from the electronic and IR spectra, elemental analysis data and magnetic moment measurements. CMC coordinates with cu(II) and Ni(II) via the carboxymethyl and hydroxyl groups. The effect of the degree of substition of the CMC on the mode of chelation is discussed. Ni(II) complexes show an octahedral geometry around the metal ion and exhibit the formula [NiL · 4H₂O]Cl. Cu(II) complexes exist in the square planar form and have the formula Cu(L)₂, where L is uninegatively charged bidentate CMC ligand. The ligand field parameters of Ni(II) complexes are also evaluated.     

Electrocatalytic oxidation of chlorophenols by electropolymerised nickel(II) tetrakis benzylmercapto and dodecylmercapto metallophthalocyanines complexes on gold electrodes

This work reports on the use of nickel(II) tetrakis benzylmercapto (NiTBMPc) and dodecylmercapto (NiTDMPc) metallophthalocyanine complexes films on gold electrodes for the electrochemical oxidation of 4-chlorophenol (4-CP) and 2,4,5-trichlorophenol (TCP). Both NiTBMPc and NiTDMPc complexes were successfully deposited on gold electrodes by electropolymerisation. The films were electro-transformed in aqueous 0.1 M NaOH solution to the ‘O-Ni-O oxo’ bridged form. For both complexes, films with different thickness were prepared and characterised by electrochemical impedance and UV-vis (on indium tin oxide) spectroscopies and the results showed typical behaviour for modified electrodes with increasing charge transfer resistance values (R_p) with polymer thickness. The poly-Ni(OH)NiPcs showed better catalytic activity than their poly-NiPcs counterparts.     

Hydrothermal synthesis and structural characterization of one-dimensional coordination polymers of cobalt(II) and nickel(II) with 1,3,5-benzenetriacetic acid

Transition metal complexes [M(Hbta)(H₂O)₄] [M=Co(II) (1), Ni(II) (2), H₃bta=1,3,5-benzenetriacetic acid] have been prepared by reaction of H₃bta with the M(OH)₂ in water by hydrothermal method. The complexes were characterized by X-ray crystallography and electrospray mass spectrometry. The coordination geometries around Co(II) and Ni(II) atoms are both distorted octahedral with O₆ donor set. And the conformation of flexible triacid is cis, trans, trans in the title complexes.     

The electrochemical redox processes in methacrylate-based polymer electrolytes II. - Study on microelectrodes

The electrochemical behaviour of ferrocene was studied in different gel polymer electrolytes based on methyl, ethyl and 2-ethoxyethyl methacrylate and compared to the liquid aprotic solution (propylene carbonate). Voltammetric and chronoamperometric measurements on microelectrodes were conducted in order to describe the qualitative as well as quantitative behaviour of ferrocene in different conditions. Heterogeneous electron-transfer rate constants and diffusion coefficients of ferrocene in polymer electrolytes were estimated to be 1.1-7.8 × 10⁻³ cm s⁻¹ and 4-13 × 10⁻⁸ cm² s⁻¹ depending on the electrolyte composition. The influence of the polymer polarity, ferrocene concentration and level of polymer cross-linkage on the kinetics of ferrocene oxidation and its transport was discussed. The electrolytes with poly(2-ethoxyethyl methacrylate) exhibit the highest ionic conductivity (2-4 × 10⁻⁴ S cm⁻¹) as well as diffusion coefficient of ferrocene (1.3 × 10⁻⁷ cm² s⁻¹) in their structure.     

Electrochemical study of gold electrodes with anodic oxide films—II. Inhibition of electrochemical redox reactions by monolayers of surface oxides

The anodically first formed oxide on gold (oxide I) reaches two complete monolayers, ie 1.5 mC cm^?2 oxide charge, before a second type of oxide (oxide II) starts to form. Electrochemical redox reactions with redox couples such as the tris(o-phenantroline) ferrous/ferric ion couple and others which are well known to behave reversibly on bare gold are inhibited completely by gold covered with this critical coverage of two monolayers of oxide I. Up to nearly completion of this two monolayer coverage, the redox reactions behave reversibly. In the transition to the completion of two monolayers the reaction appears to be increasingly irreversible. This behaviour is explained on the basis of diffusion layer thickness, heterogeneous rate constants and the size and distribution of the active bare gold sites as well as of the inhibiting oxide covered sites on the surface. The inhibition by two complete monolayers of gold oxide seems to be of general character for redox couples independent of pH and electrolyte.     

Theory of porous electrodes—XVII. Correction for anodic and cathodic reaction rates for nickel hydroxide electrode

The theory of the porous nickel hydroxide electrode presented in the preceeding communication was corrected by considering the dependence of the anodic and cathodic reaction rates on the concentration of current carriers in the solid phase. The influence of this correction on the calculated E-t discharge curves is not sufficient to account for the obseerved discrepancies between these curves and the measured ones, which are probably due to phenomena on the contact between the current collector and the active material and among the particles of the electrode mix.     

Studies concerning charged nickel hydroxide electrodes IV. Reversible potentials in LiOH,NaOH, RbOH and CsOH

The variation of reversible potential E_r with log a_moh and has been studied for several nickel hydroxide/oxyhydroxide couples in various alkali hydroxides. Both activated and deactivated -phase couples show only a small dependence ofE _r with log_moh (or where known) in LiOH, NaOH, RbOH and CsOH electrolytes. The change in MOH content on oxidation/reduction is found to be about 0.1 mol MOH per two-electron transfer and is the same as found previously in KOH. These results confirm that the bulk oxidized -phase lattice is devoid of alkali cation although a small quantity may be adsorbed by the surface. On the other hand both activated and deactivated /-phase couples show a marked dependence of 0.45 mol MOH per two-electron transfer in LiOH, NaOH and RbOH (at concentrations > 0.5 m), also in good agreement with earlier data for KOH. On the basis of these results a general stoichiometry can be inferred for the -phase, namely M_0.32NiO₂ · 0.7H₂O where M=Li⁺, Na⁺, K⁺ or Rb⁺. Measurements imply that the Cs⁺ ion or the Rb⁺ ion at low concentration (<0.5 m) do not enter the interlayer structure of the -phase. This behaviour is thought to be related to the low Rb-O and Cs-O bond strengths afforded by the -phase structure.