Liquid-phase synthesized mesoporous electrochemical supercapacitors of nickel hydroxide

Electrochemical supercapacitive (ES) properties of liquid-phase synthesized mesoporous (pore size distribution centered ∼12 nm) and of 120 m²/g surface area nickel hydroxide film electrodes onto tin-doped indium oxide substrate are discussed. The amounts of inner and outer charges are calculated to investigate the contribution of mesoporous structure on charge storage where relatively higher contribution of inner charge infers good ion diffusion into matrix of nickel hydroxide. Effect of different electrolytes, electrolyte concentrations, deposit mass and scan rates on the current-voltage profile in terms of the shape and enclosed area is investigated. Specific capacitance of ∼85 F/g at a constant current density of 0.03 A/g is obtained from the discharge curve.     

硫酸盐电铸镍内应力的影响因素

研究了NiSO4·6H2O质量浓度、NiCl2·6H2O质量浓度、温度和阴极电流密度等工艺参数对硫酸盐电铸镍层内应力的影响。通过铜箔阴极弯曲法半定量地测定了镍铸层的内应力,采用扫描电镜和X射线衍射表征了镀层在不同应力状态下的表面形貌和微观结构。结果表明,当NiSO4·6H2O质量浓度为100～150g/L时,其变化对内应力影响较大;镀液中氯离子浓度的增加会增大镀层内应力;低温和大电流密度条件下获得的镀层具有大的拉应力,高温小电流则有利于降低镀层的拉应力。     

Electrodeposition of nickel-BN composite coatings

Electrodeposition of nickel-boron nitride (Ni-BN) composites is carried out from a sulfamate bath containing up to 10 g/l of dispersed boron nitride particles with size 0.5 μm. Microhardness and wear resistance of the composites are investigated. Both the properties are influenced by the amount of incorporated boron nitride particles. Commercial surfactant containing alkyl-dimethyl-benzyl-ammonium saccharinate is used to stabilize the electrolyte: the effects on mechanical properties and structure of the electrodeposits are investigated. Morphology of the coatings and the effects of codeposited particles on metal matrix structure are reported.     

Fabrication of nickel oxide-embedded titania nanotube array for redox capacitance application

Titania nanotube array with an enlarged tube diameter of 110 nm and length of 700 nm was grown on titanium metal by a potentiostatic anodization in hydrofluoric acid-phosphoric acid-ethenyl glycol electrolyte. Nickel hydroxide was introduced into this titania nanotubes by either an electrodeposition-oxidation or hydrothermal process. Nickel oxide-titania composite was finally formed by heating treatment at 300 °C. Such a well-defined nanocomposite supported on titanium substrate was designed as a functional nanotube array electrode for the redox capacitance application. The morphology, microstructure and electrochemical properties of the nanocomposites were investigated by field emission scanning electron microscope, X-ray diffraction, energy dispersive X-ray diffraction and cyclic voltammetry measurements. It was found that nickel oxide could be embedded in titania nanotubes and extend from inner wall to top layer with an open pore mouth. The entire tube lengths were approx. 770 nm and 710 nm, meanwhile nickel-to-titanium atom ratios were determined as 9.6 at% and 36.4 at% for nickel oxide-embedded titania by an electrochemical and hydrothermal synthesis, respectively. The corresponding specific redox capacitance was also increased from 26 mF cm⁻² to 85 mF cm⁻² with highly reversible charge-discharge stability. Such an improvement was mostly ascribed to more accessible reaction interface of electroactive nickel oxide through its higher loading and a uniform dispersion on titania nanotubes. The capacitance was further increased up to 128 mF cm⁻² for 36.4 at% nickel-containing nickel oxide-titania/titanium electrode when a porous graphite carbon instead of a platinum sheet was used as a cathode.     

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.     

Bright nickel film deposited by supercritical carbon dioxide emulsion using additive-free Watts bath

This paper is aimed on studying film smoothening effect of supercritical carbon dioxide emulsion (Sc-CO₂-E) on nickel film electroplated using an additive-free Watts bath. Morphology of nickel film electroplated with Sc-CO₂-E was found to be similar to that of nickel film prepared from electroless plating. Surface roughness (R_a) of nickel film electroplated with Sc-CO₂-E was lower than that of nickel film electroplated through conventional method. A minimum R_a was found for nickel film electroplated through conventional method and Sc-CO₂-E when increasing current density from 0.010 to 0.150 A/cm². The minimum R_a was 69.8 nm at 0.020 A/cm² and 14.0 nm at 0.030 A/cm², respectively for conventional and Sc-CO₂-E case. After the minimum point, increasing rate of R_a increased was lower for Sc-CO₂-E case; this was because of higher hydrogen solubility in Sc-CO₂. Grain size of nickel film electroplated with Sc-CO₂-E was found to be finer than that of conventional case.     

Scaling-up of the electrodeposition process of nano-composite coating for corrosion and wear protection

The codeposition of hard nanoparticles into metal matrix electrodeposits usually leads to the increase of the coating hardness and abrasion resistance and causes a change to the microstructure of the deposits leading to more compact, nanostructured coatings with an increased corrosion resistance. Very often the laboratory scale results are not easily transferable to an industrial scale due to the introduction of new process variables such as the geometry and the dimensions of the component to coat.The aim of the present work was the study, in laboratory scale, of nano-composite nickel matrix coatings containing SiC nanoparticles and the transfer of this technology in industrial scale. The deposits have been produced using a Watts type bath containing 20 g/l of nanoparticles, under galvanostatic conditions using a current density of 2 A/dm². The deposits have been studied regarding their microstructure, abrasion and corrosion resistance. Based on the satisfactory results of the laboratory tests, the second part of this work contains the scaling-up and the industrialization of the process and the electrodeposition of the composite coating on ship propeller models and profiles as well as on train axles. The prototype parts were tested under actual working conditions.     

The observation of the nucleation and growth of electrolessly plated nickel deposited from different bath pH by TEM and QCM method

The important factors for fabricating thinner and more uniform films by electroless plating were discussed. Two kinds of Ni-P films were electrolessly plated from hypophosphite baths. The number density of the grains was low in the Ni-5.3 wt%P deposits which were plated from the pH 9 bath. As deposition proceeded, the grains grew and merged to form a continuous structure. In case of the Ni-12.6 wt%P deposits, which were plated from the pH 6 bath, the number density of the grains was more than twice that of the Ni-5.3 wt%P deposits. The grains formed a continuous structure, with nucleation governed by the initial deposition. Thus, the transition thickness, i.e., the thickness at which the deposits assumed a continuous structure, was lower in the case of pH 6. The difference was caused by the different autocatalytic activity of the deposits due to the difference in phosphorus content. It was found that the thinner and more uniform nickel films could be electrolessly plated under lower autocatalytic activity.     

Electrochemical behavior of activated-carbon capacitor material loaded with nickel oxide

In order to enhance specific capacitance and energy density of carbon-based supercapacitor, some nanometer-scale amorphous particles of nickel oxide were loaded into activated-carbon by suspending the activated-carbon in a Ni(NO₃)₂ solution followed by neutralization. A hybrid type electrochemical capacitor was made and tested, in which the activated-carbon loaded with nickel oxide was used as cathode material and activated-carbon was used as anode material. Although the BET surface area of the activated-carbon decreased upon nickel oxide loading compared to that of the starting material, its specific capacitance increased 10.84%, from 175.40 to 194.01 F g⁻¹ and the potential of oxygen evolution on the composite material electrode was 0.076 V higher than that of the pure activated-carbon electrode, in the electrolyte of 6 mol/L KOH solution, so the hybrid capacitor had larger energy density. Similar to the pure activated-carbon electrode, no obvious change appears on the specific capacitances of the composite material electrode at various discharge currents and the composite material electrode exhibiting good power characteristics.     

Long-term electrolytic hydrogen permeation in nickel and the effect of vanadium species addition

Nickel cathodes have been found to become deactivated under long-term polarization in the H₂ evolution region during alkaline water electrolysis. The cause of deactivation was examined using steady state polarization and measurement of hydrogen permeation through nickel foil in 8 mol/l KOH at 70 °C and 100 mA/cm². The long-term (over 50 h) permeation behaviour was explained by formation and growth of a nickel hydride phase. The rise in hydrogen overpotential was ascribed to an increase of the hydrogen surface coverage on the newly formed hydride. The effect of an electrolyte additive (a vanadium salt) on the hydrogen overpotential and permeation rate was also investigated. Upon addition of dissolved V₂O₅, the permeation rate was found to increase quickly and then slowly decrease to a steady value close to that measured for hydride-free nickel. Meanwhile, the hydrogen overpotential was observed to recover back to nearly its initial value for fresh nickel. The exhibited behaviour was attributed to decomposition of the hydride phase, after deposition of a vanadium-bearing compound. The prolonged contact between Ni and V was proposed as the main reason for hydride decomposition. The addition of more vanadium had no further result on the hydrogen overpotential.     

Ethylene polymerization using nickel α-diimine complex supported on SiO2/MgCl2 bisupport

Nickel α-diimine complex [C₆H₅-NC(CH₃)C(CH₃)N-C₆H₅]NiCl₂ was impregnated on SiO₂/MgCl₂ bisupport, and ethylene polymerizations were carried out with alkylaluminum compounds as cocatalyst. Branched polyethylenes were prepared when heptane is used as solvent. Polymerization conditions such as modified method of bisupport, cocatalyst, Al/Ni ratio, temperature and nickel concentration had a pronounced effect on catalytic activity and properties of polyethylenes. The activity of 2.9×10⁵ g PE mol Ni h⁻¹ was obtained in the presence of AlEt₂Cl as well as the bisupport without AlEt₃ modification, Al/Ni ratio 80, nickel concentration 0.12 mmol/l and temperature 14 °C. Branching degree of polyethylenes increased with temperature, and molecular weight, melting point and crystallinity of polyethylenes decreased correspondingly. Polymerization temperature had a pronounced effect on branches distribution of polyethylenes. Content of methyl branch increased sharply with temperature, but long branches dropped quickly.     

Electrochemically based low-cost high precision processing in MOEMS packaging

Precision processing in MOEMS (micro-opto-electromechanical systems) packaging has been studied based on electrochemical processes with the purpose of establishing technology for low-cost multifunctional encapsulation of microsystems and assembly of opto-electric access links in polymer.The electrochemically based processes studied in this paper include:

1.

Electroforming of a polymer moulding tool (stamper) in a nickel sulphamate electrolyte on a high-precision 3D etched silicon template.

2.

Patterning of 3D surfaces by an electrophoretic photoresist.

3.

Precision plating of Au and Sn for self-alignment of chips by eutectic Au-Sn solder.

The results show that nickel stampers with adequately low internal stress can be electroformed on 3D silicon wafers. Furthermore, 3D polymer samples manufactured by the nickel stampers can be patterned with metal lines down to 20 μm width using electrophoretic photoresist. Finally, eutectic Au-Sn solder bumps are realized by electroplating of Au and Sn followed by reflowing, satisfying the demands on dimension and alloy composition control over a 4 in. Si wafer.     

Fabrication and characterization of composite electrolyte for intermediate-temperature SOFC

In this study, a ceria-based composite electrolyte was investigated for intermediate-temperature solid oxide fuel cells (SOFCs) based on SDC-25 wt.% K₂CO₃. Sodium carbonate co-precipitation process by which SDC powder was adopted and sound cubic fluorite structure was formed after SDC powders were sintered at 750 °C for 3 h. The crystallite size of the particle was 21 nm in diameter as calculated from data obtained through X-ray diffraction. The conductivity of the composite electrolyte proposed in this study was much higher than that of pure SDC at the comparable temperature of 550-700 °C. The transition of the ionic conductivity occurred at 650 °C. Based on this type of composite electrolyte, single cell with the electrolyte thickness of 0.3 mm were fabricated using dry pressing, with nickel oxide adopted as anode and SSC as cathode. The single cell was then tested at 550-700 °C on home-made equipment in this study, using hydrogen/air. The maximum power density and open circuit voltage (OCV) achieved 600 mW cm⁻² and 1.05 V at 700 °C, respectively.     

Behaviour of heavy metals in the partial oxidation of heavy fuel oil

The behaviour of heavy metals in the partial oxidation of heavy fuel oils under a pressure of up to 100 bar (10 MPa) has been investigated. The tests were carried out in a 5 MW HP POX (High Pressure Partial Oxidation) test plant, that is operated by the IEC (Department of Energy Process Engineering and Chemical Engineering, TU Bergakademie Freiberg) in cooperation with Lurgi GmbH. In several test campaigns preheated oil with a viscosity of up to 300 cSt (= 300 mm²/s) at the burner inlet has been gasified. The heavy metals nickel Ni, iron Fe and vanadium V occur in heavy residual oils in considerable concentration and may seriously impact the gasification itself and the synthesis gas conditioning and usage. While iron is largely recovered in the gasification residue, the recovery rates of nickel and vanadium depend on the process conditions. Volatile nickel compounds were detected in the raw synthesis gas. It was found that an incomplete carbon conversion enables the capture of nickel Ni and vanadium V in the solid residue phase and can thus mitigate the problem of volatile metal compounds in the raw synthesis gas.     

Nickel oxide/hydroxide nanoplatelets synthesized by chemical precipitation for electrochemical capacitors

Nickel hydroxide powder prepared by directly chemical precipitation method at room temperature has a nanoplatelet-like morphology and could be converted into nickel oxide at annealing temperature higher than 300 °C, confirmed by the thermal gravimetric analysis and X-ray diffraction. Annealing temperature influences significantly both the electrical conductivity and the specific surface area of nickel oxide/hydroxide powder, and consequently determines the capacitor behavior. Electrochemical capacitive behavior of the synthesized nickel hydroxide/oxide film is investigated by cyclic voltammetry and electrochemical impedance spectroscope methods. After 300 °C annealing, the highest specific capacitance of 108 F g⁻¹ is obtained at scan rate of 10 mV s⁻¹. When annealing temperature is lower than 300 °C, the electrical conductivity of nickel hydroxide dominates primarily the capacitive behavior. When annealing temperature is higher than 300 °C, both electrical conductivity and specific surface area of the nickel oxide dominate the capacitive behavior.     

A novel lithium intercalation compound based on the layered structure of lithium nitridonickelates Li3−2xNixN

New lithium nickel nitrides Li_3−2xNi_xN (0.20 ≤ x ≤ 0.60) have been prepared and investigated as negative electrode in the 0.85/0.02 V potential window. These materials are prepared from a Ni/Li₃N mixture at 700 °C under a nitrogen flow. Their structural characteristics as well as their electrochemical behaviour are investigated as a function of the nickel content. For the first time are reported here the electrochemical properties of a lithium intercalation compound based on a layered nitride structure. The Li_3−2xNi_xN compounds can be reversibly reduced and oxidized around 0.5 V versus Li/Li⁺ leading to specific capacities in the range 120-160 mAh/g depending on the nickel content and the C rate. Due to a large number of lithium vacancies, the structural stability provides an excellent capacity retention of the specific capacity upon cycling.     

Co-deposition mechanism of nanodiamond with electrolessly plated nickel films

The co-deposition behavior and mechanism of nanodiamond with electrolessly plated nickel films was investigated. Due to the variation of complexing agents, various composite films with 0.9-8.0% nanodiamond were plated from electroless nickel plating baths which contained the same amount of nanodiamond (5.0 g dm⁻³) and sodium hypophosphite. In addition, composite films with 0-14% nanodiamond, semi-brilliant, were successfully fabricated from the bath which contained only citrate as a complexing agent. The plating bath was very simple and was sufficiently stable without any decomposition until termination of the plating reaction occurred due to consumption of the reducing agent. When the adsorbed amount of Ni-complex on the nanodiamond particles was large, a large amount of nanodiamond was co-deposited with the nickel. The results are interpreted to indicate that the adsorbed Ni-complex precipitates the incorporation of nanodiamond particles into the nickel matrix. In addition, incorporation becomes more probable when the adsorbed amount of Ni-complex on the nanodiamond particles was large.     

Characterisation of CoNi(Cu)/Cu multilayers deposited from a citrate electrolyte in a flow channel cell

CoNi(Cu)/Cu multilayers consisting of 50 and 200 bi-layers were deposited from a citrate electrolyte in a flow channel cell by a dual pulse plating technique. The dissolution of the ferromagnetic components during pulse plating was studied using an oscilloscope and cyclic voltammetry. It was found that the dissolution was suppressed due to the passivation of the ferromagnetic layers before the deposition of an atomic layer of nonmagnetic component on them. The passivation was a function of the nickel ion concentration in the electrolyte. X-ray studies showed that the deposit had a preferred crystal orientation of [1 1 1] and suggested the formation of a super-lattice. Atomic force microscopy studies showed a four-fold increase of the roughness of the ferromagnetic surface with increasing layer thickness from 6 to 10 nm, whereas the roughness of the nonmagnetic surface only changed slightly with increasing layer thickness. The multilayers exhibit giant magnetoresistance.     

Ni/nano-TiO2 composite electrodeposits: Textural and structural modifications

Nanocomposite coatings were obtained by electrochemical codeposition of TiO₂ nano-particles (mean diameter 21 nm) with nickel, from an additive-free Watts type bath. The electrodeposition of Ni-TiO₂ composites was carried out on a rotating disk electrode (RDE), by applying direct current. Pure Ni deposits were also produced under the same experimental conditions for comparison. The surface morphology, the crystallographic orientation of nickel matrix and the grain size of the deposits were investigated, along with the distribution and the percentage, of the embedded nano-particles in nickel matrix, as a function of pH, current density and concentration of TiO₂ nano-particles in the bath. The observed textural modifications of composite coatings are associated with specific structural modifications of Ni crystallites provoked by the adsorption-desorption phenomena occurring on the metal surface, induced by the presence of TiO₂ nano-particles. It has been observed that the presence of TiO₂ nano-particles favours the [1 0 0] texture of nickel matrix. Moreover, the codeposition of titania nano-particles with nickel was found to be favoured at low pH and low applied current values. As the titania incorporation percentage is increased, a considerable grain refinement in the nanometer region was revealed followed by an improvement of the quality of the nickel preferred orientation.     

Effects of boric acid on hydrogen evolution and internal stress in films deposited from a nickel sulfamate bath

The effects of boric acid additions on the pH close to the electrode surface, on the hydrogen evolution reaction and on the internal stress in the plated films were studied for the high speed electroplating of nickel from a nickel sulfamate bath at a current density close to the nickel ion limiting current density. The study was carried out at 50 °C and pH 4.0 using a 1.55 M nickel sulfamate plating bath containing boric acid at concentrations ranging from 0 to 0.81 mol L^–1. The variation of the internal strain in the plated nickel films was determined in situ using a resistance wire-type strain gauge fitted to the reverse side of the copper electrode substrate. The solution pH at a distance of 0.1 mm from the depositing nickel film was measured in situ using a miniature pH sensor assembly consisting of a thin wire-type antimony electrode and a Ag/AgCl/sat. KCl electrode housed in a thin Luggin capillary. The addition of boric acid was shown to effectively suppress the hydrogen evolution reaction at nickel electrodeposition rates (18.0 A dm^–2) close to the limiting current density (~20 A dm^–2). Consequently, the solution pH adjacent to the plating metal surface was maintained at a value close to that in the bulk solution and the development of high internal stresses in the deposited nickel films was avoided.