Ni Cathode Research Articles

Electrochemical performance of Y 2O 3/NiO cathode in the molten Li 0.62/K 0.38 carbonates eutectics

The preparation and subsequent oxidation of Ni cathodes modified by impregnation with yttria were evaluated by surface and bulk analysis. The electrochemical behavior of Y 2O 3/NiO cathodes was also evaluated in a molten 62 mol% Li 2CO 3 + 38 mol% K 2CO 3 eutectic at 650 °C by electrochemical impedance spectroscopy (EIS) as a function of yttria content and immersion time under the standard cathode gas condition (CO 2:O 2 = 67:33%). The stability tests of Y 2O 3/NiO cathodes showed that the yttria additive could dramatically reduce the solubility of NiO in the eutectic molten Li/K carbonates due to the preferential dissolution of yttria. The loss of yttria was confirmed by chemical analysis and X-ray diffraction (XRD). The Y 2O 3/NiO cathodes showed higher catalytic activity for oxygen reduction and lower dissolution of NiO than the pure NiO cathode. The cathode material with 1.0 wt.% of yttria showed the optimum behavior.

Structural and Electrochemical Properties of Coin Cells using Ni and Nd Doped LiMn2O4 Cathodes

not Available.

Three-dimensional thin-film Li-ion microbatteries for autonomous MEMS

Autonomous MEMS require similarly miniaturized power sources. In this paper, we present the first working three-dimensional (3-D) rechargeable Li-ion thin-film microbattery technology that is compatible with MEMS requirements. The technology has been developed, and full 3-D cells have been manufactured on both glass and silicon substrates. Our 3-D microbatteries have a sandwich-like structure of conformal thin-film electrodes, electrolyte and current collectors. The films are deposited sequentially on all available surfaces of a perforated substrate (e.g., silicon or a glass microchannel plate or "MCP") using wet chemistry. The substrate has thousands of high-aspect ratio holes per square cm, thereby providing more than an order of magnitude increase in surface area per given footprint (original 2-D substrate area). The full 3-D cell consists of a Ni cathode current collector, a MoO/sub y/S/sub z/ cathode, a hybrid polymer electrolyte (HPE) and a lithiated graphite anode that also serves as anode current collector. One 3-D cell with a roughly 1-/spl mu/m-thick cathode ran at C/10 to 2C charge/discharge rates and room temperature for 200 cycles with 0.2% per cycle capacity loss and about 100% Faradaic efficiency. The cell exhibited a capacity of 2 mAh/cm/sup 2/, about 30times higher than the capacity of a similarly built planar (2-D) cell with the same footprint and same cathode thickness.

TiO 2-coated Ni powder as a new cathode material for molten carbonate fuel cells

The properties of a new cathode material of nano-sized TiO 2-coated Ni powder for application in molten carbonate fuel cells (MCFCs) are investigated. The material is prepared by a sol–gel method. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM) with energy dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM) and Raman spectroscopy are employed to characterize the cathode material. The nano-sized TiO 2 particles are homogenously coated on the surface of the Ni powder. A stable LiTi 1− x Ni x O 2 phase is formed on the surface of the Ni powder during immersion in molten carbonate at 650 °C. The solubility of the TiO 2-coated Ni cathode is about 50% lower compare with that of a pure Ni cathode.

Tritium Separation by Electrolysis Using Solid Polymer Electrolyte

Hydrogen isotope separation effect by electrolysis of water was theoretically investigated and was compared with experimental results. The separation mechanism was analyzed as the hydrogen isotope exchange reaction between water and diatomic hydride that consists of hydrogen and cathode material. The equilibrium constants of the isotope exchange reaction were calculated from reduced partition function ratio. Using the constants, the separation factor (SF) of the isotopes was calculated according to the two-phase distribution theory for isotopes. Experimentally, light or heavy water spiked with tritiated water was electrolyzed by a device with a solid polymer electrolyte, which equipped with SUS, Ni, or carbon cathode. Thus, the SFs were experimentally obtained. Calculated SFs were well agreed with the experimentally values for SUS and Ni cathodes, and that for carbon cathode was somewhat small then the experimental value.

Investigation of hydrogen content in chemically delithiated lithium-ion battery cathodes using prompt gamma activation analysis

Lithium-ion batteries are widely used as a power source for portable electronic devices. Currently, only 50-70% of the theoretical capacity of the layered oxide cathode (positive electrode) materials could be reversibly used. The reason for this limitation is not fully understood in the literature. Recent structural and chemical characterizations of chemically delithiated (charged) cathodes suggest that loss of oxygen from the lattice may play a role in this regard. However, during the chemical delithiation process any proton inserted from the solvent could adversely affect the oxygen content analysis data. The challenge in addressing this issue is to detect and determine precisely the proton content in the chemically delithiated samples. The prompt gamma-ray activation analysis (PGAA) facility at the Nuclear Engineering Teaching Laboratory (NETL) is used to determine the proton content in the layered oxide cathode LiNi0.5Mn0.5O2 before and after chemical delithiation. The data are compared with those obtained with Fourier transform infrared (FTIR) spectroscopy, which can provide mainly qualitative analysis. The technique has proved to be promising for these compounds and will be applied to characterize several other chemically delithiated Li1-xCo1-yMyO2 (M = Cr, Mn, Fe, Ni, Cu, Mg, and Al) cathodes.

Phase changes of newly synthesized Co-coated Ni cathode in MCFC cathodic conditions

A molten carbonate fuel cell (MCFC) is expected to provide high efficiency generation of electricity and an environmentally clean means of power generation [1, 2]. However, the durability of the MCFC experiences difficulties at over 40 000 hr of operation. One of the lifetime limiting problems of a MCFC is the slow dissolution of the state of the art cathode material NiO into the electrolyte [3]. Two main methods have been adopted to solve this problem. One method is to use an alternative electrolyte. More basic molten carbonate melts adopting Li/Na eutectic carbonates instead of Li/K eutectic carbonates have been used to decrease the Ni dissolution rate in the electrolyte [4]. The other method is to develop alternative cathode materials. Among cathode materials, LiCoO2 seems to be one of the best candidates because of its higher stability in the molten carbonate, and the rate of dissolution is slower than that of the NiO cathode. However, application of LiCoO2 as a new cathode material has problems in scaling up the electrode area and a relatively higher manufacturing cost than that of the NiO cathode. Therefore, recently many investigators have attempted to resolve the problem by developing new cathode materials in which NiO grains have been coated with a small amount of LiCoO2 or CoO by various coating techniques to reduce their dissolution [5, 6]. In this study, we have tried to prepare a new candidate cathode material of Co3O4-coated Ni powders using the Pechini method [7] as a new coating technique. In addition, we report on the phase changes of the Co-coated Ni cathode in MCFC cathodic conditions. The Co3O4-coated Ni powders were prepared by the following method. A stoichiometric amount of cobalt acetate (Aldrich, USA, purity of 98+%) and citric acid (CA) (Aldrich., USA, purity of 99.5+%) were dissolved in distilled water and thoroughly mixed with an aqueous solution of ethylene glycol (EG) (CA:EG:cobalt ions = 2:1:1). After that, the solution was adjusted by adding NH4OH until pH 8 was achieved and Ni powder (filamentary nickel 255, Inco, USA) was immersed in the solution. The resultant solution was heated to 80 ◦C while being stirred until a gel precursor was produced. The gel precursor was calcined at 350 ◦C for 3 hr in air.

Perturbation analysis for the rotational spectrum of the NiBr radical in the X2Pi3/2 and A2Delta5/2 states.

The millimeter- and submillimeter-wave spectra of the NiBr radical in the X (2)Pi(3/2) and A (2)Delta(5/2) states were observed by a source-modulated microwave spectrometer. The NiBr radical was generated in a dc glow discharge through the mixture of Br(2) vapor and Ar gas by the sputtering reaction with a Ni cathode. Observed transition frequencies were independently analyzed for both electronic states using a standard polynomial expression of a Hund's case (c) approximation. Anomalous behavior of the effective molecular constants in the X (2)Pi(3/2) state was interpreted as the result of the perturbation between the X (2)Pi(3/2) and A (2)Delta(5/2) states. The deperturbed molecular constants were derived using a simplified supermultiplet Hamiltonian including the interaction terms between the two electronic states.

Detection of free nickel monocarbonyl, NiCO: rotational spectrum and structure.

Unsaturated transition metal carbonyls are important in processes such as organometallic synthesis, homogeneous catalysis, and photochemical decomposition of organometallics. In particular, a metal monocarbonyl offers a zeroth-order model for interpreting the chemisorption of a CO molecule on a metal surface in catalytic activation processes. Quite large numbers of theoretical papers have appeared which predict spectroscopic and structural properties of transition metal carbonyls. The nickel monocarbonyl NiCO has been one of the metal carbonyls most extensively studied by the theoretical calculations. At least 50 theoretical studies have been published on this simplest transition metal carbonyl up to the present time. However, experimental evidence of NiCO is much more sparse than theoretical predictions, and the actual structure of NiCO has never been determined by any experimental methods. This Communication reports the first preparation of free nickel monocarbonyl and observation of its rotational transitions. The NiCO molecule was generated by the sputtering reaction of a Ni cathode in the presence of CO. The accurate bond lengths of Ni-C and C-O were experimentally determined from isotopic data and were compared with the theoretical predictions for the first time.

Synthesis and electrochemical properties of nanocrystalline Li[NixLi(1−2x)/3Mn(2−x)/3]O2prepared by a simple combustion method

Nanocrystalline Li[NixLi(1−2x)/3Mn(2−x)/3]O2 powders were prepared by a simple combustion method and investigated using X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), scanning electron microscopy (SEM), particle size analysis (PSA), and galvanostatic charge/discharge cycling. According to the XRD analysis, single-phase compounds with a layered structure were obtained for powders with 0 ≤ x ≤ 0.25, while mixtures were obtained for powders with 0.30 ≤ x ≤ 0.50. Rietveld analysis revealed that single-phase Li[NixLi(1−2x)/3Mn(2−x)/3]O2 is basically a layered rock-salt structure in which a small amount of Ni occupies the 3a sites. The initial discharge capacity of a Li/Li[NixLi(1−2x)/3Mn(2−x)/3]O2 cell with x = 0.20 was about 288 mA h g−1, corresponding to about 91% of the theoretical value, when it was cycled in the voltage range of 4.8–2.0 V with a specific current of 20 mA g−1 at 30 °C. As far as we know, charge/discharge cycling on an Li/Li[Ni0.20Li0.20Mn0.60]O2 cell gives the highest discharge capacity of 288 mA h g−1 among the LiMO2-based (M = Co, Ni, and Mn) cathode materials. A very promising factor for high-rate capability applications was an excellent rate capability in continuous cycling at specific currents ranging from 20 mA g−1 to 900 mA g−1, due to the nanocrystalline particle size of 80–200 nm. The origin of the 4.5 V plateau was investigated by means of weight loss measurement and XAS for the charged/discharged electrodes. The weight loss measurement for the charged electrodes gave indirect evidence that the 4.5 V plateau did not originate from the ejection of oxygen. In XAS, the Mn oxidation state of 4+ did not change during the charge/discharge process, and surprisingly the Ni did not further oxidize beyond about 3+.

A study of the Co-coated Ni cathode prepared by electroless deposition for MCFCs

In this study, we made a novel alternative cathode material of molten carbonate fuel cell (MCFC) using electroless deposition of Co on the surface of the Ni powder. Using this manufacturing method, we expect that economical and large-scale cathode can be made easily. The cathode prepared by this method formed LiCo 1− y Ni y O 2 phase in molten (Li 0.62K 0.38) 2CO 3 at 650 °C under CO 2:O 2=66.7:33.3% atmosphere, its solubility is 40% lower than that of NiO cathode. In the unit cell test, the performance of the cell composed of Co-coated Ni cathode was same as that of the cell composed of NiO cathode. Thus the cathode made by Co-coated Ni powder used as an alternative cathode can maintain the advantages of NiO cathode and lengthen the lifetime of MCFC.

Electrochemical formation of Yb–Ni alloy films by Li codeposition method in a molten LiCl–KCl–YbCl 3 system

Electrochemical formation of Yb–Ni alloy films at a Ni cathode was investigated in a molten LiCl–KCl–YbCl 3 (0.5 mol%) at 723 K. A very thin YbNi 2 film (∼100 nm) was formed by potentiostatic electrolysis at 0.10 V (vs. Li +/Li) for 24 h. A much thicker YbNi 2 alloy film (∼7 μm) was formed by Li codeposition method (cathodic galvanostatic electrolysis at 50 mA cm −2) for 1 h. The formed YbNi 2 films were changed to Yb 2Ni 17 and α-Ni phases by anodic potentiostatic electrolysis depending on the applied potentials. The formation potentials of Yb 2Ni 17 and YbNi 2 were found to be 0.75 and 0.25 V, respectively.

Optimization of the hydrogen evolution activity on zinc–nickel deposits using experimental strategies

The experimental strategies including the fractional factorial design (FFD), path of the steepest ascent study, and the central composite design (CCD) coupled with the response surface methodology (RSM) was adopted to optimize the hydrogen evolution activity of Zn–Ni deposits. The key deposition variables, pH, the Zn/Ni ionic ratio and the TEPA concentration in the plating solutions, influencing the hydrogen evolution activity of Zn–Ni cathodes were found in the FFD investigation. These variables were subjected to the steepest ascent study to approach the vicinity of the optimal deposition conditions for plating the Zn–Ni deposits with the highest hydrogen evolution activity. In the CCD investigation, the optimal deposition settings, where the temperature of 50 °C, the current density of 2500 A m −2, pH of 13.0, the Zn/Ni ionic ratio of 0.89 and the TEPA concentration of 0.58 M, were obtained by means of a regression model. This highest activity of the Zn–Ni deposits mainly consisting of the γ phase structure for hydrogen evolution is due to a combination of their good electrocatalytic activity and relatively high surface area. The electrocatalytic activity of these cathodes mainly composed of the γ phase Zn–Ni alloy was damaged by the selective dissolution of Zn from the deposits in 5 M KOH.

A novel approach to preparing nano-size Co3O4-coated Ni powder by the Pechini method for MCFC cathodes

The dissolution of nickel oxide cathodes in the electrolyte is one of the major technical obstacles to the commercialization of molten carbonate fuel cells (MCFC). A novel alternative cathode material for MCFC was synthesized, which was made of nano-size Co3O4 coated on the surface of Ni powder using a polymeric precursor based on the Pechini method. X-Ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDAX), electron microprobe analysis (EPMA), and Raman spectrometry were employed in characterization of the novel alternative cathode materials. The Co-coated Ni cathode prepared by the tape-casting technique has a lower solubility in the molten carbonate than in the NiO cathode under CO2 ∶ O2 (67 ∶ 33) atmosphere at 650 °C. The reason is that the nano-size Co3O4-coated Ni powder can significantly retard the dissolution of NiO in molten carbonate due to the formation of the stable LiCo1−yNiyO2 phase on the surface of NiO in molten carbonate. During 300 h cell operation, the closed-circuit voltage (CCV) of unit cells using NiO and Co-coated Ni cathodes were found to be 0.80 V and 0.82 V, respectively, at a current density of 150 mA cm−2. The results show that the Co-coated Ni cathode used as an alternative cathode could resolve the problems in scale-up of the electrode and lengthen the lifetime of MCFC.

Performance of La 0.8Sr 0.2CoO 3 coated NiO as cathodes for molten carbonate fuel cells

La 0.8Sr 0.2CoO 3 was coated on NiO (LSC–NiO) cathodes using a sol–gel method. Dissolution studies in molten Li 2CO 3 and K 2CO 3 (62:38 mol%) at 650 °C showed lower Ni dissolution than that of the conventional nickel oxide cathode. Impedance analysis showed that the behavior of the developed cathode is similar to that of nickel oxide. The LSC coated Ni cathode has an over potential of 109 mV at an applied current density of 160 mA/cm 2. The LSC–NiO shows promise as an alternate cathode in molten carbonate fuel cells (MCFCs).

Ni–Al alloy as alternative cathode for molten carbonate fuel cells

The in situ oxidation of Ni–5at.%Al and Ni–15at.%Al alloys in Li+K carbonate melt were investigated by measuring open-circuit potential and electrochemical impedance spectroscopy under an O 2+CO 2 gas mixture in the ratio 90:10 at a total pressure of 1 atm at 650°C. In situ oxidation processes of Ni–Al alloys demonstrate three stages. The period of the oxidation process depends on the aluminum content in the alloy. The final product has probably a multilayer structure, where the inner part is compact (probably also multilayer in nature) and the outer part (solution side) is porous. Ni–5at.% Al electrode exhibited excellent stability during one-week immersion in the carbonate melt. Extension of cathode lifetime in molten carbonate fuel cells (MCFC) appears possible if the Ni cathode is modified by the addition of small concentration of aluminum.

The Effect of the ε-Caprolactam Concentration on the Electrodeposition of Nickel–Polymer Coatings

It is shown that an increase in ε-caprolactam concentration in sulfate nickel-plating baths enhances its adsorption on Ni cathode, which is followed by the formation of its complexes with nickel ions in the solution. The first process decelerates the electrode reaction, and the second one facilitates it. In the interval of the maximum deceleration of the process, nickel–polymer coatings with the greatest content of ε-caprolactam and the highest surface conductivity, substantially exceeding that of pure metal, are formed.

Preparation of LiMO 2 (M = Co), Ni cathode materials for intermediate temperature fuel cells by sol-gel processes

Preparation of LiMO 2 (M = Co), Ni cathode materials for intermediate temperature fuel cells by sol-gel processes

On a thermodynamic description of Se(IV) electroreduction and CdSe electrolytic formation on Ni, Ti and Pt cathodes in acidic aqueous solution

A discussion on tetravalent Se electroreduction and CdSe cathodic electrodeposition in terms of thermodynamics, in association with an investigation on the voltammetric behavior of Pt, Ni and Ti working electrodes in a high temperature (85 °C) acidic aqueous bath, is presented. The underpotential co-deposition of Cd with Se is described within the frame of a known electrochemical model of compound formation. The data presented serve as an effective basis for studying the electroreduction of Se(IV) as well as for determining the relevance of theoretical predictions to experimental findings on a binary compound electrodeposition process.

Evaluation of Raney–nickel cathodes prepared with aluminum powder and tin powder

Raney–Ni cathodes were prepared on nickel wire from aluminum powder and tin powder by heat treatment. The influence of tin addition to the Raney–Ni electrode on the polarization characteristics of the hydrogen evolution reaction was studied in 1 M NaOH at 303 K. The surface layer of the tin added Raney–Ni electrode was composed of nickel, aluminum, and tin. The crystallite structure of the surface was the NiAl phase and its X-ray diffraction pattern was broadened. The tin-added Raney–Ni electrode had a high catalytic activity for the hydrogen evolution reaction. The Tafel slope of the tin-added Raney–Ni electrode decreased from 120 mV/decade to 70 mV/decade. It was suggested that its mechanism of the hydrogen evolution reaction in alkaline solution was different from that of the nickel electrode.