Deformation Mechanism of Porous Nickel Oxide in Molten Li/K Carbonates

Murai, M.; Takizawa, Kenji; Soejima, K.; Sotouchi, Hiroko

doi:10.1149/1.1837034

Cited by 13 publications

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“…The reduction of NiO (NiO + H 2 → Ni + H 2 O) is a reaction with high important technological significance, not only as a source of Ni from Ni ores but also due to its importance in catalytic reactions. , From the basic point of view, the reduction of NiO is regarded as a model reaction due to its single-stage transformation fuel cell electrodes, gas sensors, or supercapacitors/battery hybrids but also for their magnetic properties since NiO is antiferromagnetic and Ni ferromagnetic. − In addition, metal−ceramic materials are also interesting since they typically exhibit enhanced mechanical properties . The methods usually employed for the reduction process are based on high-temperature treatments under H 2 atmosphere. , These studies show that the reaction is strongly influenced by the concentration of defects, in particular oxygen vacancies, in the starting material.…”

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confidence: 99%

Controlled Reduction of NiO Using Reactive Ball Milling under Hydrogen Atmosphere Leading to Ni−NiO Nanocomposites

et al. 2004

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Controlled mechanochemical reduction of NiO has been carried out by room-temperature ball milling under H 2 atmosphere. During the milling, a gradual conversion of NiO into Ni occurs, with no intermediate phases being formed. The amount of Ni and its crystallite size can be tuned by the ball-milling parameters, leading to the formation of Ni-NiO (metaloxide) nanocomposites. The initial microstructure of the NiO powder is shown to play an important role in the reduction rate and on the final microstructure of the nanocomposites formed. The results indicate that the mechanically induced defects have a strong influence on the kinetics of the reduction process.

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Section: Introductionmentioning

confidence: 99%

Controlled Reduction of NiO Using Reactive Ball Milling under Hydrogen Atmosphere Leading to Ni−NiO Nanocomposites

et al. 2004

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“…9 We also reported that the lithiation of porous NiO resulted in the growth of fine Li-NiO crystals on the NiO grain surface and the change in the crystal grain form and the porous structure depending on CO 2 partial pressure and compressive stress. 10 For the coating with LiCoO 2 , it is desirable that when Ni or NiO is lithiated, its fine crystals are also coated with LiCoO 2 uniformly. Furthermore, the LiCoO 2 coating layer must follow the changes in grain conditions and structure.…”

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Behavior of CoO-NiO Solid Solution in Molten Carbonate

Takizawa

Hagiwara

2001

J. Electrochem. Soc.

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Focusing on the fact that cobalt oxide ͑CoO͒ and nickel oxide ͑NiO͒ form a good solid solution, we examined the behavior of this material in molten carbonate in order to evaluate the feasibility of the NiO cathode coated with stable lithium cobaltite (LiCoO 2 ͒. In the molten carbonate at 650°C, the CoO-NiO solid solution created LiCoO 2 on its surface. The solubility measurement results indicated a suppression of the Ni dissolution which seems attributable to the LiCoO 2 coating. However, during the long-range immersion treatment, the LiCoO 2 layer on the solid solution surface grew and partially broke away from the solid solution matrix. In the powder-based immersion test, it was also verified that LiCoO 2 particles grew to relatively large ones. For use as an alternative cathode material, it is necessary to suppress the crystal growth of the LiCoO 2 coating layer.Molten carbonate fuel cells ͑MCFC͒ are expected to provide high efficiency generation of electricity and are now under development as the next generation fuel cell device. However, this fuel cell uses alkaline metal carbonates, which are highly corrosive, as the electrolyte. Materials used in the cell inevitably deform and deteriorate with time. Lithiated nickel oxide ͑Li-NiO͒, which is used as the cathode electrode material for MCFCs, reacts with dissolved CO 2 gas and is dissolved in the molten carbonate to form nickel ions. The nickel ions move in the electrolyte toward the anode. The nickel ions are stable near the cathode because of the oxidation atmosphere. They react with hydrogen near the anode and are reduced to metallic nickel because of the elevated hydrogen gas concentration there. Therefore, the nickel ions do not saturate in the electrolyte matrix and Li-NiO continues to dissolve. The precipitated metallic nickel grows in the electrolyte matrix and finally makes an internal short circuit in the cell, affecting the life of the cell. To suppress this nickel short-circuit phenomenon, one may think of suppressing the dissolution of Li-NiO or of controlling the nickel precipitation sites or suppressing the precipitation reactions.As a means for reducing the dissolution of Li-NiO, alternative materials except Li-NiO are sought which hardly dissolve in the molten carbonate. [1][2][3] Recently, lithium cobaltite (LiCoO 2 ) has been gaining attention as an alternative cathode material due to its reported stability in the molten carbonate. 4,5 However, this material is inferior in conductivity to Li-NiO.Therefore, the Li-NiO coated with LiCoO 2 is being examined as the means to suppress the dissolution without losing the advantages of Li-NiO. [6][7][8] It is known that the lithiation of NiO in the molten carbonate results in reducing the crystal grain size. 9 We also reported that the lithiation of porous NiO resulted in the growth of fine Li-NiO crystals on the NiO grain surface and the change in the crystal grain form and the porous structure depending on CO 2 partial pressure and compressive stress. 10

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