Nickel

About: Nickel is a research topic. Over the lifetime, 79308 publications have been published within this topic receiving 1210058 citations. The topic is also known as: Ni & element 28.

Electrochemical‐Ellipsometric Studies of Oxide Film Formed on Nickel during Oxygen Evolution

Abstract: The time variation of current density at constant potentials for oxygen evolution on metals or alloys is one of the most difficult problems needing a solution in commercial water electrolyzers. The mechanism of this phenomenon on nickel electrodes was studied in IN KOH using ellipsometry to analyze the nature of anodic oxide films. Effects of electrochemical pretreatment of oxide films on the kinetics of the oxygen evolution reaction were investigated. Nickel oxide films, formed electrochemically at 1.5 V, are more active than untreated nickel for this reaction. The time variation of current density for oxygen evolution at potentials above 1.56 V is due to the gradual conversion of active sites, Ni/sup 3 +/ ions, on the film surface to inert species, Ni/sup 4 +/ ions, for the oxygen evolution reaction. The electrocatalytic activities of aged electrodes are regained by ''rejuvenating'' the electrodes at 1.5 V. The ''rejuvenation'' of aged oxide films is essentially attributed to the recovery of active sites on the very top layers of the films, rather than the diminution of the film thickness. The higher the electrolyte temperature the shorter the period of time required for approaching a stable current density. In addition, with increasing temperature, theremore » is a more significant improvement of the electrocatalytic activity by ''rejuvenation'' on aged electrodes. Tafel plots for oxygen evolution on nickel preanodized or ''rejuvenated'' at 1.5 V exhibit only one linear region with b = approximately 40 mV, while dual Tafel regions are observed on nickel prepolarized at 1.8 or 2.0 V: b = approximately 40 mV at low eta and b = approximately 170 mV at high eta. In comparison with the thickness of oxide films, the chemical identity of the very top layers of oxide films plays a more significant role in determining the kinetics of the oxygen evolution reaction.« less

Controlled Synthesis of Hierarchical Nickel and Morphology-Dependent Electromagnetic Properties

Abstract: Nickel nanomaterials with a wide range of morphologies and sizes, such as superfine nanoparticles, urchinlike chains, smooth chains, rings, and hexagonal Ni/Ni(OH)2 heterogeneous structure plates, are synthesized in a single reaction system by simply adjusting the reaction conditions. The morphology transformation mechanism is systematically investigated. Magnetic measurement of urchinlike chains, smooth chains, and rings shows that the saturation magnetization (Ms) decreases with reduced sample size, and remanent magnetization (Mr) decreases with increasing reaction temperature. Additionally, coercivity (Hc) of urchinlike chains which is apparently larger than that of bulk nickel depends more on size than on shape anisotropy according to spherical chain reversal magnetization model. Enhanced microwave absorption of Ni/Ni(OH)2 hexagonal plates compared with smooth chains and rings is due to the synergistic effect of magnetic loss and dielectric loss. Particularly, the urchinlike nickel chains exhibit a be...

Lithium Nickel Cobalt Manganese Oxide Synthesized Using Alkali Chloride Flux: Morphology and Performance As a Cathode Material for Lithium Ion Batteries

Abstract: Li(Ni(0.8)Co(0.1)Mn(0.1))O(2) (NCM811) was synthesized using alkali chlorides as a flux and the performance as a cathode material for lithium ion batteries was examined. Primary particles of the powder were segregated and grown separately in the presence of liquid state fluxes, which induced each particle to be composed of one primary particle with well-developed facet planes, not the shape of agglomerates as appears with commercial NCMs. The new NCM showed far less gas emission during high temperature storage at charged states, and higher volumetric capacity thanks to its high bulk density. The material is expected to provide optimal performances for pouch type lithium ion batteries, which require high volumetric capacity and are vulnerable to deformation caused by gas generation from the electrode materials.