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.

Molecular Electrocatalysts for the Oxidation of Hydrogen and the Production of Hydrogen – The Role of Pendant Amines as Proton Relays

Abstract: Electrocatalysts for efficient conversion between electricity and chemical bonds will play a vital role in future systems for storage and delivery of energy. Our research on functional models of hydrogenase enzymes uses nickel and cobalt, abundant and inexpensive metals, in contrast to platinum, a precious metal used in fuel cells. A key feature of our research is a focus on the use of pendant amines incorporated into diphosphine ligands. These pendant amines function as proton relays, lowering the barrier to proton transfers to and from the catalytically active metal site. The hydride acceptor ability of metal cations, along with the basicity of pendant amines, are key thermochemical values that determine the thermodynamics of addition of H2 to a metal complex with a pendant amine incorporated into its ligand. Nickel catalysts for oxidation of H2 have turnover frequencies up to 50 s-1 (at 1 atm H2 and room temperature). Nickel and cobalt catalysts for production of H2 by reduction of protons are studied, one of which has a turnover frequency over 1000 s-1. This material is based upon work supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the US Department of Energy, Officemore » of Science, Office of Basic Energy Sciences.« less

Hardening effect induced by incorporation of SiC particles in nickel electrodeposits

Abstract: Pure Ni and nickel matrix composite electrocoatings containing micron- and nano-SiC particles (1 μm and 20 nm respectively) were produced under direct and pulse current conditions from an additive-free Watts type bath. The effect of the particle size, codeposition percentage of SiC and type of imposed current on the microhardness as well as on the microstructure of the electrodeposits were investigated. Ni/SiC composite deposits prepared under either direct or pulse current conditions exhibited a considerable strengthening effect with respect to pure Ni coatings. The improved hardness of composite coatings was associated to specific structural modifications of Ni crystallites provoked by the adsorption of H+ on the surface of SiC particles, thus leading to a (211) texture mode of Ni crystal growth. Pulse electrodeposition significantly improved the hardness of the Ni/SiC composite coatings, especially at low duty cycles, in which grain refinement and higher SiC incorporation (vol. %) was achieved. The enhanced hardness of Ni/nano-SiC deposits, as compared to Ni/micron-SiC composites, was attributed to the increasing values of the number density of embedded SiC particles in the nickel matrix with decreasing particle size. In addition, the observed hardening effects of the SiC particles might be associated to the different embedding mechanisms of the particles, which could be characterized as inter-crystalline for micron-SiC and partially intra-crystalline for nano-SiC particles.

The continuous hydrothermal synthesis of nano-particulate ferrites in near critical and supercritical water

Abstract: Magnetic spinel type oxides such as magnetite, Fe3O4, cobalt, nickel, and zinc ferrites, MFe2O4 (M = Co, Ni, Zn) and the mixed nickel and cobalt ferrite, NixCo1 − xFe2O4 have been synthesised continuously by the hydrolysis and simultaneous oxidation of mixtures of Fe(II) acetate and different M(II) acetates in near-critical and supercritical water using a flow reactor. The materials have been characterised by powder X-ray diffraction (PXD) and, in selected cases, by transmission electron microscopy (TEM). The bulk composition of the samples was determined by Atomic Absorption analysis (AA). Additionally, Energy-dispersive Detection X-ray analysis (EDX) was carried out on some of the samples. TEM pictures showed a “bimodal” particle size distribution: small particles of ca. 10 nm and larger particles of up to 100 nm, both of which are highly crystalline. Possible reaction mechanisms are discussed, which may be responsible for the observed morphology. The effects of temperature and residence time on the reaction have been studied.