Fabrication, characterization and electrochemical studies of nickel and nickel-based materials
Doctor of Philosophy
DisciplineChemistry and Materials Science
MetadataShow full item record
Nickel is a naturally abundant transition metal and is very cost effective. This, along with mechanical and magnetic characteristics, and good catalytic activity in different applications, has made it an interesting non-noble metal for various applications such as anodic/cathodic electrode materials in fuel cells, and as an electrocatalyst for oxygen and hydrogen evolution reactions. It is also consumed in various industries like the plating industry where it is an alloying element for iron or copper. Studying the effect of different factors in nickel electrochemical dissolution/ deposition would result in an enhanced understanding of the fundamental aspects of nickel electrochemistry. Here, the anodic dissolution of an electrolytic Ni electrode was quantitatively investigated by an Inductively Coupled Plasma Atomic Emission Spectroscopy to elucidate the presence of metallic impurities. The electrolytic Ni electrode was subsequently anodically dissolved through the application of current densities at 4.0, 8.0, and 16.0 mA cm-2 in Watts solution, after which its crystalline nature and morphological changes were studied. Using μ- X-ray Diffractometry, changes in the crystallinity of a particular site on the electrolytic Ni electrode was investigated over time during the anodic dissolution at an applied current density of 8.0 mA cm-2. The cubic crystalline nature was not altered during the dissolution of electrolytic Ni, while the diminishment of the crystalline plane of Ni (111), and the growth of the Ni (200) crystalline plane were observed during this process. The anodic dissolution of industrial electrolytic Ni samples in Watts solution was studied in order to better understand the possible causes behind residue formation in anode baskets under actual electroplating conditions in an industrial setup. Cyclic voltammetry and chronopotentiometry at different applied current densities were employed to characterize the dissolution behavior of these samples prior to and during a long-term dissolution process. Further, residue formation was tracked as a function of the dissolution time by collecting the residue at different stages of the process. These studies showed that the dissolution was not as uniform as desired. Likely, it began from the more susceptible sites on the surface, such as flaws or scratches, and continued through the sublayers, which resulted in a spongy structure with far lower mechanical strength. Furthermore, the residue collected throughout the long-term dissolution showed that residue formation was negligible up to final stages of the dissolution. Further, the amount of accumulated residue increased by raising the current density. Moreover, the long-term anodic dissolution of electrolytic Ni electrode was examined and electrode properties such as impedance behavior, anodic and cathodic efficiencies during the long-term anodic dissolution were assessed. Potential applications of electrocatalysts containing nickel were also studied. An efficient electrocatalyst, based on a nanocomposite involving nickel hydroxide, carbon nitride and reduced graphene oxide (rGO), was synthesized through a facile one-step electrochemical process for the oxygen reduction reaction (ORR) in alkaline media. Comparison of nanocomposites with various concentrations of nickel hydroxide showed that the catalyst containing 44% Ni in the precursor offered the best activity. As this novel nanocomposite is comprised of low cost naturally-abundant materials, the good catalytic activity, high stability and methanol tolerance make this non-precious metal based catalyst promising for practical applications. The need for environmentally compatible, less polluting, and more efficient energy systems has spurred extensive research into the development of batteries and other energy storage devices. Here, we report on a novel three-dimensional (3D) porous nickel modified with iridium oxide (IrO2) toward the design of a high-performance pseudocapacitor. The 3D porous nickel was grown directly onto a Ni plate via a facile electrochemical deposition method assisted by a simultaneously formed hydrogen bubble template. The effects of the electrodeposition time and the current density were systemically investigated, revealing that 3.0 A cm-2 and 150 s were the optimal conditions for the growth of the 3D porous nickel with the highest active surface area, which was subsequently modified with different quantities of IrO2. The electrodeposited 3D porous Ni network structure served as a suitable template to accommodate the cast iridium chloride precursor, and to anchor the formed IrO2 during subsequent thermal treatment. The formed 3D porous NiIr(10%)Ox electrode exhibited high charge/discharge stability and a superb specific capacitance 1643 F g-1 at 1.92 A g-1, which was ~175 times higher than the 3D porous NiO, and over 95 times higher than the same amount of IrO2 deposited on a smooth Ni substrate.