Solvent and thiourea adsorption/intercalation effects on the solid-state electrochemistry of a-phase nickel hydroxide nanoparticles

Nanoparticles of alpha-phase nickel hydroxide were synthesized by a single-step hydrothermal method using urea as the hydrolytic agent. Precipitated powders were of pure turbostratic alpha-phase as confirmed by x-ray diffraction profile. The ageing of alpha-Ni(OH)(2) in 1.0 M alkali solutions is investigated for pure non-intercalated alpha-Ni(OH)(2) and thiourea intercalated/absorbed alpha-phase nanomaterials. The alpha-Ni(OH)(2) powder immobilized on the surface of graphite electrodes shows a gradual alpha ->beta phase transformation with continuous voltammetric cycling, and the concentration gradient of water that exists in the layered-double-hydroxide-like interlayers of alpha-phase and the solution was shown to play a crucial role on the high electrochemical activity of this phase nickel hydroxide. To understand the role of water in the ageing process, concomitant entries of non-aqueous solvents like ethanol and acetonitrile along with thiourea were effected. Cyclic voltammetric measurements of thiourea-treated alpha-Ni(OH)(2) samples revealed that hydroxyl ion influx during the anodic oxidation depends on the counter flux of solvent molecules, and if the intercalated the solvent is acetonitrile, then the electrochemical activity of alpha-Ni(OH)(2) reduced drastically; Q(a)/Q(c) > 1 for water as solvent in the interlayers alpha-Ni(OH)(2) and Q(a)/Q(c) < 1 for ethanol and acetonitrile as solvents. The alpha-phase gets stabilized in the presence of thiourea with water and ethanol as co-intercalates. Transmission electron microscope images of alpha-Ni(OH)(2) and thiourea-treated samples show a change in particle size and morphology. Elemental CHNS analysis confirms the presence of sulphur in the thiourea intercalated samples.