P. Vishnu Kamath

Stabilized α ‐ Ni ( OH ) 2 as Electrode Material for Alkaline Secondary Cells

Hydrotalcite-like compounds of formula Ni1-xAl(x)(OH)2(CO3)x/2 . nH2O (x = 0.1 to 0.25), having the same structure as that of alpha-Ni(OH)2, have been synthesized by substituting nickel hydroxide with aluminum. Of these, the compounds of compositions x greater-than-or-equal-to 0.2 are found to have prolonged stability in strong alkaline medium. The electrodes comprising stabilized alpha-Ni(OH)2 of x = 0.2 composition are rechargeable with discharge-capacity values of 240 (+/- 15) mAh-g-1 and are attractive for applications in various alkaline secondary cells employing nickel-positive electrodes.

Polymorphism in nickel hydroxide: role of interstratification

In addition to the well-known α and β modifications, nickel hydroxide is shown to exist in a number of poorly crystalline forms—clearly distinguishable by their signature X-ray powder diffraction patterns. DIFFaX simulations combined with compositional analysis and IR spectral data indicate that these are interstratified phases consisting of α- and β-type structural motifs intermixed in varying proportions.

Electrochemical synthesis of α-cobalt hydroxide

Cathodic reduction of an aqueous solution of cobalt nitrate at low pH, high Co(II) ion concentration (≥1 M) and low current densities (<0.3 mA cm –2 ) leads to the formation of a novel layered hydroxide of Co(II) with an interlayer spacing of 8.93 A. This hydroxy deficient phase is structurally and compositionally related to α-nickel hydroxide, but likely contains Co(II) ions in a mixed octahedral/tetrahedral coordination. Under other deposition conditions, the better known β-cobalt hydroxide (a=3.17±0.01 A, c=4.61±0.02 A) is obtained.

Electrosynthesis of layered double hydroxides of nickel with trivalent cations

Abstract Layered double hydroxides (LDHs) of nickel with aluminium, chromium, manganese and iron, with the same structure as α-nickel hydroxide, have been electrosynthesized. This paves the way for their possible electrochemical impregnation in sintered nickel plaques for use as electrodes in nickel/cadmium batteries. All these LDHs stabilize the α-nickel hydroxide structure in alkaline media and retain electrochemical activity, as evidenced by cyclic voltammetric studies. The nickel-aluminium LDH shows the highest coulombic efficiency, while the nickel-iron LDH may prove to be unsuitable as a battery electrode material as it catalyzes oxygen evolution by 50 mV, as compared with pure nickel hydroxide.

The Effect of Crystallinity on the Reversible Discharge Capacity of Nickel Hydroxide

The higher reversible discharge capacity exhibited by (bc: badly crystalline)‐nickel hydroxide compared to that of β‐nickel hydroxide can be attributed to the presence of regions characterized by turbostratic disorder in the former. These regions comprise the α‐modification of nickel hydroxide existing in an interstratified form within the sample. The α‐motifs in the are anion‐free, but hydrated, by virtue of which hydroxide exhibits a higher water content (11% by weight) compared to the β‐form (<1%).

Chemical synthesis of α-cobalt hydroxide

Abstract Precipitation reactions using ammonia yield a novel cobalt hydroxide phase that is structurally and compositionally similar to α-nickel hydroxide. The use of other synthetic methods yields the well-known β-Co(OH) 2 . The slab composition, mode of anion inclusion, and thermal behavior of the hydroxides obtained by ammonia precipitation are similar to those of α-nickel hydroxide; however, the materials are poorly ordered. A DIFFaX simulation of the powder X-ray diffraction patterns offers the best visual match with the observed patterns for a 50% stacking disorder and a disc radius between 100 and 1000 A.

Homogeneous precipitation from solution by urea hydrolysis: a novel chemical route to the α-hydroxides of nickel and cobalt

Homogeneous precipitation from solution by hydrolysis of urea at elevated temperatures (T= 120 °C) yields novel ammonia-intercalated α-type hydroxide phases of the formula M(OH)x(NH3)0.4(H2O)y(NO3)2 –x where x= 2,y= 0.68 for M = Ni and x= 1.85, y= 0 for M = Co. These triple-layered hexagonal phases (a= 3.08 ± 0.01 A, c= 21.7 ± 0.05 A) are more crystalline than similar phases obtained by chemical precipitation or electrosynthesis. This method can be adapted as a convenient chemical route to the bulk synthesis of α-hydroxides.

Electroless nickel hydroxide: synthesis and characterization

An electroless method of nickel hydroxide synthesis through the complexation-precipitation route which yields a fine particle material having a specific surface area of 178 m2 g−1 has been described. The morphology of this material as revealed by electron microscopy is distinctly different from the turbostratic nature of electrosynthesized nickel hydroxide. While the long range structure as shown by the X-ray diffraction pattern is similar to that of β-Ni(OH)2, the short range structure as revealed by infrared spectroscopy incorporates characteristics similar to that of α-Ni(OH)2. Cyclic voltammetry studies show that the electroless nickel hydroxide has a higher coulombic efficiency (>90%), a more anodic reversible potential and a higher degree of reversibility compared to the electrosynthesized nickel hydroxide and conventionally prepared nickel hydroxide.

On the relationship between α-nickel hydroxide and the basic salts of nickel

Abstract α -Nickel hydroxide is isostructural with the hydroxide-rich basic salts of nickel. The anions in the basic salts are strongly grafted to the nickel hydroxide sheets, but in α -nickel hydroxide, the anions are loosely intercalated between the hydrated nickel hydroxide sheets, [Ni(OH) 2 − x (H 2 O) x ] x+ . The loose intercalation causes the sheets to become disordered and leads to a turbostratic structure. In contrast, the nickel hydroxy-anion sheets in the basic salts are stacked together in a highly ordered fashion. The basic salts of nickel transform into the α -hydroxide upon ageing in a tartarate buffer, into β -hydroxide at pH 4, and into β bc (bc: badly crystallized) phase in 1 M KOH.

Molecularly adsorbed oxygen on metals: electron spectroscopic studies

Oxygen is shown to adsorb molecularly on gold as well as on Ag and Pt. UV and X-ray photoelectron spectroscopy and Auger electron spectroscopy have been employed to investigate electron states of molecularly adsorbed oxygen.