S. Pushpavanam

Zinc-nickel alloy electrodeposits for water electrolysis

Abstract Electrodeposited zinc–nickel alloys of various compositions were prepared. A suitable electrolyte and conditions to produce alloys of various compositions were identified. Alloys produced on electroformed nickel foils were etched in caustic to leach out zinc and to produce the Raney type, porous electro catalytic surface for hydrogen evolution. The electrodes were examined by polarization measurements, to evaluate their Tafel parameters, cyclic voltammetry, to test the change in surface properties on repeated cycling, scanning electron microscopy to identify their microstructure and X-ray diffraction. The catalytic activity as well as the life of the electrode produced from 50% zinc alloy was found to be better than others.

Electrolytic preparation of magnesium perchlorate

The electrochemical preparation of magnesium perchlorate from magnesium chlorate employing a platinum anode and a rotating stainless steel cathode is described. The effect of electrolyte concentration, cathode and anode current densities, pH and temperature of the electrolyte and cathode rotation on current efficiency for the preparation of magnesium perchlorate was studied. A maximum current efficiency of 65–72% was achieved. Based on the results obtained on the laboratory scale, a 100 A cell was designed, fabricated and operated.

Electrolytic preparation of magnesium chlorate from magnesium chloride

The preparation of alkali metal chlorates by electrolysis of the corresponding chlorides has been studied by various authors [1]. However, reports of electrochemical methods for preparing alkaline earth metal chlorates are scarce, even though their salts have some specialty applications [2, 3]. In the case of the electrolysis of magnesium chloride, the precipitation of the magnesium hydroxide due to its low solubility is problematic, leading to a loss in current efficiency. Further, heavy deposits of magnesium hydroxide form on the cathode with consequently increased cell voltage. This difficulty has been obviated using a rotating stainless steel cathode which minimises hydroxide precipitation. A titanium coated metal oxide anode was used for the oxidation of magnesium chloride to magnesium chlorate. This paper presents results for the preparation of magnesium chlorate from magnesium chloride [4].

A Modified process for iridium electrodeposition

SUMMARY As a noble metal, Iridium finds many applications in the industry. Electrodeposited iridium, as a thin coating, provides a cheaper method of using the metal wherever possible. Iridium and platinum-iridium alloy are used in industrial water electrolysis as anodes because of their low oxygen overpotential. Of all the baths available for electrodepositing iridium, the bromide electrolyte appears to be the best. Different methods of preparing the bromide electrolyte are compared: the one prepared using iridium chloride gives improved performance with respect to stability, current efficiency, higher deposit thickness, and appearance of the deposits, besides its cost effectiveness.

High surface area nickel cathodes from electrocomposites

Abstract Raney-nickel cathodes prepared by different methods are increasingly applied in the two most important electrochemical technologies, i.e. chloralkali and water electrolysis. The effectiveness in enhancing the catalytic activity of nickel electrodes by employing three types of particulate materials, namely Raney-nickel, aluminium and alumina powders during the cathodic codeposition of nickel has been investigated. The amount of codeposited precursor depended on its specific gravity and the geometrical arrangement of the substrate (cathode). Composites produced by keeping the substrate horizontal during the deposition exhibited higher catalytic activity. The Tafel parameters for hydrogen evolution have been compared for the above three types of electrodes with those of mild steel and nickel. Cyclic voltammograms indicated high tolerance to current reversals with electrodes prepared using an aluminium precursor. The catalytic activity was in the order of cathodes from NiAl > NiAl2O3 > NiRaneyNi composites.

A bromide electrolyte for the electrodeposition of platinum and platinum–iridium alloy

Abstract A new electrolyte is reported for the deposition of platinum and platinum–iridium alloy. The effect of operating variables and bath composition on the cathode current efficiency and alloy composition were investigated. The bath gives 75% efficiency for platinum deposition and around 50% efficiency for the alloy deposition with 70% iridium. Alloys with varying composition could easily be produced and the deposits obtained on titanium were smooth and adherent.