Nickel hydrogen overvoltage

It has been suggested that the role of nickel (as NiAlj) is to provide sites of low hydrogen overvoltage, where cathodically liberated hydrogen may be liberated without disrupting the protective oxide . The distribution of such sites is apparently critical however, since high corrosion resistance is associated with a fine dispersion of the second phase, while the electronic conductivity of the film is probably also important . 

Temperature the hydrogen overvoltage decreases with increasing temperature. It can be zero at higher temperatures. For example, the hydrogen overvoltage on nickel is zero at 90 °C. 

Pressure at elevated pressures, the value of the hydrogen overvoltage changes only very slightly but at lower pressures, it increases sharply on certain metals, as for example in the case of copper, nickel, and mercury cathodes. 

Cathode Nickel may be an alternative for platinum metals in alkaline solutions due to its low hydrogen overvoltage and catalytic activity. The activity is especially high at the very fine dispersed Raney nickel , which is available from a layer of a nickel alloy on the cathode surface by dissolving the alloy metal (aluminum or zinc) in alkaline solution prior to use (e.g. [23, 24]. Raney nickel usually is not stable against oxygen and self-ignition in air may be possible). 

Cathodic surfaces of finely divided platinum, palladium and nickel have a low hydrogen overvoltage and the dominant electrochemical reaction is the generation of a layer of hydrogen atoms. The electrocatalytic hydrogenation of aldehydes and ketones can be achieved at these surfaces. Cathodes of platinum or palladium black operate in both acid solution [203] and in methanol containing sodium methoxide [204], The carbonyl compound is converted to the alcohol. Reduction of 4-tert-butylcyclohexanone is not stereoselective, however, 1,2-diphenylpropan-l-one is converted to the / reo-alcohol. 

The iron-nickel oxide alkaline battery system has many features in common with the nickel-cadmium system discussed above. It was first developed by Edison in the USA at the turn of the century and was patented in the same year as Jungner s first nickel-cadmium US patent, 1901. Iron can be regarded as a favourable active battery material because of its low cost, high theoretical specific capacity (twice that of cadmium) and non-toxic, pollution-free characteristics. However, because its reduction potential is below that of hydrogen, and since hydrogen overvoltage is low on iron, charge retention is poor and efficiency is low. 

H. Yamashita, T. Yamamura and K. Yoshimoto, The relation between catalytic ability for hydrogen evolution reaction and characteristics of nickel-tin alloys, J. Electrochem. Soc., 1993,140, 2242-2243 K. Yoshimoto, H. Yamashita and M. Miyashita, Development of Ni-Sn alloy plating active catholyte and application in industrial electro-dialyzer, Soda Enso (Soda Chlorine), 1994, 45, 418-427 Yoshida and T. Morimoto, A new low hydrogen overvoltage cathode for chlor-alkali cell, Electrochim. Acta, 1994, 39, 1733-1737. 

Tokuyama Soda Company developed NiS and Ni-Sn alloy coated cathodes [194-197]. The hydrogen overvoltage of the electroplated Ni-Sn alloy cathode, with a nickel content of 40-80wt%, in a mixed solution of NaOH and NaCl at 90°C, was about 100 mV. The Ni-Sn cathodes were used in retrofit-type membrane cells and filter press-type electrolyzers, both operating at 4kAm and 80°C. The cell voltages were constant for over 8 years. 

E. Endoh, M. Nakao, and Y. Takechi, Raney Nickel Dispersion-plated Low Hydrogen Overvoltage Cathode, In Proc. Vol. 99-21, The Electrochemical Society Inc., Princeton, NJ (1999), p. 245. 

Also highly catalytically active Raney nickel electrodes have been developed. Their production is possible at remarkably low cost by cathodic deposition of a Ni/Zn alloy and subsequent activation by a treatment with hot K0H[6]. These electrodes are used as cathode and anode. Their oxygen overvoltage is below 200 mV and their hydrogen overvoltage less than 100 mV at current densities of 4000-6000 A m and 100°-120 C[7]. 

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