Raney nickel electrodes

The Raney-nickel electrodes are comparable in performance up to current densities of 100 mA/cm 2 and then deviate from each other remarkably. 

Shim, J. Lee, H.-K. Improved performance of Raney nickel electrode by the addition of electrically conductive materials for hydrogen oxidation reaction. Materials Chemistry and Physics 2001 69(1-3) 72-76. 

Utley and coworkers [31,32] reported that the stereoisomeric ratio cis/trans) of 1,4-disubstituted cyclohexanes formed by the hydrogenation of the corresponding activated cyclohexenes at a mercury electrode depended on solvents and proton sources, and discussed the stereochemical mechanism in detail. On the other hand, according to Lessard and coworkers [33,34], the hydrogenation at a Raney nickel electrode always provides the trans isomers in excess. 

Commercial membrane cells use iron or nickel (e.g. Raney-nickel) electrodes as cathodes and the anodes are from the... 

Raney nickel-based electrodes are prone to deactivate for several reasons, one of them being the formation of a -Ni(OH)2, which is catalytically active but thermodynamically unstable. The long-term performance of this Raney nickel electrode is found to be significantly improved by the in situ formation of 8-Ni(OH)2, which is thermodynamically stable, but is inactive electrochemically [41,53-55]. Korovin et al. [56] suggested that while Ni(0H)2-nH20 is unstable, its cross-linked structure, noted below, may prevent further oxidation and poisoning of the electrode surface. 

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]. 

Robin D et al (1990) The electrocatalytic hydrogenation of fused polycyclic aromatic compounds at Raney nickel electrodes the influence of catalyst activation and electrolysis conditions. Can J Chem 68 1218-1227 (and refertaices in the Introduction)... 

Mahdavi B, Chapuzet JM, Lessard J (1993) The electrocatalytic hydrogenation of phenanthrene at Raney nickel electrodes the effect of periodic current control. Electrochim Acta 38 1377-1380 (and references therein)... 

Chambrion P et al (1995) The influence of surfactants on the electrocatalytic hydrogenation of organic compounds in micellar, emulsified and hydroorganic solutions at Raney nickel electrodes. Can J Chem 73 804-815... 

CyrA,HuotP,BelotG, Lessard J (1990) The efficient electrochemical reduction of nitrobenzene and azoxybenzene to aniline in neutral and basic aqueous methanolic solutions at Devarda copper and Raney nickel electrodes electrocatalytic hydrogenolysis of N-O and N-N bonds. Electrochim Acta 35 147-152... 

Shim J-P, Park Y-S, Lee H-K, Lee J-S. Hydrogen oxidation characteristics of Raney nickel electrodes with carbon black in an alkaline fuel cell. J Power Sources 1998 74(l) 151-4. 

Tomida T, Okamura K, Ashida T, Nakaboyashi I. Relation between the conditions of preparation and the polarization characteristics of spongy Raney nickel electrodes used as anodes for fuel cells. J Electrochem Soc 1992 139(4) 981—4. 

Similarly, it was only after the Second World War, in 1948, that Eduard Wilhelm Leonhard Justi (1904-1986), a German physicist, and August Winsel, a German inventor, produced the first Raney nickel electrodes, which significantly enhanced the performances of the cathode, which is the site of production of hydrogen. Such electrodes were first used in industrial electrolyzers in 1957. 

Raney nickel electrodes prepared in this way were used in many of the fuel cell demonstrations mentioned in the introduction to this chapter. Often Raney nickel was used for the anode and silver for the cathode. This combination was also used for the electrodes of the Siemens alkaline fuel cell used in submarines in the early 1990s (Strasser, 1990). They have also been used more recently, in a ground up form, in the rolled electrodes to be desCTibed in Section 5.4.4 (Gnlzow, 1996). 

Practical units of fuel cells could not operate without porous electrode structures. Porous electrodes with their large electrochemically active surface allow reasonable currents to be supplied at acceptable losses due to polarization (see section 2 of chapter II). Although a few properties, like maximum available surface of electrocatalyst and hydrogenation and dehydrogenation of carbonaceous species for Teflon-bonded platinum black electrodes, and formation of oxygen layers for Raney nickel electrodes, have been discussed in preceding chapters, a discussion of the parameters that determine the operation of porous electrodes had to be offered in a separate chapter. While the empirical aspects concerning the operation of porous electrodes are covered in this chapter, theoretical aspects are dealt with in chapter XVI. 

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