Nickel hydrogen evolution

Adequate ventilation is necessary for aH process lines to ensure worker safety. Electroless copper baths must have good ventilation to remove toxic formaldehyde vapors and caustic mist generated by the hydrogen evolution reactions and air sparging. Electroless nickels need adequate ventilation to remove nickel and ammonia vapors. Some states and municipalities requite the removal of ammonia from wastewaters. A discussion of printed circuit board environmental issues and some sludge reduction techniques is avaHable (25). 

Much of the information available on resistance of nickel-iron alloys to corrosion by mineral acids is summarised by Marsh. In general, corrosion rates decrease sharply as the nickel content is increased from 0 to 30-40%, with little further improvement above this level. The value of the nickel addition is most pronounced in conditions where hydrogen evolution is the major cathodic reaction, i.e. under conditions of low aeration and agitation. Results reported by Hatfield show that the rates of attack of Fe-25Ni alloy in sulphuric and hydrochloric acid solutions, although much lower than those of mild steel, are still appreciable (Tables 3.35 and 3.36). In solutions of nitric acid, nickel-iron alloys show very high rates of corrosion. 

Fig. 12.4 Corrosion diagram for a zinc diecasting in a nickel plating bath, pH 2-2. There are two possible cathodic reactions, hydrogen evolution (H) and nickel ion reduction (AO. The corrosion current is the sum of the partial cathode currents. Even with live entry the potential is still too high to suppress corrosion, though the rate is reduced to...

In normal battery operation several electrochemical reactions occur on the nickel hydroxide electrode. These are the redox reactions of the active material, oxygen evolution, and in the case of nickel-hydrogen and nickel-metal hydride batteries, hydrogen oxidation. In addition there are parasitic reactions such as the corrosion of nickel current collector materials and the oxidation of organic materials from separators. The initial reaction in the corrosion process is the conversion of Ni to Ni(OH)2. 

For the cathodic reduction of organic substances, electrodes of two types are used the platinum and the mercury type. Those of the first type (platinum metals, and in alkaline solutions nickel) exfiibit low polarization in hydrogen evolution their potential can be pushed in the negative direction no further than to -0.3 V (RHE). Hydrogen readily adsorbs on these electrodes, which is favorable for reduction... 

Bockris, J. O M. and Potter, E. C. (1952) The mechanism of hydrogen evolution at nickel cathodes in aqueous solutions. 

Termination of the plateau at a sufficiently high overpotential. The potential at which a consecutive electrode reaction sets in (e.g., hydrogen evolution in cathodic reactions) is determined by the composition of the electrolyte (specifically, the pH) and by the nature and state of the electrode surface (hydrogen overpotential). The reduction of ferricyanide in alkaline solution on nickel also provides a better-defined plateau in this respect than the deposition of copper in acid solution. 

Further evidence for surface effects upon the stereochemistry of electrochemical reduction of ketones comes from the discovery that the nature of the cathode material may effect stereochemistry. Reduction of 2-methylcyclo-hexanone affords pure trans-2-methylcyclohexanone at mercury or lead cathodes, a mixture of cis and trans alcohols (mostly trans) at nickel, and pure cis alcohol at copper 81 >. Reduction could not be effected at platinum presumably hydrogen evolution takes place before the potential necessary for reduction of the ketone can be reached. 

The stereochemistry of electrochemical reduction of acetylenes is highly dependent upon the experimental conditions under which the electrolysis is carried out. Campbell and Young found many years ago that reduction of acetylenes in alcoholic sulfuric acid at a spongy nickel cathode produces cis-olefins in good yields 126>. It is very likely that this reduction involves a mechanism akin to catalytic hydrogenation, since the reduction does not take place at all at cathode substances, such as mercury, which are known to be poor hydrogenation catalysts. The reduction also probably involves the adsorbed acetylene as an intermediate, since olefins are not reduced at all under these conditions and since hydrogen evolution does not occur at the cathode until reduction of the acetylene is complete. Acetylenes may also be reduced to cis olefins in acidic media at a silver-palladium alloy cathode, 27>. 

The composition of the codeposition bath is defined not only by the concentration and type of electrolyte used for depositing the matrix metal, but also by the particle loading in suspension, the pH, the temperature, and the additives used. A variety of electrolytes have been used for the electrocodeposition process including simple metal sulfate or acidic metal sulfate baths to form a metal matrix of copper, iron, nickel, cobalt, or chromium, or their alloys. Deposition of a nickel matrix has also been conducted using a Watts bath which consists of nickel sulfate, nickel chloride and boric acid, and electrolyte baths based on nickel fluoborate or nickel sulfamate. Although many of the bath chemistries used provide high current efficiency, the effect of hydrogen evolution on electrocodeposition is not discussed in the literature. 

Chonglun F., Piron D.L., Paradis R, Hydrogen evolution on electrodeposited nickel-cobalt-molybdenum in alkaline water electrolysis, Electrochim. Acta, 39(18), 2715-2722,1994. 

A clear advantage of alkaline electrolysers is the use of nickel-based electrodes, thus avoiding the use of precious metals. Catalytic research is aimed at the development of more active anodes and cathodes, primarily the development of high surface area, stable structures. Nickel-cobalt spinel electrodes for oxygen evolution and high surface area nickel and nickel cobalt electrodes for hydrogen evolution have been shown at the laboratory scale to lead to a decrease in electrolyzer cell voltage [47]. More active electrodes can lead to more compact electrolysers with lower overall systems cost. 

In a set of experiments (6), the authors have determined the electrochemical efficiency of Ni/Cu layer deposition. It was found that the copper layers deposit with 96% efficiency and the nickel deposit with 90% efficiency. This information, together with the measured coulomb input per layer, enables one to confirm the validity of the suggested formula. Alternatively, if one accepts the arguments that lead to the formula, the electrochemical efficiency values can be viewed as confirmed. The relatively slight deviation from perfect efficiency, at least in the case of nickel, is probably connected with hydrogen evolution. 

Platinum and carbon are frequently used as counter electrode materials for both anode and cathode. Platinum is resistant to corrosion while carbon is cheap and can be discarded after use. Nickel is a suitable counter cathode material in aqueous solution because of the low overpotential for hydrogen evolution. Titanium coated with platinum and then over coated with mthenium dioxide is a stable counter anode material with a low overpotential for oxygen evolution. 

Chen L, Lasia A (1991) Study of the kinetics of hydrogen evolution reaction on nickel-zinc Alloy electrodes. J Electrochem Soc 138 3321-3328... 

Trifluorophosphine is a very convenient ligand in metal atom chemistry to use along with other ligands, e.g., in the stabilization of metal arene complexes (Section III,B). Reaction of a mixture of PF3 and PH3 with nickel vapor yields Ni(PF3)3PH3 and Ni(PF3)2(PH3)2 but no Ni(PH3)4. Attempts to make Ni(PH3)4 lead to hydrogen evolution from the ligand during or after condensation with the nickel vapor (128). 

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