Hydrogen evolution from alkaline solutions

B. Electrocatalyst Coatings for Hydrogen Evolution from Alkaline Solution... 

The intermediate remains on the electrode until it is transformed into another particle during the consecutive steps that make up the overall reaction. The simplest example is (Section 7.6.2) the mechanism of hydrogen evolution, in which one possible step involves chemical recombination between adsorbed H s, put onto the electrode surface by means of the discharge of H20+ from acid or H20 from alkaline solutions. The adsorbed H is the intermediate radical. 

The hydrogen evolution reaction (h.e.r.) is of particular importance in corrosion for a number of reasons. Firstly, the reduction of the HjO ion in acid solutions or the H2O molecule in neutral and alkaline solution is a common cathodic reaction for the corrosion of metals in acid, neutral and alkaline solutions the fact that iron will corrode in neutral water free from dissolved... 

Technetium metal can be electrodeposited from an acidic solution of pertechnetate using a platimun, nickel or copper cathode. Electrolysis of neutral, unbuffered solutions, alkaline solutions, and sulfuric acid solutions lower than 2 N yield a black deposit of hydrated TcOj The current efficiencies are generally poor but the deposition is reasonably quantitative. The deposition requires the application of relatively negative cathode potentials and is therefore non-selective. Polaro-graphy indicates that the overpotentials for the evolution of hydrogen on technetium are rather low hence, electrolysis from acidic media will always include concurrent discharge of hydrogen . ... 

On the other hand, to accelerate alcoholysis of NaH and KH in solutions of benzene or THF [22.1] - [2.22] - ctyptands are used (which bind alkaline metal into a rather stable chelate complex) [1004], Quite stable, volatile per-fluorotert-butoxides were first obtained in reactions of LiH or NaH with (CF3)3COH they distill at atmospheric pressure at 218 and 232°C, respectively [467] (the application of metals would presumably lead in this case to condensation of Wurtz type). Li and Na hydrides are used as cheaper than metal raw materials for production of the corresponding metal alkoxides. In particular it has been suggested that the equipment used in production of MH could be cleaned from its residue by the mixture ofEtOH and the aromatic hydrocarbon (40 to 60% by volume). After hydrogen evolution is completed the solvent is eliminated under vacuum at < 90°C the residue is MOEt with the content of the main product > 98% [342],... 

The mechanism may change from acids to alkalis in some cases [365], This may be related to the higher sensivity of the Fe surface to oxidation in alkaline solutions [365, 367], Actually, the corrosion of Fe proceeds also under moderate cathodic load [368]. Impedance measurements have suggested that the classical mechanisms of hydrogen evolution is probably inadequate to describe the situation on Fe [377], A surface diffusion step with spillover of hydrogen to sites with lower M-H energy has been suggested. Adsorption of CN- interferes with such a diffusion. 

Over the past several years, Gruen and coworkers have examined the SH response from iron electrodes in alkaline solutions [45, 53, 172]. In their work on polycrystalline iron, they concluded that the potential dependent SH response which was observed during surface oxidation could be attributed to two intermediate phases on the electrode surface between the passive film at oxidative potentials and the reduced metal at hydrogen evolution potentials [53]. They have recently extended this work to Fe(110). In this study [172], they examined the SH rotational anisotropy from this crystal under ambient conditions. They found that the experiments reveal the presence of both twofold and threefold symmetric species at the metal/oxide interface. When their data is fit to the theory of Tom et al. [68], they conclude that the measured three-fold symmetric oxide is found to be tilted by 5° from the Fe(110) plane. The two-fold symmetric structure is aligned with the Fe(110) surface. 

To a suspension of this product in 200 ml. of water, magnetically stirred and heated at 65°C., a 10% sodium hydroxide solution is added dropwise. The compound gradually dissolves in the alkaline solution, but it is very important to add the sodium hydroxide solution slowly, especially toward the end of the operation when the product is almost all dissolved. The pH of the suspension should never go above 10. At higher pH the compound may readily decompose to a very dark, soft precipitate of higher molybdenum hydroxides with evolution of hydrogen. From 60 to 70 ml. of sodium hydroxide solution is usually needed to dissolve the compound completely. The... 

Rubidium hydrogen carbonate, RbHC03.—The primary carbonate is produced by saturating a concentrated aqueous solution of rubidium carbonate with carbon dioxide.9 It dissolves readily in water, the slightly alkaline solution being decomposed by heat, with evolution of carbon dioxide. The heat of solution at 15° C. is —4 731 Cal., and that of formation from its elements 231 92 Cal. The dissociation-pressure has been investigated by Caven and Sand.10... 

Ammonium arsenates.—Excess of ammonia precipitates normal ammonium arsenate, (NH4)3As04, from concentrated solutions of the primary and secondary salts. It yields a very alkaline solution, decomposed by zinc and by aluminium with evolution of hydrogen and arsine.14 Secondary ammonium arsenate, (NH4)2HAs04, is gradually deposited from a concentrated solution of arsenic acid and ammonium hydroxide.15 Loss of ammonia, or addition of arsenic acid to its solution, converts it into primary ammonium arsenate, NH4H2As04, crystals of density 2-307 16 or 2-3105.17... 

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