Sodium electrodeposition

If the applied current density is reduced when a tin anode has been made passive in alkaline solution with the formation of a brown him and evolution of oxygen, the surface him changes to one of yellow colour and dissolution of tin as stannite ions proceeds freely . This effect is exploited in the electrodeposition of tin from sodium or potassium stannate solutions. 

Articles of steel, copper or brass which require a thicker coating than is possible by chemical replacement, and which are difficult to tin by normal electrodeposition, may be coated by immersion in alkaline sodium stannate solution in contact with aluminium suitably placed to act as anode. 

Tin-zinc alloys of a wide range of composition can be electrodeposited from sodium stannate/zinc cyanide baths only the coatings with 20-25% zinc have commercial importance . 

Zinc is electrodeposited from the sodium zincate electrolyte during charge. As in the zinc/bromine battery, two separate electrolytes loops ("posilyte" and "nega-lyte") are required. The only difference is the quality of the separator The zinc/ bromine system works with a microporous foil made from sintered polymer powder, but the zinc/ferricyanide battery needs a cation exchange membrane in order to obtain acceptable coulombic efficiencies. The occasional transfer of solid sodium ferrocya-nide from the negative to the positive tank, to correct for the slow transport of complex cyanide through the membrane, is proposed [54],... 

A comprehensive work on the electrodeposition chemistry and characterization of anodically synthesized CdTe thin films has been presented by Ham et al. [98]. In this work, along with the electrolytic anodic synthesis of CdTe by using Cd anodes in alkaline solutions of sodium telluride, an electroless route of anodizing a Cd electrode held at open circuit in the same solution was also introduced. The anodic method was expected to produce CdTe with little contamination from Te on account of the thermodynamic properties of the system the open-circuit potential of Cd anodes in the Te electrolyte lies negative of the Te redox point, so... 

By electrodeposition of CuInSe2 thin films on glassy carbon disk substrates in acidic (pH 2) baths of cupric ions and sodium citrate, under potentiostatic conditions [176], it was established that the formation of tetragonal chalcopyrite CIS is entirely prevalent in the deposition potential interval -0.7 to -0.9 V vs. SCE. Through analysis of potentiostatic current transients, it was concluded that electrocrystallization of the compound proceeds according to a 3D progressive nucleation-growth model with diffusion control. 

Electrodeposition has been attempted also on flexible substrates within the scope of fabricating flexible solar cells. Huang et al. [177] investigated the electrodeposition of CIS on Au-coated plastic substrate from aqueous acidic (pH 1.65) solutions of millimolar CuCh, InCb, Se02, containing triethanolamine and sodium citrate. Stoichiometric, semiconductive CIS films (Eg = 1.18 eV) were obtained after annealing at 150 °C in nitrogen. 

The formation of colloidal sulfur occurring in the aqueous, either alkaline or acidic, solutions comprises a serious drawback for the deposits quality. Saloniemi et al. [206] attempted to circumvent this problem and to avoid also the use of a lead substrate needed in the case of anodic formation, by devising a cyclic electrochemical technique including alternate cathodic and anodic reactions. Their method was based on fast cycling of the substrate (TO/glass) potential in an alkaline (pH 8.5) solution of sodium sulfide, Pb(II), and EDTA, between two values with a symmetric triangle wave shape. At cathodic potentials, Pb(EDTA)2 reduced to Pb, and at anodic potentials Pb reoxidized and reacted with sulfide instead of EDTA or hydroxide ions. Films electrodeposited in the optimized potential region were stoichiometric and with a random polycrystalline RS structure. The authors noticed that cyclic deposition also occurs from an acidic solution, but the problem of colloidal sulfur formation remains. 

Photovoltaic response parameters for electrodeposited (polycrystalline) CdTe thin film electrodes in sulfide-polysulfide or alkaline sodium telluride PEC have been reported, primarily with no reference to the stability of the cells [100], In view of the instability of CdTe in aqueous solutions, Bhattacharya and Rajeshwar [101] employed two methods for the characterization of their electrodeposited CdTe-based PEC. In the first one, a coating of Pb02 (-100 nm thick) was deposited on the CdTe film surface by electroless deposition, and the coated films... 

Recendy, ID quantum dots of gallium selenide with average diameter 8-10 nm, connected in the form of chains of average length 50-60 nm, were synthesized on rro substrates by cathodic electrodeposition from acidic aqueous solutions of gallium(III) nitrate and selenious acid [186], The structural analysis from XRD patterns revealed the formation of Ga2Se3/GaSe composition. The films were found to be photoactive in aqueous sodium thiosulfate solution and showed p-type conductivity. 

It is interesting to note that Brenner and Riddell (2-4) accidentally encountered electroless deposition of nickel and cobalt during electrodeposition of nickel-tungsten and cobalt-tungsten alloys (in the presence of sodium hypophosphite) on steel tubes in order to produce material with better hardness than that of steel. They found deposition efficiency higher than 100%, which was explained by an electroless deposition contribution to the electrodeposition process. 

A Raney nickel surface is also suitable for electrocatalytic hydrogenation [205]. This surface is prepared by electrodepositing nickel from a solution containing suspended Raney nickel alloy (Ni 50% A1 50%). Some alloy particles stick to the surface, which is then activated by leaching the aluminium using hot aqueous sodium hydroxide. Cyclohexanone, acetophenone and benzil have been converted to the corresponding alcohol and there is no stereoselectivity for the formation of hydrobenzoin from benzil. 

Although the theoretical studies predict solvent medium breakdown before the onset of actinium electrodeposition, there have been reports of Ac(0) electrodeposition from aqueous solutions utilizing several different methods [8, 9]. One set of studies [8] describes the electrodeposition of actinium from nitric acid solutions, with varying pH values (1.0-4.0) being set to the appropriate level by the addition of sodium hydroxide. The anode and cathode in these studies were platinum metal, and the current density was varied from 50 to 200 mA cm . The authors found that quantitative electrodeposition of actinium could be achieved under various conditions, with the shortest electrolysis time of 1 h being obtained with a current density of200 mA cm and a pH of 2.0. A second study employed a saturated aqueous solution of urea oxalate (ca 6.6% at 30 °C) as an electrolyte for the electrodeposition of Ac onto a nickel foil cathode [9]. The authors of this study found that the yield of electrodeposited Ac increased with time and reached a near quantitative maximum yield of 97% at a current density of 53 mAcm after 2 h. The Ac electrodeposits were suitable for further study using nuclear spectroscopy. 

In many cases, the difference between these potentials—the window of operation without electrochemical decomposition of the solvent—is 3-4 V. In the aqueous case, it may in practice be as little as 1.5 V. On the other hand, even sodium can be electrodeposited from a solution of sodium acetate in ethanolamine. These advantages are countered by three factors that must be considered before a nonaqueous electrodeposition process is chosen as the best solution to co-deposition of H (Section 4.8.3). 

Two common alternatives are available for electrodepositing tin 30 alkaline and acidic baths. The alkaline bath has good throwing power but consumes more power than the acid bath. Tin is present in the alkaline bath as stannate(TV), [Sn(OH)6]2, the bath being approximately 0.25 M in free hydroxide ion (pH 13.4). The hydroxide ion is the principal charge carrier. Potassium is superior to sodium as the counter ion (greater ionic mobility) but economic factors lead to the continued use of sodium in many plants. The hydroxide ions, acting as a sink for dissolved CO2, also prevent two undesirable reactions (equations 24 and 25). 

Alkali metals have high oxidation-reduction potentials and low atomic masses. Thus they are attractive candidates for anodes in secondary batteries. In this context, it was shown in a couple of investigations that lithium and sodium can be electrodeposited from tetrachloroaluminate-based ionic liquids. 

Piersma et al. demonstrated that lithium can be electrodeposited from 1-ethyl -3-methyl-imidazolium tetrachloroaluminate ionic liquid, when lithium chloride was dissolved in the melt [3], Platinum, glassy carbon and tungsten were used as working electrodes with molybdenum and platinum foils as counter electrodes. At -2.3 V a reduction peak of Li+ is observed and at about -1.6 V the stripping of lithium occurs. They noticed that the efficiency was much less than 100%. In addition, they were able to demonstrate that the addition of proton sources like triethanolamine-HCl widens the electrochemical window and allows the plating and stripping of lithium (and also sodium). 

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