Deposition and Dissolution

Metal deposition, for the simple case of a monovalent metal ion, is commonly written as  

In the reaction represented by Eq. (3), all the solvent molecules must be removed, to allow formation of the product—a neutral silver atom, and its incorporation in the metal lattice. But charge transfer, if it were to occur by electron transfer across the interface, would have to be represented by two steps, as shown in Eqs. (4) and (5)  

The electron-transfer step represented by Eq. (4) would be very fast, of the order of 1 fs (10 s). This is too short for atoms to move. On the other hand, it should take about lO fs for the atom-transfer reaction shown by Eq. (5) to occur, i.e. for the water molecules around the neutral atom to relax to their equilibrium position in bulk water, and for the silver atom to reach the surface and be incorporated in it. 

It has been stated by several noted authors in electrochemistry that, in the case of metal deposition, charge is carried across the interface by ions rather than by electrons. Unfortunately, the above authors did not implement the consequence of this difference in the analysis of the mechanism of metal deposition and dissolution. In one instance/ the author went as far as to state that 

This approach cannot be sustained, since electron and ion transfer represent two physically different phenomena, and there is no justification to assume that they would follow the same rules. 

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Many studies have been undertaken with a view to improving lithium anode performance to obtain a practical cell. This section will describe recent progress in the study of lithium-metal anodes and the cells. Sections 3.2 to 3.7 describe studies on the surface of uncycled lithium and of lithium coupled with electrolytes, methods for measuring the cycling efficiency of lithium, the morphology of deposited lithium, the mechanism of lithium deposition and dissolution, the amount of dead lithium, the improvement of cycling efficiency, and alternatives to the lithium-metal anode. Section 3.8 describes the safety of rechargeable lithium-metal cells. 

Naoi and co-workers [55], with a QCM, studied lithium deposition and dissolution processes in the presence of polymer surfactants in an attempt to obtain the uniform current distribution at the electrode surface and hence smooth surface morphology of the deposited lithium. The polymer surfactants they used were polyethyleneglycol dimethyl ether (molecular weight 446), or a copolymer of dimethylsilicone (ca. 25 wt%) and propylene oxide (ca. 75 wt%) (molecular weight 3000) in LiC104-EC/DMC (3 2, v/v). 

Subsequent deposition and dissolution of lithium at the anodically passivated electrode by CV in the range -1000 mV to 6000 mV versus Li was successful, showing that the passivating film at the electrode is only impermeable for the anions, but not for lithium ions however, the amount of lithium deposited decreases, with cycle number. 

Upon an increase of the anodic reverse potential finally up to 8 V versus Li the cyclic voltammogran corresponding to Fig. 9 remains unchanged, showing that the passivating layer at the electrode also protects the solvents (PC and DME) from being oxidized. Subsequent deposition and dissolution of lithium at the passivated electrodes remains possible when the electrode is passivated but the cycling efficiency decreases. 

CV of solutions of lithium bis[ salicy-lato(2-)]borate in PC shows mainly the same oxidation behavior as with lithium bis[2,2 biphenyldiolato(2-)-0,0 ] borate, i.e., electrode (stainless steel or Au) passivation. The anodic oxidation limit is the highest of all borates investigated by us so far, namely 4.5 V versus Li. However, in contrast to lithium bis[2,2 -biphenyl-diolato(2-)-0,0 Jborate based solutions, lithium deposition and dissolution without previous protective film formation by oxidation of the anion is not possible, as the anion itself is probably reduced at potentials of 620-670 mV versus Li, where a... 

DespiC, A. R. Transport-Controlled Deposition and Dissolution of Metals 7... 

JoviC, V. D. Electrochemical Deposition and Dissolution of Alloys and Metal Components—Fundamental Aspects 27... 

Figure 1. Mechanisms of photoelectrochemical deposition and dissolution of silver nanoparticles (Ag NPs) (a) UV light-induced deposition and (b) visible light-induced dissolution.

Figure 1.49. Change of the strontium content and Sr/ Sr ratio of Kuroko anhydrite during the deposition and dissolution due to the mixing of hot ascending solution and cold solution (normal seawater) (Shikazono et al., 1983). R mixing ratio (in weight) = S.W./(S.W.+H.S.) in which S.W. and H.S. are seawater and hydrothermal solution, respectively. Open triangle Fukazawa deposits. Solid triangle Hanawa deposits. Open square Wanibuchi deposits. Solid square Shakanai deposits. Concentration of Ca, Sr " " and SO of H.S. are assumed to be 1,(XX) ppm, 1 ppm, and 10 mol/kg H2O, respectively. Concentrations of Ca, Sr " and SO of S.W. are taken to be 412 ppm, 8 ppm, and 2,712 ppm. Temperatures of H.S. and S.W. are assumed to be 350°C and 5°C (Shikazono et al., 1983).

Despic, A. R., Deposition and dissolution of metals and alloys, Part B, Mechanism, kinetics, texture and morphology, CTE, 7, 451 (1983). 

The rotating hemispherical electrode (RHSE) was originally proposed by the author in 1971 as an analytical tool for studying high-rate corrosion and dissolution reactions [13]. Since then, much work has been published in the literature. The RHSE has a uniform primary current distribution, and its surface geometry is not easily deformed by metal deposition and dissolution reactions. These features have made the RHSE a complementary tool to the rotating disk electrode (RDE). 

Multiple-enzyme conversion of CO2 to formate, then formaldehyde, then methanol by FateDH, FaldDH, and ADH Enzymes loaded in CaC03 followed by LbL deposition and dissolution of core, then encapsulation into a gel bead... 

Despic, A. R. and Jovic, V. D., Electrochemical Deposition and Dissolution of Alloys and Metal Composites - Fundamental Aspects, in Modern Aspects of Electrochemistry, R. E. White, J. O. M. Bockris, and B. E. Conway, Editors. 1995, Plenum Press New York, p. 143. 

Sum and Skyllas-Kazacos [44] studied the deposition and dissolution of aluminum in an acidic cryolite melt. The graphite electrode was preconditioned (immersed in cryolite melt) to saturate the surface of the electrode in sodium before aluminum deposition could be observed. Current reversal chronoamperometry was used to measure the rate of aluminum dissolution in the acidic melt. Dissolution rate was mass transport controlled [45] and in the order of 0.8 10 7 and 1.8 10 7 molcm 2s 1 at 1030 °C and 980 °C respectively [44]. 

Data presented in Figure 6.20 can be used to evaluate the Tafel slope b [Eq. (6.62a)] for the deposition and dissolution of copper. From the cathodic polarization curve we obtain the Tafel slope b as... 

In a series of papers, Kolb and coworkers have presented CV and in situ STM studies on palladium deposition on various gold single-crystal electrodes. They have found [430] that PdCU is adsorbed on Au(lll), forming a distorted hexagonal structure, which plays a crucial role in Pd deposition and dissolution. It has also been found that Pd deposition starts from the formation of a pseudomorphic layer in the underpotential region, followed by the formation of the second Pd monolayer at overpotentials. Pd nucleated... 

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