Electrochemical nonaqueous solutions

Gal D, Hodes G (2000) Electrochemical deposition of ZnSe and (Zn,Cd)Se films from nonaqueous solutions. J Electrochem Soc 147 1825-1828... 

Figure 1. Schematic representation of the electrochemical windows of the processes, occurring during cathodic polarization of graphite electrodes in nonaqueous solutions.

The rate is 400-fold faster than for the free ligand. In both cases intermolecular attack of OH at the phosphorus center is involved. Hydrolysis of the corresponding Co(III) complex is through 100% Co - O bond cleavage, thus preventing a test of the effect of metal coordination. Oxidation of Ir(H20) + yields binuclear Ir(IV) and Ir(V) species although little is known of their chemistry. 3 Electrochemical reduction in nonaqueous solution of Ir(bpy) -"... 

From a review of the recent Russian electrochemical literature it can be concluded that intensive research on nonaqueous batteries is carried out in the U.S.S.R. Although no results of the performance of such batteries are published, papers on properties of Li solutions in solvents used in Li cells, and on the behaviour of metallic Li in nonaqueous solutions, which have appeared recently in Russian literature, can be inferred to be the tip of an iceberg of research in that field. For example, the electrodeposition of Li from dimethylformaunide solutions of its salts (40), or the behaviour of Li in aprotic solutions (4la) and the solubility and conductivity of its salts in these solutions (41b) emanate from an unnamed research institute in Moscow. 

Kessler, Yu.M. et al., "Electrochemical Properties of Aluminum Compounds in Nonaqueous Solutions", Advances in Chemistry, (Russ.), 32, 261 (1964). 

Zhou Y, Itoh H, Uemura T, Naka K, Chujo Y (2002) Preparation, optical spectroscopy, and electrochemical studies of novel pi-conjugated polymer-protected stable PbS colloidal nanoparticles in a nonaqueous solution. Langmuir 18 5287-5292... 

Electrodeposition of Pa metal has been performed from both aqueous and nonaqueous solutions. An isopropanol solution of 10-20 p,gmL Pa from 8M HCl/0.01 M HE/Pa stock was employed for quantitative electrodeposition [41]. The cell consisted of a gold-plated A1 cathode and a Pt wire anode. During deposition the current was maintained at 1 mA, which produced a potential of 400-600 V during the 90-min electrolysis. The progress of the electrolysis was externally monitored by alpha-counting of the electrolysis solution before and during the electrodeposition. Deposition studies of metal from aqueous solutions are more common. Pa was electrodeposited on platinum in 95% yield at tracer concentrations from an electrolyte of [NH4]C1/HC1 [42]. Electrochemical and chemical conditions of the plating process were described for Pu solutions, which served as a model for the other actinide elements studied. Another tracer... 

Nikitas, isotherms, 936, 952, 1195 Nitrobenzene reduction, 1376 Nonaqueous solutions, coadsorption of hydrogen and organic molecules, 13-10 see also hydrogen coadsorption Non -faradaic electrochemical modification of catalytic activity, 1371 Nonlocalized adsorption, 928, 958 Nonpolarizable interfaces, 812, 857, 1055, 1060, 1111... 

Sawyer, D.T., Roberts, J.L., Jr Experimental Electrochemistry for Chemists, Wiley Sc Sons, New York, 1974 Sawyer, D.T., Sobkowiak, A., Roberts, J.L., Jr Electrochemistry for Chemists, 2nd edn, Wiley Sons, New York, 1995. Useful references on electrochemical techniques in nonaqueous solutions. 

The membrane system considered here is composed of two aqueous solutions wd and w2, separated by a liquid membrane M, and it involves two aqueous solution/ membrane interfaces WifM (outer interface) and M/w2 (inner interface). If the different ohmic drops (and the potentials caused by mass transfers within w1 M, and w2) can be neglected, the membrane potential, EM, defined as the potential difference between wd and w2, is caused by ion transfers taking place at both L/L interfaces. The current associated with the ion transfer across the L/L interfaces is governed by the same mass transport limitations as redox processes on a metal electrode/solution interface. Provided that the ion transport is fast, it can be considered that it is governed by the same diffusion equations, and the electrochemical methodology can be transposed en bloc [18, 24]. With respect to the experimental cell used for electrochemical studies with these systems, it is necessary to consider three sources of resistance, i.e., both the two aqueous and the nonaqueous solutions, with both ITIES sandwiched between them. Therefore, a potentiostat with two reference electrodes is usually used. 

The electrochemical dissolution of copper and other metals (see Sec. 3.4.2 on direct electrosynthesis), in solutions of tetramethylthiuram disulfide and its analogues in nonaqueous solutions of acetone and acetonitrile, was first carried out by Tuck and coworkers [619]. Complexes with a general formula given by M(R2NCS2) are formed with good yields under these conditions. The proposed mechanism... 

An additional study on the same system has been reported, including a comparison of direct electrochemical and conventional chemical dissolution of metallic copper in TMTD solutions in various solvents under conditions of simultaneous ultrasonic treatment of the reaction system [133,620]. It has been shown that the system TMTD-copper-solvent could serve as a perfect model to study the influence of simultaneous application of ultrasonic treatment (see Sec. 3.5) on the syntheses of complexes of the transition metals in different nonaqueous solutions, by using and testing several techniques [620]. Several other studies on the interaction of copper and iron species with thiruam sulfides have also been reviewed [621]. 

Table 3.1 Experimental Conditions for the Oxidative and Electrochemical Dissolution of Copper in Nonaqueous Solutions of [Me2N—C(S) — S—]2 (TMTD)...

As mentioned above, urea and PA are the most cheap phthalocyanine precursors and are produced on an industrial scale, so it is not surprising that numerous articles and patents have been dedicated to the study of their interactions [6,30,41-48], Flowever, only copper and some other strong metals (in relation to the PcM formation and stability) form their phthalocyanines using these precursors. There are almost no reports in the available literature about attempts to electrosynthesize PcF12 or PcM starting from urea and phthalic anhydride, except for a recent work [32] where the interaction between these two precursors, as well as phthalimide, in various nonaqueous solutions by conventional chemical and electrochemical methods is studied in detail (Example 18). 

N. S. Lewis, C. M. Gronet, G. W. Cogan, J. E. Gibbons, and G. M. Moddel,./. Electrochem. Soc. 131 2873 (1984). Nonaqueous solution study of redox reactions at light activated semiconductors confirming applicability of Schottky-type theory. 

To what extent the films grown electrochemically have decisive advantages over those grown with other techniques is not clear yet. However, one can see that great variety (e.g., ternary and quaternary alloy formations) is possible, and the availability of potentiostatic control and nonaqueous solutions may be helpful. 

Nonactive/slightly reactive electrode materials include metals whose reactivity toward the solution components is much lower compared with active metals, and thus there are no spontaneous reactions between them and the solution species. On the other hand, they are not noble, and hence their anodic dissolution may be the positive limit of the electrochemical windows of many nonaqueous solutions. Typical examples are mercury, silver, nickel, copper, etc. It is possible to add to this list both aluminum and iron, which by themselves may react spontaneously with nonaqueous solvent molecules or salt anions containing atoms of high oxidation states. However, they are not reactive due to passivation of the metal which, indeed, results from the formation of stable, thin anodic films that protect the metal at a wide range of potentials, and thus the electrochemical window is determined by the electroreactions of the solution components [51,52],... 

Besides the effect of the electrode materials discussed above, each nonaqueous solution has its own inherent electrochemical stability which relates to the possible oxidation and reduction processes of the solvent,the salts, and contaminants that may be unavoidably present in polar aprotic solutions. These may include trace water, oxygen, CO, C02 protic precursor of the solvent, peroxides, etc. All of these substances, even in trace amounts, may influence the stability of these systems and, hence, their electrochemical windows. Possible electroreactions of a variety of solvents, salts, and additives are described and discussed in detail in Chapter 3. However, these reactions may depend very strongly on the cation of the electrolyte. The type of cation present determines both the thermodynamics and kinetics of the reduction processes in polar aprotic systems [59], In addition, the solubility product of solvent/salt anion/contaminant reduction products that are anions or anion radicals, with the cation, determine the possibility of surface film formation, electrode passivation, etc. For instance, as discussed in Chapter 4, the reduction of solvents such as ethers, esters, and alkyl carbonates differs considerably in Li or in tetraalkyl ammonium salt solutions [6], In the presence of the former cation, the above solvents are reduced to insoluble Li salts that passivate the electrodes due to the formation of stable surface layers. However, when the cation is TBA, all the reduction products of the above solvents are soluble. 

There are several types of automated KF titrators available from leading companies that supply electrochemical equipment (Metrohm, for example). It should be noted that the mother solutions of these instruments are highly sensitive to side reactions with components of the nonaqueous solution. Hence, the users have to consult the suppliers of the KF mother solutions to ensure that they are compatible with the composition of the studied solution. 

The presence of contaminants in the solution, such as H20, C02, 02, and alcohols may limit the electrochemical window of nonaqueous systems. These reactive contaminants are commonly present in nonaqueous solutions and may be reduced at higher potentials (or oxidized at lower potentials), compared with the reduction (or oxidation) potentials of the other components of the solutions. 

VIII. OXIDATION PROCESSES OF NONAQUEOUS SOLUTIONS AND THE ANODIC LIMITS OF THE ELECTROCHEMICAL WINDOWS... 

The Electrochemical Behavior of Active Metal Electrodes in Nonaqueous Solutions... 

Basic issues such as surface reactions, surface film formation, passivation, ionic and electronic transport phenomena through surface films, problems in uniformity of deposition and dissolution processes, correlation between surface chemistry, morphology, and electrochemical properties are common to all active metal electrodes in nonaqueous solutions and are dealt with thoroughly in this chapter. It is believed that many conclusions related to Li, Mg, Ca, and A1 electrodes can be extended to other active metal electrodes as well. 

In conclusion, a key feature of active metal electrodes in nonaqueous solutions is their coverage by surface films which control their electrochemical behavior. Hence, transport phenomena in these films deserve special attention. 

Figure 18 Various models proposed for the surface films that cover Li electrodes in nonaqueous solutions. The relevant equivalent circuit analog and the expected (theoretical) impedance spectrum (presented as a Nyquist plot) are also shown [77]. (a) A simple, single layer, solid electrolyte interphase (SEI) (b) solid polymer interphase (SPI). Different types of insoluble Li salt products of solution reduction processes are embedded in a polymeric matrix (c) polymeric electrolyte interphase (PEI). The polymer matrix is porous and also contains solution. Note that the PEI and the SPI may be described by a similar equivalent analog. However, the time constants related to SPI film are expected to be poorly separated (compared with a film that behaves like a PEI) [77]. (With copyrights from The Electrochemical Society Inc., 1998.)...

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