Constant potential electrolysis

The low-spin Nini06 compound [Ni(bipy02)3]3+ (bipy02 = 2,2 -bipyridyl-1,1 -dioxide) is the product of constant-potential electrolysis of the Ni11 salt.176 Its violet solutions show a rhombic EPR spectrum indicative of a Jahn-Teller-distorted (dz )1 ground state. 

CPE constant potential electrolysis, controlled potential electrolysis... 

The constant potential electrolysis of tetraaikylsiianes in the presence of Et4NH3F4 at 2.3 V results in the cleavage of the C-Si bond and the formation of the corresponding fluorosilanes [21], Presumably, the first step involves the formation of the pentacoordinate anionic species (RR 3SiF ) which is oxidized... 

FIGURE 2.32. First-order reaction product (C) and second-order product (D) yields for Scheme 2.17 as a function of the competition parameter, a Constant concentration-constant potential and constant-current electrolyses, b Exhaustive constant-potential electrolysis. 

In the case of constant reactant concentration-constant potential electrolysis, equation (2.28) does not apply since... 

K(,SiW 02 )Mn I I) Manganese ion-substituted silicon polyoxotungstate can be used as a mediator for alcohol oxidation. Constant potential electrolysis of 1-phenylethanol at 1.25 V in the presence of 5 mol% of the catalyst gave acetophenone in 61% yield [33]. 

General conditions DMF as solvent and in situ formation of the EGB by constant potential electrolysis (CPE) at the potential of EGB-formation in a divided cell. 

Constant-potential electrolysis of the [Rh(dppe)2]Cl in an MeCN-Bu4NCl04-(Hg) system gives RhH(dppe)2 (325) in ca. 90% yield. When cyclohexyl chloride (334) is added to the [Rh(dppe)2] (332) electrolysis solution, the radical intermediate (335) together with Cl is produced as shown in Scheme (123) [456]. The cyclohexyl radical (335) generated in this manner has several channels for product formation. 

Using similar methodology, constant potential electrolysis, Et3N 3HF/CH3CN electrolyte, platinum anode, Fuchigami prepared the a-fluorinated derivatives of a series of different aryl 2,2,2-trifluoroethyl sulphides. 

Conjugated dienes (1,3-butadiene, isoprene) have suitable nucleophilicity to undergo cationic polymerization. There is, however, not much practical interest in these processes since the polymers formed are inferior to those produced by other (free-radical, coordination) polymerizations. A significant characteristic of these polymers is the considerably less than theoretical unsaturation due to cyclization processes.132 A fully cyclized product of isoprene has been synthesized163 by constant potential electrolysis in CH2C12. 

The deposition of Cu, Sn, and Cd occurs at a potential of 0.5, 0.3 and 0.1 V, respectively, more positive than the deposition of Zn. In these studies samples of the alloys were prepared on Ni substrates by constant potential electrolysis and examined with EDX, SEM, and XRD. It was found that the Zn content in the electrodeposits increased as the deposition potential became more negative but decreased with increasing concentrations of Cu(II), Sn(II), and Cd(II) in the solution. Increasing the deposition temperature increases the mass-transport rates... 

Pt were prepared on tungsten by constant potential electrolysis. EDX analysis of the deposits indicated that Pt and Zn were distributed uniformly in the deposits. The Pt content in the deposit decreases as the deposition potential approaches the value where bulk deposition of Zn occurs. Increasing the Pt(II) concentration in the liquid increases the Pt content in the deposits. As shown in Figure 5.4, XRD results indicated the presence of crystalline Zn and amorphous PtZn. If Zn is electrodeposited on a Pt substrate, the deposited Zn atoms interact with the Pt to form Pt-Zn surface alloys. 

Sn(II) and Nb(V) species changed their coordinations with the liquid composition. Nb-Sn alloy samples were prepared by the potentiostatic method and analyzed. The results showed that the Nb content in the alloy could be increased by increasing the bath temperature to 160 °C and increasing the NbCh content in the bath. However, increasing the NbCls mole fraction in the bath also increased the viscosity of the bath. Pulse electrolysis was found to be effective in increasing the Nb content in the alloy. The maximum Nb content in the alloy was 60.8 wt% from constant potential electrolysis and 69.1 wt% from pulse electrolysis. XRD diffraction patterns showed that the electrodeposits contained crystalline Sn and NbsSn which is a superconductor material. 

Section 2 (Fig. 1, curves A and B), usually performed at the rotating platinum electrode (anode reactions) or the dropping mercury electrode (cathode reactions), should ideally suffice to define the electroactive species and determine its half-wave potential. It may be that systems in which acid-base equilibria exist are somewhat more laborious to study due to the necessity of recording voltammetric curves over a wide pH range, but in most cases the task can be accomplished with some effort. Once the voltammetric characteristics are known, it remains to carry out preparative constant potential electrolysis (cpe) at a suitable potential in order to make sure that the electroactive species is connected with the reaction of interest. 

Exhaustive constant potential electrolysis of product oil solutions at mercury pool electrodes produced large background currents caused by interaction between Hg and the solvent-electrolyte system. The data are misleading. 

Constant Current Electrolysis and Constant Potential Electrolysis [6]... 

Constant potential electrolysis was carried out with platinum electrodes (3 x 4cm) at rtinO.1 M F.t N - SHF in DME (20 mL) containing the dithiokctal (2 mmol) using a divided cell with an anion-c. changcmembrane (ACH-45T, Tokuyama Soda). When the substrate was almost consumed (monitored by TLC and/or MS), the electrolysis solution was neutralized with sat. aq NaHCOj, and extracted with CHjClj. The combined extracts were dried (MgSO ), and concentrated under reduced pressure. The residue was purified by chromatography (silica gel, hexane/CHjClj 10 1). 

Figure 41. The current i as a function of the time t in constant potential electrolysis. The current is given by i = ij o 10 where k is a constant depending on the construction of the electrochemical cell (see Ref. 275.)...

If the current yield is of minor importance and no further oxidation or reduction than desired occurs (except reactions of the supporting electrolyte), constant current electrolysis is simpler to use than constant potential electrolysis, which is desirable especially for an introductory investigation. 

The reduction of the tetrazoles [Eq. (60)] has been used as a model for optimization of the chemical yield using an undivided cell and constant current rather than constant potential electrolysis [285,286]. Electrolysis under air rather than under nitrogen lowered the current yield from 43% to 20% (assuming a 1-F process) but increased the product selectivity (from 50% to 94%), since the intermediate, partly hydrogenated fluorophenyl ring was dehydrogenated, probably by electrogenerated superoxide ion [286]. 

The aliquot of digested sample placed in the electrochemical vessel is purged for 15-20 minutes with N2, then it is rapidly transferred and screwed under the cell head of the electrochemical device where the Hg film electrode has already been prepared, tested and rinsed. The electrolytic pre-concentration step during the analytical measurement is carried out by constant potential electrolysis. The deposition potential is set at -0.95 V for Cd and Pb and at -0.85 V for Cu. The deposition time depends on the metal concentration, a time of 20 min normally being sufficient to determine Cd and Pb concentration in samples collected in... 

The current and the cell potential changes that occur in a typical constant-potential electrolysis are illustrated in Figure 22-9. Note that the applied cell potential has to be decreased continuously throughout the electrolysis. Manual adjustment of the potential is tedious (particularly at the outset) and, above all, time consuming. Modern controlled-potential electrolyses are performed with instruments called potentiostats, which automatically maintain the working electrode potential at a controlled value versus the reference electrode. 

Before the results are presented, some important points should be mentioned in connection with the reports of CO2 reduction. Some papers give only the values of the faradaic efficiency of tire products of CO2 reduction in constant potential electrolysis without showing the values of the current density. Other ones do not present electrode potential in constant current electrolysis. It is impossible to evaluate tire rate of the reaction as well as the quality of the measurements in the electrolysis measurements without tire current density and the electrode potential. Thus these electrochemical parameters should be presented in any publications. Additionally, it is also important to state whether or not the electrolyte solution used for the work was purified by any means in tire experiment. The features of reaction change to a great extent, when tire electrode surface is contaminated with extremely small amount of impurities possibly contained in chemical reagents of the highest quality. 

---