Time of electrolysis

Thin films of fullerenes, which were deposited on an electrode surface via, for example, drop coating, were largely heterogeneous, due to the entrapping of solvent molecules into their domains. Consequently, their electrochemical behaviour displayed different degrees of reversibility and stability depending on the time of electrolysis and the... 

The potential supplied to an electrolytic cell determines whether or not electrolysis can occur, but the current flow and the time of electrolysis determine the amount of material electrolyzed. Recall Equation from Section 19-1 ... 

Fig. 5.4 Time dependence of HE profiles during chlorine evolution at a 40 at.% Ru electrode in 5 M NaCI + 0.1 M HCI at room temperature (without IR compensation), subjected to square-wave potential cycling (from 1.35 to -0.32 V versus SCE at 60s cycle-1). The numbers in the figure refer to the time of electrolysis in hours. Each Tafel plot is shifted to the right by 20 mV to avoid overlapping. 

Fig. 1. Evolution of the voltammograms of a platinum electrode recorded during the prolonged electrolysis of glyoxal at a potential plateau Ep=1.18 V/RHE. The main oxidation peaks are labelled A, B and C. The potential programme is shown in the insert. Time of electrolysis (—) 0 hr, (.) 25 hrs, (---) 50 hrs.

Amount and salt used Vol. of CJIsOH, ml. Cone, of amalgam, % by weight Time of electrolysis, hr. Average current density, amp./sq. cm. 

The problem of adequate isolation has been studied theoretically and practically in the context of coulometric titrations.36 The loss of sample by diffusion will not be greater than 0.1% if at least two fine-frit separators are used with at least 4-5 cm of electrolyte between the frit and if the time of electrolysis is short (3-15 min). A tube closed with a fine frit that contains a 12-mm layer of fine silica gel above the frit has been suggested. 

As for the acid red 14 removal by EC, 95% color removal and 85% COD removal were obtained when the pH ranged from 6 to 9, time of electrolysis was approximately 4min and current density was approximately 80 Am-2. The results also showed that an EC cell with monopolar electrodes had higher color removal efficiency than an EC cell with bipolar electrodes. Furthermore, within an EC cell, the series connection of the monopolar electrodes was more effective for the treatment process than the parallel connection in color removal (Daneshvar et al. 2004). 

Crystals of the various alkali tungsten bronzes were prepared by electrolysis from a melt of the appropriate alkali tungstate and W03. The electrolytic cell consisted of a glazed ceramic crucible, a Chromel wire cathode, and a graphite anode. Crystals were obtained under the following conditions temperatures of the melt, 750° to 900° C. current through the cell, 15 to 50 ma. time of electrolysis, 12 to 24 hours. 

Very often it is of great interest to determine the n value of an electrode reaction or the current efficiency of an electrosynthesis. Both involve a measurement of the electricity consumption, that is, an integration of the electric current over the time of electrolysis. In constant-current experiments this is, of course, an easy task. For controlled potential electrolysis, an integrating device is included in the circuit. Electronic integrators can usually be obtained from the companies that supply potentiostats. 

Analyses for "copper, cadmium, and lead were carried out continually by DPASV. Zinc determinations were excluded to permit use of a lower electrolysis potential. The samples were analyzed at pH 4.9 by sparging with carbon dioxide. An 8-min. electrolysis at —1.0 V vs. silver/ silver chloride and a 25-mV pulse were used during the Seattle-Saanich portion of the trip (Leg 1) while a 10-min. electrolysis and a 50-mV pulse were used from Saanich to Seattle (Leg 2). Application of the DPASV technique resulted in greater sensitivity and thus shorter plating times for the low levels encountered. It also afforded better resolution for "copper than linear-sweep ASV. It should be pointed out, however, that DPASV does not result in shorter analyses times because the stripping portion of the analysis is very slow. Nevertheless, it is worthwhile to limit the time of electrolysis because this also reduces the concentrations of interfering metals accumulated in the mercury fllm. Under the... 

It is found that the use of sodium bisulfite materially increases the yield of salicylic aldehyde. Further, that the lower temperatures (15° to 18°) favor the yield of salicylic aldehyde. At higher temperatures less salicylic aldehyde is produced and more of the resinous product. Up to a current density of 8 amp./sq. dm. the yield of salicylic aldehyde is increased. Intermittent electrolysis or stirring after electrolysis is necessary for good current efficiency since a sodium amalgam is built up during the electrolysis. Increasing the time of electrolysis seems to increase the quantity of resin formed. Increasing the concentration of salicylic acid (sodium salt) has little or no effect. 

Figure 14. (a) Copper deposit obtained at an overpotential of 1,000 mV Time of electrolysis 10 s, (b) the positions of formation of hydrogen bubbles and agglomerates of copper grains, and (c, d) the details from Fig. 14a and b. (Reprinted from Ref.18 with permission from Springer). 

Figure 15. Copper deposit obtained at an overpotential of 1,000 mV Time of electrolysis 30 s. (Reprinted from Ref.18 with permission from Springer).

Although a major advantage of rotating disk electrode techniques, compared to stationary electrode methods, is the ability to make measurements at steady state without the need to consider the time of electrolysis, the observation of current transients at the disk or ring following a potential step can sometimes be of use in understanding an electrochemical system. For example the adsorption of a component. 

The electrochemical (or current) efficiency, EF, defined as moles of metal dissolved per Faraday, can be readily determined by recording the current, total time of electrolysis, and weight of gallium dissolved. For a more accurate determination, a silver voltammeter can be connected in series with the cell. Current efficiencies measured in this way are close to the theoretical value of 0.5 for the fundamental process Ga -> Ga2+ + 2e". The method given here for preparing gallium(11) compounds uses an electrolyte based on acetonitrile and is a marked improvement on earlier chemical or electrolytic routes to low-valent gallium compounds,1 from which mixed products, partially oxidized to the Ga(lll) state, were often obtained. 

Number of Faradays of electrons used during electrolysis based on time of electrolysis (F) ... 

Compare the moles of electrons transferred during electrolysis as based on moles of H" " reduced, moles of copper oxidized, and the amperage and time of electrolysis. Arrange these three in terms of decreasing accuracy. Justify your arrangement. 

The carbon-fiber tip modification process consists of poly-(TMHPP)Ni film deposition on the electrode surface and confirmation of deposition followed by demetalation to poly-TMHPP and confirmation of demetalation. Polymeric film is deposited from a 0.25 mM (TMHPP)Ni solution in 0.1 M sodium hydroxide by constant-potential electrolysis at 0.70 V. The number of monolayers deposited is dependent on the initial concentration of (TMHPP)Ni and the time of electrolysis. At the end of the deposition time, the electrode is immersed in 0.1 M sodium hydroxide. The presence of (poly-TMHPP)Ni film on the electrode surface is confirmed by a peak at Ep = 0.55 V, attributable to the Ni(II)/Ni(III) couple, in a differential pulse voltammetry scan. The (poly-TMHPP)Ni film is demetalated in a chemical process by placing the electrode in 0.1 M HCl. 

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