Minimizing electrolysis time

Minimizing Electrolysis Time The current-time curve for controlled-potential coulometry in Figure 11.20 shows that the current decreases continuously throughout electrolysis. An exhaustive electrolysis, therefore, may require a long time. Since time is an important consideration in choosing and designing analytical methods, the factors that determine the analysis time need to be considered. 

A challenge in using bulk electrolysis to generate redox states for in situ spectroscopic investigations is to minimize the time for exhaustive electrolysis. The most common... 

To minimize the problem of the Ohmic drop and to further decrease the solution volume and, thereby, the electrolysis time, sandwich thin layer cell can be used (Fig. 9.11) [18]. 

A number of factors will determine whether or not an electrolysis will proceed with 100 per cent current efficiency. Certainly the presence of any electro-active impurities will cause the apparent electrolysis current to be in error so that the total number of coulombs passed will exceed the theoretical quantity of electricity required for the actual oxidation or reduction of the material to be determined. In most cases it should be possible to improve the purity of solvents, reagents, and other constituents sufficiently by pre-electrolysis or chemical means. Alternatively, the applied potential might be shifted in such a way as to minimize the effect of impurities at the expense of some increase in electrolysis time. Naturally, oxygen and other atmospheric contaminants should be eliminated by flushing with an inert gas. 

M NaOH if migration times become erratic. Buffer in both reservoirs should be replaced periodically because ions become depleted and electrolysis raises the pH at the cathode and lowers the pH at the anode. The capillary inlet should be 2 mm away from and below the electrode to minimize entry of electrolytically generated acid or base into the column.30 Stored capillaries should be filled with distilled water. 

A coastal beach in California is polluted with heavy metals. Since it is a protected wildlife habitat, a minimally intrusive electrochemical method is selected for cleanup. Assume that a constant current density of 125 pA cm-2 in a 40 x 6-foot cross section is used in the contaminant pit, which is 40 x 20 x 6 feet deep, (a) What is the total current and voltage required if the pore fluid conductivity is 21.9 mS cm-1 (approx, equivalent to 0.2 M KC1) (b) If the soil is saturated and approx. 50% pore fluid and 50% solids by volume, how long would it take to pass a charge equivalent to the ionic content of the pore fluid (c) How much acid should be added to depolarize the cathode in this time in order to ensure reaction (A) below, instead of water electrolysis, reaction (B) ... 

Summary Electroplating is carried out by utilizing identical electrolysis techniques as seen in methods 1 and 2, but instead of forming metal flakes or crystals, the cathode is composed of a desired metal object to be plated. To plate metal objects, the metal object is placed as the cathode, and a solution of either dilute hydrochloric acid and corresponding metal anode, or a solution of a water soluble metal salt utilizing a metal anode or inert anode, is electrolyzed using varying current to plate the desired metal object. The electrolysis process is rapid and can be carried out with success in minimal amounts of time. 

Electrolysis at the electrodes needs to be minimized, since this will alter electrolyte composition. Partly for this reason, impedance measurements should be made at current densities on the order of 1 xA/cm or less [17]. Making impedance measurements at 1 pA/cm or less has the added advantage of minimizing iontophoresis and electroosmosis, which can decrease the skin s impedance with time [16,17]. 

A schemahc diagram of the DEMS apparatus is shown in Fig. 5. The electrochemistry compartment corrsists of a circular block of passivated htanirrm (a) that rests above a stainless-steel support (1) cormected to the mass spectrometer. The space between the cell body and the snpport is a Teflon membrane (j) embedded on a steel mesh (k) the membrane is 75 pm thick, has 50% porosity and pore width of 0.02 pm. The single-crystal disk (h) is the working electrode its face is in contact with the electrolyte solution and separated from the cell body by another Teflon membrane (i) that functions as a spacer to form a ca 100-pm thick electrolyte layer (j). Stop-flow or continnons-flow electrolysis can be performed with this arrangement. For the latter, flow rates have to be minimal, ca 1 pL/s, to allow ample time (ca 2 s) for the electrogenerated products to diffuse to the upper Teflon membrane. Two capillaries positioned at opposite sides of the cell body (b, e) serve as electrolyte inlet and outlet as well as connection ports to the reference (f) and two auxiliary Pt-wire electrodes (d, f). 

Equipment intended to obtain kinetic data by EGA methods must minimize delay between evolution and detection by reducing, as far as possible, the distance traveled and diffusive dispersal (65). Specific detectors for an identified product may operate continuously, e.g., electrolysis cells for water or sulfur dioxide (64), infrared absorption responding to a particular bond, MS operating to detect a particular mass, etc. Alternatively, MS can be used to scan repeatedly a selected range containing several products. GC necessarily analyzes samples at time intervals dictated by the longest-retained component, and the output can use MS as a detection method. 

Cathodes have an effective depositions surface area of 1.67 m and there are 33 cathodes in a cell. A knife switch type is used for the cathode contacts. This type allows the cathode header bar to come in contact with both the clip and the equipotential bar, resulting in a wide contact area. With a self-weight contact type, the contact resistance is increased because the weight of the cathode is light at the initial stage of electrolysis. To minimize this disadvantage, the knife switch type has been consistently in use to the present time. 

As a consequence of the short time involved in gast scan experiments, total electrolysis is much smaller at microelectrodes, and fouling of electrodes by electrolysis products is minimized. 

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