Electrode impinging jet

Fig. 4. Mass transfer from an impinging jet electrode. (From ref. 48 by permission of the publisher, The Electrochemical Society, Inc.). I, Potential core region II, established flow region III, stagnation region IV, wall-jet region.

D. Chin and C. Tsang, "Mass Transfer to an Impinging Jet Electrode," Journal of The Electrochemical Society, 125 (1978) 1461-1470. 

Tube electrodes have inspired simulations since 1974 [38, 46, 87, 88, 107, 142-144], and the wall-jet or impinging jet electrode, following the theory works mentioned above, has been simulated by many [46, 91, 145-158]. 

Convection terms commonly crop up with the dropping mercury electrode, rotating disk electrodes and in what has become known as hydrodynamic voltammetry, where the electrolyte is made to flow past an electrode in some reproducible way (e.g. the impinging jet, channel and tubular flows, vibrating electrodes, etc). This is discussed in Chap. 13. 

Gabrielli and Perrot [23] carried out in situ mass measurements in well-defined flowing electrolyte with an electrochemical quartz crystal microbaiance (EQCM) adapted to a submerged impinging jet cell (wall tube configuration). The authors employed this new device for the study of nickel electrodeposition and evaluation of the cathodic efficiency. Under the conditions of their experiment (nozzle diameter d = 7 mm disc electrode diameter de = 5 mm and nozzle-to-electrode distance H = 2d), the current that flows at the electrode increases with the square root of flow rate (0-10 cm3 s"1). It should be noted that this approach is much simpler to implement than the rotating EQCM, while keeping control of the convective-diffusion conditions. 

The fundamentals of the electrochemical response at electrodes operating in a regime of forced convection, hydrodynamic electrodes, and the information that can be obtained have been reviewed [23, 24]. Some of these electrodes are good candidates for direct introduction into flow systems, in particular tube/channel electrodes and impinging jet (wall-jet and wall-tube) electrodes. Particular practical advantages of these flow-past hydrodynamic electrodes are that there is no reagent depletion while the sample plug passes the electrodes, and there is no build-up of unwanted intermediates or products. Recent advances in instrumentation also mean... 

The electrode is uniformly accessible to the diffusing ions within dimensionless electrode radius, 0.1 < R/d < 1.0, for turbulent nozzle flow and, 0.1 < R/d < 0.5, for laminar nozzle flow. Within the region of uniform accessibility, the mass transport rate is relatively independent of the electrode size in both laminar and turbulent flow for 0.2 < Hjd < 6, where H is the nozzle-to-plate distance. Beyond the region of uniform accessibility, the mass transfer rate decreases with the radial distance. In the intermediate range, 1 < R/d < 4, the turbulent impinging jet changes from the stagnation flow to the wall-jet flow and for R/d > 4 the wall-jet flow predominates (- wall-jet electrode). 

Wall-jet electrode — An electrochemical cell design wherein a streaming electrolyte solution impinges vertically onto an electrode embedded into the cell wall ... 

Tile wall jet electrode (WJE) has attracted considerable attention in analytical applications of voltammetry (see for example Brett et al., 1995,1996). In this electrode configuration, a high, fixed velocity jet of fluid is fired, through a nozzle of diameter, a, directly towards the middle of a disc electrode (radius = ri), whose centre coincides with that of the nozzle (Fig. 25). The solution thus impinges upon the electrode surface and is circulated outwards towards the extremities of the electrode surface, but the recirculated solution can never reach the electrode a second time. 

Figure 11.10 A disk electrode subjected to a submerged impinging jet a) schematic illustration b) identification of flow regimes.

Graphical methods can be used to extract information concerning mass transfer if the data are collected under well-controlled hydrodynamic conditions. The systems described in Chapter 11 that are imiformly accessible with respect to convective diffusion would be appropriate. The analysis would apply to data collected on a rotating disk electrode as a function of disk rotation speed, or an impinging jet as a function of jet velocity. 

Zjt tabulated dimensionless values for diffusion impedance where fc = 1,2,3, see equation (11.97) for a rotating disk electrode and equation (11.109) for a submerged impinging jet... 

Figure 51. Experimental setup for studying spatiotemporal patterns by means of SP microscopy. WE, working electrode RE, reference electrode CE, counter-electrode and J, impinging jet. (After Flatgen etal. TO)...

More unusual ideas involve the flow of solution through tubular electrodes or the use of so called wall jet electrodes in which a rapid jet of solution is impinged directly onto a small electrode. Since these methods involve flow of solution through tubing rather than an open cell, they introduce the possibility of automated analysis. The samples could be automatically injected into a continuous flow of fresh supporting electrolyte - flow injection analysis. Conventional polarography does not lend itself as easily to automation as does this version of stripping voltammetry. 

Fig. 16.1 Top panel. Current densities measured for oxygen reduction in the impinging jet system in 0.1 M Na2S04 (pH = 6) for the Au (100), Au(lll),and Au(llO) electrodes. Bottom panel. Effect of the pH in the oxygen reduction in the impinging jet system for the Au(lOO) electrode...

In this type of cell the eluate is delivered, via a small orifice, into the cell and directly impinges as a jet at right-angles onto the face (wall) of the working electrode before flowing radially across the surface (Figure 3.4(b)). A wall-jet electrode was applied to flow injection analysis (FIA) in 1973 by Yamada and Matsuda and very shortly afterwards applied to HPLC by Fleet and Little. For many years, the HPLC cell designed by Fleet and Little was manufactured and sold by EDT in London. There are still several commercial instruments that use wall-jet... 

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