Electrolyte flow rate

Figure 13.1 Electrooxidation of COad and Ci adsorbate layers pie-adsorbed on a Pt/Vulcan thin-film electrode (7 JLgptCm , geometric area 0.28 cm ) in 0.5 M H2SO4 solution during a first positive-going potential scan, and subsequent response of the faradaic (a) and m/z = 44 ion current (b) to the electrode potential in the thin-layer DBMS flow cell. The potential scan rate was 10 mV s and the electrolyte flow rate was 5 p,L s at room temperature. The respective adsorbates were adsorbed at 0.11 V for 10 minutes from CO-saturated solution (solid line), 0.1 M HCHO solution (dashed line), 0.1 M HCOOH solution (dash-dotted line), and 0.1 M CH3OH solution (dash-double-dotted line).

Figure 13.6 Potential-step electro-oxidation of formaldehyde on a Pt/Vulcan thin-film electrode (7 p,gpt cm, geometric area 0.28 cm ) in 0.5 M H2SO4 solution containing 0.1 M HCHO upon stepping the potential from 0.16 to 0.6 V (electrolyte flow rate 5 pL at room temperature). (a) Solid line, faradaic current transients dashed line, partial current for HCHO oxidation to CO2 dotted line, difference between the net faradaic current and that for CO2 formation, (b) Solid line, m/z = 44 ion current transients gray line potential-step oxidation of pre-adsorbed CO derived upon HCHO adsorption at 0.16 V, in HCHO-free sulfuric acid solution, (c) Current efficiency transients for CO2 formation (dashed line) and formic acid formation (dotted line).

Kinetic results such as those presented in the previous sections, which could be further extended by varying the reaction parameters (reactant concentration, electrode potential, catalyst loading, electrolyte flow rate, and reaction temperature), can serve as basis... 

A further study by the Olesik group [138] used an interface with a laminar flow in the direction of the detector. The interface was a stainless-steel tee with the capillary threaded through the colinear ends of the tee. A sheath electrolyte was delivered through the lower arm of the tee with a peristaltic pump. Both a high efficiency nebuliser (HEN) and a concentric glass nebuliser were used in the study the former was used with a conical spray chamber and the latter with a Scott double-pass spray chamber. Increasing the sheath electrolyte flow-rate enabled the laminar flow to be eliminated, therefore improv-... 

A Gamry electrochemical measurements system and a Pine Bi-Potentiostat were used to study the experimental decomposition potential and current response to the applied voltage. The experimental variables were electrolyte flow rate and temperature. Linear sweep voltammetry (LSV) technique was the main method used to study the electrolytic processes. 

In the process under study here, where S02 oxidation is the limiting half reaction, the electrolyte flow rates are controlled by volumetric pumps to ensure forced convection. Moreover, both the anode and cathode compartments are provided with a plastic mesh turbulence promoter. The flow is therefore assumed fully turbulent and a uniform velocity profile is assumed at the inlet. However, for simplification, these devices are not represented in the simulation domain. Although the turbulence promoter should actually influence the bubble population, no reference has been found on its effects. 

The model was used to study the process sensitivity to the major unknown parameters the H2 bubble size (50-200 pm) and their departure angle (30-60°). The effect of cell orientation and electrolyte flow rate in the range of the pilot facility operating conditions (75-200 L.h 1) was also investigated. Process sensitivity is measured in term of cell voltage and gas fraction maximum and average values. Gaseous phase spatial distribution is also examined. Major simulation results are summarized in table 2. 

Helmholtz layer contains the second water molecule layer. From the Helmholtz double layer toward the bulk electrolyte are the diffusion layer and the hydrodynamic layer. In the diffusion layer, the concentration of species changes from that of the bulk electrolyte to that of the electrode surface. The diffusion layer does not move, but its thickness will decrease with increasing bulk electrolyte flow rate to allow higher reaction rates. The diffusion layer thickness is inversely proportional to the square root of the flow rate. The hydrodynamic layer or Prandtl layer has the same composition as the bulk electrolyte, but the flow of the electrolyte decreases from that of the bulk electrolyte to the stationary diffusion layer. 

FIGURE 19.6 Simultaneously measured faradaic (a) and mass spectrometric (b) current response on the copper electrode potential in a thin-layer flow-through DEMS cell. Solution contained (mol L-1) CuS04 (un-hydrous)—0.008 EDTA—0.01 H2CO (solid lines) or D2CO (dotted lines)—0.02 solvent H20 (A) or D20 (B). pH = 13 (adjusted by adding NaOH or NaOD, respectively) temperature 25°C. Potential sweep rate 5 mV s Electrolyte flow rate 30 p,L s-1. Circles indicate open-circuit conditions (filled—H2 evolution, open—D2 evolution). (From Jusys, Z. and Vaskelis, A., Electrochim. Acta, 42, 449, 1997.)... 

The theory was verified experimentally using the Fe2+/H202 system and was shown to be satisfactory over a wide range of electrolyte flow rates. 

Circulation of the electrolyte through the parallel plate cell was provided by a magnetic pump (Iwaki MD 50 R) and the electrolyte flow rate was measured with a magneto hydrodynamic flow meter (Deltaflux). 

Significant technological development and research on accuracy and waste disposal make today s ECM technique a better choice than many other nonconventional as well as conventional techniques. Control of ECM process is improving all the time, with more sophisticated servo systems. However, there is still a need for basic information on electrode phenomenon at both high current densities and electrolyte flow rates [2]. Some of the improvements in ECM process have mentioned below ... 

In plate-and-frame cells it is normal to reduce the inter-electrode gap to 0.5—5.0 cm and the electrolyte flow rates are often high. The electrolyte entry ports must... 

Thus the electrolyte leaving the gap will contain both solids and hydrogen gas. It is to sweep away these products and to remove the heat that a high electrolyte flow rate must be used. 

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