Steady-state voltammetry measurements were used to assess the uniformity of reaction conditions along the length of the packed bed electrode in a two-compartment trickle bed cell. The model reaction was the cathodic reduction of oxygen in 2M caustic under various conditions of O~ pressure, cell temperature, and catholyte flow rate. Two kinds of carbon cathodes were employed: small chips of high purity graphite and a piece of reticulated vitreous carbon foam. Oxygen reduction was shown to occur at these carbons in two steps, O~ ~ HO2-; HO~-~ OH-. Generally, an increase in current density produced an increase in the potential gradient along the cathode bed, favoring the reduction of HO~-to OH-. This nonuniform potential distribution is attributed to local differences in the oxygen supply. We conclude that mass transfer in the trickle bed cell is not efficient enough to replace all the oxygen consumed by electrolysis at current densities above ca. 200 A/m s .The trickle bed cell (1) uses a three-dimensional packed bed electrode to electrolyze gaseous reactants (2-5). Mass transfer of reactant gas into the fluid phase is facilitated by the trickling flow of the electrolyte layer over each particle in the electrode bed.Previous work with the trickle bed cell suggested that the potential distribution in the cathode bed was nonuniform in the direction of current flow and, thus, the particle bed thickness was limited to ca. 3-6 mm (3). Reaction conditions along the length of the cathode bed, in the direction of gas/electrolyte flow, can also be nonuniform by virtue of the nonuniform distribution of reactants. This could impose a maximum size or current density limitation on the cell. In order to assess this latter nonuniformity, we experimentally determined the potential difference between two points along the length of the cathode bed for a two-* Electrochemical Society Active Member.
ABSTRACTA study is presented of mass transfer rates in some jet impingement systems which are suitable for electrochemical processes where high transfer rates are required. Experimental data are presented and an empirical correlating equation is proposed. An appIication to high speed electroplating of printed circuit boards is described.Jet impingement systems are used in many industrial processes which require high heat or mass transfer rates of surfaces. These systems consist of arrays of jets which are directed at the surface where the transfer process is to take place. In most applications, the 1Present address: Professor, Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139. carrier fluid is a gas. A significant literature is available on the performance of gaseous jet impingement systems, which have applications in the paper-making industry (1, 2).Jet impingement systems also have applications in electrochemical systems. Electroplating is an obvious example. Here, the maximum current at which the ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subj...
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