Steady-State Characterization of the Uniform-Injection Cell I. Theoretical Analysis

Presented isthe theoretical characterization f an electrochemical cell that is uniformly accessible to mass transfer and exhibits a nearly uniform primary current distribution over most of the electrode. Conceptually, the cell consists of two parallel, coaxial disks of radius R with a gap between the disks of length L. One disk forms the working electrode, and the other disk is a porous urface through which electrolyte isassumed to be injected with a uniform axial velocity V. The aspect ratio of the gap between the disks (L/2R) is small compared to unity. Analytic expressions analogous to the Levich equation are derived for the mass-transfer-limited current density as a function of the physical properties of the electrolyte, the injection velocity V, and the gap length L. The approximate analytic results are compared to numerical computations and are found to agree within 2 % for typical operating conditions. The effect of gap aspect ratio on the primary current distribution is also explored. Numerical solutions how that the primary current distribution is flat over most of the electrode when the gap aspect ratio is much less than unity, but, because of the cell geometry, the local current density always becomes infinite at the electrode/insulator b undary