Ohmic Voltage Losses in Porous Electrodes with Different Solid-Phase Conduction Profiles

Abstract

Using numerical calculations within a unidimensional model for porous electrodes (PE) and experimental methods (PE composed of layers of identical or different carbon felts, the anodic oxidation reaction in 0.01 M K₄Fe(CN)₆ + 0.01 M K₃Fe(CN)₆ + 1 M KOH), it is shown that, in contrast to a uniform porous matrix, where a decrease in the solid-phase conduction κ_s always leads to an increase in the ohmic voltage losses inside PE, for κ_s(x) varying across the PE thickness, the result depends on the κ_s profile. If κ_s decreases from the rear current lead to the PE front, and is higher or lower than the solution conduction in different regions of the solid phase, the entire increase in the effectively working area is reached with no increase in the losses. With a reverse κ_s profile, the matrix operation efficiency abruptly decreases and the losses increase.