The Effect of Electrode Placement and Finite Matrix Conductivity on the Performance of Flow‐Through Porous Electrodes

Abstract

A one‐dimensional model for flow‐through porous electrodes is used to predict the effluent concentration as a function of matrix conductivity and electrode length for upstream and downstream placement of the counterelectrode and current collector relative to the fluid inlet to the working electrode. Two chemical systems are considered: (i) the removal of copper from sulfate solutions, and (ii) the removal of silver from thiosulfate solutions. For an infinite matrix conductivity, the lowest effluent concentration is achieved when the counterelectrode is placed upstream to the fluid inlet of the working electrode. When the matrix conductivity is small, the lowest effluent concentration is still achieved for upstream placement of the counterelectrode; however, the optimum placement of the current collector depends on the chemical system and the value of the matrix conductivity that can be achieved in practice. Calculations show that for downstream placement of the counterelectrode a limiting current distribution cannot be achieved (for electrode lengths of interest here). The most undesirable configuration for achieving a low effluent concentration when the matrix conductivity is low is when both the counterelectrode and current collector are placed downstream of the fluid inlet. Distribution of potential, reaction rate, and electric driving force are presented for four different configurations: (i) upstream counterelectrode, downstream current collector, (ii) downstream counterelectrode, upstream current collector, (iii) upstream counterelectrode, upstream current collector, and (iv) downstream counterelectrode, downstream current collector.