Effect of Electrode Placement and Finite Matrix Conductivity on Performance of Flow-Through Porous-Electrodes
A one-dimensional model for flow-through porous electrodes is used topredict the effluent concentration as a function of matrix conductivity andelectrode length for upstream and downstream placement of the counterelectrodeand current collector relative to the fluid inlet to the working electrode.Two chemical systems are considered: (i) the removal of copper fromsulfate solutions, and (ii) the removal of silver from thiosulfate solutions.For an infinite matrix conductivity, the lowest effluent concentration isachieved when the counterelectrode is placed upstream to the fluid inlet ofthe working electrode. When the matrix conductivity is small, the lowesteffluent concentration is still achieved for upstream placement of thecounterelectrode; however, the optimum placement of the current collectordepends on the chemical system and the value of the matrix conductivitythat can be achieved in practice. Calculations show that for downstreamplacement of the counterelectrode a limiting current distribution cannot beachieved (for electrode lengths of interest here). The most undesirable configurationfor achieving a low effluent concentration when the matrix conductivityis low is when both the counterelectrode and current collector areplaced 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) downstreamcounterelectrode, upstream current collector, (iii) upstream counterelectrode,upstream current collector, and (iv) downstream counterelectrode, downstreamcurrent collector.