Studies on Flow-By Porous Electrodes Having Perpendicular Directions of Current and Electrolyte Flow

An engineering analysis was carried out on a packed-bed electrochemical reactor in which the electrolyte flowed in the axial direction and current flowed in the radial direction. Experimental measurements with a sectioned porous electrode were conducted to measure the axial current distribution both at and below the limiting current. The experiments involved deposition of copper onto stacks of copper screens with acidified copper sulfate electrolyte. Although the presence of flow channeling caused the mass transfer coefficient to be less than the value reported in the literature, an empirical correlation was established for estimating the mass transfer coefficient. The reactor system gave polarization curves which indicated that the exchange current density was 0.067 mA/cm2 in 0.001M CuSO₄ + 1.5M H2SO2. Comparison between axial current distribution data and theory was made with respect to collection efficiency, axial current distribution, electrode polarization, and total current. Agreement was found for a range of reactors having various geometric dimensions, porosities, flow rates, and reactant concentrations. The theory was used to generate criteria for estimating the volumetric reaction rate, as well as for estimating conditions under which the perpendicular configuration reactor gives higher volumetric reaction rates than when the current and electrolyte flow in parallel directions.