Unveiling the fluid dynamics and mass transfer processes in a spatially confined flow-through electrochemical reactor

Electrocatalytic oxidation is a promising technology for wastewater treatment, but poor mass transfer and low current efficiency impaded its engineering applications. To address these issues, researchers have developed flow-through electrochemical reactors (FERs) primarily based on porous electrodes, where the pore structure significantly impacts the electrochemical reaction. Therefore, this study systematically investigated the impact of different pore sizes on the fluid dynamics, current potential distribution, mass transfer processes, and degradation performance of FERs. Computational Fluid Dynamics (CFD) results indicated that smaller pore sizes (10 µm, 30 µm, and 60 µm) significantly enhanced convective effects within the fluid, reduced short fluid paths and dead volume regions within the microchannels, and facilitated mass transfer processes. Additionally, smaller pore sizes were conducive to a uniform distribution of current density. Furthermore, Fe(CN)₆^4- oxidation experiments revealed that the current density at a pore size of 160 µm was notably lower than that at 10 µm, indicating slower mass transfer of Fe(CN)₆^4- within larger channels. Calculations based on experimental results demonstrated that the mass transfer rate at a pore size of 10 µm was six times than that at 160 µm, further confirming the enhancing effect of smaller pore sizes on the mass transfer process. Lastly, experiments on tetracycline degradation showed that at a residence time of 90 s, the removal efficiencies of tetracycline were 80 % and 39.1 % for porous electrodes with pore sizes of 10 µm and 160 µm, respectively, demonstrating the superior removal efficiency of smaller pore sizes for tetracycline degradation.