Electrochemical advanced oxidation processes (EAOPs) have shown excellent capabilities to the abatement of recalcitrant organic pollutants. The Fenton-based electrochemical systems have shown great performance for in-situ generation of H2O2, allowing an efficient • OH production for the mineralization of organic pollutants. These systems have been widely applied at bench scale; however, studies to scale-up to a higher technology readiness level (TRL) are lacking. One of the main scale-up challenges of the Fenton-based systems is the implementation of air diffusion electrodes (ADE) in flow-by electrochemical cells. The ADE adds additional complexity with respect to mass transfer effects due to hydraulic reactor design and ADE gas pressure control. Therefore, this work experimentally investigated residence time distribution and platinum-sheet electrode mass transfer effects due to (a) the liquid cross-flow velocity through the electrochemical cell, (b) the gas pressure of the air-diffusion electrode (ADE), and (c) the presence of mesh sheet mass transfer promoters between the electrodes. Analysis of experimental results revealed a synergistic improvement of mass transfer with the ADE gas flow and the presence of mesh promoters. Engineers could exploit this synergistic effect to design electrochemical cells with significantly lower capital cost.