Quantitative analysis of the ohmic resistance in aqueous organic redox flow batteries

Aqueous organic redox flow batteries (AORFBs) exploit the reversible electrochemical reactions of water-soluble organic redox-active species to store electricity and have emerged as promising electrochemical energy storage technologies. To improve the battery performance related to the cell resistance, such as the power density and energy efficiency, it is essential to understand the cell resistance and determine the major contributor. Here, we conduct comprehensive electrochemical impedance spectroscopy (EIS) studies and cell polarization on a representative TEMPTMA/MV cell assembled with a commercial AMVN membrane and probe the proportion of the ohmic resistance to the total cell resistance at various stages of charge (SOCs) ranging from 10% to 100%. At 0 mA·cm⁻², the ohmic resistance is responsible for 60.3%–71.7% of the resistance of the entire cell, whereas at high current densities (for example, when the power density reaches the maximum), the ohmic resistance still contributes 47.9%–61.4%. Our quantitative analysis highlights the dominance of the ohmic resistance and anticipates that a membrane with lower resistivity may significantly increase the power density.