Applying the electrode potential slope method as a tool to quantitatively evaluate the performance of individual microbial electrolysis cell components

•The electrode potential slope method quantifies component-associated resistances.•The anode was the largest source of resistance in acetate-fed reactors (71 mΩ m2).•The cathode (18 mΩ m2) and solution (25 mΩ m2) also contributed to total resistance.•Activation losses were minimal based on standard theoretical open circuit potentials. Improving the design of microbial electrolysis cells (MECs) requires better identification of the specific factors that limit performance. The contributions of the electrodes, solution, and membrane to internal resistance were quantified here using the newly-developed electrode potential slope (EPS) method. The largest portion of total internal resistance (120 ± 0 mΩ m2) was associated with the carbon felt anode (71 ± 5 mΩ m2, 59% of total), likely due to substrate and ion mass transfer limitations arising from stagnant fluid conditions and placement of the electrode against the anion exchange membrane. The anode resistance was followed by the solution (25 mΩ m2) and cathode (18 ± 2 mΩ m2) resistances, and a negligible membrane resistance. Wide adoption and application of the EPS method will enable direct comparison between the performance of the components of MECs with different solution characteristics, electrode size and spacing, reactor architecture, and operating conditions.