Microbial peroxide producing cells (MPPCs) are a type of microbial electrochemical cells that are used to produce hydrogen peroxide (H2O2). Different catholytes were evaluated in biotic and abiotic reactors to determine their impacts on reactor performance. The abiotic reactor produced cathode efficiencies of less than 1%, leading us to investigate the potential causes of the low efficiency. An acid wash of the reactor parts was observed to significantly decrease the degradation rate of peroxide in the reactor, indicating that metal impurities in the catholyte solution was the driving cause of the low peroxide yields in the reactor. Diffusion testing confirmed that peroxide diffused across the anion exchange membrane (AEM) at a rate of 13.3 mg/L/hr, but had no significant impact on the overall peroxide produced in the reactor. We also confirmed that auto-decay of H2O2 was not responsible for the low observed yields.