The energy density of a non-aqueous redox flow battery (naRFB) is directly related to the active species concentration, cell voltage, and the number of electrons transferred per redox process. One strategy to increase the energy density is to mix multiple active components, which has the effect of increasing the overall concentration and the number of electrons transferred. In this study, ferrocene with TEMPO and cobaltocenium hexafluorophosphate with N-methylphthalimide were evaluated to be posolyte and negolyte mixtures, respectively. The resulting naRFB system exhibit two one-electron redox processes that establish a cell voltage of 1.8 V at a 50% state-of-charge. There were no interactions between the active species in electrolyte mixtures as observed by cyclic voltammetry, chronoamperometry and UV-vis absorbance spectroscopy. Charge-discharge experiments further demonstrated the suitability of the proposed electrolyte mixtures for naRFB applications. (c) 2018 The Electrochemical Society.