A novel non-aqueous redox flow battery employing tris(1,10-phenanthroline) complexes of iron(II) and cobalt(II) as active species is proposed and investigated for energy storage application. The [Fe(phen)3]2+/3+ and [Co(phen)3]+/2+ (phen = 1,10-phenanthroline) redox couples are used as the positive and negative active materials, respectively, in an electrolyte consisting of TEAPF6 and acetonitrile. Electrochemical measurements display that the two redox couples possess a superior and stable potential difference (E°) with a value of 2.1 V vs. Ag/Ag+. The charge–discharge characteristics of the cell show that the charging and discharging current densities have important influences on the battery performance. Stable cycling performance is obtained with low charge–discharge current densities with an electrolyte flow rate of 25 mL min−1. The coulomb, voltage and energy efficiencies achieve up to 80%, 40% and 39%, respectively.