Alkaline Zn-Mn aqueous flow batteries with ultrahigh voltage and energy density

Low energy densities restrict the widespread applications of redox flow batteries. Herein, we report an alkaline Zn-Mn aqueous redox flow battery (ARFB) based on Zn(OH)42-/Zn and MnO4-/MnO42- redox-pairs. The use of NaMnO4 at high concentrations (up to 3.92 M) as the positive active material gives the ARFB a high energy density, whilst the use of graphene modified carbon felt (G/CF) as the working electrode ensures durable cell operation. The resulting Zn-Mn ARFB demonstrates an ultra-high voltage of 1.98 V, long cyclability (5000 cycles), high theoretical energy densities of half-cell (208 Wh L-1catholyte) and actual discharge energy density of full-cell (97.8 Wh L-1), as well as an impressive maximum power density of 644 mW cm-2. Further, the developed Zn-Mn ARFBs worked efficiently in cell stacks, thus offering excellent scalability, which demonstrate Zn-Mn ARFBs have excellent potentials for electrical energy storage.