  Oxygen reduction/evolution reaction (ORR/OER) is a basic process for fuel
cells or metal air batteries. However, ORR/OER generally requires noble metal
catalysts and suffers from low solubility (10-3 molar per liter) of O2, low
kinetics rate (10-6 cm2/s) and low reversibility. We report a manganese
reduction/oxidation reaction (MRR/MOR) on graphene/MnO2 composites, delivering
a high capacity (4200 mAh/g), fast kinetics (0.0024 cm2/s, three orders higher
than ORR/OER), high solubility (three orders than O2), and high reversibility
(100%). We further use MRR/MOR to invent a rechargeable manganese ion battery
(MIB), which delivers an energy density of 1200 Wh/Kg (several times of lithium
ion battery), a fast charge ability (3 minutes), and a long cycle life (10,000
cycles). MRR/MOR renders a new class of energy conversion or storage systems
with a very high energy density enabling electric vehicles run much more miles
at one charge.
