Dandelion-like alpha-MnO2 hollow spheres with superior catalytic performance for Li-O-2 batteries by a facile in situ pyrolysis

To reduce the severe overpotential of oxygen reduction and evolution reaction (ORR and OER) for rechargeable Li-O-2 batteries, the dandelion-like alpha-MnO2 hollow spheres (HS) with high surface area (105.54 m(2) g(-1)) were prepared by a facile in situ pyrolysis of manganese alkoxide for the first time. The ORR diffusion limiting current density and OER current density at 1.0 versus (Ag/AgCl)/V are 6.32 and 45.82 mA cm(-2) at 1600 rpm in alkaline solution, respectively, indicating that dandelion-like alpha-MnO2-HS catalyst exhibits superior bifunctional catalytic activity. The Li-O-2 batteries with alpha-MnO2-HS catalyst can yield high initial discharge specific capacity of 7897.6 mA h g(-1) at 100 mA g(-1). Moreover, the cycle life of Li-O-2 batteries with alpha-MnO2-HS catalyst is significantly improved and can sustain 108 cycles. These results indicate that as-fabricated hollow sphere structure without adding any hard templates is favorable for superior bifunctional catalytic activity in aqueous and non-aqueous electrolyte.