Zn doped δ-MnO <inf>2</inf> nano flakes: An efficient electrode material for aqueous and solid state asymmetric supercapacitors

Asymmetric supercapacitors based on aqueous and solid-state electrolytes are useful for a variety of applications. The birnessite δ-MnO 2 is one of the efficient materials from the MnO x family characterized by large interlayer distance (∼7.3 Å) and high theoretical specific capacitance (∼1370 F g −1 ). However the main concern which hinders its usage for practical applications is its low electronic conductivity (∼10 −6 S cm −1 ). There are different means to enhance the conductivity and in the present studies, two simultaneous methods viz; a method of synthesis of nano-flakes along with Zn-doping in δ-MnO 2 is implemented. A specific capacitance of ∼466 F g −1 at a current density of 0.5 A g −1 is obtained for an optimum Zn doping concentration of 1 mol% which is almost two times more than the corresponding pristine one. Both aqueous and solid-state asymmetric supercapacitor devices are fabricated using Zn doped δ-MnO 2 as electrode material which can be easily scalable to industrial level. A lab-scale demonstration prototype is constructed which essentially validated the charging of solid-state supercapacitor using battery and allowing the supercapacitor to discharge through a red-LED by means of a two-way switch.