Design of a unique 3D-nanostructure to make MnO2 work as supercapacitor material in acid environment

Abstract Novel 3D-nanostructured TiO 2 nanotube arrays @MnO 2 nanosheets@ polypyrrole (TMP) supercapacitor material has been designed with the capability to work in acidic condition efficiently. In this structure, TiO 2 nanotube arrays (TNAs) served as the scaffold to support MnO 2 nanosheets and polypyrrole (PPy) as a barrier to limit the dissolution of MnO 2 during discharge process. The dissolution mechanism of MnO 2 in acidic solution during discharge process was further investigated. The synergistic effect of the three components in this structure enhanced the cycling stability of MnO 2 from just 1 cycle to thousand cycles. It is found that the capacitance of TMP in 1 M H 2 SO 4 solution was even 2-fold of that in traditional neutral solution (1 M Na 2 SO 4 solution) due to the superior conductivity of acid solution. Finally, a full flexible solid-state asymmetric supercapacitor device composed of TMP and carbon nanotubes (TMP//CNTs) was fabricated and worked in a wide voltage window of 0–2.4 V in acidic condition, which was profited from the “passivation effect” of acidic electrolyte. The device showed excellent electrochemical performance with a high specific energy of 2.12 mW h cm −3 at a power density of 0.04 W cm −3 and remarkable cycling stability with 80.3% specific capacitance retention even after 20,000 cycles.