Boosting the volumetric capacitance of MoO3-x free-standing films with Ti3C2 MXene

Abstract

The high theoretical capacitance of molybdenum trioxide (MoO3) renders it an attractive supercapacitor electrode material. However, its low electronic conductivity restricts charge transfer and slows its reaction kinetics. Herein, we vacuum filtered porous, free-standing, flexible and highly conductive films comprised of oxygen vacancy-rich MoO3-x nanobelts and delaminated Ti3C2 MXene in a mass ratio of 80:20, respectively. When tested as supercapacitor electrodes, in a 5 M LiCl electrolyte, volumetric capacitances of 631 F cm−3 at 1 A g−1, and 474 F cm−3 at 10 A g−1 were obtained. To increase the energy density, asymmetric supercapacitors, wherein the anodes were MoO3-based and the cathodes were nitrogen-doped activated carbon were assembled and tested. The resulting volumetric energy density was 48.6 Wh L−1. After 20,000 continuous charge/discharge cycles at 20 A g−1, 96.3 % of the initial charge remained. These values are outstanding for free-standing supercapacitor electrodes, especially in aqueous electrolytes.