Investigating the Influence of Sodium Preintercalation on the Electrochemical Behavior of Ultrathin MnO<sub>2</sub> Nanowires for Enhanced Supercapacitor Performance
Muhammad Usman Khalid, Sonia Zulfiqar, Muhammad Farooq Warsi, Imran Shakir, M. S. Al-Buriahi, Eric W. Cochran
Abstract
We have successfully synthesized bare and Na + preintercalated MnO 2 nanowires (NWs) (Na x MnO 2, x = 0.05, 0.1, and 0.15) using a facile hydrothermal method. Supercapacitors are the state-of-the-art technology to overcome the global energy crisis, owing to their fast charging/discharging rates and higher power density. One-dimensional morphology (nanorods, nanowires, etc.) boosts the inherent low conductivity of transition metal oxides including MnO 2 by confining charge transport only in one direction. Here, we have preintercalated Na + ions into MnO 2 nanowires (NWs) as a conductivity booster as well as a tunnel-stabilizing agent for α-MnO 2 . Morphological analysis reveals that nanowires have <50 nm diameter and their surface gets cracked with Na + preintercalation, offering a less dead area. Linear sweep voltammetry (LSV) results revealed an increase in oxygen evolution overpotential by Na + preintercalation, which can enable the supercapacitor to operate at an extended potential window. Na + preintercalation and control on morphology not only increased the conductivity but also shielded the electrode pulverization against tedious charging/discharging cycles and reduced the electrolyte diffusion pathway. These features enabled Na 0.10 MnO 2 NWs to exhibit a specific capacitance of 1061 F g –1 @1 A g –1 and an excellent rate capability of 85.6% at 9 A g –1 along with 95.9% capacitance retention after 6000 charging–discharging cycles at 12 A g –1 current density. This study showed that Na + preintercalation in MnO 2 could improve the electrochemical performance and open up new horizons to manufacture high-performance next-generation supercapacitors.