Charge storage performances and mechanisms of MnO₂ nanospheres, nanorods, nanotubes and nanosheets

Abstract

Manganese dioxide (MnO) has been widely used as an active material for high-performance supercapacitors due to its high theoretical capacitance, high cycling stability, low cost, and environmental friendliness. However, the effect of its crystallographic phase on charge storage performances and mechanisms is not yet clear. Herein, MnO-based supercapacitors with different structures including nanospheres, nanorods, nanotubes, and nanosheets have been fabricated and investigated. Among such structures, δ-MnO nanosheets exhibit the highest specific capacitance of 194.3 F g at 1 A g when compared with other phases and shapes. The maximum specific energy of the δ-MnO nanosheet supercapacitor is 23.4 W h kg at 971.6 W kg and the maximum specific power is 4009.2 W kg at 15.9 W h kg with a capacity retention of 97% over 15 000 cycles. The δ-MnO nanosheet mainly stores charges via a diffusion-controlled mechanism at the scan rates of 10-100 mV s, whilst the α-MnO with different morphologies including nanospheres, nanorods, and nanotubes store charges via a non-faradaic or non-diffusion controlled process especially at fast scan rates (50-100 mV s). Understanding the charge storage performance and mechanism of the MnO nanostructures with different crystallographic phases and morphologies may lead to the further development of supercapacitors.

Effects of electrodeposition time on a manganese dioxide supercapacitor

“…However, EDLCs always show much lower specic capacitance and energy density than PCs owing to the fact that EDLCs mainly rely on the charge storage on the interface between the electrode material and the electrolyte ions. [9][10][11] However, PCs depend on the rapid and reversible faradaic reactions that occur on the surface of the electrode material. 12,13 The key to pseudocapacitors is the preparation of electrode materials.…”

Manganese‐Oxide‐Based Electrode Materials for Energy Storage Applications: How Close Are We to the Theoretical Capacitance?

“…The morphology also has an impact on how charges are stored by MnO x ‐based electrodes. In Sawangphruk's work, for example, it was found that for MnO 2 nanosheets, diffusion was the dominant process during charge storage; while for MnO 2 nanospheres, nanorods, and nanotubes, charge was stored by both diffusion and nondiffusion controlled processes. The morphology of a specific MnO x nanomaterial can be tuned through facet engineering .…”

Enhanced pseudocapacitance from finely ordered pristine α-MnO2 nanorods at favourably high current density using redox additive

“…Supercapacitors are classified into electric double layer capacitors (EDLC) where the charges are stored electrostatically through separation of charges and pseudocapacitors (PC) where the charges are stored faradaically involving electrochemical redox reaction, electrosorption and intercalation of ions or atoms between electrode and electrolyte [12,13]. Faradaic storage mechanism of charge makes pesudocapacitors meritorious by giving higher energy density than EDLC [14][15][16]. Transition metal oxide is considered as an ideal pesudocapacitor electrode material attributing to their intrinsically high pseudocapacitive behaviour of fast and reversible surface redox reactions [17][18][19].…”