Enhanced Reaction Kinetics of N–MnO₂ Nanosheets with Oxygen Vacancies via Mild NH₃·H₂O Bath Treatment for Advanced Aqueous Supercapacitors

Abstract

Suffering from the sluggish kinetics resulting from the inferior conductivity of manganese dioxide (MnO 2 ), many endeavors have been devoted to promoting the electrochemical performance of MnO 2 . Doping heteroatoms into host materials has emerged as an effective strategy to generate lattice vacancies for fast diffusion of ions/electrons in MnO 2 -based materials for supercapacitors (SCs). To eliminate the use of dangerous solvents and the severe reaction conditions used in previous reports, in this work, we first obtain N-doped MnO 2 (N−MnO 2 ) nanosheets with abundant oxygen vacancies simultaneously by a mild hydrothermal reaction. Thus, thanks to the mutual effect of N doping and oxygen vacancies, the capability of ion diffusion for N−MnO 2 /NGCF (NGCF represents N-doped single-wall carbon nanotube cross-linked graphene composite film) has increased an order of magnitude (1.68 × 10 −11 cm 2 s −1 compared with 8.42 × 10 −13 cm 2 s −1 for MnO 2 /NGCF) and shows superior rate capability, where at 30 A g −1 a capacitance retention of 51.7% remains, i.e., 185.1 F g −1 , compared with 44% at 15 A g −1 for MnO 2 /NGCF. In addition, we apply ex situ X-ray diffraction (XRD) and scanning electron microscopy (SEM) to verify the fact that nitrogen doping with abundant vacancies will benefit reversible intercalation/stripping of Na + by triggering the phase change from MnO 2 to MnOOH for N−MnO 2 compared with MnO 2 with adsorption/desorption during the charge−discharge process, which has never been discussed before. Excitingly, an asymmetric supercapacitor (ASC), fabricated by N−MnO 2 /NGCF as a cathode and MnO 2 /NGCF as an anode, delivers a maximum energy and power density of 75.3 Wh kg −1 and 18.1 × 10 3 W kg −1 , respectively. This work provides an approach to design self-standing advanced N-doped MnO 2 and a deeper insight into the mode of reaction of MnO 2 in neutral electrolyte for aqueous SCs.

Investigating the Influence of Sodium Preintercalation on the Electrochemical Behavior of Ultrathin MnO2 Nanowires for Enhanced Supercapacitor Performance

“…71 The oxygen vacancies have been reported to be advantageous for electrochemical studies by offering more active sites. 72…”

“…The increase in carrier charge density by Na + preintercalation into MnO 2 lattice also suggests the formation of oxygen vacancies . The oxygen vacancies have been reported to be advantageous for electrochemical studies by offering more active sites …”

CNTs-Supercapacitors: A Review of Electrode Nanocomposites Based on CNTs, Graphene, Metals, and Polymers

“…They demonstrated that the CNT/graphene/N-doped -Co3S4 supercapacitor has energy and power densities of 37.69 Wh/kg and 8000 W/kg, respectively. In another study, the supercapacitor based on the CNT/graphene/N-doped-MnO 2 electrode exhibited energy and power densities of 75.3 Wh/kg and 18,100 W/kg, respectively [88]. Hybrid nanostructures have been used to design flexible supercapacitors.…”

Supercapacitive performance of C-axis preferentially oriented TiO2 nanotube arrays decorated with MoO3 nanoparticles

“…15–17 Transition metal oxide (TMO) nanomaterials such as RuO 2 , V 2 O 5 , Fe 3 O 4 , MnO 2 , Co 3 O 4 , CuO, MoO 3 , and IrO 2 are used as electrode materials for supercapacitors. 18–28…”

“…[15][16][17] Transition metal oxide (TMO) nanomaterials such as RuO 2 , V 2 O 5 , Fe 3 O 4 , MnO 2 , Co 3 O 4 , CuO, MoO 3 , and IrO 2 are used as electrode materials for supercapacitors. [18][19][20][21][22][23][24][25][26][27][28] As a promising transition metal oxide, molybdenum trioxide (MoO 3 ) exhibits the advantages of rich valence state, high thermal stability and chemical stability. 29 MoO 3 with layered structure has been considered to be an alternative potential electrode material for energy storage devices due to its outstanding theoretical specific capacitance (2700 F g À1 ) and high electrochemical activity for supercapacitors.…”