Synergistic effects of nanoarchitecture and oxygen vacancy in nickel molybdate hollow sphere towards a high‐performance hybrid supercapacitor

Abstract

The facile design and fabrication of nanoarchitectured binary transition metal oxide electrode materials are essentially required for the advancement of highperformance supercapacitors (SCs). Herein, we prepared an oxygen-vacant NiMoO 4 (Ov-NiMoO 4 ) hollow sphere via a simple hydrothermal approach and subsequent heat treatment under an argon atmosphere. In particular, the oxygen vacancy is confirmed by using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Raman, and differential reflectance spectroscopy (DRS) UV-Vis spectra studies. Furthermore, the generation of the oxygen vacancy could enhance the electrical conductivity and improve Faradaic redox sites. Significantly, the Ov-NiMoO 4 hollow sphere depicts a larger specific capacity (C sp ) of 496 mA h g À1 at 1 A g À1 than the bare-NiMoO 4 (b-NiMoO 4 ; 279 mA h g À1 ) thermally treated under air. Furthermore, the hybrid SC (HSC) is fabricated based on the Ov-NiMoO 4 //activated carbon, revealing a high specific capacitance (C s ) of 120 F g À1 and providing a large energy density (ED) of 37.49 W h kg À1 and power density (PD) of 36.61 kW kg À1 . Moreover, the HSC shows considerable cyclic stability of ~91.14% over 20 000 cycles. The results divulge that the poor crystallinity and the introduction of oxygen vacancies play a vital role in enhancing the charge-storage capability of the materials.

Synchronous Defect and Interface Engineering of NiMoO4 Nanowire Arrays for High-Performance Supercapacitors

“…Evidently both samples had two strong bands with BEs located at 236.0 eV and 232.9 eV, which could be assigned to Mo 3d 3/2 and Mo 3d 5/2 of Mo 6+ cations in the NiMoO 4 lattice [ 56 ]. In addition, another pair of doublets was noted for the NiMoO 4− x @C sample, verifying the existence of Mo 4+ in the NiMoO 4− x @C composite [ 41 , 42 , 57 ] possibly produced during the amorphous carbon coating process. From Figure 6 e, the O 1s spectrum of the NiMoO 4 NWs sample was deconvoluted into three bands.…”

“…To overcome the poor electronic conductivity of pristine NiMoO 4 , various NiMoO 4 /carbon composites have been synthesized by hybridizing NiMoO 4 nanostructures with graphene [ 30 , 31 ], carbon nanotubes [ 32 ], conducting polymers [ 33 ], and porous carbon architectures [ 34 , 35 ] Alternatively, intentional doping of NiMoO 4 with several kinds of heteroatoms such as Mn [ 36 , 37 ], P [ 38 ], Zn [ 39 ], Ce [ 40 ], or the creation of oxygen vacancies [ 14 , 41 , 42 , 43 ] in the lattice have recently been reported. In addition, NiMoO 4 has also been coupled with other metal oxides [ 44 , 45 , 46 , 47 , 48 , 49 ] or sulfides [ 50 , 51 , 52 ] to form heterostructure electrodes for supercapacitors with improved electrochemical performances.…”

Impact of oxygen‐defects induced electrochemical properties of three‐dimensional flower‐like CoMoO 4 nanoarchitecture for supercapacitor applications

“…[26][27][28][29][30] In addition to morphological architecture, the crystalline feature and the defect engineering (oxygen-defects) could impact the conductivity of the electrode materials, which distinctly improves the electrochemical performance. [31][32][33] For instance, Cai et al introduced oxygen vacancies into NiCo 2 O 4 nanoarrays and showed high specific capacitance of 1389 mF cm À2 at 0.5 mA cm À2 with remarkable capacitance retention. 17 Fan et al fabricated oxygenvacancy rich MnO 2 nanowires @ NiMn x O yÀδ nanosheets core-shell heterostructure for supercapacitor, revealed a specific capacitance of 463.5 C g À1 at 1 A g À1 and demonstrating the superior cyclic stability.…”

“…Thus, to improve the capacitive properties of the CMO electrode material, the design of various morphological approaches is explored to improve the ionic transport effectiveness and more electrochemical utilization 26‐30 . In addition to morphological architecture, the crystalline feature and the defect engineering (oxygen‐defects) could impact the conductivity of the electrode materials, which distinctly improves the electrochemical performance 31‐33 . For instance, Cai et al introduced oxygen vacancies into NiCo 2 O 4 nanoarrays and showed high specific capacitance of 1389 mF cm −2 at 0.5 mA cm −2 with remarkable capacitance retention 17 .…”

“…Ma et al developed reduced vacancy‐rich Co 3 O 4 nanoribbons, provided a high specific capacitance of 464.9 F g −1 and a reduced charge transfer resistance 41 . Moreover, the oxygen‐defects in electrode materials act as shallow donors as well as efficient electroactive sites, which can further facilitate the path for improving the electrical conductivity and decrease the energy barrier to enrich electrochemical redox kinetics to a higher degree 32,42 . Thus, developing a strategy for designing well‐defined morphology combined with defect engineering is in great demand for further breakthroughs in enhancing the electrochemical performance of electrode materials.…”