Li-ion hybrid electrochemical capacitors (Li-HECs) with higher energy density than electric double layer capacitors (EDLC) and larger power density than current rechargeable batteries are attractive candidates in future energy related applications. However, the electrochemical properties of current Li-HECs are greatly restricted by its Li-ion insertion type of electrode materials. Herein, we report an efficient approach to prepare one dimensional T-Nb2O5 nanowires growth on activated carbon cloth as freestanding hybrid electrodes for Li-HECs. The T-Nb2O5 nanowires with diameter of 20∼50 nm and length of several micrometers cross with each other and form a three dimensional (3D) porous network. The designed hybrid electrodes can deliver a gravimetric capacitance as high as 220 mAh g−1 at current density of 0.5 C and advanced cycle life with capacity retention of 86% after 1000 cycles at 5 C. The outstanding electrochemical performances are mainly attributed to the reduction in the lithium ion diffusion length brought by the crossed porous structure. And the enhancement of electron transportation enjoys the benefit from the in-situ growth of T-Nb2O5 nanowires on carbon cloth and the binder-free electrode structure.
Sodium-ion hybrid supercapacitors (Na-HSCs) by virtue of synergizing the merits of batteries and supercapacitors have attracted considerable attention for high-energy and high-power energy-storage applications. Orthorhombic Nb 2 O 5 ( T -Nb 2 O 5 ) has recently been recognized as a promising anode material for Na-HSCs due to its typical pseudocapacitive feature, but it suffers from intrinsically low electrical conductivity. Reasonably high electrochemical performance of T -Nb 2 O 5 -based electrodes could merely be gained to date when sufficient carbon content was introduced. In addition, flexible Na-HSC devices have scarcely been demonstrated by far. Herein, an in situ encapsulation strategy is devised to directly grow ultrathin graphene shells over T -Nb 2 O 5 nanowires (denoted as Gr-Nb 2 O 5 composites) by plasma-enhanced chemical vapor deposition, targeting a highly conductive anode material for Na-HSCs. The few-layered graphene capsules with ample topological defects would enable facile electron and Na + ion transport, guaranteeing rapid pseudocapacitive processes at the Nb 2 O 5 /electrolyte interface. The Na-HSC full-cell comprising a Gr-Nb 2 O 5 anode and an activated carbon cathode delivers high energy/power densities (112.9 Wh kg −1 /80.1 W kg −1 and 62.2 Wh kg −1 /5330 W kg −1 ), outperforming those of recently reported Na-HSC counterparts. Proof-of-concept Na-HSC devices with favorable mechanical robustness manifest stable electrochemical performances under different bending conditions and after various bending–release cycles.
A facile soft chemistry route was described to prepare a composite material of Nb2O5 nanowires modified with Pd nanoparticles having an average diameter of 7.9 nm. The Pd/w-Nb2O5 catalyst was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), Brunauer–Emmett–Teller (BET) and X-ray photoelectron spectroscopy (XPS) techniques. In comparison with Pd/s-Nb2O5 and Pd/Al2O3, the Pd/w-Nb2O5 had a more substantial catalysis effect on the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) under ambient conditions. The results showed that the conversion rate of 4-NP (20 mg L−1, 100 mL) was about 98.3% after 4 min using 10 mg of the catalyst, Moreover, after the catalyst had been reused 10 times, the conversion rate still remained 85.3%. The significant enhancement in the catalysis activity can be ascribed to acidity and morphology of the catalyst support Nb2O5.
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