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Research Article Issue
Rational design of 3D porous niobium carbide MXene/rGO hybrid aerogels as promising anode for potassium-ion batteries with ultrahigh rate capability
Nano Research 2023, 16 (2): 2463-2473
Published: 14 October 2022
Downloads:35

An effective method is designed to construct three-dimensional (3D) Nb2C/reduced graphene oxide (rGO) hybrid aerogels through a low-temperature graphene oxide (GO)-assisted hydrothermal self-assembly followed by freeze-drying and annealing. The intimately coupled Nb2C/rGO hybrid aerogel combines the advantages of large specific surface area and rich 3D interconnected porous structure of aerogel as well as high conductivity and low potassium diffusion energy barrier of Nb2C, which not only effectively prevents the self-restacking of Nb2C nanosheets to allow more active sites exposed and accommodate the volume change during the charge/discharge process, but also increases the accessibility of electrolyte and promotes the rapid transfer of ions/electrons. As a result, Nb2C/rGO-2 as the anode of potassium ion batteries (KIBs) delivers a large reversible specific capacity (301.7 mAh·g−1 after 500 cycles at 2.0 A·g−1), an ultrahigh rate capability (155.5 mAh·g−1 at 20 A·g−1), and an excellent long-term large-current cycle stability (198.8 mAh·g−1 after 1,000 cycles at 10 A·g−1, with a retention of 83.3%). Such a high-level electrochemical performance, especially the ultrahigh rate capability, is the best among transition metal carbides and nitride (MXene)-based materials reported so far for KIBs. The diffusion kinetics of K+ is investigated thoroughly, and the synergetic charge–discharge mechanism and the structure–performance relationship of Nb2C/rGO are revealed explicitly. The present work provides a good strategy to solve the self-restacking problem of two-dimensional materials and also enlarges the potential applications of MXenes.

Research Article Issue
Ultrahigh rate capability of 1D/2D polyaniline/titanium carbide (MXene) nanohybrid for advanced asymmetric supercapacitors
Nano Research 2022, 15 (1): 285-295
Published: 24 April 2021
Downloads:36

High energy density and enhanced rate capability are highly sought-after for supercapacitors in today's mobile world. In this work, polyaniline/titanium carbide (MXene) (PANI/Ti3C2Tx) nanohybrid is synthesized through a facile and cost-effective self-assembly of one-dimensional (1D) PANI nanofibers and two-dimensional (2D) Ti3C2Tx nanosheets. PANI/Ti3C2Tx delivers greatly improved specific capacitance, ultrahigh rate capability (67% capacitance retention from 1 to 100 A·g−1) as well as good cycle stability. Electrochemical kinetic analysis reveals that PANI/Ti3C2Tx is featured with surface capacitance-dominated process and has a quasi-reversible kinetics at high scan rates, giving rise to an ultrahigh rate capability. By using PANI/Ti3C2Tx as positive electrode, an 1.8 V aqueous asymmetric supercapacitor (ASC) is successfully assembled, showing a maximum energy density of 50.8 Wh·kg−1 (at 0.9 kW·kg−1) and a power density of 18 kW·kg−1 (at 26 Wh·kg−1). Moreover, an 3.0 V organic ASC is also elaborately fabricated by using PANI/Ti3C2Tx, achieving an ultrahigh energy density of 67.2 Wh·kg−1 (at 1.5 kW·kg−1) and a power density of 30 kW·kg−1 (at 26.8 Wh·kg−1). The present work not only improves fundamental understanding of the structure-property relationship towards ultrahigh rate capability electrode materials, but also provides valuable guideline for the rational design of high-performance energy storage devices with both high energy and power densities.

Research Article Issue
Thermostable Nitrogen-Doped HTiNbO5 Nanosheets with a High Visible-Light Photocatalytic Activity
Nano Research 2011, 4 (7): 635-647
Published: 25 March 2011
Downloads:15

Nitrogen-doped HTiNbO5 nanosheets have been successfully synthesized by first exfoliating layered HTiNbO5 in tetrabutylammonium hydroxide (TBAOH) to obtain HTiNbO5 nanosheets and then heating the nanosheets with urea. The resulting samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy and N2 adsorption–desorption measurements. It was found that N-doping resulted in a much higher thermostability of the layered structure, intrinsic bandgap narrowing and a visible light response. The doped nitrogen atoms were mainly located in the interstitial sites of TiNbO5 lamellae and chemically bound to hydrogen ions. Compared with N-doped HTiNbO5, N-doped HTiNbO5 nanosheets had a much larger specific surface area and richer mesoporosity due to the rather loose and irregular arrangement of titanoniobate nanosheets. Both N-doped layered HTiNbO5 and HTiNbO5 nanosheets showed a very high visible-light photocatalytic activity for the degradation of rhodamine B (RhB) aqueous solution. Moreover, due to the considerably larger surface area, richer mesoporosity and stronger acidity, N-doped HTiNbO5 nanosheets had an even higher activity than N-doped HTiNbO5, although the latter had a stronger absorption in the visible region. The dye molecules were mainly degraded to aliphatic organic compounds and partially mineralized to CO2 and/or CO, rather than being simply decolorized. The effect of photosensitization was insignificant and RhB was degraded mainly via the typical photocatalytic reaction routes. Two different reaction routes for the photodegradation of RhB under visible light irradiation over N-doped HTiNbO5 nanosheets have been proposed. The present method can be extended to a large number of layered metal oxides that have the characteristics of intercalation and exfoliation, thus providing new opportunities for the fabrication of highly effective and potentially practical visible-light photocatalysts.

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