Nitrogen-doped carbon nanofiber webs (CNFWs) with high surface areas are successfully prepared by carbonization-activation of polypyrrole nanofiber webs with KOH. The as-obtained CNFWs exhibit a superhigh reversible capacity of 943 mAh g(-1) at a current density of 2 A g(-1) even after 600 cycles, which is ascribed to the novel porous nanostructure and high-level nitrogen doping.
HIGHLIGHTS • The traditional and novel etching methods are summarized and compared, especially fluorine-free method. The methods for accelerating exfoliation of Ti 3 C 2 T x are classified. • The energy storage mechanisms of Ti 3 C 2 T x in different electrolytes are compared. Based on energy storage mechanisms, the influencing factors of morphology and surface functional groups are discussed.
Three types of MnO2 nanostructures, viz., α-MnO2 nanotubes, hollow β-MnO2 bipyramids, and solid β-MnO2 bipyramids, have been synthesized via a simple template-free hydrothermal method. Cyclic voltammetry and galvanostatic charge/discharge measurements demonstrate that the hollow β-MnO2 bipyramids exhibit the highest specific capacity and the best cyclability; the capacity retains 213 mAh g(-1) at a current density of 100 mA g(-1) after 150 cycles. XRD patterns of the lithiated β-MnO2 electrodes clearly show the expansion of lattice volume caused by lithiation, but the structure keeps stable during lithium insertion/extraction process. We suggest that the excellent performance for β-MnO2 can be attributed to its unique electrochemical reaction, compact tunnel-structure and hollow architecture. The hollow architecture can accommodate the volume change during charge/discharge process and improve effective diffusion paths for both lithium ions and electrons.
We have successfully assembled graphene nanosheets into spherical shells using polystyrene spheres as templates. Compared with stacked planar graphene, the as-prepared graphene spherical shells have more free space in between the spheres, which results in a larger accessible surface area for adsorption of electrolyte ions in supercapacitors. Electrochemical tests show that the graphene hollow spheres exhibit a high specific capacitance of 273 F g À1 and excellent electrochemical stability.
Nitrogen‐doped carbon‐dots (N‐CDs) are synthesized using a solid‐state method and applied as nanofertilizers. Specifically, 70 g of mung bean seeds are cultivated in the aqueous solution of N‐CDs (0.2 mg mL−1) and yields 646 g of bean sprouts; this yield is significantly higher than that obtained in the pure water control (i.e., 550 g of bean sprouts from 70 g of beans). Furthermore, blue florescence is observed during the sprouting process, which gradually migrates from the beans to the root ends, implying the absorption and migration of the N‐CDs during this process. This work demonstrates that the N‐CDs not only serve as a new fertilizer for promoting plant growth but also enable in vivo monitoring of the plant growth progress of plants, opening up new possibilities of CDs‐related materials for future agricultural applications.
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