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A type of core–shell structured N-doped C-coated Ni nanocapsules (Ni@NC) with a size range of 20–70 nm was prepared by a simple strategy of the arc discharge. And the microwave absorption capability of the Ni@NC nanocapsules can be conveniently tuned by N-doping content varying from changing nitrogen pressure in their preparation process. The study revealed that the variable microwave absorption capability of the Ni@NC nanocapsules results from their tuned dielectric behavior. The tuned dielectric responses depend on the degrees of the broken atomic symmetry of the graphite carbon for carbon atoms substituted with nitrogen ones. The optimized impedance matching of the Ni@NC nanocapsules can be achieved by the appropriate content of N doping in graphite C shells. An optimal reflection loss value − 50.7 dB at 14.43 GHz with a thin thickness of 1.8 mm is acquired while choosing the pressure of 15 kPa nitrogen for the preparation of the Ni@NC nanocapsules (the N content in Ni@NC is about 4.62 at.% estimated by XPS). Therefore, it is a feasible strategy to tuning the microwave absorption properties of the Ni@NC nanocapsules by changing the content of N doping, which is of great significance for the study microwave absorbing materials at the atomic scale. [ABSTRACT FROM AUTHOR]

We adopted a facile method consisting of the arc discharge method combined with the in situ self-polymerization process to synthesize the cubic TiN@CN nanocapsules in this work, and we also investigated the electrochemical performance and microwave absorption properties of the TiN@CN nanocapsules in detail. The results show that the TiN@CN nanocapsules exhibit excellent electrochemical performance. The specific capacitance of the TiN@CN nanocapsules is 119 F g−1 at 1 A g−1, and their capacitance retention rate is 92% after 5000 cycles at the current density of 2 A g −1. Besides, the cubic TiN@CN nanocapsules also exhibit powerful microwave absorption capacity. The reflection loss (RL) below − 20 dB is achieved in a wide frequency range of 7.2–15.5 GHz with a thickness range of 1.1–2.3 mm, and the optimal RL value is − 40.6 dB at 10.6 GHz with a relatively thin thickness of 1.6 mm. Therefore, TiN@CN nanocapsules are promising and applicable as electrode materials for supercapacitors and as microwave absorbers. [ABSTRACT FROM AUTHOR]

In this study, the three types of core–shell structured Fe-based nanocapsules with different shapes were synthesized using arc-discharge method via fine-tuning Al content in Fe–Al raw material alloy. The synthetic parameters on the microstructure and shape as well as microwave absorption properties of Fe-based nanocapsules were investigated in detail. The results show that the Al content in Fe–Al raw material alloy will affect the shape and microwave absorption properties of the synthesized Fe-based nanocapsule absorbent. The polyhedral Fe@FeOx–Al2O3 nanocapsules absorbents can be obtained while Fe–Al raw material alloy containing Al 3 wt% was used as an anode in arc-discharge process, and their microwave absorption properties can be significantly improved, compared with those of the prepared other two Fe-based nanocapsules. Reflection loss (RL) values below − 20 dB for polyhedral Fe@FeOx–Al2O3 nanocapsules absorbent are acquired in the frequency range of 3.21–18 GHz within 1.2–5.5 mm thickness, covering few S-bands and whole C–Ku bands. Besides, the FexAly phase existed in Fe-based nanocapsules cause the frequency band of the strongest RL (exceeding − 20 dB) shifting low-frequency region, which can be of help in further researching microwave absorption (L–S wave band) of FexAly alloy or other Al-magnetic transition metal nanoparticles absorbent in future work. These results demonstrate that the polyhedral Fe nanocapsules hold excellent microwave absorption properties, which could be promising candidate materials for the manufacture of microwave devices with broadband. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract A facile strategy for synthesis of the Ni@C(N) nanocapsules was adopted, including arc-discharge method and in-suit self-polymerization method. The morphology, component, catalytic reduction performance as well as catalytic reduction mechanism were studied in detail. The results reveal that the well-dispersed Ni core is firmly coated by N-doped carbon shell. The Ni@C(N) nanocapsules exhibit enhanced catalytic properties for reduction of 4-nitrophenol (4-NP) and methylene blue (MB), due to better synergetic effect between the Ni core and N doped C shell, compared with Ni@C nanocapsules. The kinetic reaction rate constant of the Ni@C(N) nanocapsules is about five times larger than that of Ni@C nanocapsules. Furthermore, the Ni@C(N) nanocapsules display strong recyclability for reduction of 4-NP. [ABSTRACT FROM AUTHOR]

An arc-discharge method together with in-situ self-polymerization method was adopted to synthesize Ni@C/NC nanocapsules. With this method, the Ni@C/NC nanocapsules with enhanced microwave absorption properties were obtained. This enhanced microwave absorption property is due to the modification on Ni@C nanocapsule with accreted N-doped C shell on its surface. The microstructure and microwave absorption property of as-prepared nanocapsules were studied in detail. A reflection loss (RL) below − 20 dB is obtained in the wide frequency range of 4.4-18 GHz of Ni@C/NC nanocapsules, when an appropriate absorber thickness from 1.5 to 5.2 mm is chosen. An optimal RL value − 38.3 dB is observed at 11.7 GHz on Ni@C/NC nanocapsules-paraffin composites with an absorber thickness of 2.4 mm. Moreover, the amplitude of RL values of Ni@C/NC nanocapsules is about 2-3 times as many as that of Ni@C nanocapsules within absorber thickness ranging from 1.5 to 5.2 mm. This result shows that N-doped graphite C accreted on the surface of Ni@C nanocapsules could induce strong dielectric resonance and increase permittivity values of the Ni@C/NC nanocapsules. As a result, microwave absorbing performance of the Ni@C/NC nanocapsules is significantly enhanced. [ABSTRACT FROM AUTHOR]

[Display omitted] • N-doped graphite coated Ni (Ni@CN) nanocapsules were prepared by one-step method. • The Ni@CN have efficient dual-functional behavior in HER and microwave absorption. • The Ni@CN shows a low overpotential of 85 mV at 10 mA cm−2 in HER. • Complementarity between CN shell and Ni core induce superior properties. • Doping N into graphite boosts the electronic transmission ability of graphite C. Developing high efficient, stable, and earth-abundant materials is still a great challenge both in the electrocatalytic and microwave absorption fields nowadays. Herein, we construct unique core-shell structured N-doped graphite coated Ni (Ni@CN) nanocapsules through a facile one-step arc-discharge method. The as-obtained Ni@CN show superior hydrogen evolution reaction (HER) activities with a low overpotential of 85 mV at 10 mA cm−2, a small Tafel slope of 69 mV dec-1, and strong long-term stability of 10 h. Besides, the Ni@CN nanocapsules exhibit high microwave absorption performance as microwave absorbers. Their optimal value of reflection loss (RL) is -35.8 dB at 11.7 GHz with a thickness of 2.3 mm. The dual-functional behavior of Ni@CN nanocapsules in catalytic and microwave absorption is due to their strong synergistic effect between the N-doped graphite shell and Ni core, the high electrical conductivity of Ni, and the abundant defects caused by the N doping into the graphite shell. [ABSTRACT FROM AUTHOR]