Organic ligands and metal ions in the metal–organic frameworks (MOFs, a type of porous magnetic metal/carbon nanocomposites obtained through high-temperature carbonization) have caused widespread concerns in the field of microwave absorption because of the existence of various microwave loss mechanisms in these materials. However, MOF-driven microwave absorbing materials with high absorption intensity and wide absorption band still require further research and development. In this work, hollow sphere trimetallic FeCoNi@C microwave absorbing materials via high-temperature carbonization were obtained using FeCoNi-based MOF-74 (FeCoNi-MOF) as the precursor. The effects of different carbonization conditions on the microwave absorption properties of the materials were studied. FeCoNi-MOF-74 annealed at 700 °C showed superior microwave absorption capacity, where the RL value reached −64.75 dB at 15.44 GHz corresponding to the actual application thickness of the absorber (only 2.1 mm), and the minimum RL values reached −69.03 dB at 5.52 GHz. Furthermore, the as-prepared sample can fully cover the Ku band and X band at only 2.1 and 3.1 mm, respectively. The maximum EAB reached 8.08 GHz (9.92–18 GHz) when the thickness of the absorber was 2.47 mm. Such remarkable absorption performance is attributed to the synergetic effects between the multiple loss mechanisms of the FeCoNi@C, and the improved impedance matching characteristic came from the hollow sphere morphology.
Magneto-carbon composites are promising materials for mitigating electromagnetic pollution due to combined dielectric and magnetic loss mechanisms. However, such absorbers often have unsatisfactory wave-absorbing properties due to the difficulty in matching the magnetic permeability with the dielectric properties. The multilayered hollow carbon cubes anchored to a ternary FeCoNi alloy were fabricated using a self-tempered engineering strategy. The multilayer structures are formed in two steps and have an iron cobalt-nickel alloy core encapsulated in a hollow cubic carbon shell. Initially, a phenolic resin (PR)-coated FeCoNi-Prussian blue analogue (PBA) was prepared, followed by high-temperature vacuum pyrolysis. The inner carbon layer, derived from PBA, exhibits high crystallinity, while the outer PR-derived carbon layer is amorphous, preventing agglomeration of the carbonized FeCoNi alloy particles. The amorphous outer layer enables electromagnetic waves to be better absorbed and consumed within the absorber due to its ability to effectively modulate conductivity and impedance matching. By leveraging heterogeneous interface polarization and modulating electrical conductivity through control of graphite crystallinity, a minimum reflection loss (RL min ) of −74.2 dB and an effective absorption bandwidth (EAB) of 5.8 GHz across the 2–18 GHz range were achieved. The study provides an effective approach to broaden the application prospects of advanced magneto-carbon composite absorbers by using a multilayer structure to achieve a balance between magnetic loss and dielectric properties.
Lei Yang,Ziyi Zhao,Wanxin Wu,Yujue Li,Ziyuan Zhao,Jiahui Wang,Le Xu,Xueqin Yuan
FeCoNi/C hybrid nanowires serve as free-standing anodes for LIBs. • FeCoNi/C outperforms Fe/C and FeCoNiMn/C in LIB performance. • Diameter optimization of free-standing anodes can enhance the performance of LIB. Designing an integrated anode architecture that eliminates the need for binders and conductive agents is a promising approach to enhance both the energy density and rate capability of lithium-ion batteries (LIBs). Herein, we report the synthesis of free-standing Fe/C, FeCoNi/C and FeCoNiMn/C hybrid nanowire electrodes prepared by a facile electrospinning technique followed by a reduction treatment in Ar/H 2 atmosphere. The resulting C nanowire networks, embedded with uniformly distributed alloy nanoparticles, can be directly utilized as the anodes of LIBs. Electrochemical characterizations reveal that the FeCoNi/C-25 G electrode demonstrates superior cycling stability and rate capability compared with the Fe/C-25 G and FeCoNiMn/C-25 G counterparts, delivering a reversible capacity of 518.2 mAh/g after 100 cycles at 100 mA/g with a capacity retention of 84.5%. Furthermore, by varying the electrospinning needle gauge (19 G, 25 G and 30 G, the needle inner diameters are 0.75 mm, 0.26 mm and 0.16 mm, respectively), we optimized the nanowires diameter and found that the FeCoNi/C-30 G electrode exhibits the best performance, with a capacity of 564.4 mAh/g at 100 mA/g and 402.3 mAh/g at an ultrahigh current density of 4000 mA/g. The high performance of FeCoNi/C-30 G is attributed to the synergistic effects of the multi-component alloy system and the conductive C network. The reduced nanowire diameter also contributes to the excellent performance because it can facilitate ion/electron transport, increase active-site exposure and improve structural stability. This work offers a straightforward strategy for developing flexible, high performance binder-free anodes for next-generation LIBs.
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