Multifunctional MXene/C Aerogels for Enhanced Microwave Absorption and Thermal Insulation

Two-dimensional transition metal carbides and nitrides(MXene)have emerged as promising candidates for microwave absorption(MA)materials.However,they also have some drawbacks,such as poor impedance matching,high self-stacking tendency,and high density.To tackle these challenges,MXene nanosheets were incorporated into polyacrylonitrile(PAN)nanofibers and subsequently assembled into a three-dimensional(3D)network structure through PAN carbonization,yielding MXene/C aerogels.The 3D network effectively extends the path of microcurrent transmission,leading to enhanced conductive loss of electromagnetic(EM)waves.Moreover,the aerogel’s rich pore structure significantly improves the impedance matching while effectively reducing the density of the MXenebased absorbers.EM parameter analysis shows that the MXene/C aerogels exhibit a minimum reflection loss(RL_(min))value of−53.02 dB(f=4.44 GHz,t=3.8 mm),and an effective absorption bandwidth(EAB)of 5.3 GHz(t=2.4 mm,7.44–12.72 GHz).Radar cross-sectional(RCS)simulations were employed to assess the radar stealth effect of the aerogels,revealing that the maximum RCS reduction value of the perfect electric conductor covered by the MXene/C aerogel reaches 12.02 dB m^(2).In addition to the MA performance,the MXene/C aerogel also demonstrates good thermal insulation performance,and a 5-mm-thick aerogel can generate a temperature gradient of over 30℃ at 82℃.This study provides a feasible design approach for creating lightweight,efficient,and multifunctional MXene-based MA materials.

MXenes with applications in supercapacitors and secondary batteries:A comprehensive review

Two-dimensional(2D)materials have received tremendous attention because they possess a set of merits not available in bulk materials,such as large specific surface area,low energy barrier for electron transportation and short ion diffusion path.These advantages are desirable especially for the electrodes in electrochemical energy storage devices.MXenes,first synthesized in 2011 by etching their MAX phase precursors,have plural reasons to represent a new family of 2D materials.Their rich diversity in structure and composition together with the uncommon combination of good electrical conductivity and hydrophilicity makes themselves outstand in the whole 2D materials world.Based on these advantages,MXenes hold great promise for various technologically important applications,particularly in developing new energy storage techniques for advanced smart systems,such as portable and flexible electronics.There have been remarkable research achievements in the synthesis and application of MXene-based materials.While new synthesis routes being continuously reported,MXenes with new composition and novel structure have also been routinely discovered,which will undoubtedly help understand the fundamental properties and expand the application scope of MXenes.As for their energy storage-related applications,to cope with the intrinsic weakness of MXenes,many endeavors have been made by doping,structure-tuning and compositing with hybrid ingredients.In this review,the current status of MXenes synthesis and up-to-date progress of their applications in supercapacitors,metal-ion batteries and lithium sulfur batteries are summarized and discussed,and the typical work on the application of MXenes for the aforementioned three categories is respectively tabulated for reference and comparison.

One-dimensional core-sheath Sn/SnO_(x)derived from MAX phase for microwave absorption

One-dimensional(1D)metals are highly conductive and tend to form networks that facilitate electron hopping and migration.Hence,they have tremendous potential as microwave-absorbing(MA)materials.Traditionally,1D metals are mainly precious metals such as gold,silver,nickel,and their preparation methods often have low yield and are not environmentally friendly,which has limited the exploration in this area.Herein,the unique nanolaminate structure and chemical bond characteristics of Ti_(2)SnC MAX phase is successfully taken advantages for large-scale preparation of Sn whiskers,and then,core-sheath Sn/SnO_(x)heterojunctions are obtained by simply annealing at different temperatures.The heterojunction annealed at 500℃possesses favorable MA performance with an effective absorption bandwidth of 5.3 GHz(only 1.7 mm)and a minimum reflection loss value of51.97 dB;its maximum radar cross section(RCS)reduction value is 29.59 dB·m^(2),confirming its excellent electromagnetic wave attenuation ability.Off-axis electron holography is used to visually characterize the distribution of charge density at the cylindrical heterogenous interface,confirming the enhanced interfacial polarization effect.Given the diversity of MAX phases and the advantages of the fabrication method(e.g.,green,inexpensive,and easily scalable),this work provides significant guidance for the design of 1D metal-based absorbers.