Heterostructure design of hydrangea-like Co_(2)P/Ni_(2)P@C multilayered hollow microspheres for high-efficiency microwave absorption

Structural design and elemental doping are research hotspots for the preparation of lightweight absorbers with high absorption performance and low filling ratio.Herein,a P-doped hydrangea-like layered compos-ite(Co_(2)P/Ni_(2)P@C)encapsulated with Ni-LDH was successfully synthesized by solvothermal method fol-lowed by phosphorization.The defects generated by P doping and the generation of multilayered nonuni-form interfaces enhance the dielectric loss induced by polarization.Simultaneously,the magnetic phos-phides induce magnetic loss and modulate the dielectric properties of the carbon matrix to enhance the conductive loss.The multilayered hollow structure of this composite promotes the scattering and reflec-tion of electromagnetic waves and optimizes the impedance characteristics.As a result,the multilayered hollow Co_(2)P/Ni_(2)P@C composite exhibits an optimum reflection loss value(RL)of–64.6 dB at 15.1 GHz with a thickness of 2 mm and a filler ratio of only 10 wt%.The radar cross-section(RCS)attenuation further demonstrates that the material can dissipate microwave energy in practical applications.Overall,this work provides an effective development strategy for the design of multilayered high-performance electromagnetic wave(EMW)absorbers doped with strongly polarized elements.

Ultra-fine Cu clusters decorated hydrangea-like titanium dioxide for photocatalytic hydrogen production

Hydrogen,with the merits of zero emissions and high energy density,is one of the promising green energy sources.Seeking for high efficiency and low-cost catalysts is one of the key issues for hydrogen evolution and its practical applications.Nano-structured metal cocatalysts are widely used to improve the photocatalytic performance via surface electronic structure/properties optimization of the catalyst.Herein,we report ultra-fine(*1 nm)Cu clusters decorated hydrangea-like TiO_(2)systems for photocatalytic hydrogen evolution.The pristine hydrangea-like TiO_(2)support shows a promising performance of hydrogen evolution(1.8 mmol·h^(-1)·g^(-1)),which is*10.7 times higher than that of the commercial P25(168 lmol·h^(-1)·g^(-1)).After ultra-fine Cu clusters decoration,a maximal hydrogen evolution performance(3.7 mmol·h^(-1)·g^(-1))is achieved in the optimized system 6Cu–TiO_(2)(6 wt%).Experimental and theoretical studies demonstrate that the ultra-fine Cu clusters decoration could promote the charge separation and transfer process effectively.The Cu clusters also act as reaction sites for reduction of H_(2)O to H2.These results are of great importance for the study of Cu-based co-catalyst systems and also shed light on the development of other non-noble metal co-catalysts in photocatalysis hydrogen evolution.

Construction of hydrangea-like core-shell SiO_(2)@Ti_(3)C_(2)T_(x)@CoNi microspheres for tunable electromagnetic wave absorbers

Ti_(3)C_(2)T_(x)MXene shows great potential in the application as microwave absorbers due to its high attenuation ability.However,excessively high permittivity and self-stacking are the main obstacles that constrain its wide range of applications.To tackle these problems,herein,the microspheres of SiO_(2)@Ti_(3)C_(2)T_(x)@CoNi with the hydrangea-like core-shell structure were designed and prepared by a combinatorial electrostatic assembly and hydrothermal reaction method.These microspheres are constructed by an outside layer of CoNi nanosheets and intermediate Ti_(3)C_(2)T_(x)MXene nanosheets wrapping on the core of modified SiO_(2),engendering both homogenous and heterogeneous interfaces.Such trilayer SiO_(2)@Ti_(3)C_(2)T_(x)@CoNi microspheres are“magnetic microsize supercapacitors”that can not only induce dielectric loss and magnetic loss but also provide multilayer interfaces to enhance the interfacial polarization.The optimized impedance matching and core-shell structure could boost the reflection loss(RL)by electromagnetic synergy.The synthesized SiO_(2)@Ti_(3)C_(2)T_(x)@CoNi microspheres demonstrate outstanding microwave absorption(MA)performance benefited from these advantages.The obtained RL value was-63.95 dB at an ultra-thin thickness of 1.2 mm,corresponding to an effective absorption bandwidth(EAB)of 4.56 GHz.This work demonstrates that the trilayer core-shell structure designing strategy is highly efficient for tuning the MA performance of MXene-based microspheres.

Hollow hydrangea-like nitrogen-doped NiO/Ni/carbon composites as lightweight and highly efficient electromagnetic wave absorbers

Hierarchical hollow-structured magnetic–dielectric materials are considered to be promising and competitive functional absorbers for microwave absorption(MA).Herein,a hierarchical hollow hydrangea multicomponent metal oxides/metal-carbon was designed and successfully produced via a facile self-assembly method and calcination process.Adequate magnetic NiO and Ni nanoparticles were suspended within the hollow hydrangea-like nitrogen-doped carbon matrix(HH N-NiO/Ni/C),constructing a unique hierarchical hollow structured multicomponent magnetic–dielectric MA composite.The annealing temperature and oxidation time were carefully regulated to investigate the complex permittivity and permeability.HH N-NiO/Ni/C delivers exceptional MA properties with maximum reflection loss of–45.8 dB at 1.7 mm thickness and displays a wide effective absorption frequency range of 5.6 GHz.The superior MA performance can be attributed to the following aspects:(1)The hierarchical hollow multicomponent structure offers plentiful of heterojunction interfaces triggering interfacial polarization;(2)nitrogen doped-carbon(N-C)facilitates the conductive loss by the unique electron migration path in the graphitized C and NiO/Ni;(3)magnetic NiO/Ni nanoparticles homogeneously dispersed within N-C form extensive C skeleton and strengthen the magnetic response ability;(4)hierarchical hollow wrinkled structures possess a large interspace and heterogeneous interface improving polarization loss and enhancing multireflection process and the unique structure satisfies magnetic and dielectric loss simultaneously resulting from synergistic effects of different components within the composites.

具有分级结构的Co_3O_4绣球花状微米球的构筑及其锂离子电池负极性能研究

采用溶剂热法合成了绣球花状Co_3O_4纳米材料,并利用扫描电子显微镜和X射线衍射仪进行了微观形貌和结构的表征,结果显示样品的形貌为4~6μm绣球花状分级结构微米球,结晶良好,无杂相生成。该绣球花状Co_3O_4纳米材料用做锂离子电池负极材料时表现出很高的可逆比容量和良好的循环性能。在300 m A/g电流密度下,首次放电比容量达1 508 m A·h/g,经过20次循环可逆比容量为1 300 m A·h/g。其良好的电化学性能归功于绣球花状Co_3O_4材料的独特形貌,其多级结构能够缩短锂离子的传输路径,并且拥有足够大的孔隙,来适应和缓解电极材料在循环过程的体积效应。

“绣球”状中空C/Nb2O5微球的制备及其电化学性能研究

以草酸铌为铌源,空心碳球为模板,采用简单的水热法合成了具有独特形貌的“绣球”状中空C/Nb2O5微球。采用X射线衍射(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)表征了所制备中空C/Nb2O5微球的微观结构,并采用电化学工作站研究了其作为负极材料的锂离子电池的电化学性能。研究结果表明,直径约为1μm的空心碳球被Nb2O5包覆,中空C/Nb2O5微球呈现出独特的“绣球”形状,使其比表面积明显增大;在电流密度为40 mA/g下,中空C/Nb2O5微球和Nb2O5微球作为负极材料的锂离子电池的初始放电比容量分别为402.26 mA·h/g和336.44 mA·h/g,经过50次充放电循环后,当电流密度返回40 mA/g时,中空C/Nb2O5微球的放电容量为192.38 mA·h/g,而Nb2O5微球的放电容量仅为4.86 mA·h/g。说明这种特殊的“绣球”状中空结构有效地增加了Nb2O5的表面积,并使得中空C/Nb2O5微球负极材料具有高的比容量和良好的可逆性能。

绣球荚蒾状硫化钴@富氮炭的设计与构建及超级电容性能

本文采用简单的溶剂热法制备了一种独特的具有大量电化学活性位点的绣球荚蒾状硫化钴(HVCS)。接着通过原位聚合将聚苯胺(PANI)组装到HVCS表面,最后将聚苯胺进一步碳化,得到绣球荚蒾状硫化钴@富氮炭复合材料(HVCS@NC)。得益于独特的微观结构设计和两组分电化学性能优势的互补,电化学分析表明制备所得HVCS@NC纳米复合电极具有理想的超级电容器电化学性能。该材料在电流密度为1 A·g^(-1)时展现出622 F·g^(-1)的比电容值,以HVCS@NC和活性炭(AC)分别作正极和负极组装的不对称超级电容器,在功率密度为1912.3 W·kg^(-1)时能量密度达19.9 W·h·kg^(-1)。研究表明:将导电高分子PANI定位组装在具有特殊微观形貌结构硫化钴表面并碳化的工艺可以获得高性能硫化物基超级电容器电极材料,聚苯胺的可塑性及碳化处理后富含氮元素的特性对于改善过渡金属硫化物的电化学性能具有很大优势,这种结构设计策略可以潜在地扩展并应用到其他过渡金属硫化物基超级电容器电极材料的电化学性能提升。