In situ formation of multiple catalysts for enhancing the hydrogen storage of MgH_(2) by adding porous Ni_(3)ZnC_(0.7)/Ni loaded carbon nanotubes microspheres

MgH_(2) is considered one of the most promising hydrogen storage materials because of its safety,high efficiency,high hydrogen storage quantity and low cost characteristics.But some shortcomings are still existed:high operating temperature and poor hydrogen absorption dynamics,which limit its application.Porous Ni_(3)ZnC_(0.7)/Ni loaded carbon nanotubes microspheres(NZC/Ni@CNT)is prepared by facile filtration and calcination method.Then the different amount of NZC/Ni@CNT(2.5,5.0 and 7.5 wt%)is added to the MgH_(2) by ball milling.Among the three samples with different amount of NZC/Ni@CNT(2.5,5.0 and 7.5 wt%),the MgH_(2)-5 wt%NZC/Ni@CNT composite exhibits the best hydrogen storage performances.After testing,the MgH_(2)-5 wt%NZC/Ni@CNT begins to release hydrogen at around 110℃ and hydrogen absorption capacity reaches 2.34 wt%H_(2) at 80℃ within 60 min.Moreover,the composite can release about 5.36 wt%H_(2) at 300℃.In addition,hydrogen absorption and desorption activation energies of the MgH_(2)-5 wt%NZC/Ni@CNT composite are reduced to 37.28 and 84.22 KJ/mol H_(2),respectively.The in situ generated Mg_(2)NiH_(4)/Mg_(2)Ni can serve as a"hydrogen pump"that plays the main role in providing more activation sites and hydrogen diffusion channels which promotes H_(2) dissociation during hydrogen absorption process.In addition,the evenly dispersed Zn and MgZn2 in Mg and MgH_(2) could provide sites for Mg/MgH_(2) nucleation and hydrogen diffusion channel.This attempt clearly proved that the bimetallic carbide Ni_(3)ZnC_(0.7) is a effective additive for the hydrogen storage performances modification of MgH_(2),and the facile synthesis of the Ni_(3)ZnC_(0.7)/Ni@CNT can provide directions of better designing high performance carbide catalysts for improving MgH_(2).

Recent advances in the nanoconfinement of Mg-related hydrogen storage materials:A minor review

Hydrogen is an ideal clean energy because of its high calorific value and abundance of sources.However,storing hydrogen in a compact,inexpensive,and safe manner is the main restriction on the extensive utilization of hydrogen energy.Magnesium(Mg)-based hydrogen storage material is considered a reliable solid hydrogen storage material with the advantages of high hydrogen storage capacity(7.6wt%),good performance,and low cost.However,the high thermodynamic stability and slow kinetics of Mg-based hydrogen storage materials have to be overcome.In this paper,we will review the recent advances in the nanoconfinement of Mg-related hydrogen storage materials by loading Mg particles on different supporting materials,including carbons,metal-organic frameworks,and other materials.Perspectives are also provided for designing high-performance Mg-based materials using nanoconfinement.

Optimizing impedance matching by a dual-carbon Co-regulation strategy of Co_(3)O_(4)@rGO/celery stalks derived carbon composites for excellent microwave absorption

Both macroscopic composition and microstructure should be considered for reasonable microwave ab-sorbent designing.In this study,Co_(3)O_(4)@reduced graphene oxide(rGO)/Celery stalks derived carbon(CDC)was prepared by loading Co_(3)O_(4) particles into rGO and biomass-derived carbon mixture through oxidation precipitation.By changing the mass ratio of rGO to CDC,the dielectric and impedance matching proper-ties of the composites can be easily regulated.The RL min value of Co_(3)O_(4)@rGO/CDC_(13) composite(weight ratio for rGO:CDC is 1:3)reaches-84.3 dB with a thickness of 4.6 mm,and the widest effective band-width can be obtained at 4.5 GHz with a matching thickness of 2.8 mm.The Co_(3)O_(4)@rGO/CDC_(13) compos-ite with multiple components(Co_(3)O_(4),CDC,rGO)and 3D net structure produces magnetic/dielectric loss combinations,interfacial polarization,and multiple reflections and scattering,and the CDC with half tube and half sheet structure is conducive to the optimization of impedance matching.The strategy of co-regulating dielectric properties of materials with double carbon provides a novel pathway for the prepa-ration of lightweight,low-cost,and high-performance absorbers.

Boosted lithium storage performance by local build-in electric field derived by oxygen vacancies in 3D holey N-doped carbon structure decorated with molybdenum dioxide

Three-dimensional holey nitrogen-doped carbon matrixes decorated with molybdenum dioxide(MoO_(2))nanoparticles have been successfully synthesized via a NaCl-assisted template strategy.The obtained MoO_(2)/C composites offered multi-advantages,including higher specific surface area,more active sites,more ions/electrons transmission channels,and shorter transmission path due to the synergistic effect of the uniformly distributed MoO_(2) nanoparticles and porous carbon structure.Especially,the oxygen vacancies were introduced into the prepared composites and enhanced the Li^(+)intercalation/deintercalation process during electrochemical cycling by the Coulomb force.The existence of the local built-in electric field was proved by experimental data,differential charge density distribution,and density of states calculation.The uniquely designed structure and introduced oxygen vacancy defects endowed the MoO_(2)/C composites with excellent electrochemical properties.In view of the synergistic effect of the uniquely designed morphology and introduced oxygen vacancy defects,the MoO_(2)/C composites exhibited superior electrochemical performance of a high capacity of 918.2 mAh g^(-1) at 0.1 A g^(-1) after 130 cycles,562.1 mAh g^(-1) at 1.0 A g^(-1) after 1000 cycles,and a capacity of 181.25 mAh g^(-1) even at 20.0 A g^(-1).This strategy highlights the path to promote the commercial application of MoO_(2)-based and other transition metal oxide electrodes for energy storage devices.

Morphology controllable urchin-shaped bimetallic nickel-cobalt oxide/carbon composites with enhanced electromagnetic wave absorption performance

The microscopic morphology of electromagnetic wave absorbers influences the multiple reflections of electromagnetic waves and impedance matching,determining the absorption properties.Herein,the urchin-shaped bimetallic nickel-cobalt oxide/carbon(NiCo_(2)O_(4)/C)composites are prepared via a hy-drothermal route,whose absorption properties are investigated by different morphologies regulated by changing calcination temperature.A minimum reflection loss(RL_(min))of-75.26 dB is achieved at a match-ing thickness of 1.5 mm,and the effective absorption bandwidth(EAB)of 8.96 GHz is achieved at 2 mm.Multi-advantages of the synthesized NiCo_(2)O_(4)/C composites contribute to satisfactory absorption proper-ties.First,the interweaving of the needle-like structures increases the opportunities for scattering and multiple reflections of incident electromagnetic waves,and builds up a conductive network to facilitate the enhancement of conductive losses.Second,the carbon component in the NiCo_(2)O_(4)/C composites en-hances the interfacial polarization and reduces the density of the absorber.Besides,generous oxygen va-cancy defects are introduced into the NiCo_(2)O_(4)/C composites,which induces defect polarization and dipole polarization.In summary,the ternary coordination of components,defects and morphology led to out-standing electromagnetic wave absorption,which lightened the path for improving the electromagnetic wave absorption property and enriching the family of NiCo_(2)O_(4) absorbers with excellent performance.

Pseudocapacitance boosted N-doped carbon coated Fe7S8 nanoaggregates as promising anode materials for lithium and sodium storage

Herein,the core-shell structured N-doped carbon coated Fe7S8 nano-aggregates(Fe7S8@NC)were controllably prepared via a simple three-step synthesis strategy.The appropriate thickness of N-doped carbon layer outside Fe7S8 nano-aggregates can not only inhibit the particle pulverization induced by the big volume changes of Fe7S8,but can increase the electron transfer efficiency.The hierarchical Fe7S8 nano-aggregates composed of some primary nanoparticles can accelerate the lithium or sodium diffusion kinetics.As anode materials for Li-ion batteries(LIBs),the well-designed Fe7S8@NC nanocomposites exhibit outstanding lithium storage performance,which is better than that of pure Fe7S8,Fe3O4@NC and Fe7S8@C.Among these nanocomposites,the N-doped carbon coated Fe7S8 with carbon content of 26.87 wt.%shows a high reversible specific capacity of 833 mAh·g^−1 after 1,000 cycles at a high current density of 2 A·g^−1.The above electrode also shows excellent high rate sodium storage performance.The experimental and theoretical analyses indicate that the outstanding electrochemical performance could be attributed to the synergistic effect of hierarchical Fe7S8 nanostructure and conductive N-doped carbon layer.The quantitative kinetic analysis indicates that the charge storage of Fe7S8@NC electrode is a combination of diffusion-controlled battery behavior and surface-induced capacitance behavior.

TM_(3)(TM=V,Fe,Mo,W)single-cluster catalyst confined on porous BN for electrocatalytic nitrogen reduction

Confined metal clusters as sub-nanometer reactors for electrocatalytic N_(2) reduction reaction(eNRR)have received increasing attention due to the unique metal-metal interaction and higher activity than singleatom catalysts.Herein,the inspiration of the superior capacitance and unique microenvironment with regular surface cavities of the porous boron nitride(p-BN)nanosheets,we systematically studied the catalytic activity for NRR of transition-metal single-clusters in the triplet form(V_(3),Fe_(3),Mo_(3) and W_(3))confined in the surface cavities of the p-BN sheets by spin-polarized density functional theory(DFT)calculations.After a two-step screening strategy,Mo_(3)@p-BN was found to have high catalytic activity and selectivity with a rather low limiting potential(-0.34 V)for the NRR.The anchored Mo_(3) singlecluster can be stably embedded on the surface cavities of the substrate preventing the diffusion of the active Mo atoms.More importantly,the Mo atoms in the Mo_(3) single-cluster would act as“cache”to accelerate electron transfer between active metal centers and nitrogen-containing intermediates via the intimate Mo-Mo interactions.The cooperation of Mo atoms can also provide a large number of occupied and unoccupied d orbitals to make the"donation-backdonation"mechanism more effective.This work not only provides a quite promising electrocatalyst for NRR,but also brings new insights into the rational design of triple-atom NRR catalysts.

新疆喀什地区脑瘫儿童青少年视觉障碍特征分析

目的:首次全面精准分析新疆喀什地区脑瘫儿童青少年的视觉障碍特征和治疗情况,促进其视觉康复和全身康复的早期开展。方法:横断面调查研究。选取2018年10月于新疆维吾尔自治区喀什地区某综合医院集中行眼部筛查的脑瘫儿童青少年,对其进行眼科检查,包括屈光状态、眼位、眼前节和眼底检查,并调查其眼科治疗情况。采用卡方检验对数据进行分析。结果:纳入176例脑瘫儿童青少年,年龄0.8~12(6.4±2.7)岁,其中0.8~6岁有97例(55.1%),维吾尔族169例(96.0%),男性104例(59.1%)。存在视觉障碍人数105例(59.7%),3例(1.7%)同时伴有2种视觉障碍,视觉障碍的发生率为108例(61.7%),包括屈光不正(48例,27.3%)、斜视(43例,24.4%)和其他眼部疾病(17例,9.7%)。所有脑瘫儿童青少年屈光不正以远视为主(20例,11.4%),斜视以外斜视最常见(25例,14.2%),占比最高的前3种其他眼部疾病是视神经萎缩、先天性白内障和先天性青光眼,均为4例(2.3%)。仅27例(15.3%)脑瘫儿童青少年以往接受过眼科检查,剩余149例(84.7%)均为第1次接受眼科检查;105例视觉障碍者中仅6例(5.7%)以往接受过眼科检查。所有脑瘫儿童青少年近视发生率为9.7%(17例),不同性别、年龄段、民族以及是否斜视之间近视的发生率差异没有统计学意义。结论:脑瘫儿童青少年视觉障碍发生率高于同年龄段儿童,且斜视发生率非常高。这也提示在脑瘫儿童青少年中普及眼健康筛查的迫切性和重要性,可作为今后开展脑瘫患者康复工作的重点内容之一。