N-doped porous carbon nanofibers sheathed pumpkin-like Si/C composites as free-standing anodes for lithium-ion batteries

Dramatic capacity fading and poor rate performance are two main obstacles that severely hamper the widespread application of the Si anode owing to its large volume variation during cycling and low intrinsic electrical conductivity.To mitigate these issues,free-standing N-doped porous carbon nanofibers sheathed pumpkin-like Si/C composites(Si/C-ZIF-8/CNFs)are designed and synthesized by electrospinning and carbonization methods,which present greatly enhanced electrochemical properties for lithium-ion battery anodes.This particular structure alleviates the volume variation,promotes the formation of stable solid electrolyte interphase(SEI)film,and improves the electrical conductivity.As a result,the as-obtained free-standing Si/C-ZIF-8/CNFs electrode delivers a high reversible capacity of 945.5 mAh g^(-1) at 0.2 A g^(-1) with a capacity retention of 64% for 150 cycles,and exhibits a reversible capacity of 538.6 mA h g^(-1) at 0.5 A g^(-1) over 500 cycles.Moreover,the full cell composed of a freestanding Si/C-ZIF-8/CNFs anode and commercial LiNi_(1/3)Co_(1/3)Mn_(1/3)O_(2)(NCM)cathode shows a capacity of 63.4 mA h g^(-1) after 100 cycles at 0.2 C,which corresponds to a capacity retention of 60%.This rational design could provide a new path for the development of high-performance Si-based anodes.

VN nanoparticle-assembled hollow microspheres/N-doped carbon nanofibers:An anode material for superior potassium storage

Thanks to inexpensive and bountiful potassium resources,potassium ion batteries(PIBs)have come into the spotlight as viable alternatives for next-generation battery systems.However,poor electrochemical kinetics due to the large size of the K^(+) is a major challenge for PIB anodes.In this paper,an ingenious design of VN nanoparticleassembled hollow microspheres within N-containing intertwined carbon nanofibers(VN-NPs/N-CNFs)via an electrospinning process is reported.Employed as PIB anodes,VN-NPs/N-CNFs exhibit a superb rate property and prolonged cyclability,surpassing that of other reported metal nitride-based anodes.This is ascribed to:(i)the VN NP-assembled hollow microspheres,which shorten the K^(+) diffusion distance,and mitigate volume expansion;and(ii)the interconnected N-CNFs,which supply numerous active sites for K^(+) adsorption and facilitate rapid electron/ion transport.

Nitrogen-Doped Porous Carbon Nanofiber Supported Platinum as Promising Oxygen Reduction Reaction Electrocatalysts

Heteroatoms doped Carbon materials have been proved as promising catalyst support material for oxygen reduction reaction (ORR) in proton exchange membrane fuel cell (PEMFC). In this paper, nitrogen-doped porous nanofibers (N-PCNF) were fabricated via cost effective electrospinning technique by blending the PI and PAN as precursors, followed by heat treatment procedures. The N-PCNFs were used as support to prepare platinum (Pt) catalyst (Pt/N-PCNFs). SEM figure indicated that the porous structures not only existed on the surface but also in the cross session of the fibers. XPS and TEM displayed that with the help of heteroatoms nitrogen, the fiber had rougher surface and more defective structure, contributing to the dispersion of Pt nanoparticles. The catalytic performance for ORR was evaluated by cyclic voltammetry (CV) and liner sweep voltammetry (LSV) with a rotating disk electrode (RDE). According to the results, Pt/N-PCNF exhibited superior property (more positive onset potential and half-wave potential) than that of JM20. The excellent ORR activity of Pt/N-PCNF was attributed to the enriched nitrogen heteroatoms coordinated within the microstructure which increased the exposure of more active sites and dispersion of Pt nanoparticles.

Electrospinning fabrication and ultra-wideband electromagnetic wave absorption properties of CeO_(2)/N-doped carbon nanofibers

The impedance mismatch of carbon materials is a key factor limiting their widespread use in electromagnetic(EM)wave absorption.In this work,the novel CeO_(2)/nitrogen-doped carbon(CeO_(2)/N-C)nanofiber was prepared to solve the problem by electrospinning and sintering.X-ray diffraction(XRD),Raman,X-ray photoelectron spectroscopy(XPS),and transmission electron microscopy(TEM)analyses demonstrated CeO_(2)was successfully loaded onto the surface of partially graphitized carbon fibers.Different sintering temperatures change the graphitization degree of material,and the oxygen vacancy structure of CeO_(2)and defects from N doping optimize the impedance matching of the material.When the sintering temperature reaches 950℃,CeO_(2)/N-C fiber possesses the minimum reflection loss(RLmin)value of−42.59 dB at 2.5 mm with a filler loading of only 3 wt.%in polyvinylidene difluoride(PVDF).Meanwhile,the CeO_(2)/N-C fiber achieves a surprising wideband(8.48 GHz)at a thickness of 2.5 mm,covering the whole Ku-band as well as 63%of the X-band at the sintering temperature of 650℃.This work provides the research basis for widely commercial applications of carbon-based nanofiber absorbers.

Anchoring ultrafine CoP and CoSb nanoparticles into rich N-doped carbon nanofibers for efficient potassium storage

Transition-metal compounds have received extensive attention from researchers due to their high reversible capacity and suitable voltage platform as potassium-ion battery anodes.However,these materials commonly feature a poor conductivity and a large volume expansion,thus leading to underdeveloped rate capability and cyclic stability.Herein,we successfully encapsulated ultrafine CoP and CoSb nanoparticles into rich N-doped carbon nanofibers(NCFs)via electrospinning,carbonization,and phosphorization(antimonidization).The N-doped carbon fiber prevents the aggregation of nanoparticles,buffers the volume expansion of CoP and CoSb during charging and discharging,and improves the conductivity of the composite material.As a result,the CoP/NCF anode exhibits excellent potassium-ion storage performance,including an outstanding reversible capacity of 335mAh g^(-1),a decent capacity retention of 79.3%after 1000 cycles at 1Ag^(-1)and a superior rate capability of 148mAh g^(-1)at 5Ag^(-1),superior to most of the reported transition-metalbased potassium-ion battery anode materials.

Edge-Plane Exposed N-Doped Carbon Nanofibers Toward Fast K-Ion Adsorption/Diffusion Kinetics for K-Ion Capacitors

Sluggish kinetics severely limit the development of potassium-ion hybrid capacitors(PIHCs).Exposing active sites is recognized as an ideal strategy to resolve this issue,but the corresponding material design is challenging.Herein,carbon nanofibers with abundant,exposed edge-plane active sites due to(002)orientation adjustment were developed by a molten salt-assisted procedure.Importantly,due to the radial(002)orientation with more active edge-plane sites to adsorb K and shorten the K diffusion distance,the obtained carbon nanofibers harvest improved K adsorption/diffusion kinetics.

Amorphous Cu^0 on Carbon Nanofiber as Recyclable Heterogeneous Catalyst for N-Arylation Reactions

A novel heterogeneous catalyst,amorphous Cu^0 on the carbon nanofibers was developed and characte-rized by means of several characterization techniques.The prepared Cu^0 was investigated as a heterogeneous catalyst for N-arylation reaction.The results show it is an excellent catalyst with recyclability,high consistency and catalytic activity.After the catalyst was used for 5 cycles in the N-arylation reaction,amorphous Cu^0 reunited into crystalline copper nanoparticles with different particle sizes and its good heterogeneity in the catalytic system was confirmed after the catalyst recovery.

Encapsulated MnO in N-doping carbon nanofibers as efficient ORR electrocatalysts

Development of cheap,abundant and noblemetal-free materials as high efficient oxygen reduction electrocatalysts is crucial for future energy storage system. Here,one-dimensional（1D） MnO N-doped carbon nanofibers（MnO-NCNFs） were successfully developed by electrospinning combined with high temperature pyrolysis. The MnO-NCNFs exhibit promising electrochemical performance,methanol tolerance,and durability in alkaline medium. The outstanding electrocatalytic activity is mainly attributed to several issues.First of all,the uniform 1D fiber structure and the conductive network could facilitate the electron transport. Besides,the introduction of Mn into the precursor can catalyze the transformation of amorphous carbon to graphite carbon,while the improved graphitization means better conductivity,beneficial for the enhancement of catalytic activity for oxygen reduction reaction（ORR）. Furthermore,the porous structure and high surface area can effectively decrease the mass transport resistance and increase the exposed ORR active sites,thus improve utilization efficiency and raise the quantity of exposed ORR active sites. The synergistic effect of MnO and NCNFs matrix,which enhances charge transfer,adsorbent transport,and delivers efficiency in the electrolyte solution,ensures the high ORR performance of MnO-NCNFs.

负载型非晶态合金催化剂Ni-Fe-Rh-P/CNFs的制备及其催化性能

研究了化学镀Ni-Fe-Rh-P非晶态合金镀层的工艺,考察了镀液成分和工艺参数对沉积速率和镀层质量的影响。利用优化的工艺配方在经过敏化、活化处理后的纳米碳纤维(CNFs)表面沉积了Ni-Fe-Rh-P合金镀层,分别利用能量色散X射线谱(EDS)、X射线衍射仪(XRD)及扫描电子显微镜(SEM)等手段对镀层的成分、结构、形貌进行了表征,采用液相硝基苯催化加氢反应表征了制备催化剂的催化活性。结果表明,利用化学镀技术可以在纳米碳纤维表面负载连续、均匀的Ni-Fe-Rh-P合金镀层,且镀层为非晶态结构;负载型非晶态合金催化剂Ni-Fe-Rh-P/CNFs具有很高的催化活性和良好的循环使用性能。

火焰法制备非晶态“实心”炭纳米纤维的结构模型及其电输运行为

火焰法制备的非晶态"实心"炭纳米纤维内部原子排列无序紊乱,依靠常规的表征手段,难以得到其三维原子构型分布。根据非晶态"实心"炭纳米纤维的XRD图谱提供的衍射强度数据,采用逆向蒙特卡罗法,重构了非晶态"实心"炭纳米纤维的微观原子构型,并对获得的模型进行充分的误差分析。计算得到了非晶态炭纳米纤维的费米能级及其导电机制,认为其具有半导体特征;实验测量单根非晶态"实心"炭纳米纤维的电输运行为发现,其I-V曲线呈现对称和非线性特征,且电阻随着温度的升高而下降,进一步证明非晶态"实心"炭纳米纤维的原子构型具有一定的真实性。

纳米碳纤维表面非晶态Ni-Fe-Ru-P合金镀层的制备与表征

在铁片试样上研究以次磷酸钠为还原剂的化学镀Ni—Fe—Ru-P合金镀层的工艺，考察了金属盐浓度对化学镀反应沉积速率的影响。利用优化的工艺配方在经过敏化、活化处理后的纳米碳纤维表面沉积Ni—Fe-Ru-P合金镀层，分别利用EDS、XRD、SEM等手段对镀层的成分、结构、形貌进行了表征，并对其进行了热处理。结果表明，利用化学镀技术可以在纳米碳纤维表面获得连续、均匀的Ni—Fe—Ru—P合金镀层，且镀层为非晶态结构。在350℃以下热处理不会改变镀层的结构，

杯[4]醌/N掺杂的无定形碳纳米纤维复合材料储锂性能

生物质甲壳素来源丰富、廉价易得、N含量高且具有纤维结构,经高温碳化即可获得导电性良好的多孔碳材料。杯[4]醌(Calix[4]quinone,C4Q)的理论比容量高达447mA·h/g,但它在传统电解液中的高溶解性和导电性差限制了其在锂电池中的实际应用。为了解决上述问题,本文以甲壳素为原料,经高温处理制得了N掺杂的无定形碳纳米纤维材料(NACF),并利用其多孔结构吸附C4Q,制备出C4Q/NACF(质量比为1∶1)复合材料。该复合材料在0.1C电流密度下,首圈放电比容量为426mA·h/g,循环100圈后比容量为213mA·h/g,甚至在1 C电流密度下,C4Q/NACF复合材料仍有188mA·h/g的放电比容量。实验结果表明,利用NACF碳材料固载C4Q的方法可以提高C4Q锂离子电池的循环稳定性和导电性。

In situ embedded bismuth nanoparticles among highly porous carbon fibers for efficient carbon dioxide reduction

Electrocatalysis provides an optimal approach for the conversion of carbon dioxide(CO_(2))into high-value chemicals,thereby presenting a promising avenue toward achieve carbon neutrality.However,addressing the selectivity and stability challenges of metal catalysts in electrolytic reduction remains a daunting task.In this study,the electrospinning method is employed to fabricate porous carbon nanofibers loaded with bismuth nanoparticles with the help of in situ pyrolysis.The porous carbon nanofibers as conductive support would facilitate the dispersion of bismuth active sites while inhibiting their aggregation and promoting the mass transfer,thus enhancing their electrocatalytic activity and stability.Additionally,nitrogen doping induces electron delocalization in bismuth atoms through metal-support interactions,thus enabling efficient adsorption of intermediates for improving selectivity based on the theoretical calculation.Consequently,Bi@PCNF-500 exhibits the exceptional selectivity and stability across a wide range of potential windows.Notably,its faradaic efficiency(FE)of formate reaches 92.7%in H-cell and94.9%in flow cell,respectively,with good electrocatalytic stability.The in situ characterization and theoretical calculations elucidate the plausible reaction mechanism to obtain basic rules for designing efficient electrocatalyst.

Hybrid Silicon-Carbon Nanostructured Composites as Superior Anodes for Lithium Ion Batteries

We have successfully fabricated a hybrid silicon-carbon nanostructured composite with large area （about 25.5 in^2） in a simple fashion using a conventional sputtering system. When used as the anode in lithium ion batteries, the uniformly deposited amorphous silicon （a-Si） works as the active material to store electrical energy, and the pre-coated carbon nanofibers （CNFs） serve as both the electron conducting pathway and a strain/stress relaxation layer for the sputtered a-Si layers during the intercalation process of lithium ions. As a result, the as-fabricated lithium ion batteries, with deposited a-Si thicknesses of 200 nm or 300 nm, not only exhibit a high specific capacity of 〉2000 mA.h/g, but also show a good capacity retention of over 80% and Coulombic efficiency of 〉98% after a large number of charge/discharge experiments. Our approach offers an efficient and scalable method to obtain silicon-carbon nanostructured composites for application in lithium ion batteries.