1成果简介 

　　碳纳米纤维（CNFs）凭借其高比表面积、优异导电性、化学稳定性好等优势，是超级电容器电极的理想材料。将CNFs高效组装为三维（3D）固体结构，可满足功能性织物和可穿戴器件对柔性、动态自适应导电结构的迫切需求。然而，碳纳米纤维在组装过程中面临一个核心难题——纤维间融合（inter-fiber fusion）。传统碳化过程中，相邻碳纤维在高温下发生界面融合和结构坍缩，导致3D网络的孔隙率降低、比表面积急剧下降、离子传输通道堵塞，严重削弱超级电容器的储能性能。如何有效抑制纤维间融合，保持碳纳米纤维的独立性和高比表面积，同时实现3D网络的高效构筑，是碳纤维基电极材料走向高性能超级电容器的关键挑战。现有策略（如模板法、冷冻干燥法等）存在工艺复杂、成本高、难以规模化等问题，亟需发展一种通用且可扩展的新策略。

　　本文，安徽大学白玮教授、张青 副教授等在《ACS Applied Materials & Interfaces》期刊发表名为"Interfiber Isolation Synthesis Strategy via Nanosheet Wrapping toward 3D Carbon Nanofiber Networks for High-Performance Supercapacitors"的论文。该研究创新性地提出了"纤维间隔离（Interfiber Isolation）"合成策略，巧妙利用二维纳米材料（MXene）的纳米片包裹效应，从天然纳米纤维原位构筑3D碳纳米纤维网络。

　　该策略的核心创新在于：(1) 纳米片包裹隔离——MXene纳米片紧密包裹在天然纳米纤维（如细菌纤维素纳米纤维）表面，形成"核-壳"隔离层，在碳化过程中有效阻止相邻纤维间的热融合，保持纤维的独立性和高比表面积；(2) 通用可扩展——该策略适用于多种天然纳米纤维前驱体和二维纳米材料，工艺简洁，易于规模化；(3) MXene原位转化——碳化过程中MXene转化为导电性优异的碳化物衍生碳/氧化物，同步增强3D网络的导电性和电化学活性。最终，3D碳纳米纤维网络在超级电容器中展现出高比电容、优异倍率性能和超长循环稳定性。

　　2图文导读  

　　图 1. (a) Schematic illustration of the fabrication of M-iso-CNF-X, which prevents the “fusion to carbon chunks” with MXene wrapping to isolate SNFs from each other. (b1) SNFs as extracted from degummed silk and (b2) the carbonized one showing the carbon chunks due to SNF fusion. (c1) SNFs mixed with and embedded in MXene, i.e., M-iso-SNF, and (c2) the carbonized one, i.e., M-iso-CNF, preserving the fibrous feature and admitting an average CNF diameter of less than 100 nm.

　　图2. (a) Schematic illustration of SNFs separated by MXene wrapping and that directly make contact with each other without MXene wrapping. CNFs produced from carbonizing SNF with different levels of MXene wrapping: (b) M-iso-CNF-16, (c) M-iso-CNF-32, (d) M-iso-CNF-48, and (e) M-iso-CNF-64. (f) The corresponding average diameters of M-iso-CNF-X.

　　图3. (a) The X-ray diffraction (XRD) results of M-iso-CNFs. (b) The Raman spectra of M-iso-CNF-32. (c) Survey of M-iso-CNF-0 and M-iso-CNF-32. (d) N 1s with peak fitting of M-iso-CNF-32. (e) Nitrogen adsorption–desorption isotherms and (f) pore size distribution of the M-iso-CNFs. (g) Total specific surface area (SSA) calculated based on the isotherms and SSA corresponding to mesopores and micropores, and their ratio, i.e., Smeso/Smicro.

　　图4. (a) Cubes of M-iso-SNF-X sponges and M-iso-CNF-X sponges showing different levels of shrinkage upon carbonization. (b) The storage modulus G′ versus frequency at a constant strain of 0.1% and (c) the electrical conductivity of M-iso-CNF-X with different MXene ratios.

　　图5. Electrochemical performance of the M-iso-CNFs in a two-electrode system with 6 M KOH as the electrolyte: CV curves at (a) a faster scan rate of 500 mV s–1 and (b) a slower scan rate of 5 mVs–1, (c) the specific capacitance at different scan rates, and (d) the capacitance retention as the scan rate increases from 2 to 500 mV s–1. (e) The Nyquist plots with the classical Warburg region of 45° highlighted. (f) Linear relationship between Z′ and ω–1/2 in the classical Warburg region and (g) the calculated Warburg slopes. (h) Photos taken at 0 and 2 s of M-iso-CNF-0 and M-iso-CNF-32 showing different contact angles and (i) contact angle vs time of all M-iso-CNFs. (j) M-iso-CNF-32 charged/discharged at different current densities for 150 cycles for each current density. (k) The cyclic stability and Coulombic efficiency of M-iso-CNF-32 cycled at 1 A g–1 and 10 A g–1.

　　图6. (a) SNFs embedded in GO with an SNF/GO weight ratio of 32:1 and (b) after carbonization. (c) The diameter distribution of CNFs prepared using GO wrapping.

　　3小结 

　　综上所述，本文提出了一种易于实施的“纤维间隔离”合成策略，并制备了三维宏观碳纳米纤维互连网络，作为超级电容器的有前景的电极材料。Ti3C2Tx MXene 作为包覆材料，在碳化过程中能够完美地保持 SNF 的纳米纤维特征，表现出极佳的适用性。在缩小纤维直径以改善离子扩散与保持纤维间连接以实现高效电导之间的微观结构平衡下，M-iso-CNFs展现出增强的电容和倍率性能，并在10 A g–1的电流密度下保持超过340,000次循环的长期稳定性。此外，“纤维间隔离”策略也可推广至其他二维纳米材料，例如仅需添加极少量氧化石墨烯（GO）即可实现。本研究为制备具有可调微结构、电化学稳定的生物质来源三维碳纳米纤维固体提供了可行途径，为将碳纳米结构应用于需要可定制机械和结构特性且符合环境可持续性的技术领域铺平了道路。

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