Developing carbon felt (CF) electrodes with sufficient mass transfer channels and highly active catalytic interfaces remains a great challenge for high-rate vanadium flow batteries (VFBs). Herein, a well-defined 3D hierarchical N-doped carbon nanotube (NCNT) network is designed and grown onto CF via a facile bottom-up strategy, which features a high bonding strength, controllable growth morphology, and tunable electron structure. In the strategy, ZIF-67 arrays as both precursors and catalysts are self-assembled on CF followed by decomposition of melamine as an initiator into C and N sources for controlled growth of NCNTs during pyrolysis. By precisely regulating the microstructure of ZIF-67 precursors and the usage amount of melamine, the NCNT-modified CF composite electrode simultaneously achieves fast electron transport, facile mass transport, and high catalytic performance toward VO²⁺/VO₂⁺ and V²⁺/V³⁺ redox reactions. Electrostatic potential calculations further indicate that N dopants alter the electronic structure of CNTs and serve as the preferential sites for the adsorption of vanadium ions to promote the redox kinetics. Consequently, the battery assembled with the composite electrodes exhibits an impressive energy efficiency of 76.6% at 300 mA cm^–2 and demonstrates prolonged stability throughout 550 consecutive charge–discharge cycles at 200 mA cm^–2. These encouraging achievements shed fresh insights into the controlled synthesis of CNTs onto CF for high-rate VFBs.

中文翻译：

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氮掺杂碳纳米管网络的受控构建赋予碳毡优异的高倍率钒液流电池性能

开发具有足够传质通道和高活性催化界面的碳毡（CF）电极仍然是高倍率钒液流电池（VFB）面临的巨大挑战。在此，设计了一个明确的3D分层N掺杂碳纳米管（NCNT）网络，并通过简单的自下而上策略生长在CF上，该网络具有高键合强度、可控生长形貌和可调电子结构。在该策略中，ZIF-67阵列作为前体和催化剂在CF上自组装，然后三聚氰胺作为引发剂分解成C和N源，以在热解过程中控制NCNT的生长。通过精确调节ZIF-67前驱体的微观结构和三聚氰胺的用量，NCNT修饰的CF复合电极同时实现了快速的电子传输、轻松的传质以及对VO ²⁺ /VO ₂ ⁺和V ²⁺的高催化性能/V ³⁺氧化还原反应。静电势计算进一步表明，氮掺杂剂改变了碳纳米管的电子结构，并作为吸附钒离子的优先位点以促进氧化还原动力学。因此，用复合电极组装的电池在 300 mA cm ^{–2下表现出高达 76.6% 的能源效率，并在 200 mA cm –2}下的 550 个连续充放电循环中表现出长期稳定性。这些令人鼓舞的成就为高倍率 VFB 的 CF 上的 CNT 受控合成提供了新的见解。