MnO_x-based materials have limited capacity and poor conductivity over various voltages, hampering their potential for energy storage applications. This work proposes a novel approach to address these challenges. A self-oriented multiple-electronic structure of a 1D-MnO₂-nanorod/2D-Mn₂O₃-nanosphere composite was assembled on 2D-graphene oxide nanosheet/1D-carbon nanofiber (GO/CNF) hybrids. Aided by K⁺ ions, the MnO₂ nanorods were partially converted to Mn₂O₃ nanospheres, while the GO nanosheets were combined with CNF through hydrogen bonds resulting in a unique double binary 1D–2D mixed morphology of MnO₂/Mn₂O₃-GO/CNF hybrid, having a novel mechanism of multiple Mn ion redox reactions facilitated by the interconnected 3D network. The morphology of the MnO₂ nanorods was controlled by regulating the potassium ion content through a rinsing strategy. Interestingly, pure MnO₂ nanorods undergo air-annealing to form a mixture of nanorods and nanospheres (MnO₂/Mn₂O₃) with a distinct morphology indicating pseudocapacitive surface redox reactions involving Mn²⁺, Mn³⁺, and Mn⁴⁺. In the presence of the GO/CNF framework, the charge storage properties of the MnO₂/Mn₂O₃-GO/CNF composite electrode show dominant battery-type behavior because of the unique mesoporous structure with a crumpled morphology that provides relatively large voids and cavities with smaller diffusion paths to facilitate the accumulation/intercalation of charges at the inner electroactive sites for the diffusion-controlled process. The corresponding specific capacity of 800 C g^–1 or 222.2 mAh g^–1 at 1 A g^–1 and remarkable cycling stability (95%) over 5000 cycles at 3 A g^–1 were considerably higher than those of the reported electrodes of similar materials. Moreover, a hybrid supercapacitor device is assembled using MnO₂/Mn₂O₃-GO/CNF as the positive electrode and activated carbon as the negative electrode, which exhibits a superior maximum energy density (∼25 Wh kg^–1) and maximum power density (∼4.0 kW kg^–1). Therefore, the as-synthesized composite highlights the development of highly active low-cost materials for next-generation energy storage applications.

中文翻译：

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基于自立式导电 GO/CNF 框架上组装的纳米棒/纳米球复合材料自定向生长的高性能电池型超级电容器


MnO _x 基材料在各种电压下容量有限且导电性差，限制了其储能应用的潜力。这项工作提出了一种解决这些挑战的新方法。在二维石墨烯上组装了 1D-MnO ₂ -nanorod/2D-Mn ₂ O ₃ -纳米球复合材料的自取向多电子结构氧化物纳米片/一维碳纳米纤维（GO/CNF）混合物。在K ⁺ 离子的辅助下，MnO ₂ 纳米棒部分转化为Mn ₂ O ₃ 纳米球，而GO纳米片则结合在一起通过氢键与 CNF 形成独特的双二元 1D-2D 混合形态的 MnO ₂ /Mn ₂ O ₃ -GO/CNF 杂化物，具有由互连的 3D 网络促进的多个 Mn 离子氧化还原反应的新机制。通过漂洗策略调节钾离子含量来控制 MnO ₂ 纳米棒的形貌。有趣的是，纯MnO ₂ 纳米棒经过空气退火形成纳米棒和纳米球的混合物（MnO ₂ /Mn ₂ O ₃ ）具有独特的形态，表明涉及 Mn ²⁺ 、 Mn ³⁺ 和 Mn ⁴⁺ 的赝电容表面氧化还原反应。在GO/CNF骨架存在下，MnO ₂ /Mn ₂ O ₃ -GO/CNF复合电极的电荷存储性能表现出主导电池性能-型行为，因为具有褶皱形态的独特介孔结构提供了相对较大的空隙和空腔以及较小的扩散路径，以促进电荷在扩散控制过程的内部电活性位点处的积累/嵌入。 1 A g ^–1 下相应的比容量为 800 C g ^–1 或 222.2 mAh g ^–1 ，并且在 3 下经过 5000 次循环后具有显着的循环稳定性 (95%) g ^–1 明显高于已报道的类似材料电极。此外，以MnO ₂ /Mn ₂ O ₃ -GO/CNF为正极，活性炭为负极组装混合超级电容器装置，它表现出卓越的最大能量密度（∼25 Wh kg ^–1 ）和最大功率密度（∼4.0 kW kg ^–1 ）。因此，合成的复合材料突出了用于下一代储能应用的高活性低成本材料的开发。