Abstract：
MnOx-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.
摘要：
基于MnOx的材料在各种电压下具有有限的容量和差的导电性,阻碍了他们在储能应用中的潜力。这项工作提出了一种解决这些挑战的新方法。在2D-氧化石墨烯纳米片/1D-碳纳米纤维（GO/CNF）杂化物上组装了1D-MnO2-纳米棒/2D-Mn2O3-纳米球复合材料的自取向多电子结构。在K+离子的帮助下，MnO2纳米棒部分转化为Mn2O3纳米球，而GO纳米片通过氢键与CNF结合，形成独特的MnO2/Mn2O3-GO/CNF杂化物的双二元1D-2D混合形态，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。通过冲洗策略调节钾离子含量来控制MnO2纳米棒的形态。有趣的是,纯MnO2纳米棒进行空气退火，形成纳米棒和纳米球（MnO2/Mn2O3）的混合物，具有明显的形态，表明涉及Mn2+的拟电容表面氧化还原反应，Mn3+,Mn4+。在GO/CNF框架存在的情况下，MnO2/Mn2O3-GO/CNF复合电极的电荷储存性质显示出主要的电池型行为,因为具有褶皱形态的独特介孔结构提供相对较大的空隙和空腔,具有较小的扩散路径,以促进电荷在内部电活性位点处的累积/嵌入,用于扩散控制过程。在1Ag-1下800Cg-1或222.2mAhg-1的相应比容量以及在3Ag-1下5000次循环的显着循环稳定性（95％）明显高于所报道的类似材料的电极。此外，以MnO2/Mn2O3-GO/CNF为正极,以活性炭为负极,表现出优异的最大能量密度(~25Whkg-1)和最大功率密度(~4.0kWkg-1)。因此,合成后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。
