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Charge storage mechanisms of electrospun Mn3O4 nanofibres for high-performance supercapacitors

机译：高性能超级电容器用电纺Mn 3 O 4 纳米纤维的电荷存储机制

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Mixed oxidation states of manganese oxides are widely used as the electrodes in supercapacitors due to their high theoretical pseudocapacitances. However, their charge storage mechanisms are not yet fully understood. In this work, the charge storage mechanism of Mn3O4 or Mn2+(Mn3+)2O4 nanofibres was investigated using a synchrotron-based X-ray absorption spectroscopy (XAS) technique and an in situ electrochemical quartz crystal microbalance (EQCM). The average oxidation state of the Mn in the as-synthesized Mn3O4 is +2.67. After the first charge, the average oxidation states of Mn at the positive and negative electrodes are +2.61 and +2.38, respectively. The significant change in the oxidation state of Mn at the negative electrode is due to phase transformation of Mn3O4 to NaδMnOx·nH2O. Meanwhile, the charge storage mechanism at the positive electrode mainly involves the adsorption of counter ions or solvated SO42?. After the first discharge, the calculated Mn average oxidation numbers are +2.51 and +2.53 at the positive and negative electrodes, respectively. At the negative electrode, the solvated Na+ is desorbed from the electrode surface. At the same time, the solvated SO42? is desorbed from the positive electrode. The mass change of solvated Na+ during charging/discharging is ca. 80 ng per cm2 of the Mn3O4 electrode. A symmetric supercapacitor constructed from Mn3O4 nanofibres in 0.5 M Na2SO4 provides a working potential of 1.8 V, a specific energy of 37.4 W h kg?1 and a maximum specific power of 11.1 kW kg?1 with 98% capacity retention over 4500 cycles. The understanding of the charge storage mechanism of the mixed oxidation states of Mn2+(Mn3+)2O4 presented in this work could lead to further development of metal oxide-based pseudocapacitors.
机译：锰氧化物的混合氧化态由于其较高的理论假电容而被广泛用作超级电容器中的电极。但是，它们的电荷存储机制尚未完全理解。在这项工作中，Mn 3 O 4 或Mn 2的电荷存储机制+ （Mn 3 + ） 2 O 使用基于同步加速器的X射线吸收光谱（XAS）技术和原位电化学石英晶体微天平（EQCM）研究了4 纳米纤维。合成后的Mn 3 O 4 中Mn的平均氧化态为+2.67。第一次充电后，正极和负极上Mn的平均氧化态分别为+2.61和+2.38。负极上Mn氧化态的显着变化是由于Mn 3 O 4 到Na δ MnO x ·< em> n H 2 O。同时，正极的电荷存储机制主要涉及抗衡离子或溶剂化SO 4 2？ 。第一次放电后，正极和负极的Mn平均氧化值分别为+2.51和+2.53。在负极上，溶剂化的Na + 从电极表面解吸。同时，溶剂化的SO 4 2？ 从正极上解吸。 Na + 在充放电过程中的溶剂化质量变化为 ca。 80 ng / cm 2 Mn 3 O 4 电极的。由Mn 3 O 4 纳米纤维在0.5 M Na 2 <中构成的对称超级电容器/ sub> SO 4 提供的工作电压为1.8 V，比能量为37.4 W h kg ？1 ，最大比功率为11.1 kW kg ？1 ，在4500个循环中保持98％的容量。对Mn 2 + （Mn 3 + ）的混合氧化态的电荷存储机理的理解这项工作中介绍的small> 2 O 4 可能会导致基于金属氧化物的伪电容器的进一步发展。

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