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3725865 
Journal Article 
Investigation into the origin of high stability of delta-MnO2 pseudo-capacitive electrode using operando Raman spectroscopy 
Yang, L; Cheng, S; Wang, J; Ji, Xu; Jiang, Yu; Yao, M; Wu, P; Wang, M; Zhou, Jun; Liu, M 
2016 
30 
293-302 
WOS:000390636100036 
Manganese oxides of different structures, especially alpha-MnO2, have been extensively studied as electrodes for pseudocapacitors. However, the poor stability associated with intercalation of proton has been the main obstacle to their commercial applications. To effectively mitigate this problem, it is necessary to fully understand the energy storage mechanism of the MnO2 phases. In this study, delta phase MnO2 has been synthesized through controllable electroplating on architectural Ga-doped ZnO (GZO) bones, demonstrating a high specific capacitance of 1068 F g(-1) and high stability (slight performance drop focus on the first 2000 cycles and then remained relatively constant in the subsequent 13,000 cycles). The charge storage mechanism of the delta-MnO2 coated GZO has been carefully investigated under this extreme reaction condition. Results suggest that the amount of charge stored in the electrode material correlates well with the amount of Na+ inserted into the electrode material from the electrolyte. It is also noted that no spectral features corresponding to Na+ insertion were detected during cycling when the sample was probed using in operando Raman spectroscopy. Therefore, for layered delta-MnO2, a charge storage mechanism of Na+ intercalation/deintercalation dominated, accompanied by interlayer spacing expansion/contraction, was proposed. Moreover, theoretical calculations also confirmed that the insertion of Na+ is more energetically favorable than H+ at all sites of the interlayer in delta-MnO2, offering a rational explanation of the proposed mechanism and the observed excellent stability. 
delta-MnO2; Pseudo-capacitor; Charge storage mechanism; in situ Raman spectroscopy; DFT calculation