Deng Lei, Wang Zaifa, Cui Hantao, Guo Yunna, Ye Zhangran, Li Hui, Zhang Xinyu, Jia Peng, Zhang Qiaobao, Zhang Liqiang
Clean Nano Energy Center, State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao, 066004, China.
Hebei Key Laboratory of Applied Chemistry, College of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao, 066004, China.
Adv Mater. 2024 Nov;36(46):e2408476. doi: 10.1002/adma.202408476. Epub 2024 Sep 20.
Manganese dioxide (α-MnO) has attracted significant research interest in supercapacitors recently. However, the reaction mechanism of α-MnO in supercapacitors remains unclear. Therefore, a nano-supercapacitor using Environmental transmission electron microscopy (ETEM) is conducted and investigated the reaction mechanism of α-MnO based on three ionic liquids (ILs). It found that in the aprotic ionic liquid (AIL) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIMOTF), α-MnO nanowires (NWs) undergo an oxidation reaction due to the presence of an active proton at the second position (H2) of the imidazole ring. As a result, α-MnO NWs undergo a phase transition and transform into MnO, exhibiting pseudo-capacitive properties. Furthermore, characterization of the macroscopic α-MnO electrodes after cycling reveals that after the initial charging cycles, the dominant energy storage mechanism of the supercapacitor transitions from pseudo-capacitance to a dual-layer capacitance formed by the combination of MnO and unreacted α-MnO. Simultaneously, due to the coexistence of these two energy storage mechanisms, the specific capacitance of the supercapacitor in EMIMOTF electrolyte reaches up to 80 F g, and the cycle number reaches as high as 1000 cycles. The results are expected to provide insights into the selection of electrolytes in supercapacitors and offer a fundamental understanding of the internal reaction mechanisms in capacitors.
