3 years ago

High-Performance 2.6 V Aqueous Asymmetric Supercapacitors based on In Situ Formed Na0.5MnO2 Nanosheet Assembled Nanowall Arrays

High-Performance 2.6 V Aqueous Asymmetric Supercapacitors based on In Situ Formed Na0.5MnO2 Nanosheet Assembled Nanowall Arrays
Hui Xia, Qiuying Xia, Ahmad Hussain, Shuo Sun, Junwu Zhu, Nawishta Jabeen
The voltage limit for aqueous asymmetric supercapacitors is usually 2 V, which impedes further improvement in energy density. Here, high Na content Birnessite Na0.5MnO2 nanosheet assembled nanowall arrays are in situ formed on carbon cloth via electrochemical oxidation. It is interesting to find that the electrode potential window for Na0.5MnO2 nanowall arrays can be extended to 0–1.3 V (vs Ag/AgCl) with significantly increased specific capacitance up to 366 F g−1. The extended potential window for the Na0.5MnO2 electrode provides the opportunity to further increase the cell voltage of aqueous asymmetric supercapacitors beyond 2 V. To construct the asymmetric supercapacitor, carbon-coated Fe3O4 nanorod arrays are synthesized as the anode and can stably work in a negative potential window of −1.3 to 0 V (vs Ag/AgCl). For the first time, a 2.6 V aqueous asymmetric supercapacitor is demonstrated by using Na0.5MnO2 nanowall arrays as the cathode and carbon-coated Fe3O4 nanorod arrays as the anode. In particular, the 2.6 V Na0.5MnO2//Fe3O4@C asymmetric supercapacitor exhibits a large energy density of up to 81 Wh kg−1 as well as excellent rate capability and cycle performance, outperforming previously reported MnO2-based supercapacitors. This work provides new opportunities for developing high-voltage aqueous asymmetric supercapacitors with further increased energy density. Birnessite Na0.5MnO2 nanosheet assembled nanowall arrays are grown on carbon cloth via in situ electrochemical oxidation from spinel Mn3O4 nanowall arrays. By coupling with carbon-coated Fe3O4 nanorod arrays as the anode, a 2.6 V aqueous asymmetric supercapacitor is successfully developed. It exhibits a high energy density of 81 Wh kg−1 as well as excellent power capability and cycle performance.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/adma.201700804

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