School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing, 210094, China.
Herbert Gleiter Institute of Nanoscience, Nanjing University of Science and Technology, Nanjing, 210094, China.
Adv Mater. 2017 Aug;29(32). doi: 10.1002/adma.201700804. Epub 2017 Jun 22.
The voltage limit for aqueous asymmetric supercapacitors is usually 2 V, which impedes further improvement in energy density. Here, high Na content Birnessite Na MnO 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 Na MnO nanowall arrays can be extended to 0-1.3 V (vs Ag/AgCl) with significantly increased specific capacitance up to 366 F g . The extended potential window for the Na MnO electrode provides the opportunity to further increase the cell voltage of aqueous asymmetric supercapacitors beyond 2 V. To construct the asymmetric supercapacitor, carbon-coated Fe O 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 Na MnO nanowall arrays as the cathode and carbon-coated Fe O nanorod arrays as the anode. In particular, the 2.6 V Na MnO //Fe O @C asymmetric supercapacitor exhibits a large energy density of up to 81 Wh kg as well as excellent rate capability and cycle performance, outperforming previously reported MnO -based supercapacitors. This work provides new opportunities for developing high-voltage aqueous asymmetric supercapacitors with further increased energy density.
水系不对称超级电容器的电压限制通常为 2 V，这阻碍了其能量密度的进一步提高。在此，通过电化学氧化，在碳布上原位形成了具有高 Na 含量的水钠锰矿 NaMnO 纳米片组装的纳米墙阵列。有趣的是，发现 NaMnO 纳米墙阵列的电极电位窗口可以扩展到 0-1.3 V（相对于 Ag/AgCl），比电容显著增加至 366 F/g。NaMnO 电极的扩展电位窗口为将水系不对称超级电容器的电池电压进一步提高到 2 V 以上提供了机会。为了构建不对称超级电容器，合成了碳包覆的 Fe2O3 纳米棒阵列作为阳极，并且可以在-1.3 到 0 V（相对于 Ag/AgCl）的负电位窗口中稳定工作。首次使用 NaMnO 纳米墙阵列作为阴极和碳包覆的 Fe2O3 纳米棒阵列作为阳极，展示了 2.6 V 的水系不对称超级电容器。特别地，2.6 V 的 NaMnO//Fe2O3@C 不对称超级电容器表现出高达 81 Wh/kg 的高能量密度以及出色的倍率性能和循环性能，优于以前报道的基于 MnO 的超级电容器。这项工作为开发具有进一步提高的能量密度的高压水系不对称超级电容器提供了新的机会。
