Butterfly-like metal-silicates derived from natural green algaes for supercapacitors with enhanced electrochemical properties by alkali etching

The 3D N, S, P-doped C-metal-silicates (C-MSi, M = Ni, Co and Ni/Co) are derived from green algaes (GAs) calcined by N 2 . Then the alkali etching technique is used to treat the as-synthesized C-MSi by 3 M NaOH aqueous solution for 12 h (e-C-MSi). The electrochemical performance can be significantly improved due to the acquisition of the more hierarchical pores and larger specific surface area by alkali etching. In detail, the e-C-NiSi-3, e-C-CoSi-3 and e-C-NiCoSi-3 show higher specific capacitances and cycling performances than those of C-MSi in the three-electrode system. The solid-state hybrid supercapacitor (HSC) devices (C-MSi//AC and e-C-MSi//AC, M = Ni, Co and Ni/Co) are fabricated by the metal-silicates and activated carbon (AC). The e-C-MSi//AC HSC devices exhibit better electrochemical properties than those of C-MSi//AC in the two-electrode system: higher specific capacitances, larger energy densities and better cycle performance. For instance, e-C-NiCoSi-3//AC HSC device (479 mF cm −2 at 2 mA cm −2 , 3.97 W h m −2 at 2.31 W m −2 , 92 % after 5000 cycles) is superior to C-NiCoSi-3//AC HSC device (432 mF cm −2 at 2 mA cm −2 , 3.15 W h m −2 at 2.14 W m −2 , 87 % after 5000 cycles). These results demonstrate that the high-performance supercapacitors can be prepared by the natural GAs using simple method. Alkali etching technique can be used as a conventional and positive method to improve the electrochemical performance of metal-silicates, and can provide electrodes for applying to high-performance SCs. • The etching metal-silicates (e-C-MSi) are obtained by etching C-MSi synthesized from green algaes. • e-C-MSi composes of micropores, mesopores and macropores. • e-C-MSi present excellent capacitance than C-MSi. • e-C-MSi//AC devices show good cyclic stability after 5000 cycles.