Metal silicates for supercapacitors derived from the multistep treatment of natural green algaes

Abstract

Natural green algaes (GAs) was treated with NaCl solution to prepare metal- silicates (S-C-FeSi-3 and S-C-CuSi-3) with high electrochemical performance. Then, the as-synthesized samples were soaked in NaOH solution to obtain etched metal silicates (e-S-C-FeSi-3 and e-S-C-CuSi-3). This novel method was used to generate a more porous structure with a higher specific surface area. In the three-electrode system, e-S-C-FeSi-3 and e-S-C-CuSi-3 showed the best electrochemical performance (476 F g^-1 and 458 F g^-1 at 0.5 A g^-1, 96 % and 97% after 10,000 cycles, respectively). The solid-state hybrid supercapacitor (HSC) devices (denoted as e-S-C-FeSi-3//AC and e-S-C-CuSi-3//AC), manufactured by metal- silicates and activated carbon (AC), were tested in a two-electrode system. e-S-C-MSi-3//AC exhibited much better electrochemical properties such as areal specific capacitances (603 and 615 mF cm^-2 at 2 mA cm^-2), energy densities (4.57 and 4.43 Wh m^-2 at the power density of 19.2 and 21.0 W m^-2) and cycle performances (74.5 % and 76.3 % after 6,000 cycles) than those of C-MSi-3//AC, e-C-MSi-3//AC and S-C-MSi-3//AC (M = Fe and Cu). This study confirms that supercapacitors with excellent electrochemical performance can be prepared by naturally polluted GAs. Furthermore, treatment with porogens is shown to be an effective method to enhance the electrochemical properties of metal- silicates and to prepare electrode materials applied for high-performance supercapacitors.

Keywords: Electrochemical performance; Green algaes; Metal- silicates; Multistep treatment; Supercapacitor.