Hierarchical hollow tubular fibrous brucite-templated carbons obtained by KOH activation for supercapacitors

Abstract

Hierarchical hollow tubular porous carbons have been widely used in applications of supercapacitors, batteries, CO₂ capture and catalysis due to their hollow tubular morphology, large aspect ratio, abundant pore structure and superior conductivity. Herein, hierarchical hollow tubular fibrous brucite-templated carbons (AHTFBC_s) were prepared using natural mineral fiber brucite as the template and KOH as the chemical activator. The effects of different KOH additions on the pore structure and capacitive performance of AHTFBC_s were systematically studied. The specific surface area and micropore content of AHTFBC_s after KOH activation were higher than those of HTFBC. The specific surface area of the HTFBC is 400 m² g⁻¹, while the activated AHTFBC₅ has a specific surface area of up to 625 m² g⁻¹. In particular, compared with HTFBC (6.1%), a series of AHTFBC_s (22.1% for AHTFBC₂, 23.9% for AHTFBC₃, 26.8% for AHTFBC₄ and 22.9% for AHTFBC₅) with significantly increased micropore content were prepared by controlling the amount of KOH added. The AHTFBC₄ electrode displays a high capacitance of 197 F g⁻¹ at 1 A g⁻¹ and the capacitance retention of 100% after 10 000 cycles at 5 A g⁻¹ in the three-electrode system. And an AHTFBC₄//AHTFBC₄ symmetric supercapacitor exhibits the capacitance of 109 F g⁻¹ at 1 A g⁻¹ in 6 M KOH and an energy density of 5.8 W h kg⁻¹ at 199.0 W kg⁻¹ in 1 M Na₂SO₄ electrolyte. In addition, the capacity retention of AHTFBC₄ in the symmetric supercapacitor was maintained at 92% after 5000 cycles in both 6 M KOH and 1 M Na₂SO₄ electrolytes.