Hierarchical\nMicroporous/Mesoporous Carbon Nanosheets\nfor High-Performance Supercapacitors

Abstract

A straightforward one-pot approach\nfor the synthesis of highly\nporous carbon nanosheets with an excellent performance as supercapacitor\nelectrodes is presented. The procedure is based on the carbonization\nof an organic salt (i.e., sodium gluconate) at a temperature in the\nrange of 700–900 °C. The carbon nanosheets have a large\naspect ratio (length/thickness ≈ 10²–10³), a thickness within the range of 40–200 nm, high\nBET surface areas (<i>S</i>_BET) of up to 1390\nm² g^–1, and a porosity with a hierarchical\norganization in the micropore–mesopore range. Importantly,\nvia an additional activation step, the textural properties can be\nsubstantially enhanced (<i>S</i>_BET up to 1890\nm² g^–1). Both the nanosheet morphology\n(short diffusional paths) and the hierarchical microporous/mesoporous\npore structure allow the rapid transport of ions throughout the carbonaceous\nmatrix, leading to excellent electrochemical performance. Thus, the\nhierarchical nanosheets exhibit specific capacitances of up to 140\nF g^–1 at an ultrahigh discharge current of 150 A\ng^–1 in 1 M H₂SO₄ and 100 F\ng^–1 at 120 A g^–1 in 1 M TEABF₄/AN. The maximum specific power recorded in an aqueous electrolyte\nis ∼20–30 kW kg^–1 and ∼90–110\nkW kg^–1 in an organic electrolyte. These promising\npower characteristics are accompanied by excellent cycling stability.