Ultrathin Hierarchical Porous Carbon Nanosheets for High-Performance Supercapacitors and Redox Electrolyte Energy Storage

Abstract

The design of advanced high-energy-density supercapacitors requires the design of unique materials that combine hierarchical nanoporous structures with high surface area to facilitate ion transport and excellent electrolyte permeability. Here, shape-controlled 2D nanoporous carbon sheets (NPSs) with graphitic wall structure through the pyrolysis of metal–organic frameworks (MOFs) are developed. As a proof-of-concept application, the obtained NPSs are used as the electrode material for a supercapacitor. The carbon-sheet-based symmetric cell shows an ultrahigh Brunauer–Emmett–Teller (BET)-area-normalized capacitance of 21.4 µF cm⁻² (233 F g⁻¹), exceeding other carbon-based supercapacitors. The addition of potassium iodide as redox-active species in a sulfuric acid (supporting electrolyte) leads to the ground-breaking enhancement in the energy density up to 90 Wh kg⁻¹, which is higher than commercial aqueous rechargeable batteries, maintaining its superior power density. Thus, the new material provides a double profits strategy such as battery-level energy and capacitor-level power density.

Shape-controlled 2D hierarchical nanoporous carbon sheets derived from metal–organic framework achieving excellent surface-area-normalized capacitance are prepared. Further, the effect of the addition of KI redox-active species in the aqueous electrolyte to enhance the performance is explored.

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