Ultrathin hierarchical porous carbon nanosheets for high‐performance supercapacitors and redox electrolyte energy storage

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.
K.J. is grateful to the Alexander von Humboldt (AvH) foundation for a postdoctoral fellowship. D.P.D. acknowledges the support of University of Adelaide, Australia for grant of Research Fellowship (VC Fellow). D.P.D. and P.G.R. acknowledge funding from MINECO‐FEDER (MAT2015‐68394‐R) and AGAUR (NESTOR 2014_SGR_1505) ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV‐2013‐0295) and funding from the CERCA Programme/Generalitat de Catalunya. The authors also gratefully acknowledge support by the Catalysis Research Centre (CRC) at TU Munich, the support from the Ministry of Education, Youth and Sports of the Czech Republic (LO1305), and the assistance provided by the Research Infrastructure NanoEnviCz, supported by the Ministry of Education, Youth and Sports of the Czech Republic under Project No. LM2015073. The work was further supported by the Operational Programme Research, Development and Education—European Regional Development Fund, Project No. CZ.02.1.01/0.0/0.0/15_003/0000416 of the Ministry of Education, Youth and Sports of the Czech Republic.