Compact and Light Supercapacitor Electrodes from a Surface‐Only Solid by Opened Carbon Nanotubes with 2 200 m2 g−1 Surface Area

An approach is presented to make a "surface-only solid" with a surface area of 2 240 m 2 g -1 (1 310 m 2 cm -3 ), corresponding to 85% of the atoms constituting a surface, by opening single-walled carbon nanotube forests and solids via controlled oxidation. The controllability of the approach is demonstrated by tailoring the hole size to match the guest molecule, for example, nitrogen, fullerene, or solvated ions. These features make the surface-only solid an ideal vessel for material and energy storage, as demonstrated by its use for electrodes to realize a light and compact supercapacitor with high energy (24.7 W h kg -1 ) and power (98.9 kW kg -1 ) densities, exceeding those of activated carbon (16.9 W h kg -1 and 35.7 kW kg -1 ).