Facile method to produce sub-1 nm pore-rich carbon from biomass wastes for high performance supercapacitors

Sub-1 nm pores can lead to an anomalous increase in the supercapacitive performance [1], but it still faces great challenges from its relatively low sub-1 nm pore content, complicated preparation process, low yield and high cost. Here we successfully prepared a sub-1 nm pore-rich carbon from biomass wastes using a facile method by pre-treating walnut shell powder at 380 ℃ in air for different times to delicately tailor carbon defects, followed by KOH activation at 700 ℃. The as-prepared optimal material delivers the highest sub-1 nm pore content (V_{sub-1 nm} = 0.57 cm³ g^-1, V_{sub-1 nm}/V_t = 58.4 %) among all reported porous carbons. A supercapacitor made from the material accomplishes an ultrahigh specific capacitance of 298.7F g^-1 at 1 A g^-1 in a two-electrode device, excellent rate capability (78.8 % retention from 1 to 10 A g^-1) and long-cyclic life (94 % retention after 10,000 cycles at 10 A g^-1) in KOH. Even in Et₄NBF₄ electrolyte that is often used in commercial supercapacitors, a high energy density of 82.8 Wh kg^-1 at 7 kW kg^-1 and excellent cycling performance (90 % retention after 10,000 cycles at 5 A g^-1) can be achieved, ranking the best among all reported carbon-based electrical double layer capacitors tested in the same electrolyte. More importantly, it drives a light-emitting-diode (LED) to operate for as long as 20 min, vividly demonstrating the great potential of sub-1 nm pore-rich carbon-based high performance supercapacitors in practical applications.