High Yield and High Volumetric Capacitance Activated Carbons by One‐step Homogeneous Activation of Diaphragma Juglandis Fructus for Supercapacitors

Abstract Diaphragma juglandis fructus (DJF) is selected as a precursor of activated carbon (AC). Saturated absorption of solution containing desirable amount of KOH in DJF leads to one‐step homogeneous activation which produces AC‐1 comprising non‐honeycombed smaller particles with lower energy consumption compared with AC‐2 by the conventional two‐step method. The non‐honeycombed morphology of AC‐1 results in a high yield of 24.2 % and a high packing density of 0.78 g cm −3 . Although the specific surface area of AC‐1 is only 1030 m 2 g −1 , the specific capacitance reaches 244 F g −1 at 0.5 A g −1 in 6 mol L −1 KOH in a three‐electrode cell, higher than that of AC‐2 due to the reasonable pore distribution. In a symmetrical supercapacitor with the 6 mol L −1 KOH electrolyte, the maximum specific cell capacitance is 58.1 F g −1 at 0.25 A g −1 , corresponding to a high volumetric capacitance of 181 F cm −3 for a single electrode. The flexible supercapacitor with PVA/KOH electrolyte shows areal capacitance of 637 mF cm −2 and can maintain 70 % of the initial value after 180° bending for 400 times. The AC‐1 cell with the ionic liquid electrolyte has a maximum specific energy of 30.6 Wh kg −1 , which can illuminate 16 light‐emitting diodes simultaneously.