Synthesis of natural nitrogen-rich soybean pod carbon with ion channels for low cost and large areal capacitance supercapacitor
High performance and low cost electrode materials are vital for sustainable application of today's supercapacitors. As one of the nitrogen-rich biomass wastes, soybean pod was applied to synthesize porous carbon by alkali activation. The effects of alkali/carbonized soybean pod mass ratio (1-5) on surface area and electrochemical performances were investigated. At optimal reactant ratio of 4, the outstanding surface area of soybean pod carbon material was recorded as 2612 ± 64 m2 g-1. The soybean pod carbon displayed parallel tube array structure with nitrogen content of 1.52 ± 0.06%. Using symmetrical electrodes with a voltage of 1.8 V in 1 M Na2SO4 electrolyte at 0.5 A g-1, the specific capacitances of as-prepared and commercial carbon were 352.6 ± 16.2 and 242.7 ± 12.5 F g-1. During long life of 50,000 cycles, such a soybean pod carbon exhibited larger capacitance retention of 94.2 ± 3.0% than 84.7 ± 2.7% of commercial one. With high mass loading of 20 mg cm-2, the robust and flexible soybean pod carbon electrode revealed a superior areal capacitance of 4.70 F cm-2 at 10 mA cm-2, and the value could still retain as 4.38 F cm-2 after 10,000 cycles. It could be indicated that the soybean pod carbon was a potential and renewable candidate to construct inexpensive and advanced energy storage devices.