Abstract
A series of heteroatom-containing porous carbons with high surface area and hierarchical porosity were successfully prepared by hydrothermal, chemical activation, and carbonization processes from soybean residues. The initial concentration of soybean residues has a significant impact on the textural and surface functional properties of the obtained biomass-derived porous carbons (BDPCs). SRAC5 sample with a BET surface area of 1945 m2 g−1 and a wide micro/mesopore size distribution, nitrogen content of 3.8 at %, and oxygen content of 15.8 at % presents the best electrochemical performance, reaching 489 F g−1 at 1 A g−1 in 6 M LiNO3 aqueous solution. A solid-state symmetric supercapacitor (SSC) device delivers a specific capacitance of 123 F g−1 at 1 A g−1 and a high energy density of 68.2 Wh kg−1 at a power density of 1 kW kg−1 with a wide voltage window of 2.0 V and maintains good cycling stability of 89.9% capacitance retention at 2A g−1 (over 5000 cycles). The outstanding electrochemical performances are ascribed to the synergistic effects of the high specific surface area, appropriate pore distribution, favorable heteroatom functional groups, and suitable electrolyte, which facilitates electrical double-layer and pseudocapacitive mechanisms for power and energy storage, respectively.
Highlights
Among the devices used as electrical energy storage systems, supercapacitors are the devices between conventional capacitors and rechargeable batteries and have found wide applications in aircrafts (Airbus 380), consumer electronics, emergency backup powers, and hybrid or electric vehicles [1]
Based on the mechanism of energy store of EDLCs, the supercapacitive performance relies on the interface between the carbon electrode and electrolyte solution
The pore size within carbon electrode materials should be larger than those of the ion size of the electrolyte and the pore size larger than 0.5 nm could be beneficial for access of the ions of aqueous electrolytes [14]
Summary
Among the devices used as electrical energy storage systems, supercapacitors are the devices between conventional capacitors and rechargeable batteries and have found wide applications in aircrafts (Airbus 380), consumer electronics, emergency backup powers, and hybrid or electric vehicles [1]. It has been reported that porous carbon-based materials with high specific surface area, suitable pore structure, and favorable functional groups have the promising applications as the electrode materials for EDLCs and hybrid supercapacitors [2,4]. Two approaches were taken to produce low-cost BDPCs as the highly effective electrode materials for high energy EDLCs. The first approach was the usage of soybean residues to make nitrogen-containing hierarchical porous carbons with high specific surfaces. The symmetric SRAC5/Ni//SRAC5/Ni supercapacitor demonstrated a remarkable high specific energy of 67.3 Wh kg−1 at a power density of 2.0 kW kg−1 at 2 A g−1 in a wide voltage window of 0–2.0 V and an excellent 89.9% capacitance retention after 5000 cycles These facts demonstrate that the use of hydrothermal carbonization/chemical activation process accomplished with a suitable electrolyte can be the green and facile strategies for fabrication large-scale commercial supercapacitors
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