Efficient construction of a carbon-based symmetric supercapacitor from soybean straw by coupling multi-stage carbonization and mild activation

Hierarchical porous carbon materials were successfully prepared and controlled through a multi-step carbonization and mild-activation route using soybean straw from agricultural and forestry waste as raw material. Developing the unique hierarchical structure of soybean straw as a template during pre-carbonization process, is beneficial for regulation of micro-mesoporous structure at mild-activation route. The specific surface area of the obtained sample is controlled by adjusting the pyrolysis temperature, and reaches 2266.19 m(2) g(-1) in the presence of a small amount of alkaline activator (mass ratio of soybean straw carbon: KOH=1:2). Moreover, the abundant porosity and specific chemical structure of nitrogen and oxygen in soybean straw-based carbon materials are favorable for an better electrochemical behavior of carbon-based supercapacitor devices. In the three electrode system, the optimal sample (SSC-700) exhibits the capacitance as high as 380.5 F g(-1) at a current density of 0.5 A g(-1) , and capacitance retention 73.97% after 10000 charge and discharge cycles, and produces a high energy density of 13.2 W h kg(-1) at a power density of 52.03 W kg(-1). In the two-electrode system, the SSC700-based symmetric supercapacitor exhibits a high energy density of 8.95 W h kg(-1) at a power density of 25 W kg(-1) and is able to maintain 5 W h kg(-1) at 2500 W kg(-1). Furthermore, carbon-based symmetrical supercapacitors also show good cycle capacity, with a capacity loss rate of 0.5% in 5000 cycles. This work shows that soybean straw-based carbon materials have great application potential in high-performance energy storage devices

Automated summary

Hierarchical porous carbon materials were successfully prepared and controlled using soybean straw as raw material. The materials exhibited abundant porosity and specific chemical structure, leading to excellent electrochemical performance and high application potential in energy storage devices.