Novel carbon material with 3-D hierarchical micro-meso-macro porous derived from nitrogen-fixing biomass: A scalable route toward carbon electrodes

Constructing biomass hierarchical porous carbon composite electrodes with ultra-high specific surface area, reasonable distribution of pores, and fast redox atoms for super-capacitors (SCs), is still a constant pursuit goal of current researchers. Herein, biochar containing heteroatoms with micro-meso-macro porous were successfully prepared from soybean straw as the precursor. Remarkably, an exclusive synthesis strategy, via hydrothermal reaction, alkali activation, and acid etching dual chemical treatments at specific carbonization temperature, was applied for controlling pore structure in this work, affording three dimensions (3D) hierarchical porous and a certain disordered graphitized structure of carbon material: SSP-900. SSP-900 exhibits the property of ultra-high specific surface area and reasonable distribution (SBET=1283 m2 g−1, Smicro/SBET= 65%, Pore Volume= 0.73 cm3 g−1). Furthermore, it also displays the key merits of electrode materials candidate for SCs, including the superb specific capacity of 357 F g−1 at 0.5 A g−1 in the three-electrode system. Additionally, single electrode of SSP-900//SSP-900 demonstrates a splendid specific capacitance of 320 F g−1 in current density of 0.15 A g−1, the high energy density (11.2 Wh kg−1) and power density (37.8 W kg−1), a great rate capability retention (42%), and outstanding cycling stability up to 10,000 times (only 10% loss of capacitance) in two-electrode system. Its splendid electrochemical performances originate from the synergistic contribution of the special pore structure and built-in redox atom (N and O). As such SSP-900 may be seen as a promising SCs electrode material. This research provides an effective method for controlling the pore structure of biochar to be of great application in the SCs field.