Conversion of soybean waste to sub-micron porous-hollow carbon spheres for supercapacitor via a reagent and template-free route

Sub-micron porous-hollow carbon spheres are synthesized from ground soybean waste via a facile and economical hydrothermal carbonization and high-temperature heat-treatment in different media. The sub-micron porous-hollow carbon spheres after the heat treatment with the flow of argon have an average size of 398 ± 10 nm and an average shell thickness of ∼40 nm. The carbon in the porous-hollow spheres is amorphous. The electrochemical analyses of the porous-hollow spheres reveal that the porous-hollow carbon spheres heat-treated with the flow of the mixture of N₂ and H₂O steam have good capacitive properties and high specific capacitances, and the porous-hollow carbon spheres heat-treated in an inert medium (N₂ or Ar)possess relatively low capacitances with good rate capability. The results reported in this work likely provide a new and simple route for preparing functional materials with designed structures.