Sustainable Porous Carbon with High Specific Surface Area from Soybean Shell via Hydrothermal Carbonization with H3PO4 for Electric Double‐Layer Capacitor Applications

Abstract

Soybean shell (SS), as the byproduct of soybeans, is converted into porous carbon (PC) with a high specific surface area (SSA) via hydrothermal carbonization with H3PO4 followed by KOH activation. No obvious effect on the crystal structure of PC can be found by addition of H3PO4 during the hydrothermal process. However, the SSA of PC increases remarkably compared with hydrothermal carbonization without H3PO4, as H3PO4 assists in hydrothermal carbonization dehydration reactions and creates some pores beneficial for KOH activation. The SSA of the obtained PC reaches 2523 m2 g−1, and the hierarchical pore structure is mainly in 0.6–50 nm. The sample prepared by hydrothermal carbonization with 10 wt% H3PO4 and activation by KOH with the ratio of KOH/10‐hydrochar 3 under 700 °C exhibits a specific capacitance of 301 F g−1 in 6 m KOH electrolyte at the current density of 0.1 A g−1. It also has an excellent cycling stability with the specific capacitance remaining at 93.8% after 15 000 cycles. Furthermore, the energy density is 8.1 Wh kg−1 in the two‐electrode system. These results display that PC based on SS is a promising electrode material for the electric double‐layer capacitor.