Construction of 3D Porous Carbon Frameworks for Supercapacitors: Abundant Pore Structure and Proper Hydrophilicity

A biomass-derived 3D porous carbon (3DPC) framework with multi-heteroatom (N, O, and S) doping was easily fabricated by an easy, efficient, and low-cost method. In the approach, the template action and pore activation were simplified into one step, which differed from previous methods of preparing porous carbon. By exfoliating the porous carbon into graphene-like laminar nanosheets using NaCl and expanding the pore structure with KOH during the ball milling process, followed by carbonization under a suitable temperature, the prepared porous carbon afforded good electric conductivity (6.3 S cm^–1 under 7 MPa), large surface area (731 m² g^–1), and abundant pores (macropores, mesopores, and micropores). The determined relaxation time constant (τ₀ = 0.35 s) indicated that the consecutive porous structure is conductive to fast ion diffusion. The heteroatoms introduced via the biomass itself not only conferred additional pseudo-capacitance but also improved the surface wettability. Thus, when carbonized at 750 °C, the 3DPC possessed high specific capacitance, excellent rate capacity (82.8% retention when the current density was increased to 20 A g^–1), and outstanding cycling stability (96.3% after 10,000 cycles) in aqueous electrolytes. In an all-solid-state symmetric capacitor, 3DPC delivered high energy and power densities.