Functionalized three-dimensional hierarchical porous carbon (THPC) is prepared via a facile modified chemical activation route with polypyrrole microsheets as precursor and KOH as activating agent. The as-obtained THPC presents a large specific surface area (2870 m² g⁻¹), high-level heteroatom doping (N: 7.7 wt%, O: 12.4 wt%), excellent electrical conductivity (5.6 S cm⁻¹), and hierarchical porous nano-architecture containing macroporous frameworks, mesoporous walls and microporous textures. Such unique features make the THPC an ideal electrode material for electrochemical energy storage. As the electrode material for a supercapacitor, the THPC exhibits a high capacitance, excellent rate performance and long-term stability in both aqueous and organic electrolytes.

A porous hard carbon material was synthesized by the simple pyrolysis of H₃PO₄-treated biomass, i.e., pomelo peels, at 700 °C in N₂. The as-obtained hard carbon had a 3D connected porous structure and a large specific surface area of 1272 m² g⁻¹. XPS analysis showed that the carbon material was functionalized by O-containing and P-containing groups. The porous hard carbon was used as an anode for sodium ion batteries and exhibited good cycling stability and rate capability, delivering a capacity of 181 mA h g⁻¹ at 200 mA g⁻¹ after 220 cycles and retaining a capacity of 71 mA h g⁻¹ at 5 A g⁻¹. The sodium storage mechanisms of the porous hard carbon can be explained by Na⁺ intercalation into the disordered graphene layers, redox reaction of the surface O-containing functional groups and Na⁺ storage in the nanoscale pores. However, the porous hard carbon demonstrated a low coulombic efficiency of 27%, resulting from the formation of a solid electrolyte interphase film and the side reactions of surface phosphorus groups.

S-doped carbon is investigated as a high-performance anode material for sodium-ion batteries. Due to the introduction of a high-content of S atoms, the as-obtained S-doped carbon shows an enlarged interlayer distance. As an anode, a high specific capacity of up to 303 mAh g⁻¹ is achieved, even after 700 cycles at 0.5 A g⁻¹.