Versatile N,S,O tri-heteroatom doped porous biocarbons for high-performance supercapacitors and zinc ion capacitors

Porous biocarbons possess special features, such as well-developed and tunable porosity, and adjustable surface chemistry, which make them standout candidates for supercapacitors. Heteroatom doping, such as sulfur (S), nitrogen (N), and oxygen (O), further enhances energy storage capacity and stability. Herein, we present a versatile method for synthesizing in situ heteroatom-doped porous carbons by integrating solid-state activation and thiourea doping. Material optimization was achieved by varying the amount of thiourea used for doping during activation. This approach successfully incorporates multiple heteroatoms, including N, S, and O, into the carbon framework, yielding an optimized, high-surface-area (3494 m² g⁻¹) and large-pore-volume (1.86 cm³ g⁻¹) material, THBC-2. These features contribute to an exceptional 3E capacitance (373 F g⁻¹/0.5 A g⁻¹) in 3 M KOH. Additionally, THBC-2 was evaluated as a zinc-ion capacitor (ZIC) cathode, achieving impressive energy cum power densities (101 Wh kg⁻¹ and 399 W kg⁻¹) and good cycling stability. Ex situ characterization during charge/discharge processes provided valuable insights into the formation and dissolution of intermediate phases, which influence the stability and performance of the ZIC system. The materials presented demonstrate strong potential for use in supercapacitors and can be extended to other electrochemical applications.