Novel sulfur-doped hierarchical porous carbon from marine biomass for high-performance supercapacitor

Although hierarchical porous carbon materials are known for their excellent rate capability, they often suffer from low energy density in supercapacitors. Here, we present a novel approach to synthesizing hierarchical micro-mesoporous, sulfur-doped carbon derived from carrageenan biomass, which is being evaluated as a supercapacitor electrode material. The CA material is characterized by a high sulfur content (2.7 at. %), primarily in the form of sulfur-functionalized C-S-C bonds, alongside a variety of oxidized sulfur species. The ideal porous structure, with a micropore ratio of 63 %, is the result of the unique cation-induced self-assembly of carrageenan. The CA material exhibits an impressive specific capacitance of 204 F g⁻¹ and higher capacitance retention rates of 74.5 % in a three-electrode configuration. When assembled into a symmetric supercapacitor, it delivers an exceptionally high energy density of 16.6 Wh kg⁻¹ at 199 W kg⁻¹ in a 1 M Na₂SO₄ aqueous electrolyte. These values exceed those of most previously reported hierarchical porous and heteroatom-doped carbon materials. This study presents a green, scalable synthesis route for producing sulfur-doped, hierarchical, porous carbon materials. The method uses the intrinsic -OSO₃⁻ groups and metal ions in carrageenan to enable in situ sulfur doping and self-templated pore formation. This avoids the need for toxic sulfur-containing precursors or gases, which are typically required in conventional approaches. The resulting material exhibits promising potential for application in high-performance, industrial-scale supercapacitors.