LAUSR

Slash is a waste product generated from commercial forestry operations. In 2022, flooding slash caused devastating damage when Cyclone Gabrielle directly impacted the Hawke's Bay region of New Zealand. This study addresses the dual challenges of waste management and sustainable materials development by converting forestry slash into high‐performance carbon electrodes through an innovative in situ sulfur doping process. Building upon prior research involving waste‐derived materials, this study develops a hydrothermal sulfurization technique that transforms New Zealand slash into sulfur‐doped, highly graphitized carbon materials with excellent energy storage properties. The hydrothermally sulfurized slash‐derived electrode material (C‐HS‐New Zealand Slash (NZS)) exhibits a high specific capacitance of 148 F g− 1 at a current density of 0.5 A g− 1. A supercapacitor device assembles with the C‐HS‐NZS electrode achieves a capacitance of 440 F g− 1 at the same current density. The energy density reaches 15.3 Wh kg− 1 at a power density of 250 W kg− 1. Furthermore, the C‐HS‐NZS‐based device delivers a maximum capacitance of 384 F g− 1 and retains 360 F g− 1 after 10,000 cycles, demonstrating excellent capacity retention and long‐term electrochemical stability.