Recycling biowaste into energy storage: waste tea leaves-derived hierarchical porous activated carbon for supercapacitors

Biodegradable wastes, like tea leaves, play an essential role in promoting a sustainable waste management strategy by reducing pollution and providing chances to exploit valuable resources. In this study, discarded tea leaves are utilized to fabricate an electrochemical double-layer capacitor (EDLC) containing hierarchical porous activated carbon (AC) electrodes and an aqueous sodium sulfate (Na₂SO₄) electrolyte. With its various micro/mesoporous structural architecture, the resulting AC is well-suited for EDLCs. The device demonstrates high specific capacitance, energy, and power values of approximately 282 F g⁻¹ (at 0.9 Ag^-1), 28.3 Wh kg⁻¹, and 35 kW kg⁻¹, respectively. Notably, the enhanced device demonstrated its capability by powering a light-emitting diode (LED) for more than 11 min. In addition to maintaining a largely steady specific capacitance over 10,000 charge-discharge cycles with a retention rate of about 93 %, the device also attains 97–100 % coulombic efficiency. This study highlights that leftover tea leaves serve as a sustainable resource for energy storage devices, offering significant benefits to both society and the environment.