Valorization of Tea-Waste Biochar for Energy Storage

Biochar, a carbonaceous material derived from biomass by pyrolysis, stands out as environmentally friendly and low-cost carbon material with specific features that could be exploited for various applications, which range from the safe and long-term storage of carbon in the environment, to soil improvement and energy storage. It can be envisaged that the desired properties of biochar could be fine-tuned by chemical and structural modification for enhanced performance of this sustainable material. In this work, biochar derived from industrial tea waste was valorized by surface functionalization and graphitization to enhance the electrochemical properties and achieve higher capacitance. Several oxidative treatments have been assessed; waste-free UV-generated ozone exposure, nitric acid mediated oxidation, and harsh treatment with sulfonitric acid mixture. Subsequently, metal impregnation was investigated to reveal Fe-mediated catalytic effect on the graphitization process, allowing use of lower temperatures with consequent energy saving. The effects on BC were characterized by transmission electron microscopy (TEM), Fourier-transformed infrared (FT-IR) and Raman spectroscopy, thermogravimetric analysis (TGA) under air or nitrogen gas, physisorption, and electrochemical measurements. The structural design with chemical and physical treatments increased the capacitance from 0.041 to 7.734 F/g at the scan rate of 10 mV/s for pristine and modified biochar, respectively. Graphical