Activated Carbons Prepared through H₃PO₄‐Assisted Hydrothermal Carbonisation from Biomass Wastes: Porous Texture and Electrochemical Performance

Hydrothermal treatment of biomass in the presence of phosphoric acid is proposed for the production of activated carbons (ACs). Interestingly, H₃ PO₄ promotes the fixation of carbon atoms in the solid during hydrothermal treatment, which renders higher preparation yields than those of the conventional impregnation method. Upon carbonisation of the resulting hydrochars at 450 °C, a notable development of porosity is achieved by using a low amount and concentration of phosphoric acid; these conditions are not adequate for conventional activation. The viability of this process for the sustainable production of ACs has been successfully checked in four biomasses of different composition and structures, and ACs of surface areas above 2000 m² g⁻¹ and tuneable pore size distribution have been obtained. Electrochemical characterisation of ACs prepared at 750 °C in 1 m H₂ SO₄ demonstrates that capacitances of approximately 150 F g⁻¹ with acceptable rate performance can be obtained through this simple method.