Carbon nano-sponge with enhanced electrochemical properties: A new understanding of carbon activation

The activation of biomass using solid-phase reagents has been widely adopted to produce porous carbons. This approach, however, has remained without any improvement for decades. In the current work, we detail a simple activation and purification method where a silica-rich biomass waste (sugar press-mud, SPM) is sono-impregnated and fractionated with an alkaline solution. Upon heat-treatment, the fractionated alkali-soluble matter, which accounts for around 53 wt% of the dry SPM, results in a reasonable yield of carbon with a distinct texture of an interconnected porous structure with a high surface area of 2,066 m²·g⁻¹ and large pore-size-distribution. The impedance spectroscopy showed that the resulting carbon has an enhanced electrochemical response and less ionic diffusion-induced ohmic losses compared to that of a typical activated carbon due to its large pore-channels and enhanced ion-in-pore admittance. The ash content (mainly silica) in the final product was found to be less than expected. By tracking silica throughout the activation process, the reduction of ash content was assigned to the silica attack reactions. In these reactions, silica is transformed into water-soluble and/or low boiling point potassium silicates which facilitates its deportment from the final product resulting in a high-porosity and purity carbon.