Almond skin derived porous biocarbon nanoarchitectonics with tunable micro and mesoporosity for CO2 adsorption and supercapacitors

The careful selection of carbon precursors for chemical activation is critical in obtaining cost-effective and efficient porous activated biocarbons with multifunctional properties. Herein, we report on utilising almond skin to synthesize porous activated biocarbons via solid-state KOH activation. Through precise manipulation of the impregnation ratio of KOH to the non-porous carbon, a range of materials with intriguing properties including high surface area, large pore volume, tunable micro and mesopores, and surface functionalization with oxygen were synthesized. The optimized material ASPC5-4 displayed an extremely high surface area (3535 m2 g−1), a large pore volume (1.9 cm3 g−1), a high proportion of mesopores (96.5 %) and a notable surface oxygen content (6.93 wt %). These excellent features allowed ASPC5-4 to adsorb a record amount of CO2 at 0 °C/30 bar (39.81 mmol g−1). Another material ASPC5-2 exhibited a high content of micropores and adsorbed 5.92 mmol g−1 of CO2 at 0 °C/1 bar. ASPC5-4 also exhibited great potential as a supercapacitor electrode, displaying a high specific capacitance in both a three-electrode (354 F g−1/0.5 A g−1) and two-electrode (203 F g−1/0.5 A g−1) systems. It also demonstrated high power and energy densities of 638 W kg−1 and 47 W h kg−1, respectively.