Biorefining of sugarcane bagasse to fermentable sugars and surface oxygen group-rich hierarchical porous carbon for supercapacitors

In this work, a biorefinery process was demonstrated for co-production of fermentable sugars and hierarchical porous carbon with oxygen-rich groups for energy storage devices from sugarcane bagasse. By using the biorefinery process, every one tonne of sugarcane bagasse can produce approximately 234 kg glucose from pretreatment and enzymatic hydrolysis and 71 kg porous carbon from enzymatic hydrolysis (lignin-rich) residue following a fast and catalyst-free hydrothermal carbonisation (240 °C for 3 h) and a subsequent KOH-assisted activation process (C-hydrochar). In contrast, only 51 kg of activated carbon (C-residue) from the lignin-rich residue and 81 kg activated carbon (C-bagasse) but no sugars from the whole sugarcane bagasse were produced using a one-step pyrolysis/activation process. Compared to the C-residue and C-bagasse, the C-hydrochar had a comparable specific surface area of 1436.7 m2 g−1. However, the C-hydrochar demonstrated the highest volume proportion of micropores and the highest surface O/C ratio. As a result, the C-hydrochar demonstrated a high electrochemical performance with specific capacitance of 185.5 F g−1 at a current density of 0.5 A g−1, and 150.7 F g−1 at a current density of 20 A g−1, respectively. The symmetric supercapacitor that was assembled by using two identical as-synthesized C-hydrochar porous carbon electrodes exhibited a high-power density of 6120 W kg−1 with energy density of 1.02 Wh kg−1 and a high energy density of 5.86 Wh kg−1 at power density of 405 W kg−1. Additionally, the device showed superior cycling performance with 96% capacitance retention after 10,000 cycles at a current density of 10 A g−1. Compared to previous report, this study indicates that pore volume distribution and surface oxygen-containing groups rather than specific surface area play more critical roles in the electrochemistry performance of carbon materials.