Honeycombed activated carbon with greatly increased specific surface by direct activation of glucose for supercapacitors

Highlights: • Homogeneous activation of deoxygenated glucose produced honeycombed carbon. • Honeycombed carbon of 1912 m² g⁻¹ vs. bulk carbon of 130 m² g⁻¹. • Relationship between C/O ratio of deoxygenated glucose and capacitance was built. • Honeycombed carbon of 268 F g⁻¹ vs. bulk carbon 105 F g⁻¹ in KOH. • Maximum specific energy of 24 Wh kg⁻¹ was obtained in KBr. -- Abstract: In the production of activated carbons (ACs), glucose as a precursor is prone to producing the graphitic char intermediates after carbonization, which are difficult to be activated in the subsequent activation. In order to obtain a desirable specific surface area, either twice activation after carbonization or hydrothermal treatments of glucose before activation is applied. In this research, the direct activation of glucose has been executed to produce honeycombed ACs via deoxygenation of the glucose precursor in the KOH aqueous solution for appropriate time at room temperature. It is found that when glucose is subjected to the alkaline circumstance, dehydration and polymerization reactions increase the C/O ratio while the degradation and oxidation decrease the C/O ratio. The AC from the deoxygenated product with the highest C/O ratio has a superior specific surface area of 1912 m² g⁻¹ which is much higher than 130 m² g⁻¹ for the AC by the conventional two-step method. The Honeycombed morphology and the specific surface increased by one order of magnitude lead to good performance of 268 F g⁻¹ in the KOH and 24.5 Wh kg⁻¹ in the KBr electrolyte.