Zeolitic imidazolate framework-8-assisted synthesis of glucose-derived carbon spheres via hydrothermal carbonization for supercapacitors

In this study, zeolitic imidazolate framework-8 (ZIF-8) was introduced as an additive to enable the hydrothermal synthesis of glucose-derived carbon spheres under challenging conditions: high glucose concentration (up to 4 M, representing the upper limit for sphere formation) and short reaction time (2 h). The effects of ZIF-8 dosage, hydrothermal time, glucose concentration and polyacrylic acid sodium (PAAS) on the morphology of carbon spheres were investigated in detail. Results show that ZIF-8 not only promotes the formation of uniform carbon spheres but also significantly increases the apparent yield—even at 4 M glucose. Notably, while carbon spheres can be formed at glucose concentrations as high as 4 M, the optimal electrochemical performance was achieved at 3 M glucose, under fixed hydrothermal volume of 40 mL with 0.1 g ZIF-8, 2 h reaction time, and 24 mg PAAS. After KOH activation (KOH: carbon = 1:1), the resulting material exhibited a high specific surface area (1617 m 2 /g), large pore volume (1.00 cm 3 /g), average pore size of 2.48 nm, and strong microporosity (94.9% contribution). It delivered a specific capacitance of 171.5 F/g at 0.5 A/g and retained 85.14% of its capacity after 10,000 cycles at 2 A/g. This work demonstrates that ZIF-8-assisted hydrothermal carbonization is an effective strategy to increase the apparent yield of carbon sphere, and provides a feasible pathway for expanding the application of glucose-derived hydrothermal carbon spheres.