Synthesis of carbon spheres from glucose using the hydrothermal carbonization method for the fabrication of EDLCs

Carbon spheres (CSs) from glucose were synthesized by the hydrothermal carbonization method. We explored the effect of glucose concentration used in the synthesis on the yield as well as on the morphology of the CSs, and how this affects their electrochemical capacitance. For the possible application of CSs in commercial electrical double-layer capacitors (EDLCs), it is necessary to synthesize them in large quantities. For this reason, one of the main goals of this work was to increase the amount of CSs synthesized by increasing the concentration of glucose used in the synthesis process, affecting their electrochemical properties as little as possible for its use in EDLCs. Two post-synthesis procedures were performed on the CSs: 1) heat treatment at 800 °C in an argon atmosphere and 2) sulfonation process with subsequent heat treatment. The morphology of the six synthesized samples was analyzed. All the synthesized samples have the characteristic of generating large agglomerates of CSs; some are interconnected and fused forming a three-dimensional network of microspheres and other irregular shapes. This agglomeration of CSs may appear to be a negative effect on the performance of the electrodes, due to the apparent reduction in specific surface area. However good electrochemical capacitance results are obtained, because this morphology favors the creation of mesopores and, therefore, a greater facility for the insertion of ions in charging and discharging processes. The electrodes of CSs with better performance showed a capacitance of 85 F g−1 at 50 mV s−1.