Supercapacitors (also known as ultracapacitors) are considered to be the most promising candidate for alternative energy storage/conversion devices [1-3]. However, the low energy density limits their applications that require high cycle life and power density. Compared with pseudocapacitors, the working mechanism of electric double layer capacitors (EDLCs) is a physical process, and it has the advantages of fast charging and discharging, good cycle performance, low cost, and no degradation after tens of thousands of cycles. For EDLCs, highly porous carbon materials are commonly used as supercapacitor electrodes. In recent decades, lots of works has been focused on improving the capacitive performance of porous carbon electrodes by the introduction of good-performance electrode materials. However, the relatively easily produced and low-cost carbon materials with proper porosity and good electrical conductivity are highly desirable.

In this work, glucose was firstly used as the precursor to produce porous carbon electrodes by hydrothermal carbonization (HTC) at 260℃, which is accomplished under mild and simple condition and is adaptable for wide feedstocks. Then, the porosity of the carbon electrodes has been improved by chemical activation with different amount of KOH at 800℃. The effects of different mass ratio of glucose to KOH (1:0, 1:1, 1:2, 1:3 and 1:1) on chemical activation efficiency have been studied. Scanning electron microscopy (SEM) images and Raman spectra of the porous carbon electrodes before and after activation are shown Fig. 1. Clearly, the glucose-derived porous carbon exhibits a sphere shape, and the pore structure has been greatly changed before and after KOH activation. It is notable that microspores of the porous carbon sphere were clearly enlarged after activation, and the enlarged mesopores are proper candidate as supercapacitor electrode.

Fig. 2 presents the current-voltage (C-V) curves of different glucose-derived porous carbon microelectrodes at different scan rate in 1M Na₂SO₄electrolyte. For all samples, the CV curves exhibits a symmetric rectangular shape, which indicates the behavior of electric double layer capacitors. The increased corresponding currents of glucose-derived porous carbon indicates the specific capacitance is increased after KOH activation. The specific capacitances of glucose-derived porous carbon with 1:3 (mass ratios of glucose to KOH) is reached 207 F/g. The The electric capacitance is strongly associated with the improved porous structure after KOH activation.

References

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