Hydrothermal synthesis of microalgae-derived microporous carbons for electrochemical capacitors

Abstract

N-doped highly microporous carbons have been successfully fabricated from N-rich microalgae by the combination of low-cost hydrothermal carbonization and industryadopted KOH activation processes. The hydrothermal carbonization process was found to be an essential step for the successful conversion of microalgae into a carbon material. The materials thus synthesized showed BET surface areas in the range ~ 1800-2200 m 2 g-1 exclusively ascribed to micropores. The carbons showed N contents in the 0.7-2.7 wt.%, owing to the use of N-rich microalgae as a carbon precursor. When tested in symmetric double layer capacitors (occasionally called supercapacitors) based on aqueous LiCl electrolytes, pseudocapacitance was only observable for the sample synthesized at the lowest temperature, 650 ºC, which is the one exhibiting the largest amount of N-and O-containing groups. The samples synthesized at 700-750ºC exhibited excellent rate capability (only 20 % of capacitance loose at 20 A g-1), with specific capacitances of 170-200 F g-1 at 0.1 A g-1. These materials showed excellent long-term cycling stability under high current densities.

Preparation and characterization of porous carbon from expanded graphite for high energy density supercapacitor in aqueous electrolyte

“…The energy density of AEG based symmetric supercapacitor is higher than those previously reported for carbon-based symmetric supercapacitors in aqueous electrolyte [34][35][36]. Table 3 Cycling test based on floating has been used to investigate the long-term stability of the symmetric device based on AEG.…”

Biomass-derived renewable carbon materials for electrochemical energy storage

“…Additionally, by coupling with chemical activation, the specific surface area and surface chemistry of the final carbon products could be further improved and modified by adding special oxidizing agent. Various carbon materials with high specific surface areas and modified functional groups have been produced from biomass precursors for supercapacitors, such as cellulose, potato starch and eucalyptus wood saw dust [111], hemicellulose [112], paper pulp mill sludge [113], D-glucosamine [114], fungi [70], fungus [115], bamboo waste [116], microalgae [117], watermelon [118] and hemp [119]. For example, Sevilla et al produced microporous carbons from the microalgae by a HTC process accompanied with a post-KOH activation treatment (Figure 7(a)).…”

Electrochemical behaviour of activated carbons obtained via hydrothermal carbonization

“…Another feature is that HTCderived carbons usually exhibit high amount of oxygen functional groups [11,22] because the process is performed under mild conditions, maintaining most of the precursor initial oxygen content. This important result can be applied to other heteroatom-containing precursors, what led to the preparation of N-doped carbons by using the HTC method [15,23] which contained a higher nitrogen amount than those prepared by the conventional methods. Moreover, it was demonstrated that this high nitrogen amount prevails even after the chemical activation.…”

“…Nevertheless, the hydrothermal carbonization was claimed as an alternative to obtain carbon materials, due to its low cost, mild synthesis conditions and environmentally friendly manufacture. Hence, biomass derived HTC carbons were considered as very promising materials for being used in supercapacitors [11,[14][15][16][17].…”