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Based on the biological structure of biomass materials, the preparation of carbon materials with special pore structures and rich surface groups is an important route in the development of new carbon materials for electrodes. In this work, a nitrogen self-doped carbon with unique tubular channel structures was synthesized from garlic peels for the high-performance supercapacitor electrode application. The mild KHCO 3 was selected as the activator and therefore the biological structure of garlic peels is well preserved, showing a large number of long tubular channels with a diameter of around 50 nm. It was found that a nitrogen self-doped porous carbon material (SPC-4KC) with a nitrogen relative content of 1.77% and a large specific surface area of 1993.73 m2 g−1 was formed at 800 ℃ at a KHCO 3 /SPC mass ratio of 4:1. Using as the electrode material, the mass-specific capacitance of the SPC-4KC-based electrode reached 303.38 F g−1 at a current density of 1 A g−1 in the three-electrode system. In the two-electrode system, when the energy density is 7.42 W h kg−1, the power density is 314.33 W kg−1. Also, the material exhibits excellent cycle stability, with a capacitance retention of 94.87% after 5000 cycles at a current density of 10 A g−1. • Waste garlic peels were green synthesized into nitrogen self-doped porous carbon materials. • Nitrogen self-doped porous carbon materials have unique mesoporous tubular channels. • A mild, environmentally friendly activator, KHCO 3 , is employed and effective. • The obtained carbon electrode shows a high specific capacitance of 303.38 F g−1. • The material exhibits excellent cycle stability, with a capacitance retention of 94.87% after 5000 cycles at a current density of 10 A g−1. [ABSTRACT FROM AUTHOR]

• Hydrothermal carbonization (HTC) was performed to upgrade the sawdust. • Hydrochar characterizing and kinetics analysis were conduted. • The HTC temperature plays an important role in hydrochar performance. • The CO 2 , CO, CH 4 , and H 2 O were main gas products from hydrochar pyrolysis. This work intends to reveal the pyrolysis behavior of hydrochar from hydrothermal carbonization (HTC) of pinewood sawdust. The elemental analysis and pyrolysis test were performed to study the effect of HTC on hydrochar performance. The elemental analysis indicates that the fuel properties could be highly upgraded by the HTC process. Compared with raw biomass (48.10 % and 19.12 MJ/kg), the carbon content and heating value was improved to 69.05 % and 26.66 MJ/kg for HTC-260. The atomic ratios H/C and O/C were decreased from 1.31 to 0.90 and 0.72 to 0.26, respectively, by means of dehydration and decarboxylation in the HTC process. The pyrolysis test implies that the thermal stability of hydrochars has been improved by the HTC. The hydrochars decomposition temperature and the pyrochar yields became higher and higher with the HTC temperature. For the HTC-260, the pyrochar yield was increased from 24.4%–53.02% at a pyrolysis temperature of 800 ºC. According to the TGA-FTIR, the main gas products were CO 2 , CO, CH 4 , and H 2 O. Higher HTC temperature promoted more CH 4 production due to the devolatilization, decarboxylation, dehydration and polymerization occurred in the HTC process. 240–260 °C could be considered as a good option to maximize the energy efficiency when taking the HTC as a pretreatment procedure over thermal drying or torrefaction. All these results indicate the HTC is promising to upgrade high-moist biomass for multi-value-added products. [ABSTRACT FROM AUTHOR]