Self-sacrificial template synthesis of heteroatom doped porous biochar for enhanced electrochemical energy storage

In this study, a heteroatom-doped porous biochar from waste biomass was prepared via a facile self-sacrificial template strategy for enhanced electrochemical capacitive performance. Numerous narrow pores and carbonized frameworks were formed by hydrothermally decomposing the unstable components in the biomass, which were further broadened to micropores and even larger mesopores through a molten salt activation method. The synthesized porous biochar displayed apparently increased specific surface area, up to 1138 m2 g−1, well-developed porous structure, and moderate heteroatom doping (5.35 at.% O and 1.02 at.% N), which offered more active storage sites and charge capacities. Consequently, the modified biochar exhibited significantly enhanced specific capacitance of 447 F g−1 at 0.2 A g−1, which was 1.6 and 6.0 times higher than that of the samples carbonized directly by molten salt and inert reduction methods, respectively. The findings indicate that the facile self-sacrificial template synthetic route of biochar does not only provide larger pores for reducing the ion diffusion resistance, but also introduces heteroatoms into the carbon frame to increase charge mobility. Moreover, the assembled two-electrode symmetric supercapacitor presented not only a specific capacitance of 367 F g−1 with an energy density of 12.75 Wh∙kg−1 but also an excellent stability after 10000 cycles.