Biomass-tar-derived oxygen-enriched porous carbon as a high-performance carbon electrode material for double electric layer and zinc-ion hybrid supercapacitor

Carbon-based capacitor electrodes have the advantages of high capacitance value, superior recyclability, and inexpensive raw materials, which fuel the application of capacitors in large-scale energy storage. Biomass tar is a hazardous waste that can be recycled as a low-cost carbon electrode precursor for capacitors, due to its retaining biomass-based heteroatom. In this study, hierarchically porous carbon with cross-linked structure was fabricated by using a nano-Al2O3 template combined with the KOH activation technique, in which the gamma-Al2O3 has a size of only 10 nm with high specific surface area, thus optimizing the pore structure of the carbon material. The resulting optimal material, BTC-0.2-2-800, contains abundant pore structure and extremely high oxygen content, delivers low resistance and excellent rate performance with high specific capacitance of 292.1 F g- 1 and 221.7 F g- 1 at 1 A g- 1 and 20 A g- 1, respectively, in double electric layer supercapacitors (EDLCs). Besides, no significant capacity degradation after 10,000 charging and discharging cycles at 10 A g- 1 was found. The two-electrode device prepared using Na2SO4 electrolyte achieves a high energy density of 43.18 Wh kg- 1 at the power density of 1000 W kg- 1, which can light up a 2 V LED lamp. Moreover, Zinc-ion hybrid supercapacitor (ZIHSC) fabricated with BTC-0.2-2-800 carbon electrode accounts for the energy densities of 69.82 Wh kg- 1 and 49.39 Wh kg- 1 at the power densities of 40 W kg- 1 and 400 W kg- 1, respectively. This study reveals the great potential of biomass-tar-derived carbon as a high-performance electrode material, which may provide an opportunities for the resource utilization of hazardous wastes.