Nickel-catalyzed formation of mesoporous carbon structure promoted capacitive performance of exhausted biochar

[Display omitted] •Waste nickel-laden biochar was reclaimed to produce capacitor material.•Good capacitance (~190 F g−1) and excellent stability of EDLC material was achieved.•Ni intensified carbonate decomposition promoting formation of mesoporous structure.•Ni enhanced carbon layer erosion in KOH activation facilitating mesopores-formation.•Ni catalyzed sp3 to sp2 hybridization benefiting conductivity and stability of EDLC. Biochar is widely studied to adsorb heavy metals in wastewater, while the reclamation of exhausted biochar becomes a challenge. In this study, biochar adsorbing Ni2+ with two concentration levels were used as precursors to prepare electrical double layer capacitor (EDLC) materials. A good performance of capacitance (188.9 F g−1 at 0.5 A g−1) and stability (capacitance retention maintained 95.9% after 1000 cycles) were achieved with the precursor of nickel-laden biochar of 100 mg g−1 and activation temperature of 600 °C, while the capacitance of control without nickel was only 98.4 F g−1. Power X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer-Emmete-Teller (BET) and the Raman Imaging combined with Emission Scanning Electron Microscope (RISE) identified that metallic nickel promoted carbonate decomposition and invaded into carbon layer, which assisted mesopores (551.8 m2 g−1) formation and contributed to a high capacitance. Moreover, nickel catalyzed the transfer of sp3 carbon to sp2 hybridization, which enhanced the conductivity and stability of EDLC. This study provides a feasible and simple strategy of reclaiming waste biochar after adsorbing nickel to prepare energy intensive material and implies the possibility and necessity of cascading applications of biowastes from environmental remediation to energy storage.