Nitrogen and boron co-doped densified laser-induced graphene for supercapacitor applications

•N and B co-doped densified LIG is prepared based on duplicate laser pyrolysis.•The effects of H3BO3 loadings and laser pyrolysis power on LIG are investigated.•NB-dLIG shows remarkable capacitive enhancement compared to N-dLIG and undoped-sLIG. This study demonstrates a facile and versatile approach to the fabrication of N and B co-doped and simultaneously densified laser-induced graphene (NB-dLIG) based on a duplicate laser pyrolysis method for supercapacitor applications. The LIG obtained after the first laser pyrolysis is coated with an additional thin layer of polyamic acid /H3BO3 and additionally irradiated with a laser, resulting in the simultaneous densification and incorporation of N and B heteroatoms into the graphene-like structure of LIG. The NB-dLIG with optimized H3BO3 loading (1 wt%) and duplicate laser power (2.4 W; NB1-dLIG-2.4) exhibits remarkably improved capacitive performance due to the synergistic effect of N and B co-doping. The NB1-dLIG-2.4 electrode delivers a specific areal capacitance (CA) of 104.3mF/cm2, which is nearly 2.5 and 12 times higher than N-doped dLIG (42.4mF/cm2) and undoped single pyrolyzed LIG (9.0mF/cm2), respectively, at 0.2 mA/cm2 using a three-electrode assembly. Furthermore, a solid-state flexible supercapacitor is fabricated with NB1-dLIG-2.4 and PVA-H2SO4 gel electrolyte, attaining a high CA (40.4mF/cm2 at 0.05 mA/cm2), with excellent cycling stability, Coulombic efficiency, and mechanical flexibility. This work opens a new avenue for fabricating LIG doped with multiple heteroatoms, which can be used in various electrochemical applications.