Laser-induced and KOH-activated 3D graphene: A flexible activated electrode fabricated via direct laser writing for in-plane micro-supercapacitors

[Display omitted] •Synchronous induction & activation of porous graphene on flexible substrate in air.•The activation mechanism of porous graphene via direct laser writing is demonstrated.•The effects of KOH on morphology, composition and wettability are studied.•Medium concentration of KOH can improve the quality and wettability of graphene.•IMSCs provide 10 times higher energy density than that without activation. Laser-induced graphene (LIG) from polymers has aroused considerable attentions for its low cost and high efficiency fabrication and prospect applications in flexible micro-energy storage devices. However, its electrochemical performance has been constrained by its purity and macropore-dominated structures. Herein, a one-step, facile approach is reported for synchronous induction and activation of 3D porous graphene from KOH-coated polyimide film by direct laser writing in ambient air. To explore the activation mechanism, the effects of two physical forms of KOH (crystal and solution) with various concentrations are investigated. Studies reveal that medium concentrations of KOH are able to improve the quality, heteroatoms (nitrogen and oxygen) doping and wettability of porous graphene in comparison with lower KOH. Additionally, high concentrations of KOH contribute to the formation of carbon atomic defects and mesoporous structures with increased content of nitrogen (4.94%). Benefiting from the improvement of activation, the laser-induced and activated graphene-based in-plane micro-supercapacitors present an areal capacitance of 32.00 mF/cm2 (4.27 μWh/cm2), which is about 10 times higher than that without KOH activation. Good cycling stability, excellent mechanical flexibility, and outstanding modular integration have been accomplished. As such, these high-performance devices hold enormous potentials for flexible and wearable electronics.