Laser-oxidized Fe3O4 nanoparticles anchored on 3D macroporous graphene flexible electrodes for ultrahigh-energy in-plane hybrid micro-supercapacitors

Flexible battery-type in-plane hybrid micro-supercapacitors (IHMSCs), which combine fast charging rate of micro-supercapacitors and high energy density of batteries, provide great potentials for flexible microdevices. However, their low-efficiency, high-cost process and limited energy density still hinder their practical applications. Herein, we report the high-efficient fabrication of Fe3O4 nanoparticle-anchored laser-induced graphene (LIG/Fe3O4) with hierarchical porous structures on a flexible substrate wherein aggregated Fe3O4 nanoparticles (~24.08 nm) with mesopores are self-deposited onto macroporous LIG scaffolds by laser in one step. The unique 3D structures in LIG/Fe3O4 give rise to superhydrophilic and capillary effects with a pumping capacity of up to 0.096 μm in water, resulting in continuous superior wettability between electrodes and water-based electrolyte. Benefiting from the reversible H+ ion (de)intercalation reaction with Fe3O4 nanoparticles, the resulting IHMSCs based on LIG/Fe3O4 as the anode and LIG as the cathode deliver an ultrahigh areal capacitance of 719.28 mF/cm2, which is over 100 times higher than that of LIG micro-supercapacitors, and an areal energy density of 60.20 μWh/cm2, superior to those of most previously reported IHMSCs. Furthermore, the IHMSCs exhibit a good cycling stability and mechanical flexibility. Our method is applicable to other capillary-functionalized flexible electronics and may open new avenues for large-scale industrial fabrication of flexible electronics. © 2020 Elsevier Ltd