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Hybrid nanocomposites comprised of metal oxide nanoparticles and three-dimensional (3D) graphene possess the advantages of metal oxide and graphene, which have generated extensive attention. Here, we fabricate flexible micro-supercapacitors (MSCs) based on hybrid materials of single-walled carbon nanotubes (SWCNT)-bridged laser-induced graphene fibers (LIGF) decorated with manganese dioxide (MnO2) nanoparticles. SWCNT is deposited on the LIGF surface and the space between LIGF, which can bridge LIGF to form more conductive paths and provide more active areas to grow with MnO2 nanoparticles. Profiting from the synergistic effect between conductive SWCNT-bridged LIGF network and the MnO2 nanoparticles with high theoretical capacitance, the obtained flexible MSCs based on LIGF-C4/MnO2 hybrid electrodes deliver an outstanding areal capacitance of 156.94 mF cm−2, which is about 8 times higher than that of LIGF-MnO2 based MSC (20 mF cm−2). Additionally, the LIGF-C4/MnO2 MSCs also exhibit considerable areal energy density of 21.8 μWh cm−2, long-term cycling stability, remarkable modular integration capability, and exceptional mechanical flexibility (with 90.5% capacitance retention after 1200 bending cycles). Therefore, the design of hybrid electrode materials proposed in this work offers a facile and novel method to develop flexible energy storage devices with high performance, suggesting great prospects for applications in future various wearable electronics.

Heteroatoms modification of carbon electrodes is an effective strategy to boost its electrochemical performance. In this work, we demonstrate a one-step and scalable method to manufacture phosphorus-doped (P-doped) 3D porous graphene electrodes from a flexible H3PO4-incorporated polyimide (PI)/Polyvinyl alcohol (PVA) composite film via laser direct writing. Benefiting from the synchronous P-doping and activation caused by H3PO4, the optimal P-doped porous graphene-based micro-supercapacitors (MSCs) present an impressive areal capacitance of 55.5 mF cm−2, good long-term cyclability (with ∼85% capacitance retention after 10000 cycles), superior mechanism flexibility, and outstanding capability of modular integration in series and parallel. Furthermore, density functional theory (DFT) calculations were also carried out to prove that P-doping could enhance the affinity towards electrolyte ions on the carbon surface to improve the electrochemical performance. In particular, due to the highly hydrophilic nature and good film-forming properties of PVA, other dopants can be also well dissolved in the PI/PVA slurry to synthesize a dopants-incorporated PI/PVA composite membrane. Hence, this method offers a convenient and potential route to prepare free-standing heteroatom-doped porous graphene electrodes, which has promising applications for various flexible/wearable electronics.

This study proposes an efficient, facile, and scalable strategy to synthesize in situ heteroatom-doped porous graphene via laser direct writing on the precursor-doped polyimide (PI) film, which is fabricated for the first time through incorporating PI powder and precursors with sodium carboxymethyl cellulose (CMC) binder by a drop-casting and low-temperature drying process. The resulting microsupercapacitors (MSCs) based on the as-prepared heteroatom-doped porous graphene exhibit remarkable capacitive performance. The typical boron-doped MSC prepared on borax-doped polyimide film possesses an ultrahigh areal capacitance of 60.6 mF cm-2 at 0.08 mA cm-2, which is approximately 20 times larger than that of undoped MSC. Furthermore, the boron-doped MSC has impressive cycling stability (with the capacitance retention of 96.3% after 20 000 cycles), exceptional mechanical flexibility, tunable capacitance, and voltage output through arbitrary modular serial and parallel integration. Besides, the nitrogen-doped porous graphene with excellent capacitive performance is also prepared by laser direct scribing on the sulfonated melamine-doped polyimide film, demonstrating excellent scalability and generality of this strategy. Hence, one-step laser direct writing on precursor-doped polyimide films can realize in situ heteroatom doping and generation of hierarchical porous graphene electrodes simultaneously, which opens a new avenue for the facile, cost-effective, and scalable fabrication of heteroatom-doped porous graphene, thus promising for MSCs and various flexible and wearable electronics at large-scale production.

In this work we consider bubbles that can form spontaneously when a two-dimensional (2D) crystal is transferred to a substrate with gases or liquids trapped at the crystal-substrate interface. The underlying mechanics may be described by a thin sheet on an adhesive substrate with the trapped fluid applying uniform transverse pressure. What makes this apparently simple problem complex is the rich interplay among geometry, interface, elasticity and instability. Particularly, extensive small-scale experiments have shown that the 2D crystal surrounding a bubble can adhere to and, meanwhile, slide on the substrate. The radially inward sliding causes hoop compression to the 2D crystal which may exploit wrinkling instabilities to relax or partially relax the compression. We present a theoretical model to understand the complex behaviors of even a linearly elastic 2D crystal due to the combination of nonlinear geometry, adhesion, sliding, and wrinkling in bubble systems. We show that this understanding not only successfully predicts the geometry of a spontaneous bubble but also reveals the strain-coupled physics of 2D crystals, e.g., the pseudomagnetic fields in graphene bubbles.