Rapid Fabrication of Graphene Derived Micro-Supercapacitors on Flexible Substrates Using Millisecond Photothermal Flash Lamp Carbonization

Abstract

Graphene offers excellent electrical conductivity and very high surface area, which holds great promise for energy storage applications including supercapacitors. Current preparation methods for graphene require relatively long processing times, extremely high temperatures within controlled atmospheres, and/or involve multi-step reactions that present challenges for high throughput fabrication of graphene-based devices. We report a novel photothermal route to large-scale production of graphene within milliseconds using a commercially available benzoxazine polymer and a high intensity xenon flash lamp on various substrates including carbon fiber, Kapton and stainless steel at ambient conditions. The xenon flash lamp provides large-area illumination and a wide emission band (300 nm –1100 nm) that was used to convert the polymeric material directly into graphene upon millisecond exposures. The absorption spectrum of the precursor overlaps well with the maxima of the xenon flash lamp emission spectrum. The precursor material is heated to extremely high temperatures in a fraction of a second – a duration that is much shorter than the timescale for thermal equilibrium. This enables the conversion of the polymeric material to graphene in air and at room temperature, and without thermally damaging the substrate. Characterization of these graphene composites revealed high porosity, excellent conductivity, and good adhesion. Using carbon fiber as the substrate, we prepared micro-supercapacitors exhibiting a very high areal capacitance of 3.2 mF/cm². Furthermore, we utilized the mechanically and chemically stable graphene/carbon fiber composite as a substrate for the electrochemical deposition of MnO₂ which boosted the energy storage capability of the device. The obtained pseudocapacitor has an exceptional capacitance of 300 mF/cm² at 1mA/cm². The device retained more than 88% of its capacitance after charging/discharging for 2000 cycles. The preparation of high-quality graphene via photothermal pyrolysis of appropriate precursors is amenable to roll-to-roll processing, and thus large-scale production of electrochemical energy storage devices can be enabled by this approach.