A. Bhardwaj, J.J. Watkins
University of Massachusetts Amherst,
Keywords: porous graphene network, supercapacitors, large area processibility
Summary:Graphene materials are attractive for energy storage applications due to remarkably high surface areas, excellent electrical conductivities, and chemical and mechanical stabilities. Of particular interest is graphene on carbon fiber considering its applicability in numerous fields which requires high mechanical stability, light-weight, and high performance under extreme working conditions. The production of graphene typically requires relatively long processing times, extremely high temperatures within controlled atmospheres, and/or involves multi-step reactions that present challenges for high-throughput fabrication of energy storage devices, including supercapacitors. Moreover, supercapacitor devices fabricated using graphene suffer from low areal capacitance mainly due to the tortuous path of electrolyte in accessing the bulk of the material limiting the charge storage and transport throughout the thickness of the device. We have developed an efficient photothermal route to large-scale production of few-layer graphene within milliseconds from polymers using high intensity xenon flash lamp on carbon fiber at ambient conditions. The xenon flash lamp provides large-area illumination and a wide emission band (400 nm –1100 nm) that was used to convert the polymeric material directly into few-layer graphene upon millisecond exposures. Specifically, photothermally heating of polyaniline, a rod like polymer with a large absorption cross-section in the emission spectra of xenon flash lamp, led to the formation of macroporous network. Characterization performed depicted the formation of few layer graphene ( ID/IG ratio less than 0.3) with good adhesion to the carbon fiber support, enabling the formation of devices in-situ. The supercapacitor devices prepared with porous few-layer graphene network exhibited a superior areal capacitance of 200 mF/cm2 at 10 mV/s which is an order of magnitude higher than few layer graphene with a conventional film like structure. Also, the devices retained more than 70% of their capacitance, even at scan rates as high as 100 mV/s. Moreover, large area processability enabled by this photothermal approach allowed us to easily produce graphene-derived high-performance supercapacitor devices over areas greater than 100 cm2 within a few milliseconds at ambient conditions. Hence, this work provides an energy efficient and scalable route to produce high-quality few layer graphene devices with superior energy storage capabilities.