Increasing global energy demands and climate change concerns related to energy use require developing enduring and efficient energy technologies. Supercapacitors could significantly contribute to energy technology in this respect due to their long cycle life and rapid charge/discharge capabilities. However, supercapacitors suffer from poor energy density which severely limits their application. Because supercapacitors store energy capacitively at electrode surfaces, one obvious strategy to improve energy density is to use high surface area and high capacitance electrode materials. Graphene nanoribbons, long and narrow strips of graphene, are a promising supercapacitor electrode material due to i) good electrical conductivity, ii) high surface area as a two-dimensional material, and iii) abundant edges which have enhanced capacitance compared to the graphene basal plane. Current graphene nanoribbon fabrication procedures are either unscalable or incorporate polymer and/or metal contaminants, but we have developed a high yield bottom-up PECVD synthesis of high quality graphene nanoribbons. Deposition takes place at ca. 500 mTorr in a 0.5 inch (outer diameter) quartz tube on copper foil in a hydrogen/methane plasma with 1,2-dichlorobenzene precursor. Graphene nanoribbon growth begins as benzene radicals seed onto copper foil, and aromatic/methane carbon species propagate growth. Characterization confirms the synthesis of graphene nanoribbons. Raman spectroscopy measurements show G and 2D peaks corresponding to graphene structure and a strong D peak corresponding to graphene edge states. UPS measurements reveal a work function of 4.45 eV compared to 4.5 eV for pristine graphene. EDS and SAD measurements in a TEM confirm atomic purity and a hexagonal lattice consistent with graphene. Finally, SEM images demonstrate high aspect ratios with widths less than 500 nm and lengths greater than 5 μm. Although these graphene nanoribbons are too wide for many applications, this represents a starting point for developing a very large scale integrable synthesis of graphene nanoribbons as we are able to produce graphene nanoribbons at a rate of 0.05 mg/cm2/min. Graphene nanoribbons have been characterized for supercapacitor application and demonstrate excellent power and energy densities.

High yield bottom-up PECVD synthesis of graphene nanoribbons and their application in supercapacitors

255th National Meeting (2018)

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