GUITAR (Graphene from the University of Idaho Thermolyzed Asphalt Reaction) is a newly discovered allotrope of carbon. It has a layered structure similar to graphites but differs in basal plane geometry. Atomic forces microscopy (AFM) reveals a basal plane with semi-random 10-50 nm pits that are 20 nm in amplitude which are not observed with graphites and graphenes (G/G). On the other hand, step defects and grain edges observed with AFM on G/G are missing on GUITAR. Raman spectroscopy indicates a disordered sp2 carbon structure with 5 nm grain size. GUITAR has favorable characteristics for improvement of aqueous ultracapacitors (UC). Power densities of UC’s are superior to batteries and fuel cells. However UC energy density is modest (up to 10 Wh/kg) relative to redox based energy storage systems (up to 1000 Wh/kg). Two considerations are relevant in improving UC energy density (E = ½CV2), capacitance (C) and cell voltage (V). Disorder within the basal plane of GUITAR increases the density of electronic states which increases capacitance from 10 mF/cm2 observed with G/G to 70 mF/cm2 in 1 M H2SO4 as measure by cyclic voltammetry at 50 mV/s. This capacitance is boosted to 10 mF/cm2 by oxidative treatments through either chemical or electrochemical methods. Increase in capacitance with anodized GUITAR is 3 orders of magnitude greater over G/G materials. The basal plane morphology of GUITAR works in its favor in increasing the aqueous cell voltage of UC’s. On the basal planes of G/G, step defects and grain boundaries are active sites for hydrogen and oxygen gassing and corrosion. As GUITAR lacks these features the electrochemical cell voltage is extended from 1.1 volts to 1.6 volts. Taken together increases in C and V with GUITAR, performance is approximately 2000 mJ/cm2 vs. 5 mJ/cm2 for commercial activated carbon UC systems. The Thermolyzed Asphalt Reaction is capable for producing high surface area nanostructures. We will report on a GUITAR/silica nanospring composite of 100 m2/g. The energy density performance of this device is expected to approach or be equal to batteries and/or fuel cells.

GUITAR: A new carbon allotrope and application in ultracapacitors

251st National Meeting (2016)

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