Publications by Year: 2016

Uralcan, B. ; Aksay, I. A. ; Debenedetti, P. G. ; Limmer, D. T. Concentration Fluctuations and Capacitive Response in Dense Ionic Solutions. Journal of Physical Chemistry Letters 2016, 7 2333-2338.Abstract
We use molecular dynamics simulations in a constant potential ensemble to study the effects of solution composition on the electrochemical response of a double layer capacitor. We find that the capacitance first increases with ion concentration following its expected ideal solution behavior but decreases upon approaching a pure ionic liquid in agreement with recent experimental observations. The nonmonotonic behavior of the capacitance as a function of ion concentration results from the competition between the independent motion of solvated ions in the dilute regime and solvation fluctuations in the concentrated regime. Mirroring the capacitance, we find that the characteristic decay length of charge density correlations away from the electrode is also nonmonotonic. The correlation length first decreases with ion concentration as a result of better electrostatic screening but increases with ion concentration as a result of enhanced steric interactions. When charge fluctuations induced by correlated ion-solvent fluctuations are large relative to those induced by the pure ionic liquid, such capacitive behavior is expected to be generic.
Bozym, D. J. ; Korkut, S. ; Pope, M. A. ; Aksay, I. A. Dehydrated Sucrose Nanoparticles as Spacers for Graphene-Ionic Liquid Supercapacitor Electrodes. ACS Sustainable Chemistry & Engineering 2016, 4 7167-7174.Abstract
The addition of dehydrated sucrose nano particles increases the gravimetric capacitance of electrochemical double-layer capacitor electrodes produced via the evaporative consolidation of graphene oxide-water-ionic liquid gels by more than two-fold. Dehydrated sucrose adsorbs onto graphene oxide and serves as a spacer, preventing the graphene oxide from restacking during solvent evaporation. Despite 61 wt % of the solids being electrochemically inactive dehydrated sucrose nanoparticles, the best electrodes achieved an energy density of similar to 13.3 Wh/kg, accounting for the total mass of all electrode components.
Aksay, I. A. ; Korkut, S. ; Pope, M. ; Punckt, C. Graphene-Ionic Liquid Composites, 2016.Abstract
Method of making a graphene-ionic liquid composite. The composite can be used to make electrodes for energy storage devices, such as batteries and supercapacitors. Disclosed and claimed herein is method of making a graphene-ionic liquid composite, comprising combining a graphene source with at least one ionic liquid and heating the combination at a temperature of at least about 130 °C.
Roy-Mayhew, J. D. ; Pope, M. A. ; Punckt, C. ; Aksay, I. A. Intrinsic Catalytic Activity of Graphene Defects for the Co-II/III(bpy)(3) Dye-Sensitized Solar Cell Redox Mediator. ACS Applied Materials & Interfaces 2016, 8 9134-9141.Abstract
We demonstrate that functionalized graphene, rich with lattice defects but lean with oxygen sites, catalyzes the reduction of Co-III(bpy)(3) as well as platinum does, exhibiting a rate of heterogeneous electron transfer, k(0), of similar to 6 x 10(-3) cm/s. We show this rate to be an order of magnitude higher than on oxygen-site-rich graphene oxide, and over 2 orders of magnitude higher than on the basal plane of graphite (as a surrogate for pristine graphene). Furthermore, dye-sensitized solar. cells using defect-rich graphene monolayers perform similarly to those using platinum nanoparticles as the catalyst.
Liu, J. ; Aksay, I. A. ; Kou, R. ; Wang, D. H. Mesoporous Metal Oxide Graphene Nanocomposite Materials, 2016.Abstract
A nanocomposite material formed of graphene and a mesoporous metal oxide having a demonstrated specific capacity of more than 200 F/g with particular utility when employed in supercapacitor applications. A method for making these nanocomposite materials by first forming a mixture of graphene, a surfactant, and a metal oxide precursor, precipitating the metal oxide precursor with the surfactant from the mixture to form a mesoporous metal oxide. The mesoporous metal oxide is then deposited onto a surface of the graphene.
Pan, S. Y. ; Aksay, I. A. ; Prud'homme, R. K. Multifunctional Graphene-Silicone Elastomer Nanocomposite, Method of Making the Same, and Uses Thereof, 2016.Abstract
A nanocomposite composition having a silicone elastomer matrix having therein a filler loading of greater than 0.05 wt %, based on total nanocomposite weight, wherein the filler is functional graphene sheets (FGS) having a surface area of from 300 m2/g to 2630 m2/g; and a method for producing the nanocomposite and uses thereof.
Crain, J. M. ; Lettow, J. S. ; Aksay, I. A. ; Korkut, S. ; Chiang, K. S. ; Chen, C. H. ; Prud'homme, R. K. Printed Electronics, 2016.Abstract
Printed electronic device comprising a substrate onto at least one surface of which has been applied a layer of an electrically conductive ink comprising functionalized graphene sheets and at least one binder. A method of preparing printed electronic devices is further disclosed.
Aksay, I. A. ; Buyukdincer, B. ; Javeherian, N. ; Lettow, J. S. ; Pino, G. ; Redmond, K. ; Yildirim, I. Reinforced Polymeric Articles, 2016.Abstract
The present invention relates to polymeric articles reinforced with a reinforcing agent made from compositions comprising at least one polymer and graphene sheets.
Aksay, I. A. ; Buyukdincer, B. ; Javaherian, N. ; Lettow, J. S. ; Pino, G. ; Redmond, K. ; Yildirim, I. O. Reinforced Polymeric Articles, 2016.Abstract
Polymeric article reinforced with a reinforcing component. The reinforcing component includes a composition made from at least one polymer and graphene sheets.
Punckt, C. ; Pope, M. A. ; Liu, Y. F. M. ; Aksay, I. A. Structure-Dependent Electrochemistry of Reduced Graphene Oxide Monolayers. Journal of the Electrochemical Society 2016, 163, H491-H498.Abstract
While graphene and other carbonaceous nanomaterials have shown promise in a variety of electrochemical applications, measurement of their intrinsic performance is often confounded with effects related to the complexities due to diffusion in a porous medium. To by-pass this limitation, we use effectively non-porous tiled monolayers of reduced graphene oxide as a model platform to study how rates of heterogeneous electron transfer evolve as a function of graphene structure/chemistry. A variety of electrochemical systems are investigated including the standard ferri/ferrocyanide redox probe, several common biomolecular redox systems as well as copper electrodeposition. We show that the rates of heterogeneous electron transfer can vary by as much as 3 orders of magnitude depending on the reduction or annealing conditions used and the redox system investigated. Performance changes are linked to graphene chemistry, and we show that the graphene oxide reduction procedure must be chosen judiciously to maximize the electrochemical performance for particular applications. (C) 2016 The Electrochemical Society. All rights reserved.