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Aksay, Ilhan A., Sibel A. Korkut, Jeffery Kaczmarczyk, Sezen Gurdag, and Deniz Korkmaz. “Graphene Dispersions.” : n. pag. Print.
Method of making a composition comprising graphene sheets and at least one solvent, comprising dispersing a mixture of graphene sheets and graphite particles in a solvent, wherein the graphite particles have more than about 50 layers, separating the graphene sheets and the graphite particles to obtain a dispersion of graphene sheets that contains no more than 25% of graphite particles having more than about 50 layers, based on the total number of graphite particles and graphene sheets, and flocculating the dispersion of graphene sheets. The flocculated dispersion can be added to a polymer matrix to make a composite. The composite can be formed into articles.
Pope, Michael A., Valérie Alain-Rizzo, Daniel M. Dabbs, John S. Lettow, and Ilhan A. Aksay. “Batteries Incorporating Graphene Membranes for Extending the Cycle-Life of Lithium-Ion Batteries.” : n. pag. Print.
Embodiments of the present invention relate to energy storage devices and associated methods of manufacture. In one embodiment, an energy storage device comprises an electrolyte. An anode is at least partially exposed to the electrolyte. A selectively permeable membrane comprising a graphene-based material is positioned proximate to the anode. The selectively permeable membrane reduces a quantity of a component that is included in the electrolyte from contacting the anode and thereby reduces degradation of the anode.
Aksay, Ilhan A., and Kevin Sallah. “Conducting Elastomers.” : 15pp. Print.
The present invention relates to conducting elastomers and assocd. fabrication methods. In one embodiment, the conducting elastomer comprises a filler powder and a polymer. The filler powder includes carbon black and functionalized graphene sheets. The polymer has a mol. wt. of about 200 g/mol to about 5000 g/mol and is a liquid at room temperature.
Embodiments of the present invention relate to battery electrodes incorporating composites of graphene and selenium-sulfur compds. for improved rechargeable batteries. In one embodiment, a conductive compn. comprises a conductive compn. having a Se-S compd., a conductive additive. The Se-S compd. is present as SexS8-x, wherein x is greater than zero and less than eight.
Aksay, Ilhan A., Valerie Alain-Rizzo, Michael Bozlar, David J. Bozym, Daniel M. Dabbs, Nicholas Szamreta, and Cem B. Ustundag. “Electrohydrodynamically Formed Structures of Carbonaceous Material.” : 34pp. Print.
A method for the electrohydrodynamic deposition of carbonaceous materials utilizing an electrohydrodynamic cell comprising two electrodes comprised of a conductive material, by first combining a solid phase comprising a carbonaceous material and a suspension medium, placing the suspension between the electrodes, applying an electric field in a first direction, varying the intensity of the electric field sufficiently to drive lateral movement, increasing the electric field to stop the lateral transport and fix the layers in place, then removing the applied field and removing the electrodes. Among the many different possibilities contemplated, the method may advantageously utilize: varying the spacing between the electrodes; removing the buildup from one or both electrodes; placing the electrodes into different suspensions; adjusting the concentration, pH, or temperature of the suspension(s); and varying the direction, intensity or duration of the electric fields.

2018

Aksay, Ilhan A., Sibel Korkut, Michael Pope, and Christian Punckt. “Graphene-Ionic Liquid Composites.” 2018: n. pag. Print.
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.
A thermal overload device containing a polymer composite, which contains at least one polymer and a modified graphite oxide material, containing thermally exfoliated graphite oxide having a surface area of from about 300 m2/g to 2600 m2/g, and a method of making the same.
Aksay, Ilhan A., David L. Milius, Sibel Korkut, and Robert K. Prud’homme. “Functionalized Graphene Sheets Having High Carbon to Oxygen Ratios.” 2018: n. pag. Print.
Functionalized graphene sheets having a carbon to oxygen molar ratio of at least about 23:1 and method of preparing the same.
Aksay, Ilhan A., Bora Buyukdincer, Nurcin Javaherian, John S. Lettow, Gustavo Pino, Kate Redmond, and Ibrahim O. Yildirim. “Reinforced Polymeric Articles.” 2018: n. pag. Print.
Polymeric article reinforced with a reinforcing component. The reinforcing component includes a composition made from at least one polymer and graphene sheets.
Crain, John M., John S. Lettow, Ilhan A. Aksay, Sibel Korkut, Katherine S. Chiang, Chuan-Hua Chen, and Robert K. Prud’homme. “Printed Electronics.” 2018: n. pag. Print.
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.
Pan, Shuyang, Ilhan A. Aksay, and Robert K. Prud’homme. “Multifunctional Graphene-Silicone Elastomer Nanocomposite, Method of Making the Same, and Uses Thereof.” 2018: n. pag. Print.
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.

2017

A conductive circuit containing a polymer composite, which contains at least one polymer and a modified graphite oxide material, containing thermally exfoliated graphite oxide having a surface area of from about 300 m2/g to 2600 m2/g, and a method of making the same.
Aksay, I.A., D. L. Milius, S. Korkut, and R. K. Prud’homme. “Functionalized Graphene Sheets Having High Carbon to Oxygen Ratios.” 2017: n. pag. Print.
The present invention relates to functionalized graphene sheets having low oxygen content and methods for their prepartion.
Alifierakis, M., K. S. Sallah, I.A. Aksay, and J. H. Prevost. “Reversible Cluster Aggregation and Growth Model for Graphene Suspensions.” AIChE Journal 63 (2017): 5462–5473. Print.
We present a reversible cluster aggregation model for 2-D macromolecules represented by line segments in 2-D; and, we use it to describe the aggregation process of functionalized graphene particles in an aqueous SDS surfactant solution. The model produces clusters with similar sizes and structures as a function of SDS concentration in agreement with experiments and predicts the existence of a critical surfactant concentration (C-crit) beyond which thermodynamically stable graphene suspensions form. Around C-crit, particles form dense clusters rapidly and sediment. At C << C-crit, a contiguous ramified network of graphene gel forms which also densifies, but at a slower rate, and sediments with time. The deaggregation-reaggregation mechanism of our model captures the restructuring of the large aggregates towards a graphite-like structure for the low SDS concentrations. (C) 2017 American Institute of Chemical Engineers

2016

Roy-Mayhew, J. D., M. A. Pope, C. Punckt, and I.A. Aksay. “Intrinsic Catalytic Activity of Graphene Defects for the Co-II III(bpy)(3) Dye-Sensitized Solar Cell Redox Mediator.” ACS Applied Materials & Interfaces 8 (2016): 9134–9141. Print.
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.
Punckt, C., M. A. Pope, Y. F. M. Liu, and I.A. Aksay. “Structure-Dependent Electrochemistry of Reduced Graphene Oxide Monolayers.” Journal of the Electrochemical Society 163 (2016): H491-H498. Print.
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.
Aksay, I.A., B. Buyukdincer, N. Javaherian, J.S. Lettow, G. Pino, K. Redmond, and I.O. Yildirim. “Reinforced Polymeric Articles.” 2016: n. pag. Print.
Polymeric article reinforced with a reinforcing component. The reinforcing component includes a composition made from at least one polymer and graphene sheets.
Liu, J., I.A. Aksay, R. Kou, and D. H. Wang. “Mesoporous Metal Oxide Graphene Nanocomposite Materials.” 2016: n. pag. Print.
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., I.A. Aksay, and R. K. Prud’homme. “Multifunctional Graphene-Silicone Elastomer Nanocomposite, Method of Making the Same, and Uses Thereof.” 2016: n. pag. Print.
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.
Aksay, I.A., S. Korkut, M. Pope, and C. Punckt. “Graphene-Ionic Liquid Composites.” 2016: n. pag. Print.
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.
Crain, J.M., J.S. Lettow, I.A. Aksay, S. Korkut, K.S. Chiang, C.H. Chen, and R. K. Prud’homme. “Printed Electronics.” 2016: n. pag. Print.
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., B. Buyukdincer, N. Javeherian, J.S. Lettow, G. Pino, K. Redmond, and I. Yildirim. “Reinforced Polymeric Articles.” 2016: n. pag. Print.
The present invention relates to polymeric articles reinforced with a reinforcing agent made from compositions comprising at least one polymer and graphene sheets.
Uralcan, B., I.A. Aksay, P.G. Debenedetti, and D. T. Limmer. “Concentration Fluctuations and Capacitive Response in Dense Ionic Solutions.” Journal of Physical Chemistry Letters 7 (2016): 2333–2338. Print.
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., S. Korkut, M. A. Pope, and I.A. Aksay. “Dehydrated Sucrose Nanoparticles As Spacers for Graphene-Ionic Liquid Supercapacitor Electrodes.” ACS Sustainable Chemistry & Engineering 4 (2016): 7167–7174. Print.
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.

2015

Crain, J.M., J.S. Lettow, I.A. Aksay, S. Korkut, K.S. Chiang, C.H. Chen, and R. K. Prud’homme. “Printed Electronics.” 2015: n. pag. Print.
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., B. Buyukdincer, N. Javaherian, J.S. Lettow, G. Pino, K. Redmond, and I. Yildirim. “Reinforced Polymeric Materials.” 2015: n. pag. Print.
Polymeric article reinforced with a reinforcing component. The reinforcing component includes a composition made from at least one polymer and graphene sheets.
Liu, J., I.A. Aksay, D. W. Choi, D. H. Wang, and Z. G. Yang. “Nanocomposite of Graphene and Metal Oxide Materials.” 2015: n. pag. Print.
Nanocomposite materials comprising a metal oxide bonded to at least one graphene material. The nanocomposite materials exhibit a specific capacity of at least twice that of the metal oxide material without the graphene at a charge/discharge rate greater than about 10 C.
Crain, J.M., J.S. Lettow, I.A. Aksay, R. K. Prud’homme, and S. Korkut. “Coatings Containing Functionalized Graphene Sheets and Articles Coated Therewith.” 2015: n. pag. Print.
Coatings are provided containing functionalized graphene sheets and at least one binder. In one embodiment, the coatings are electrically conductive.
Liu, J., I.A. Aksay, D. W. Choi, R. Kou, Z. M. Nie, D. H. Wang, and Z. G. Yang. “Self-Assembled Multi-Layer Nanocomposite of Graphene and Metal Oxide Materials.” 2015: n. pag. Print.
Nanocomposite materials having at least two layers, each layer consisting of one metal oxide bonded to at least one graphene layer were developed. The nanocomposite materials will typically have many alternating layers of metal oxides and graphene layers, bonded in a sandwich type construction and will be incorporated into an electrochemical or energy storage device.
Lee, Y.J., L. Huang, H. Wang, M.L. Sushko, B. Schwenzer, I.A. Aksay, and J. Liu. “Structural Rearrangement and Dispersion of Functionalized Graphene Sheets in Aqueous Solutions.” Colloids Interf. Sci. Comm. 8 (2015): 1–5.

Surfactants are widely used for dispersing graphene and functionalized graphene sheets (FGS) in colloidal suspensions, but there have been few studies of the structure of the dispersed graphene–surfactant complexes in suspension and of their time evolution. Here, we combine experimental study of efficiencies of ionic surfactants/polymers in suspending FGS in water with characterization using atomic force microscopy, small angle neutron scattering, and molecular simulations to probe the detailed structures of FGSs. The small angle scattering technique provides quantitative measurement of structure of graphene sheets in the solution. This study suggests that in both ionic and nonionic surfactants, the dispersion tends to degrade over time through detachment of the surfactant molecules and structural rearrangements. Ionic surfactants with strong interfacial binding and large molecular weight increase the dispersing power by over an order of magnitude.

Zhang, C., D. M. Dabbs, L.-M. Liu, I.A. Aksay, R. Car, and A. Selloni. “Combined Effects of Functional Groups, Lattice Defects, and Edges in the Infrared Spectra of Graphene Oxide.” J. Phys. Chem. C 119 (2015): 18167–18176. Print.

Infrared spectroscopy in combination with density functional theory calculations has been widely used to characterize the structure of graphene oxide and its reduced forms. Yet, the synergistic effects of different functional groups, lattice defects, and edges on the vibrational spectra are not well understood. Here, we report first-principles calculations of the infrared spectra of graphene oxide performed on realistic, thermally equilibrated, structural models that incorporate lattice vacancies and edges along with various oxygen-containing functional groups. Models including adsorbed water are examined as well. Our results show that lattice vacancies lead to important blue and red shifts in the OH stretching and bending bands, respectively, whereas the presence of adsorbed water leaves these shifts largely unaffected. We also find unique infrared features for edge carboxyls resulting from interactions with both nearby functional groups and the graphene lattice. Comparison of the computed vibrational properties to our experiments clarifies the origin of several observed features and provides evidence that defects and edges are essential for characterizing and interpreting the infrared spectrum of graphene oxide.

Pope, M. A., and I.A. Aksay. “Four-Fold Increase in the Intrinsic Capacitance of Graphene through Functionalization and Lattice Disorder.” J. Phys. Chem. C 119 (2015): 20369–20378. Print.

Graphene has been heralded as a promising electrode material for high energy and power density electrochemical supercapacitors. This is in spite of recent work confirming the low double-layer capacitance (CDL) of the graphene/electrolyte interface limited by graphene’s low quantum capacitance (CQ), an effect known for the basal plane of graphite for over four decades. Consistent with this limit, much of the supercapacitor research implies the use of pristine graphene but, in contrast, uses a functionalized and defective graphene formed through the reduction of graphene oxide, without clarifying why reduced graphene oxide is needed to achieve high capacitance. Herein, we show that an optimal level of functionalization and lattice disorder in reduced graphene oxide yields a 4-fold increase in CDL over that of pristine graphene, suggesting graphene-based materials can indeed be tailored to engineer electrodes with significantly higher gravimetric capacitance limits exceeding 450 F/g than what has been achieved (∼ 274 F/g) thus far, even in nonaqueous electrolytes capable of high voltage operation.

Pope, M. A., and I.A. Aksay. “Structural Design of Cathodes for Li-S Batteries.” Adv. Energy Mater. 5.16 (2015): 1500124. Print.

Battery technologies involving Li-S chemistries have been touted as one of the most promising next generation systems. The theoretical capacity of sulfur is nearly an order of magnitude higher than current Li-ion battery insertion cathodes and when coupled with a Li metal anode, Li-S batteries promise specific energies nearly five-fold higher. However, this assertion only holds if sulfur cathodes could be designed in the same manner as cathodes for Li-ion batteries. Here, the recent efforts to engineer high capacity, thick, sulfur-based cathodes are explored. Various works are compared in terms of capacity, areal mass loading, and fraction of conductive additive, which are the critical parameters dictating the potential for a device to achieve a specific energy higher than current Li-ion batteries (i.e., >200 Wh kg−1 ). While an inferior specific energy is projected in the majority of cases, several promising strategies have the potential to achieve >500 Wh kg−1 . The challenges associated with the limited cycle-life of these systems due to both the polysulfide shuttle phenomenon and the rapid degradation of the Li metal anode that is experienced at the current densities required to charge high specific energy batteries in a reasonable timeframe are also discussed.

Bozym, D. J., B. Uralcan, D. T. Limmer, M. A. Pope, N.J. Szamreta, P.G. Debenedetti, and I.A. Aksay. “Anomalous Capacitance Maximum of the Glassy Carbon-Ionic Liquid Interface through Dilution With Organic Solvents.” J. Phys. Chem. Lett. 6 (2015): 2644–2648. Print.

We use electrochemical impedance spectroscopy to measure the effect of diluting a hydrophobic room temperature ionic liquid with miscible organic solvents on the differential capacitance of the glassy carbon − electrolyte interface. We show that the minimum differential capacitance increases with dilution and reaches a maximum value at ionic liquid contents near 5 − 10 mol% (i.e., ∼ 1 M). We provide evidence that mixtures with 1,2-dichloroethane, a low- dielectric constant solvent, yield the largest gains in capacitance near the open circuit potential when compared against two traditional solvents, acetonitrile and propylene carbonate. To provide a fundamental basis for these observations, we use a coarse-grained model to relate structural variations at the double layer to the occurrence of the maximum. Our results reveal the potential for the enhancement of double-layer capacitance through dilution.

Li, Y., V. Alain-Rizzo, L. Galmiche, P. Audebert, F. Miomandre, G. Louarn, M. Bozlar, M. A. Pope, D. M. Dabbs, and I.A. Aksay. “Functionalization of Graphene Oxide by Tetrazine Derivatives: A Versatile Approach Toward Covalent Bridges Between Graphene Sheets.” Chem. Mater. 27 (2015): 4298–4310. Print.

We have covalently grafted tetrazine derivatives to graphene oxide through nucleophilic substitution. Since the tetrazine unit is electroactive and nitrogen-rich, with a reduction potential sensitive to the type of substituent and degree of substitution, we used electrochemistry and X-ray photoelectron spectroscopy to demonstrate clear evidence for grafting through covalent bonding. Chemical modification was supported by Fourier transform infrared spectroscopy and thermal analysis. Tetrazines grafted onto graphene oxide displayed different mass losses compared to unmodified graphene and were more stable than the molecular precursors. Finally, a bridging tetrazine derivative was grafted between sheets of graphene oxide to demonstrate that the separation distance between sheets can be maintained while designing new graphene-based materials, including chemically bound, redox structures.

Hsieh, A. G., C. Punckt, and I.A. Aksay. “High-Rate Li+ Storage Capacity of Surfactant-Templated Graphene-TiO2 Nanocomposites.” J. Electrochem. Soc. 162.8 (2015): A1566-A1573. Print.
Graphene-TiO2 nanocomposites are a promising anode material for Li-ion batteries due to their good high-rate capacity, inherent safety, and mechanical and chemical robustness. However, despite a large number of scientific reports on the material, the mechanism of the enhanced high-rate Li+ storage capacity that results from the addition of graphene to TiO2 – typically attributed to improved electrical conductivity – is still not well understood. In this work, we focus on optimizing the processing of surfactant-templated graphene-TiO2 hybrid nanocomposites. Towards this end, we examine the influence of various processing parameters, in particular the surfactant-mediated colloidal dispersion of graphene, on the material properties and electrochemical performance of graphene-TiO2. We investigate the influence of electrode mass loading on Li+ storage capacity, focusing mainly on high-rate performance. Furthermore, we demonstrate an approach for estimating power loss during charge/discharge cycling, which offers a succinct method for characterizing the high-rate performance of Li-ion battery electrodes.

2014

Crain, John M., John S. Lettow, Ilhan A. Aksay, Sibel A. Korkut, Katherine S. Chiang, Chuan-Hua Chen, and Robert K. Prud’homme. “Printed Electronics.” 2014: n. pag. Print.
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.
A conductive circuit containing a polymer composite, which contains at least one polymer and a modified graphite oxide material, containing thermally exfoliated graphite oxide having a surface area of from about 300 m2/g to 2600 m2/g, and a method of making the same.
Aksay, Ilhan A., Dudley A. Saville, Hak Fei Poon, Sibel Korkut, and Chuan-Hua Chen. “Electrohydrodynamic Printing and Manufacturing.” 2014: n. pag. Print.
An stable electrohydrodynamic filament is obtained by causing a straight electrohydrodynamic filament formed from a liquid to emerge from a Taylor cone, the filament having a diameter of from 10 nm to 100 µm. Such filaments are useful in electrohydrodynamic printing and manufacturing techniques and their application in liquid drop/particle and fiber production, colloidal deployment and assembly, and composite materials processing.
Roy-Mayhew, J. D., and I.A. Aksay. “Graphene Materials and Their Use in Dye-Sensitized Solar Cells.” Chemical Reviews 114 (2014): 6323–6348. Print.
Punckt, C., M. A. Pope, and I.A. Aksay. “High Selectivity of Porous Graphene Electrodes Solely Due to Transport and Pore Depletion Effects.” Journal of Physical Chemistry C 118 (2014): 22635–22642. Print.
We contrast the performance of monolayer electrodes and thin porous film electrodes of highly reduced functionalized graphene to demonstrate that the introduction of electrode porosity gives rise to strong apparent electrocatalytic effects resulting in vastly improved electrode selectivity. This is despite graphene showing no intrinsic advantage over glassy carbon electrodes when used as a monolayer. The simultaneous electrooxidation of ascorbic acid, dopamine and uric acid is used as an experimental model electrolyte system. Our results suggest that a large number of reports claiming the superior surface chemistry of carbon nanomaterials as the reason for outstanding electrochemical characteristics should be revisited considering electrode morphology as a significant contributor to the observed behavior. Our experimental results are supported by numerical simulations explaining the porosity-induced electrode selectivity by the dominance of pore depletion over diffusion-limited currents.
Xiao, J., P. Meduri, H.H. Chen, Z.G. Wang, F. Gao, J.Z. Hu, Feng, M. Hu, S. Dai, S. Brown, J.L. Adcock, Z.Q. Deng, Liu, G.L. Graff, I.A. Aksay, and J.G. Zhang. “Energetics of Defects on Graphene through Fluorination.” ChemSusChem 7.5 (2014): 1295–1300. Print.

Functionalized graphene sheets (FGSs) comprise a unique member of the carbon family, demonstrating excellent electrical conductivity and mechanical strength. However, the detailed chemical composition of this material is still unclear. Herein, we take advantage of the fluorination process to semiquantitatively probe the defects and functional groups on graphene surface. Functionalized graphene sheets are used as substrate for low-temperature (<150 °C) direct fluorination. The fluorine content has been modified to investigate the formation mechanism of different functional groups such as CF, CF2, OCF2 and (C=O)F during fluorination. The detailed structure and chemical bonds are simulated by density functional theory (DFT) and quantified experimentally by nuclear magnetic resonance (NMR). The electrochemical properties of fluorinated graphene are also discussed extending the use of graphene from fundamental research to practical applications.

Tavakol, B., M. Bozlar, C. Punckt, G. Froehlicher, H. A. Stone, I.A. Aksay, and D. P. Holmes. “Buckling of Dielectric Elastomeric Plates for Soft, Electrically Active Microfluidic Pumps.” Soft Matter 10 (2014): 4789–4794. Print.
Elastic instabilities, when properly implemented within soft, mechanical structures, can generate advanced functionality. In this work, we use the voltage-induced buckling of thin, flexible plates to pump fluids within a microfluidic channel. The soft electrodes that enable electrical actuation are compatible with fluids, and undergo large, reversible deformations. We quantified the onset of voltage-induced buckling, and measured the flow rate within the microchannel. This embeddable, flexible microfluidic pump will aid in the generation of new stand-alone microfluidic devices that require a tunable flow rate.
Vijayakumar, M., B. Schwenzer, V. Shutthanandan, J.Z. Hu, J. Liu, and I.A. Aksay. “Elucidating Graphene-Ionic Liquid Interfacial Region: A Combined Experimental and Computational Study.” Nano Energy 3 (2014): 152–158. Print.
Graphene and ionic liquids are promising candidates for electrode materials and electrolytes, respectively, for modern energy storage devices such as supercapacitors. Understanding the interactions at the interfacial region between these materials is crucial for optimizing the overall performance and efficiency of supercapacitors. The interfacial region between graphene and an imidazolium-based ionic liquid is analyzed in a combined experimental and computational study. This dual approach reveals that the imidazolium-based cations mostly orient themselves parallel to the graphene surface due to pi-pi stacking interaction and form a primary interfacial layer, which is subsequently capped by a layer of anions from the ionic liquid. However, it also becomes apparent that the molecular interplay at the interfacial region is highly influenced by functional group defects on the graphene surface, in particular by hydroxyl groups. (C) 2012 Elsevier Ltd. All rights reserved.

2013

Aksay, Ilhan A., Bora Buyukdincer, Nurcin Javaherian, John S. Lettow, Gustavo Pino, Kate Redmond, and Ibrahim O. Yildirim. “Reinforced Polymeric Articles.” 2013: n. pag. Print.
Polymeric article reinforced with a reinforcing component. The reinforcing component includes a composition made from at least one polymer and graphene sheets.
Liu, Jun, Ilhan A. Aksay, Daiwon Choi, Donghai Wang, and Zhengou Yang. “Nanocomposite of Graphene and Metal Oxide Materials.” 2013: n. pag. Print.
Nanocomposite materials comprising a metal oxide bonded to at least one graphene material. The nanocomposite materials exhibit a specific capacity of at least twice that of the metal oxide material without the graphene at a charge/discharge rate greater than about 10 C.
Liu, Jun, Ilhan A. Aksay, Daiwon Choi, Rong Kou, Zimin Nie, Donghai Wang, and Zhenguo Yang. “Self Assembled Multi-Layer Nanocomposite of Graphene and Metal Oxide Materials.” 2013: n. pag. Print.
Nanocomposite materials having at least two layers, each layer consisting of one metal oxide bonded to at least one graphene layer were developed. The nanocomposite materials will typically have many alternating layers of metal oxides and graphene layers, bonded in a sandwich type construction and will be incorporated into an electrochemical or energy storage device.
Hsieh, A. G., C. Punckt, S. Korkut, and I.A. Aksay. “Adsorption of Sodium Dodecyl Sulfate on Functionalized Graphene Measured by Conductometric Titration.” Journal of Physical Chemistry B 117 (2013): 7950–7958. Print.
We report on the adsorption of sodium dodecyl sulfate (SDS) onto functionalized graphene sheets (FGSs) in an aqueous system, measured at broad SDS and FGS concentration ranges by conductometric surfactant titration. At dilute SDS concentrations (<12 mu M in bulk solution), there is evidence of a counterion exchange between hydronium ions (from the dissociation of acidic chemical functionalities on FGS) and sodium ions coadsorbing with dodecyl sulfate monomers onto FGSs. We find that, for FGS with a carbon-to-oxygen ratio of similar to 18, monolayer adsorption of SDS on FGS reaches full surface coverage by similar to 12 mu M SDS. Additionally, the critical surface aggregation concentration (csac) for surface micelle formation on FGS is measured to be similar to 1.5 mM SDS The transition from monolayer adsorption to surface micelle formation appears to occur at a similar SDS concentration on FGSs as on graphite, suggesting there is little difference in the surfactant adsorption behavior on both materials. We estimate that the FGS surface area available for SDS adsorption is similar to 600 m(2)/g which is significantly less than expected for FGSs in suspension and indicates the presence of regions on FGS on which SDS adsorption does not occur.
Jan, L., C. Punckt, and I.A. Aksay. “Cementation of Colloidal Particles on Electrodes in a Galvanic Microreactor.” ACS Applied Materials & Interfaces 5 (2013): 6346–6353. Print.
We have studied the processes leading to the cementation of colloidal particles during their autonomous assembly on corroding copper electrodes within a Cu-Au galvanic rnicroreactor. We determined the onset of particle immobilization through particle tracking, monitored the dissolution of copper as well as the deposition of insoluble products of the corrosion reactions in situ, and showed that particle immobilization initiated after reaction products (RPs) began to deposit on the electrode substrate. We further demonstrated that the time and the extent of RP precipitation and thus the strength of the particle-substrate bond could be tuned by varying the amount of copper in the system and the microreactor pH. The ability to cement colloidal particles at locations undergoing corrosion illustrates that the studied colloidal assembly approach holds potential for applications in dynamic material property adaptation.
Jan, L., C. Punckt, B. Khusid, and I.A. Aksay. “Directed Motion of Colloidal Particles in a Galvanic Microreactor.” Langmuir 29 (2013): 2498–2505. Print.
The mechanisms leading to the deposition of colloidal particles in a copper-gold galvanic microreactor are investigated. Using in situ current density measurements and particle velocimetry, we establish correlations between the spatial arrangement and the geometry of the electrodes, current density distribution, and particle aggregation behavior. Ionic transport phenomena are responsible for the occurrence of strongly localized high current density at the edges and corners of the copper electrodes at large electrode separation, leading to a preferential aggregation of colloidal particles at the electrode edges. Preferential aggregation appears to be the result of a combination of electrophoretic effects and changes in bulk electrolyte flow patterns. We demonstrate that electrolyte flow is most likely driven by electrochemical potential gradients of reaction products formed during the inhomogeneous copper dissolution.