379 results found
Niu L, Wu T, Chen M, et al., 2022, Conductive Metal-Organic Frameworks for Supercapacitors., Adv Mater
As a class of porous materials with crystal lattices, metal-organic frameworks (MOFs), featuring an outstanding specific surface area, tunable functionality, and versatile structures, have attracted huge attention in the past two decades. Since the first conductive MOF was successfully synthesized in 2009, considerable progress has been achieved for the development of conductive MOFs, allowing their use in diverse applications for electrochemical energy storage. Among those applications, supercapacitors have received great interest because of their high power density, fast charging ability, and excellent cycling stability. In this review, we summarize the efforts hitherto devoted to the synthesis and design of conductive MOFs and their auspicious capacitive performance. Using conductive MOF as a unique platform medium, we discuss the electronic and molecular aspects of the energy storage mechanism in supercapacitors with MOF electrodes, highlighting the advantages and limitations to inspire new ideas for the development of conductive MOFs for supercapacitors. This article is protected by copyright. All rights reserved.
de Souza JP, Pivnic K, Bazant MZ, et al., 2022, Structural Forces in Ionic Liquids: The Role of Ionic Size Asymmetry, JOURNAL OF PHYSICAL CHEMISTRY B, Vol: 126, Pages: 1242-1253, ISSN: 1520-6106
Haimov E, Chapman A, Bresme F, et al., 2021, Theoretical demonstration of a capacitive rotor for generation of alternating current from mechanical motion, Nature Communications, Vol: 12, Pages: 3678-3678, ISSN: 2041-1723
Innovative concepts and materials are enabling energy harvesters for slower motion, particularly for personal wearables or portable small-scale applications, hence contributing to a future sustainable economy. Here we propose a principle for a capacitive rotor device and analyze its operation. This device is based on a rotor containing many capacitors in parallel. The rotation of the rotor causes periodic capacitance changes and, when connected to a reservoir-of-charge capacitor, induces alternating current. The properties of this device depend on the lubricating liquid situated between the capacitor’s electrodes, be it a highly polar liquid, organic electrolyte, or ionic liquid – we consider all these scenarios. An advantage of the capacitive rotor is its scalability. Such a lightweight device, weighing tens of grams, can be implemented in a shoe sole, generating a significant power output of the order of Watts. Scaled up, such systems can be used in portable wind or water turbines.
McEldrew M, Goodwin ZAH, Bi S, et al., 2021, Ion clusters and networks in water-in-salt electrolytes, Journal of The Electrochemical Society, Vol: 168, Pages: 1-12, ISSN: 0013-4651
Water-in-salt electrolytes (WiSEs) are a class of super-concentrated electrolytes that have shown much promise in replacing organic electrolytes in lithium-ion batteries. At the extremely high salt concentrations of WiSEs, ionic association is more complicated than the simple ion pair description. In fact, large branched clusters can be present in WiSEs, and past a critical salt concentration, an infinite percolating ionic network can form spontaneously. In this work, we simplify our recently developed thermodynamic model of reversible ionic aggregation and gelation, tailoring it specifically for WiSEs. Our simplified theory only has a handful of parameters, all of which can be readily determined from simulations. Our model is able to quantitatively reproduce the populations of ionic clusters of different sizes as a function of salt concentration, the critical salt concentration for ionic gelation, and the fraction of ions incorporated into the ionic gel, as observed from molecular simulations of three different lithium-based WiSEs. The extent of ionic association and gelation greatly affects the effective ionic strength of solution, the coordination environment of active cations that is known to govern the chemistry of the solid-electrolyte interface, and the thermodynamic activity of all species in the electrolyte.
McEldrew M, Goodwin ZAH, Zhao H, et al., 2021, Correlated ion transport and the gel phase in room temperature ionic liquids, The Journal of Physical Chemistry B: Biophysical Chemistry, Biomaterials, Liquids, and Soft Matter, Vol: 125, Pages: 2677-2689, ISSN: 1520-5207
Here we present a theory of ion aggregation and gelation of room temperature ionic liquids (RTILs). Based on it, we investigate the effect of ion aggregation on correlated ion transport—ionic conductivity and transference numbers—obtaining closed-form expressions for these quantities. The theory depends on the maximum number of associations a cation and anion can form and the strength of their association. To validate the presented theory, we perform molecular dynamics simulations on several RTILs and a range of temperatures for one RTIL. The simulations indicate the formation of large clusters, even percolating through the system under certain circumstances, thus forming a gel, with the theory accurately describing the obtained cluster distributions in all cases. However, based on the strength and lifetime of associations in the simulated RTILs, we expect free ions to dominate ionic conductivity despite the presence of clusters, and we do not expect the percolating cluster to trigger structural arrest in the RTIL.
Groda Y, Dudka M, Kornyshev AA, et al., 2021, Superionic Liquids in Conducting Nanoslits: Insights from Theory and Simulations, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 125, Pages: 4968-4976, ISSN: 1932-7447
Pivnic K, Bresme F, Kornyshev AA, et al., 2020, Electrotunable friction in diluted room temperature ionic liquids: implications for nanotribology, ACS Applied Nano Material, Vol: 3, Pages: 10708-10719, ISSN: 2574-0970
Using nonequilibrium molecular dynamics (NEMD) simulations, we study the mechanism of electrotunable friction in the mixture of a room temperature ionic liquid (RTIL), BMIM PF6, and an organic solvent, acetonitrile. The dilution itself helps to reduce the viscosity and thereby reduce the viscous contribution to friction. At the same time, we find that under nanoscale confinement conditions, diluted RTIL solutions, of just ∼10% molar fraction, still feature a remarkable variation of the friction force with the electrode surface charge density, not weaker than had been earlier shown for nanoconfined pure RTILs. In both classes of systems the electrotunable friction response is due to accumulation of counterions at charged surfaces. For both diluted mixtures and pure RTILs, the friction force is minimal for uncharged surfaces and it increases with surface charge of either sign but only in the range of low and moderate surface charges (16–32 μC/cm2). At higher surface charges (43–55 μC/cm2), the effect is different: in the pure RTIL, the friction force continues to increase with the surface charge, while in the diluted RTIL mixture it features a maximum, with a reduction of friction with the increasing surface charge. This contrasting behavior is explained by the difference in the slip conditions found for the pure and the diluted RTIL solutions in contact with highly charged surfaces. Overall, we demonstrate that nanoscale films of diluted mixtures of RTIL provide lower friction forces than the pure RTIL films, preserving at the same time a significant electrotunable response when the liquids are confined between symmetrically charged surfaces. Nanoconfinement between asymmetrically charged surfaces leads to a reduction of friction compared to the symmetric case, with a concomitant decrease in the range of friction variation with the surface charge density. Our results highlight the potential of diluted RTIL mixtures as cost-effective electrotunab
Di Lecce S, Kornyshev AA, Urbakh M, et al., 2020, Lateral ordering in nanoscale ionic liquid films between charged surfaces enhances lubricity., ACS Nano, Vol: 14, Pages: 13256-13267, ISSN: 1936-0851
Electric fields modify the structural and dynamical properties of room temperature ionic liquids (RTILs) providing a physical principle to develop tunable lubrication devices. Using nonequilibrium molecular dynamics atomistic simulations, we investigate the impact of the composition of imidazolium RTILs on the in-plane ordering of ionic layers in nanogaps. We consider imidazolium cations and widely used anions featuring different molecular structures, spherical ([BF4]-), elongated surfactant-like ([C2SO4]-), and elongated with a more delocalized charge ([NTf2]-). The interplay of surface charge, surface polarity, and anion geometry enables the formation of crystal-like structures in [BF4]- and [NTf2]- nanofilms, while [C2SO4]- nanofilms form disordered layers. We study how the ordering of the ionic liquid lubricant in the nanogap affects friction. Counterintuitively, we find that the friction force decreases with the ability of the RTILs to form crystal-like structures in the confined region. The crystallization can be activated or inhibited by changing the polarity of the surface, providing a mechanism to tune friction with electric fields.
Ma Y, Sikdar D, He Q, et al., 2020, Self-assembling two-dimensional nanophotonic arrays for reflectivity-based sensing, Chemical Science, Vol: 11, Pages: 9563-9570, ISSN: 2041-6520
We propose a nanoplasmonic platform that can be used for sensing trace levels of heavy metals in solutions via simple optical reflectivity measurements. The considered example is a lead sensor, which relies on the lead-mediated assembly of glutathione-functionalized gold nanoparticles (NPs) at a self-healing water/DCE liquid | liquid interface (LLI). Capillary forces tend to trap each NP at the LLI while the negatively charged ligands prevent the NPs settling too close to each other. In the presence of lead, due to chelation between the lead ion and glutathione ligand, the NPs assemble into a dense quasi-2D interfacial array. Such a dense assembly of plasmonic NPs can generate a remarkable broad-band reflectance signal, which is absent when NPs are adsorbed at the interface far apart from each other. The condensing effect of the LLI and the plasmonic coupling effect among the NP array gives rise to a dramatic enhancement of the reflectivity signals. Importantly, we show that our theory of the optical reflectivity from such an array of NPs works in perfect harmony with the physics and chemistry of the system with the key parameter being the interparticle distance at the interface. As a lead sensor, the system is fast, stable, and can achieve detection limits down to 14 ppb. Future alternative recognizing ligands can be used to build sister platforms for detecting other heavy metals.
de Souza JP, Goodwin ZAH, McEldrew M, et al., 2020, Interfacial Layering in the Electric Double Layer of Ionic Liquids, PHYSICAL REVIEW LETTERS, Vol: 125, ISSN: 0031-9007
Zagar C, Griffith R-R, Podgornik R, et al., 2020, On the voltage-controlled assembly of nanoparticle arrays at electrochemical solid/liquid interfaces, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, Vol: 872, ISSN: 1572-6657
Zhang Y, Ye T, Chen M, et al., 2020, Enforced freedom: electric-field-induced declustering of ionic-liquid ions in the electrical double layer, Energy & Environmental Materials, Vol: 3, Pages: 414-420, ISSN: 2575-0356
Ions in the bulk of solvent‐free ionic liquids bind into ion pairs and clusters. The competition between the propensity of ions to stay in a bound state, and the reduction of the energy when unbinding in electric field, determines the portion of free ions in the electrical double layer. We present the simplest possible mean‐field theory to study this effect. “Cracking” of ion pairs into free ions in electric field is accompanied by the change of the dielectric response of the ionic liquid. The predictions from the theory are verified and further explored by molecular dynamics simulations. A particular finding of the theory is that the differential capacitance vs potential curve displays a bell shape, despite the low concentration of free charge carriers, because the dielectric response reduces the threshold concentration for the bell‐ to camel‐shape transition. The presented theory does not take into account overscreening and oscillating charge distributions in the electrical double layer. But in spite of the simplicity of the model, its findings demonstrate a clear physical effect: a preference to be a charged monopole rather than a dipole (or higher order multipole) in strong electric field.
Kornyshev AA, 2020, Electrochemical metamaterials, JOURNAL OF SOLID STATE ELECTROCHEMISTRY, Vol: 24, Pages: 2101-2111, ISSN: 1432-8488
Sikdar D, Pendry JB, Kornyshev AA, 2020, Nanoparticle meta-grid for enhanced light extraction from light-emitting devices., Light Sci Appl, Vol: 9
Based on a developed theory, we show that introducing a meta-grid of sub-wavelength-sized plasmonic nanoparticles (NPs) into existing semiconductor light-emitting-devices (LEDs) can lead to enhanced transmission of light across the LED-chip/encapsulant interface. This results from destructive interference between light reflected from the chip/encapsulant interface and light reflected by the NP meta-grid, which conspicuously increase the efficiency of light extraction from LEDs. The "meta-grid", should be inserted on top of a conventional LED chip within its usual encapsulating packaging. As described by the theory, the nanoparticle composition, size, interparticle spacing, and distance from the LED-chip surface can be tailored to facilitate maximal transmission of light emitted from the chip into its encapsulating layer by reducing the Fresnel loss. The analysis shows that transmission across a typical LED-chip/encapsulant interface at the peak emission wavelength can be boosted up to ~99%, which is otherwise mere ~84% at normal incidence. The scheme could provide improved transmission within the photon escape cone over the entire emission spectrum of an LED. This would benefit energy saving, in addition to increasing the lifetime of LEDs by reducing heating. Potentially, the scheme will be easy to implement and adopt into existing semiconductor-device technologies, and it can be used separately or in conjunction with other methods for mitigating the critical angle loss in LEDs.
Kornyshev A, Pendry J, Sikdar D, 2020, Nanoparticle meta-grid for enhanced light extraction from light emitting devices, Light: Science and Applications, Vol: 9, Pages: 1-11, ISSN: 2047-7538
Based on a developed theory, we show that introducing a meta-grid of sub-wavelength-sized plasmonic nanoparticles (NPs) into existing semiconductor light-emitting-devices (LEDs) can lead to enhanced transmission of light across the LED-chip/encapsulant interface. This results from destructive interference between light reflected from the chip/encapsulant interface and light reflected by the NP meta-grid, which conspicuously increase the efficiency of light extraction from LEDs. The “meta-grid”, should be inserted on top of a conventional LED chip within its usual encapsulating packaging. As described by the theory, the nanoparticle composition, size, interparticle spacing, and distance from the LED-chip surface can be tailored to facilitate maximal transmission of light emitted from the chip into its encapsulating layer by reducing the Fresnel loss. The analysis shows that transmission across a typical LED-chip/encapsulant interface at the peak emission wavelength can be boosted up to ~99%, which is otherwise mere ~84% at normal incidence. The scheme could provide improved transmission within the photon escape cone over the entire emission spectrum of an LED. This would benefit energy saving, in addition to increasing the lifetime of LEDs by reducing heating. Potentially, the scheme will be easy to implement and adopt into existing semiconductor-device technologies, and it can be used separately or in conjunction with other methods for mitigating the critical angle loss in LEDs.
McEldrew M, Goodwin ZAH, Bi S, et al., 2020, Theory of ion aggregation and gelation in super-concentrated electrolytes, Journal of Chemical Physics, Vol: 152, Pages: 1-19, ISSN: 0021-9606
In concentrated electrolytes with asymmetric or irregular ions, such as ionic liquids and solvent-in-salt electrolytes, ion association is more complicated than simple ion-pairing. Large branched aggregates can form at significant concentrations at even moderate salt concentrations. When the extent of ion association reaches a certain threshold, a percolating ionic gel network can form spontaneously. Gelation is a phenomenon that is well known in polymer physics, but it is practically unstudied in concentrated electrolytes. However, despite this fact, the ion-pairing description is often applied to these systems for the sake of simplicity. In this work, drawing strongly from established theories in polymer physics, we develop a simple thermodynamic model of reversible ionic aggregation and gelation in concentrated electrolytes accounting for the competition between ion solvation and ion association. Our model describes, with the use of several phenomenological parameters, the populations of ionic clusters of different sizes as a function of salt concentration; it captures the onset of ionic gelation and also the post-gel partitioning of ions into the gel. We discuss the applicability of our model, as well as the implications of its predictions on thermodynamic, transport, and rheological properties.
Bi S, Banda H, Chen M, et al., 2020, Molecular understanding of charge storage and charging dynamics in supercapacitors with MOF electrodes and ionic liquid electrolytes, Nature Materials, Vol: 19, Pages: 552-558, ISSN: 1476-1122
We performed constant-potential molecular dynamics simulations to analyse the double-layer structure and capacitive performance of supercapacitors composed of conductive metal-organic framework (MOF) electrodes and ionic liquids. The molecular modelling clarifies how ions transport and reside inside polarized porous MOFs, and then predicts the corresponding potential-dependent capacitance in characteristic shapes. The transmission line model was adopted to characterize the charging dynamics, which further allowed evaluation of the capacitive performance of this class of supercapacitors at the macroscale from the simulation-obtained data at the nanoscale. These 'computational microscopy' results were supported by macroscopic electrochemical measurements. Such a combined nanoscale-to-macroscale investigation demonstrates the potential of MOF supercapacitors for achieving unprecedentedly high volumetric energy and power densities. It gives molecular insights into preferred structures of MOFs for accomplishing consistent performance with optimal energy-power balance, providing a blueprint for future characterization and design of these new supercapacitor systems.
Zaboronsky AO, Kornyshev AA, 2020, Ising models of charge storage in multifile metallic nanopores., Journal of Physics: Condensed Matter, Vol: 32, Pages: 1-12, ISSN: 0953-8984
Ising type models of charging of conductive nanopores with ions have already been proposed and investigated for single file cylindrical or single layer slit nanopores. In such pores, the state of ions, the coulombic interactions of which are exponentially screened by their images in pore walls, was named superionic. In the present work we extend the analysis of the superionic state to nanopores that can accommodate multiple rows of ions. By grouping multiple charges in the same row into 'supercharges', we map the arrangement of ions in polarised electrodes on a multi-row Ising model in an external field. We investigate one-, two- and three-row cases, which we solve exactly, using a purpose-built semi-numerical transfer matrix method. For pores of different radii, which can accommodate the corresponding number of ion rows, we calculate the dependence of the electrical capacitance and stored energy density on electrode potential. As in charging the single file pores, we find that in narrower pores higher energy densities can be achieved at low applied potentials, while wider pores perform better as the voltage is increased.
Ma Y, Sikdar D, Fedosyuk A, et al., 2020, Electrotunable nanoplasmonics for amplified surface enhanced Raman spectroscopy, ACS Nano, Vol: 14, Pages: 328-336, ISSN: 1936-0851
Tuning the properties of optical metamaterials in real time is one of the grand challenges of photonics. Being able to do so will enable a new class of photonic materials for use in applications such as surface enhanced Raman spectroscopy and reflectors/absorbers. One strategy to achieving this goal is based on the electrovariable self-assembly and disassembly of two-dimensional nanoparticle arrays at a metal liquid interface. As expected the structure results in plasmonic coupling between NPs in the array but perhaps as importantly between the array and the metal surface. In such a system the density of the nanoparticle array can be controlled by the variation of electrode potential. Due to the additive effect, we show that less than 1 V variation of electrode potential can give rise to a dramatic simultaneous change in optical reflectivity from ~93 % to ~1 % and the amplification of the SERS signal by up to 5 orders of magnitude. The process allows for reversible tunability. These concepts are demonstrated in this manuscript, using a platform based on the voltage-controlled assembly of 40 nm Au-nanoparticle arrays at a TiN/Ag electrode in contact with an aqueous electrolyte. We show that all the physics underpinning the behaviour of this platform works precisely as suggested by the proposed theory, setting the electrochemical nanoplasmonics as a promising new direction in photonics research.
Di Lecce S, Kornyshev AA, Urbakh M, et al., 2020, Electrotunable lubrication with ionic liquids: the effects of cation chain length and substrate polarity., ACS Applied Materials and Interfaces, Vol: 12, Pages: 4105-4113, ISSN: 1944-8244
Electrotunable lubrication with ionic liquids (ILs) provides dynamic control of friction with the prospect to achieve superlubrication. We investigate the dependence of the frictional and structural forces with 1-n,2-methyl-imidazolium tetrafluoroborate [C n MIM]+[BF4]- (n = 2, 4, 6) ILs as a lubricant on the molecular structure of the liquid, normal load, and polarity of the electrodes. Using non-equilibrium molecular dynamics simulations and coarse-grained force-fields, we show that the friction force depends significantly on the chain length of the cation. ILs containing cations with shorter aliphatic chains show lower friction forces, ∼40% for n = 2 as compared to the n = 6 case, and more resistance to squeeze-out by external loads. The normal load defines the dynamic regime of friction, and it determines maxima in the friction force at specific surface charges. At relatively low normal loads, ∼10 MPa, the velocity profile in the confined region resembles a Couette type flow, whereas at high loads, >200 MPa, the motion of the ions is highly correlated and the velocity profile resembles a "plug" flow. Different dynamic regimes result in distinctive slippage planes, located either at the IL-electrode interface or in the interior of the film, which ultimately lead, at high loads, to the observation of maxima in the friction force at specific surface charge densities. Instead, at low loads the maxima are not observed, and the friction is found to monotonously increase with the surface charge. Friction with [C n MIM]+[BF4]- as a lubricant is reduced when the liquid is confined between positively charged electrodes. This is due to better lubricating properties and enhanced resistance to squeeze out when the anion [BF4]- is in direct contact with the electrode.
Levy A, Bazant M, Kornyshev A, 2020, Ionic activity in concentrated electrolytes: Solvent structure effect revisited, Chemical Physics Letters, Vol: 738, Pages: 1-5, ISSN: 0009-2614
We revisit the role of the local solvent structure on the activity coefficients of electrolytes within a nonlocal dielectric function approach. We treat the concentrated electrolyte as a dielectric medium and suggest an interpolation formula for its nonlocal dielectric response. The water dielectric response is approximated based on MD simulations and experimental data, that gives strong over-screening and oscillations in the potential, which are absent in the standard “primitive model” predictions. We obtain mathematically tractable closed-form expressions for the activity coefficients, in reasonable agreement with experimental data.
Sikdar D, Kornyshev A, 2019, An electro-tunable Fabry–Perot interferometer based on dual mirror-on-mirror nanoplasmonic metamaterials, Nanophotonics, Vol: 8, Pages: 2279-2290, ISSN: 2192-8606
Mirror-on-mirror nanoplasmonic metamaterials, formed based on voltage-controlled reversible selfassembly of sub-wavelength-sized, metallic nanoparticles (NPs) on thin metallic-film electrodes, are promisingcandidates for novel electro-tunable optical devices. Here, we present a new design of electro-tunable Fabry–Perotinterferometers (FPI), in which two parallel mirrors — each composed of a monolayer of NPs self-assembled on athin metallic electrode — form an optical cavity, which is filled with aqueous solution. The reflectivity of the cavitymirrors can be electrically adjusted, simultaneously or separately, via a small variation of electrode potentials thatwould alter the inter-NP separation in the monolayers. To investigate optical transmittance from the proposed FPIdevice we develop a nine-layer-stack theoretical model, based on our effective medium theory and multi-layer Fresnelreflection scheme, which produces excellent match when verified against full-wave simulations. We show that strongplasmonic coupling among silver NPs forming monolayer on a thin silver-film substrate makes reflectivity of eachcavity-mirror highly sensitive to the inter-NP separation. Such a design allows continuous tuning of the multiple,narrow and intense transmission peaks emerging from an FPI cavity via electrotuning the inter-NP separation in-situ— reaping the benefits from both inexpensive bottom-up fabrication and energy efficiency of tuning.
Pivnic K, Bresme F, Kornyshev AA, et al., 2019, Structural forces in mixtures of ionic liquids with organic solvents, Langmuir: the ACS journal of surfaces and colloids, Vol: 35, Pages: 15410-15420, ISSN: 0743-7463
Using molecular dynamics simulations, we study the impact of electrode charging and addition of solvent (acetonitrile, ACN) on structural forces of the BMIM PF6 ionic liquid (IL) confined by surfaces at nanometer separations. We establish relationships between the structural forces and the microscopic structure of the confined liquid. Depending on the structural arrangements of cations and anions across the nanofilm, the load-induced squeeze-out of liquid layers occurs via one-layer or bilayer steps. The cations confined between charged plates orient with their aliphatic chain perpendicular to the surface planes and link two adjacent IL layers. These structures facilitate the squeeze-out of single layers. For both pure IL and IL-ACN mixtures, we observe a strong dependence of nanofilm structure on the surface charge density, which affects the simulated pressure–displacement curves. Addition of solvent to the IL modifies the layering in the confined film. At high electrode charges and high dilution of IL (below 10% molar fraction), the layered structure of the nanofilm is less well defined. We predict a change in the squeeze-out mechanism under pressure, from a discontinuous squeeze-out (for high IL concentrations) to an almost continuous one (for low IL concentrations). Importantly, our simulations show that charged electrodes are coated with ions even at low IL concentrations. These ion-rich layers adjacent to the charged plate surfaces are not squeezed out even under very high normal pressures of ∼5 GPa. Hence, we demonstrate the high performance of IL–solvent mixtures to protect surfaces from wear and to provide lubrication at high loads.
Dudka M, Kondrat S, Bénichou O, et al., 2019, Superionic liquids in conducting nanoslits: A variety of phase transitions and ensuing charging behavior, The Journal of Chemical Physics, Vol: 151, ISSN: 0021-9606
We develop a theory of charge storage in ultranarrow slitlike pores of nanostructured electrodes. Our analysis is based on the Blume-Capelmodel in an external field, which we solve analytically on a Bethe lattice. The obtained solutions allow us to explore the complete phase diagramof confined ionic liquids in terms of the key parameters characterizing the system, such as pore ionophilicity, interionic interaction energy,and voltage. The phase diagram includes the lines of first- and second-order, direct and re-entrant phase transitions, which are manifestedby singularities in the corresponding capacitance-voltage plots. Testing our predictions experimentally requires monodisperse, conductingultranarrow slit pores, to permit only one layer of ions, and thick pore walls, to prevent interionic interactions across the pore walls. However,some qualitative features, which distinguish the behavior of ionophilic and ionophobic pores and their underlying physics, may emerge infuture experimental studies of more complex electrode structures.
Kornyshev A, Sikdar D, Weir H, 2019, Optical response of electro-tuneable 3D superstructures of plasmonic nanoparticles self-assembling on transparent columnar electrodes, Optics Express, Vol: 19, Pages: 26483-26498, ISSN: 1094-4087
Electrically tuneable, guided self-assembly of plasmonic nanoparticles (NPs) at polarized, patterned solid–liquid interfaces could enable numerous platforms for designing nanoplasmonic optical devices with new tuneable functionalities. Here, we propose a unique design of voltage-controlled guided 3D self-assembly of plasmonic NPs on transparent electrodes, patterned as columnar structures — arrays of vertical nanorods. NP assembly on the electrified surfaces of those columnar structures allows formation of a 3D superstructure of NPs, comprising stacking up of NPs in the voids between the columns, forming multiple NP-layers. A comprehensive theoretical model, based on quasi-static effective medium theory and multilayer Fresnel reflection scheme, is developed and verified against full-wave simulations for obtaining optical responses — reflectance, transmittance, and absorbance — from such systems of 3D self-assembled NPs. With a specific example of small gold nanospheres, self-assembling on polarized zinc oxide columns, we show that the reflectance spectrum can be controlled by the number of stacked NP-layers. Numerical simulations show that peak reflectance can be enhanced up to ~1.7 times, along with spectral broadening by a factor of ~2 — allowing wide range tuning of optical reflectivity. Smaller NPs with superior mobility would be preferable over large NPs for realizing such devices for novel photonic and sensing applications.
Vasilyev OA, Kornyshev AA, Kondrat S, 2019, Connections matter: On the importance of pore percolation for nanoporous supercapacitors, ACS Applied Energy Materials, Vol: 2, Pages: 5386-5390, ISSN: 2574-0962
Nanoporous supercapacitors play a key role in energy storage and thereby attract growing interest from the research community. Development of porous electrodes for supercapacitors is of the paramount importance, but their characterization still remains a challenge. Herein, we analyze two examples of the popular carbide-derived and activated carbon electrodes from the point of view of interpore connectivity and ion permeation. Due to limited percolation, the effective porosity, as seen by an ion, decreases with an increase in the ion size, which can reduce the stored energy density substantially. Our results highlight the importance of high quality well-percolated porous electrodes for supercapacitors and suggest that the interpore connectivity is an important characteristic to consider when optimizing the existing and developing new electrode materials.
Kondrat S, Vasilyev OA, Kornyshev AA, 2019, Feeling your neighbors across the walls: How interpore ionic interactions affect capacitive energy storage., Journal of Physical Chemistry Letters, Vol: 10, Pages: 4523-4527, ISSN: 1948-7185
Progress in low-dimensional carbon materials has intensified research on supercapacitors with nanostructured/nanoporous electrodes. The theoretical and simulation work so far has focused on charging single nanopores or nanoporous networks and the effects due to ionic interactions inside the pores, while the effect of interpore ion-ion correlations has received less attention. Herein, we study how the interactions between the ions in the neighboring pores across the pore walls affect capacitive energy storage. We develop a simple lattice model for the ions in a stack of parallel-aligned nanotubes, solve it by using the perturbation and "semi-mean-field" theories, and test the results by Monte Carlo simulations. We demonstrate that the interpore ionic interactions can have a profound effect on charge storage; in particular, such interactions can enhance or diminish the stored energy density, depending on the sign of like-charge interactions. We also find that charging can proceed either continuously or via a phase transition. Our results call for more detailed investigations of the properties of carbon pore walls and suggest that tuning their electrostatic response may be promising for the rational design of an optimal supercapacitor.
Ma Y, Sikdar D, Fedosyuk A, et al., 2019, An auxetic thermo-responsive nanoplasmonic optical switch., ACS Applied Materials and Interfaces, ISSN: 1944-8244
Development and use of metamaterials have been gaining prominence in large part due to the possibility of creating platforms with 'disruptive' and unique optical properties. However, to date the majority of such systems produced using micro or nanotechnology, are static and can only perform certain target functions. Next-generation multifunctional smart optical metamaterials are expected to have tuneable elements with the possibility of controlling the optical properties in real time via variation in parameters such as pressure, mechanical stress, voltage, or through non-linear optical effects. Here, we address this challenge by developing a thermally controlled optical switch, based on the self-assembly of poly(N-isopropylacrylamide)-functionalised gold nanoparticles on a planar macroscale gold substrate. We show that such meta-surfaces can be tuned to exhibit substantial changes in the optical properties both in terms of wavelength and intensity, through the temperature-controlled variation of the interparticle distance within the nanoparticle monolayer as well as its separation from the substrate. This change is based on temperature induced auxetic expansion and contraction of the functional ligands. Such a system has potential for numerous applications, ranging from thermal sensors to regulated light harnessing.
Montelongo Y, Sikdar D, Ma Y, et al., 2019, Author Correction: Electrotunable nanoplasmonic liquid mirror., Nat Mater, ISSN: 1476-1122
In the version of this Article originally published, the last sentence of the acknowledgements incorrectly read 'L.V. acknowledges the support of a Marie Skodowska-Curie fellowship (N-SHEAD)'; it should have read 'L.V. and D.S. acknowledge the support of Marie Skłodowska-Curie fellowships, N-SHEAD and S-OMMs, respectively'.
Sikdar D, Ma Y, Kucernak AR, et al., 2019, Nanoplasmonic metamaterial devices as electrically switchable perfect mirrors and perfect absorbers, Conference on Lasers and Electro-Optics (CLEO), Publisher: IEEE, Pages: 1-2, ISSN: 2160-9020
We introduce nanoplasmonic metamaterial devices — electrically-switchable between perfect- mirror/absorber states — based on voltage-controlled assembly/disassembly of gold nanoparticles on silver films. These are investigated using effective-medium-theory, verified with simulations and experiments.
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