Potential-dependent hydration structures at aqueous solution/graphite interfaces by electrochemical frequency modulation atomic force microscopy

Utsunomiya, Toru; Yokota, Yasuyuki; Enoki, Toshiaki; Fukui, Ken–ichi

doi:10.1039/c4cc07093c

Cited by 32 publications

(24 citation statements)

References 30 publications

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“…The structural solvation forces observed at liquid/solid interfaces have been an important subject for elucidating molecular-scale interface structures. 38,[47][48][49][50][51][52][53][54][55][56] Previous studies of IL/solid interfaces have revealed that the structural solvation layer spacing of ILs agrees well with the ionpair diameter calculated from the cubic root of the volume per IL ion pair (molecular volume). 52 The spacings of the valleys Thick and thin lines represent the approach and retraction curves, respectively.…”

Section: High Resolution Imagingmentioning

confidence: 85%

“…The experimental details are described elsewhere. [33][34][35][36][37][38] Gold backcoated cantilevers (Tap 300GD-G, BudgetSensors or PPP-NCHAuD, Nonosensors) with approximately 40 N m À1 force constants were used. The cantilever surfaces were cleaned prior to use by the method proposed by Fujihira et al 39 All FM-AFM images presented in this study are topographies obtained at a constant frequency shift (Df ) and at a constant vibrational amplitude (A p-p ).…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Molecularly clean ionic liquid/rubrene single-crystal interfaces revealed by frequency modulation atomic force microscopy

Yokota

Hara

Morino

et al. 2015

Phys. Chem. Chem. Phys.

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The structural properties of ionic liquid/rubrene single-crystal interfaces were investigated using frequency modulation atomic force microscopy. The spontaneous dissolution of rubrene molecules into the ionic liquid was triggered by surface defects such as rubrene oxide defects, and the dissolution rate strongly depended on the initial conditions of the rubrene surface. Dissolution of the second rubrene layer was slower due to the lower defect density, leading to the formation of a clean interface irrespective of the initial conditions. Molecular-resolution images were easily obtained at the interface, and their corrugation patterns changed with the applied force. Force curve measurements revealed that a few solvation layers of ionic liquid molecules formed at the interface, and the force needed to penetrate the solvation layers was an order of magnitude smaller than typical ionic liquid/inorganic solid interfaces. These specific properties are discussed with respect to electric double-layer transistors based on the ionic liquid/rubrene single-crystal interface.

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Section: High Resolution Imagingmentioning

confidence: 85%

Section: Methodsmentioning

confidence: 99%

Molecularly clean ionic liquid/rubrene single-crystal interfaces revealed by frequency modulation atomic force microscopy

Yokota

Hara

Morino

et al. 2015

Phys. Chem. Chem. Phys.

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“…With improvements of experimental techniques it has become possible to image solid-water interfaces with unprecedented detail [4]. A common observation at these interfaces is the layered arrangement of water: Hydration layers have been observed at a large variety of solid-water interfaces, including mineral-water interfaces [5][6][7], graphite-water [8], and metalwater interfaces [9,10]. Layers at solid-water interfaces have been observed using x-ray reflectivity measurements [11][12][13], the surface force apparatus [14][15][16][17], and with high-resolution three-dimensional (3D) atomic force microscopy (AFM) [5].…”

mentioning

confidence: 99%

Hydration layers at the graphite-water interface: Attraction or confinement

et al. 2019

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Water molecules at solid surfaces typically arrange in layers. The physical origin of the hydration layers is usually explained by two different reasons: (1) the attraction between the surface and water and (2) the water confinement due to the surface. While the attraction is specific to the particular solid, the confinement is a general property of surfaces; a differentiation between the two effects is, therefore, critical for research on interactions at aqueous interfaces. Here, we investigate the graphite-water interface, which is a widely used model system where the solid-water attraction is often considered to be negligible. Similar to previous studies, we observe hydration layers using three-dimensional atomic force microscopy at the graphite-water interface. We explain why the confinement could cause the formation of hydration layers even in the absence of attraction between surface and water by employing Monte Carlo simulations. Using additional molecular dynamics simulations, we continue to show that at ambient conditions, however, the confinement alone does not cause the formation of layers at the graphite-water interface. We thereby demonstrate that there is a significant graphite-water attraction.

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“…[ 9d ] Simulation on the dynamics of the hydration layers shows that the negative potential is more disruptive. [ 9e ] Experimentally, the formation and the structure of hydration layer was measured by scanning probe microscopy [ 10 ] and X‐ray reflectivity. [ 11 ] An interesting experimental evidence of the hydrophobic hydration layer is the reversible wettability of graphene on UV exposure that forms oxygen and hydroxyl radicals that react with graphene to make the interface hydrophilic which can be reversed to hydrophobic surface on storing in the dark.…”

Section: Introductionmentioning

confidence: 99%

Electrostatics of Single Monolayer Graphene Coated Metal Electrode in Electrolyte

Saraf

Keramatnejad

Arcila

et al. 2021

Adv Materials Inter

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electrolytes emerge from two rather disparate properties. Like oxide-free noble metals, graphene is electrically conducting. [3] However, similar to other carbonaceous materials, it is considered largely hydrophobic, [4] given some contribution from hydrocarbon contamination on the surface. [5] As a result, the ions will be attracted to the surface due to conductivity (i.e., image charge), but the hydrophobicity will tend to repel them. [6] As a result, the interface of electrolyte with graphene is unusual. It is experimentally shown by X-ray reflectivity [7] and supported by simulation [7] that the interface of graphene supported on a metal will also have an ≈1 nm thick low density water layer (also called "vacuum layer"), consistent with other hydrophobic surfaces. [8] To reconcile the hydrophobic and electrically conducting nature of graphene, simulation studies show a formation of a "hydrophobic" hydration layer on the interface between the graphene and the bulk aqueous solution; [4a,9] There are two hydration layers, at ≈0.3 and ≈0.6 nm, and the ions in the solution appear to disrupt the layer farther from the interface. [9b] Simulation of electrowetting on graphene/metal surface shows that the polarization of hydration layer causes dramatic and complete screening of the electric field on graphene. [9c] It was estimated, that hydration screens over 85% of ion-graphene molecular electric field. [9d] Simulation on the dynamics of the hydration layers shows that the negative potential is more disruptive. [9e] Experimentally, the formation and the structure of hydration layer was measured by scanning probe microscopy [10] and X-ray reflectivity. [11] An interesting experimental evidence of the hydrophobic hydration layer is the reversible wettability of graphene on UV exposure that forms oxygen and hydroxyl radicals that react with graphene to make the interface hydrophilic which can be reversed to hydrophobic surface on storing in the dark. [12] By contrast, simulations of density fluctuations at the interface point to a hydrophilic nature of graphene, [13] which have also been concluded by contact angle measurements on free standing films. [14] Furthermore, the low density of states compared to metals at the Dirac Point gives rise to quantum capacitance that lowers the overall interfacial capacitance. [15] Thus, the electrostatics of electrolyte/graphene interface that affects a range of electrochemical application remains a subject of intense research with potentially undiscovered phenomenon.Here, the dynamic nature of the interface was experimentally studied by differential reflectivity to probe the electrostatics Unlike metals, graphene forms a hydration layer at the electrode/electrolyte interface, which is unusual for a conducting material. Here, the electrostatic properties of the hydration layer are studied by measuring the oscillation of ions at the interface due to an applied AC potential by differential reflectivity during cyclic voltammetry (CV). The amplitude of ion oscillation at picomet...

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Potential-dependent hydration structures at aqueous solution/graphite interfaces by electrochemical frequency modulation atomic force microscopy

Cited by 32 publications

References 30 publications

Molecularly clean ionic liquid/rubrene single-crystal interfaces revealed by frequency modulation atomic force microscopy

Molecularly clean ionic liquid/rubrene single-crystal interfaces revealed by frequency modulation atomic force microscopy

Hydration layers at the graphite-water interface: Attraction or confinement

Electrostatics of Single Monolayer Graphene Coated Metal Electrode in Electrolyte

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