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1.
Phys Chem Chem Phys ; 26(1): 293-303, 2023 Dec 21.
Article in English | MEDLINE | ID: mdl-38060245

ABSTRACT

Nitrogen-doped graphenes were among the first promising metal-free carbon-based catalysts for the oxygen reduction reaction (ORR). However, data on the most efficient catalytic centers and their catalytic mechanisms are still under debate. In this work, we study the associative mechanism of the ORR in an alkaline medium on graphene containing various types of nitrogen doping. The free energy profile of the reaction is constructed using grand-canonical DFT at a constant electrode potential in combination with an implicit electrolyte model. It is shown that the reaction mechanism differs from the generally accepted one and depends on the surface potential and doping type. In particular, as the potential decreases, coupled electron-proton transfer changes to sequential electron and proton transfer, and the potential at which this occurs depends on the doping type. It has been shown that oxygen chemisorption is the limiting step. The electrocatalytic mechanism of the nitrogen dopants involves reducing the oxygen chemisorption energy. Calculations predict that, at different potentials, different types of nitrogen impurities most effectively catalyze the ORR.

2.
ACS Appl Mater Interfaces ; 15(23): 28370-28386, 2023 Jun 14.
Article in English | MEDLINE | ID: mdl-37253093

ABSTRACT

The artificial olfaction units (or e-noses) capable of room-temperature operation are highly demanded to meet the requests of society in numerous vital applications and developing Internet-of-Things. Derivatized 2D crystals are considered as sensing elements of choice in this regard, unlocking the potential of the advanced e-nose technologies limited by the current semiconductor technologies. Herein, we consider fabrication and gas-sensing properties of On-chip multisensor arrays based on a hole-matrixed carbonylated (C-ny) graphene film with a gradually changed thickness and concentration of ketone groups of up to 12.5 at.%. The enhanced chemiresistive response of C-ny graphene toward methanol and ethanol, of hundred ppm concentration when mixing with air to match permissible exposure OSHA limits, at room-temperature operation is signified. Following thorough characterization via core-level techniques and density functional theory, the predominant role of the C-ny graphene-perforated structure and abundance of ketone groups in advancing the chemiresistive effect is established. Advancing practice applications, selective discrimination of the studied alcohols is approached by linear discriminant analysis employing a multisensor array's vector signal, and the fabricated chip's long-term performance is shown.

3.
Phys Chem Chem Phys ; 25(5): 4359, 2023 Feb 01.
Article in English | MEDLINE | ID: mdl-36647841

ABSTRACT

Correction for 'Modulation of the kinetics of outer-sphere electron transfer at graphene by a metal substrate' by Sergey V. Pavlov et al., Phys. Chem. Chem. Phys., 2022, 24, 25203-25213, https://doi.org/10.1039/D2CP03771H.

4.
Phys Chem Chem Phys ; 24(41): 25203-25213, 2022 Oct 27.
Article in English | MEDLINE | ID: mdl-36254968

ABSTRACT

Solid-supported graphene is a typical configuration of electrochemical devices based on single-layer graphene. Therefore, it is necessary to understand the electrochemical features of such heterostructures. In this work, we theoretically investigated the effect of the metal type on the nonadiabatic electron transfer (ET) at the metal-supported graphene using DFT calculations. We considered five metals Au, Ag, Pt, Cu, and Al on which graphene is physically adsorbed. It is shown that all metals catalyze the ET. The electrocatalytic effect increases in the following series Al < Au ≲ Ag ≈ Cu < Pt. The enhanced ET in the presence of the metal substrate is explained by the hybridization of metal and graphene states, due to which the coupling between the reactant in an electrolyte and metal is increased. Metal-dependent electrocatalytic effect is explained both by different densities of states at the Fermi level of the systems and by differences in the behaviour of the tails of hybridized wave functions in the electrolyte region. The shift of the Fermi level with respect to the Dirac point in graphene when charging at the metal/graphene/electrolyte interface does not affect the kinetics due to the small contribution of graphene states to the electron transfer.

5.
Nanomaterials (Basel) ; 13(1)2022 Dec 21.
Article in English | MEDLINE | ID: mdl-36615934

ABSTRACT

The derivatization of graphene to engineer its band structure is a subject of significant attention nowadays, extending the frames of graphene material applications in the fields of catalysis, sensing, and energy harvesting. Yet, the accurate identification of a certain group and its effect on graphene's electronic structure is an intricate question. Herein, we propose the advanced fingerprinting of the epoxide and hydroxyl groups on the graphene layers via core-level methods and reveal the modification of their valence band (VB) upon the introduction of these oxygen functionalities. The distinctive contribution of epoxide and hydroxyl groups to the C 1s X-ray photoelectron spectra was indicated experimentally, allowing the quantitative characterization of each group, not just their sum. The appearance of a set of localized states in graphene's VB related to the molecular orbitals of the introduced functionalities was signified both experimentally and theoretically. Applying the density functional theory calculations, the impact of the localized states corresponding to the molecular orbitals of the hydroxyl and epoxide groups was decomposed. Altogether, these findings unveiled the particular contribution of the epoxide and hydroxyl groups to the core-level spectra and band structure of graphene derivatives, advancing graphene functionalization as a tool to engineer its physical properties.

6.
Small ; 17(52): e2104316, 2021 Dec.
Article in English | MEDLINE | ID: mdl-34704658

ABSTRACT

Engineering of the 2D materials' electronic structure is at the forefront of nanomaterials research nowadays, giving an advance in the development of next-generation photonic devices, e-sensing technologies, and smart materials. Herein, employing core-level spectroscopy methods combined with density functional theory (DFT) modeling, the modification of the graphenes' valence band (VB) upon its derivatization by carboxyls and ketones is revealed. The appearance of a set of localized states in the VB of graphene related to molecular orbitals of the introduced functionalities is signified both experimentally and theoretically. Applying the DFT calculations of the density of states projected on the functional groups, their contributions to the VB structure are decomposed. An empirical approach, allowing one to analyze and predict the impact of a certain functional group on the graphenes' electronic structure in terms of examination of the model molecules, mimicking the introduced functionality, is proposed and validated. The interpretation of the arising states origin is made and their designation, pointing out their symmetry type, is proposed. Taken together, these results guide the band structure engineering of graphene derivatives and give a hint on the mechanisms underlying the alteration of the VB structure of 2D materials upon their derivatization.

7.
Phys Chem Chem Phys ; 23(40): 22984-22991, 2021 Oct 20.
Article in English | MEDLINE | ID: mdl-34611675

ABSTRACT

The effect of a gold underlayer on the outer-sphere non-adiabatic electron transfer on a graphene surface is investigated theoretically using both periodic and cluster DFT calculations. We propose a model that describes the alignment of energy levels and charge redistribution at the metal/graphene/redox electrolyte interface. Model calculations were performed for the [Fe(CN)6]3-/4- and [Ru(NH3)6]3+/2+ redox couples. It is shown that the gold support increases the rate constant of electron transfer. Gold electronic states hybridize with graphene wave functions, which provides an effective overlap with reactant orbitals outside the graphene layer and favors an increasing reaction rate. Although the Fermi level shift relative to the Dirac point in graphene depends significantly on the redox couple, this weakly affects the electron transfer kinetics at the Au(111)/graphene/electrolyte interface due to a small contribution of graphene states to the rate constant as compared to gold ones.

8.
Materials (Basel) ; 12(19)2019 Sep 27.
Article in English | MEDLINE | ID: mdl-31569827

ABSTRACT

The process of advanced aluminum-alumina powders production for selective laser melting was studied. The economically effective method of obtaining aluminum-alumina powdery composites for further selective laser melting was comprehensively studied. The aluminum powders with 10-20 wt. % alumina content were obtained by oxidation of aluminum in water. Aluminum oxidation was carried out at ≤200 °C. The oxidized powders were further dried at 120 °C and calcined at 600 °C. Four oxidation modes with different process temperatures (120-200 °C) and pressures (0.15-1.80 MPa) were investigated. Parameters of aluminum powders oxidation to obtain composites with 10.0, 14.5, 17.4, and 20.0 wt. % alumina have been determined. The alumina content, particle morphology, and particle size distribution for the obtained aluminum-alumina powdery composites were studied by XRD, SEM, laser diffraction, and volumetric methods. According to the obtained characteristics of aluminum-alumina powdery composites, they are suitable for the SLM process.

9.
Chemphyschem ; 20(15): 1960-1966, 2019 07 05.
Article in English | MEDLINE | ID: mdl-31189020

ABSTRACT

Influence of cation size on solvation strength, diffusion, and kinetics of the association reaction with anions O2- in aprotic solvents, such as acetonitrile and dimethyl sulfoxide, has been investigated by means of molecular dynamics simulations. The work is motivated by the need to understand the molecular nature of the solvent-induced changes in capacity of Li-air batteries. We have shown that the dependence of the solvation shell stability on the cation size has a maximum at a particular ion radius that corresponds to a solvent coordination number of 4. The shell stability maximum coincides with the diffusion coefficient minimum. The variation of the cation shell stability has a crucial impact on the kinetics of the cation-O2- association. We have demonstrated that profound inhibition of the association reaction for Li+ in dimethyl sulfoxide is a result of the lock-and-key effect that cannot be described in the framework of Hard Soft Acid Base theory.

10.
Chemphyschem ; 19(1): 75-81, 2018 Jan 05.
Article in English | MEDLINE | ID: mdl-29121449

ABSTRACT

The molecular life of intermediates, namely, O2- and Li+ , produced during the discharge of aprotic Li-O2 batteries was investigated by molecular dynamics simulation. This work is of potential interest in the development of new electrolytes for Li-air batteries. We present the results on the structure and stability of the Li+ and O2- solvation shells and the thermodynamics and kinetics of the ion-association reaction in solvents such as dimethyl sulfoxide (DMSO), dimethoxyethane (DME), and acetonitrile (ACN). The residence time of solvent molecules in the Li+ solvation shell increases with the solvent donor number and is 100 times larger in DMSO than in ACN. In DMSO and DME, the Li+ ion diffuses with its solvation shell as a whole. On the contrary, in ACN it diffuses as a "bare" ion because of weak solvation. The rate constant for the association of the lithium ion with the superoxide anion in DMSO is two orders of magnitude slower than that in ACN due to fact that the free-energy barrier is 2.5 times larger in DMSO than in ACN. In addition, we show that despite the strong dependence of the Li+ shell stability on donor number, the rate of association does not necessarily correlate with this solvent property.

11.
Phys Chem Chem Phys ; 17(47): 31947-55, 2015 Dec 21.
Article in English | MEDLINE | ID: mdl-26568158

ABSTRACT

Molecular dynamics simulations were performed to address the permeability of defectless alkanethiol self-assembled monolayers (SAMs) on charged and uncharged Au(111) surfaces in 1-butyl-3-methylimidazolium ([bmim][BF4]) room-temperature ionic liquid (IL). We demonstrate that ionic permeation into the monolayer does not start until a critical surface charge density value is attained (both for positive and negative surface charges). The free energy barrier for the permeation of IL components is shown to include nearly equal contributions from ion desolvation and the channel formation in the dense monolayer. Long chain alkanethiols (hexadecanethiol SC16H33) exhibit superior barrier properties as compared with short chain alkanethiols (hexanethiol SC6H13) due to the dense packing of alkanethiol chains in highly ordered zigzag conformation oriented at the same tilt angle. Computed critical charge densities correspond to the electrode potential values beyond the limits of the monolayer stability, which might indicate the impermeability of the defectless monolayer towards the IL components. Experimental findings on increased interfacial capacitance are interpreted, therefore as some manifestation of the monolayer defectiveness occurring in real electrochemical systems. The potential of the mean force is constructed for a typical redox probe ferrocene/ferrocenium (Fc/Fc(+)) as well, to investigate a possible permeation of the solute from the IL into the SC6H13 monolayer.

12.
Phys Chem Chem Phys ; 12(37): 11245-50, 2010 Oct 07.
Article in English | MEDLINE | ID: mdl-20714582

ABSTRACT

The influence of temperature on the structure and dynamics of the [BMIM][PF(6)] ionic liquid/graphite interface has been investigated by molecular dynamics simulations. The performed simulations cover a 100 K wide temperature interval, ranging from 300 K to 400 K. It was shown that the magnitudes of density peaks of anions in the vicinity of the surface decrease with increasing temperature while in the case of cations anomalous temperature behaviour of the density profile is observed: the magnitude of the second peak of cations increases with the increase of temperature. To characterize interface dynamics the local self-diffusion coefficients D(x) of ions in the normal direction to the surface and the residence time of ions in the first and second interfacial layer have been estimated. It was shown that the local self-diffusion coefficients in the vicinity of the surface correlate with the local ion density; the maxima of the function D(x)(x) for the cations (anions) coincide with the regions of reduced cation (anion) density and vice versa. Finally, the influence of temperature on the screening potential in the vicinity of a charged graphite surface has been studied. It was shown that the increase of temperature from 300 K to 400 K induces the decrease of the potential drop across the interface that implies the increase of the capacitance of the electrical double layer.

13.
Phys Chem Chem Phys ; 11(27): 5584-90, 2009 Jul 21.
Article in English | MEDLINE | ID: mdl-19842475

ABSTRACT

The structure of the electrical double layer in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) near a basal plane of graphite was investigated by molecular dynamics simulation. The calculations were performed both for an uncharged graphite surface and for positively and negatively charged ones. It is found that near an uncharged surface the ionic liquid structure differs from its bulk structure and represents a well-ordered region, extending over approximately 20 A from the surface. Three dense layers of ca 5 A thick are clearly observed at the interface, composed of negative ions and positively charged rings. It is established that in the first adsorption layer the imidazolium ring in the [BMIM]+ cation tends to be arranged in parallel to the graphite surface at a distance of 3.5 A. The [PF6]- anion is oriented in such a way that the phosphorus atom is at a distance of 4.1 A from the surface and triplets of fluorine atoms form two planes parallel to the graphite surface. Ions adsorbed at the uncharged surface are arranged in a highly defective 2D hexagonal lattice and the corresponding lattice spacing is approximately four times larger than that of the graphene substrate. The influence of the electrode potential on the distribution of electrolyte ions and their orientation has also been investigated. Increase in the electrode potential induces broadening of the angle distribution of adsorbed rings and a shift of the most probable tilt angle towards bigger values. It was shown that there are no adsorbed anions on the negatively charged surface (sigma = -8.2 microC cm(-2)), but the surface concentration of adsorbed cations on the positively charged surface (sigma = +8.2 microC cm(-2)) has a nonzero value. In addition, the influence of the surface charge (+/- sigma) on the volume charge density and electric potential profiles in an electrolyte was studied. The differences in the cation and anion structure result in the fact that the integral capacitance of the electrical double layer depends on the electrode polarity and equals C = 4.6 microF cm(-2) at sigma = -8.2 microC cm(-2) and C = 3.7 microF cm(-2) at sigma = +8.2 microC cm(-2).

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