Excess Charge Density Research Articles

Theoretical Investigation of the Potential-Dependent CO Adsorption on Copper Electrodes.

Despite the importance of CO adsorption in many electrocatalytic reaction mechanisms, there has been little investigation of the dependence of the free energy of CO adsorption on the applied potential. Herein, we report on the potential-dependent adsorption of CO on Cu electrodes using a grand-canonical density functional theory approach. We demonstrate that, within the working potential range of electrocatalytic CO2 reduction on Cu(111) and Cu(100), the CO adsorption strength can change by over 0.1 eV. Our analyses explain the potential dependence through an interfacial capacitance loss upon CO adsorption as well as orbital relaxation induced by the electrode potential. Via sensitivity analysis with respect to two electrolyte model parameters (solvent dielectric constant and Debye screening length), we find that the surface excess charge density is a useful descriptor of the CO adsorption free energy.

Effective interaction between guest charges immersed in 2D jellium

The model under study is an infinite 2D jellium of pointlike particles with elementary charge e, interacting via the logarithmic potential and in thermal equilibrium at the inverse temperature β. Two cases of the coupling constant Γ≡βe2 are considered: the Debye–Hückel limit Γ→0 and the free-fermion point Γ=2 . In the most general formulation, two guest particles, the one with charge qe (the valence q being an arbitrary integer) and the hard core of radius σ > 0 and the pointlike one with elementary charge e, are immersed in the bulk of the jellium at distance d⩾σ . Two problems are of interest: the asymptotic large-distance behavior of the excess charge density induced in the jellium and the effective interaction between the guest particles. Technically, the induced charge density and the effective interaction are expressed in terms of multi-particle correlations of the pure (translationally invariant) jellium system. It is shown that the separation form of the induced charge density onto its radial and angle parts, observed previously in the limit Γ→0 , is not reproduced at the coupling Γ=2 . Based on an exact expression for the effective interaction between guest particles at Γ=2 , oppositely ( q=0,−1,−2,… ) charged guest particles always attract one another while likely ( q=1,2,… ) charged guest particles repeal one another up to a certain distance d between them and then the mutual attraction takes place up to asymptotically large (finite) distances.

Janus molybdenum di-chalcogenides based van der Waals bilayers for supercapacitor electrode design- effects of interlayer stacking orientations on quantum capacitance

In this work, for the first time, the quantum capacitance of an artificial two-dimensional (2D) material system based on van der Waals (vdW) bilayer heterostructures of Janus Molybdenum Di-chalcogenides, MoXY (X≠Y, X/YS, Se, Te) have been extensively investigated for electrode design of electrical double-layer (EDL) supercapacitor. The effects of different interlayer stacking orientations on local charge distribution, interlayer charge transfer, energy band structure, and density of states (DOS) have been comprehensively analyzed and correlated with the excess charge density and quantum capacitance variation with local electrode potential. Furthermore, the total capacitance reduction with respect to EDL capacitance has been analyzed over a wide range of EDL capacitance, and the performance of vdW Janus bilayers has been systematically benchmarked against the natural monolayers/bilayers and Janus monolayers of Molybdenum Di-chalcogenides. The results demonstrate that the large interlayer charge transfer induced built-in interlayer electric field significantly reduces the energy band gap of vdW Janus bilayers for S–Te and Se–Te interlayer stacking, thus leading to a significantly superior quantum capacitance. Finally, the favorable valley-dependent effective mass and band-degeneracy in MoSTe/MoSeTe have greatly enhanced quantum capacitance in S–Te and Se–Te stacking, rendering these bilayers a highly attractive candidate for supercapacitor electrode design.

Observational features of charge distribution in Earth’s inner magnetosphere

Understanding the motion of charged particles in the electromagnetic field in the inner magnetosphere is essential for space science and space weather. Charge accumulation can occur due to the dipole magnetic and convective electric fields in this region. However, until the recent Magnetospheric Multiscale (MMS) mission, there were few means to detect charge distribution in situ. We report unambiguous in situ observation of the spatial distribution of the excess charge density in the inner magnetosphere by the MMS mission. We find that a positive (negative) charge accumulates in the dusk (dawn) side inner magnetospheres, which is contrary to the long assumed overall quasi-neutrality of space plasma. These observations and results offer insight into magnetosphere–ionosphere coupling.

Biomimetic noncationic lipid nanoparticles for mRNA delivery.

Although the tremendous progress has been made for mRNA delivery based on classical cationic carriers, the excess cationic charge density of lipids was necessary to compress mRNA through electrostatic interaction, and with it comes inevitably adverse events including the highly inflammatory and cytotoxic effects. How to develop the disruptive technologies to overcome cationic nature of lipids remains a major challenge for safe and efficient mRNA delivery. Here, we prepared noncationic thiourea lipids nanoparticles (NC-TNP) to compress mRNA by strong hydrogen bonds interaction between thiourea groups of NC-TNP and the phosphate groups of mRNA, abandoning the hidebound and traditional electrostatic force to construct mRNA-cationic lipids formulation. NC-TNP was a delivery system for mRNA with simple, convenient, and repeatable preparation technology and showed negligible inflammatory and cytotoxicity side effects. Furthermore, we found that NC-TNP could escape the recycling pathway to inhibit the egress of internalized nanoparticles from the intracellular compartment to the extracellular milieu which was a common fact in mRNA-LNP (lipid nanoparticles) formulation. Therefore, NC-TNP-encapsulated mRNA showed higher gene transfection efficiency in vitro and in vivo than mRNA-LNP formulation. Unexpectedly, NC-TNP showed spleen targeting delivery ability with higher accumulation ratio (spleen/liver), compared with traditional LNP. Spleen-targeting NC-TNP with mRNA exhibited high mRNA-encoded antigen expression in spleen and elicited robust immune responses. Overall, our work establishes a proof of concept for the construction of a noncationic system for mRNA delivery with good inflammatory safety profiles, high gene transfection efficiency, and spleen-targeting delivery to induce permanent and robust humoral and cell-mediated immunity for disease treatments.

Predicting streaming potential in reactive media: the role of pore geometry during dissolution and precipitation

SUMMARY Dissolution and precipitation processes modify the structure of the porous media at microscale which significantly affects the macroscopic properties of the media. These variations in the pore geometry result in changes in the hydraulic properties that control the groundwater flow, and also modify the electrokinetic properties associated to the displacement of electrical charges carried by the flow which originates the streaming potential. Under the hypothesis of a uniform dissolution or precipitation of the pores and based on the effective excess charge density approach, we present a physically based theoretical model for estimating the effective excess charge density as a function of time. The model is based on the assumption that the pore structure can be represented by an ensemble of capillary tubes with a smooth periodic variation of their radius and a fractal pore size distribution. The analytical expressions obtained to describe the effective excess charge density depend on the chemical parameters of the fluid and the petrophysical properties of the medium. In addition, the periodic variations assumed in the pore geometry represent a more realistic description of a porous medium than considering the pores as constant radii capillaries. These irregularities allow us to include the hysteresis phenomenon in the electrokinetic properties. The expressions of the proposed model have been tested with experimental data consisting of sets of effective excess charge density-effective saturation, permeability-effective saturation, porosity-time and permeability-time values. In all cases, the model is able to satisfactorily reproduce the behaviour of the data.

Water Table and Permeability Estimation From Multi‐Channel Seismoelectric Spectral Ratios

AbstractRecent developments in predicting and interpreting seismoelectric (SE) signals suggest a great potential for studying near‐surface hydrogeological properties, particularly in the vadose zone. Previous studies have revealed that the SE spectral ratios obtained from earthquake‐triggered SE data contain valuable hydrogeological information concerning porous media (e.g., permeability, porosity, fluid viscosity, and salinity). This study introduces Multi‐Channel SeismoElectric Spectral Ratios (MC‐SESRs) by considering an active seismic source acting on the ground surface. The frequency‐ and saturation‐dependent excess charge density is adopted to calculate the cross‐coupling coefficients. Applying a supervised learning task based on a flat neural network, the so‐called “broad learning (BL)” model, to map and extract the features of MC‐SESRs data, we seek to determine the permeability and the water table depth. Our results indicate that (a) MC‐SESRs are sensitive to the water table depth and permeability; (b) using more traces of SESRs data for inversion can increase accuracy; and (c) the changing water table can be rapidly determined by the MC‐SESRs by resorting to the BL inverse model, and it can attain an excellent accuracy while disturbed by data noise and misspecified model parameters (e.g., porosity and permeability) with errors of up to 20%. The proposed MC‐SESRs inversion has potential applications for non‐invasive monitoring in shallow porous media (e.g., frost thawing and geothermal upwelling).

How to minimize voltage and fill factor losses to achieve over 20% efficiency lead chalcogenide quantum dot solar cells: Strategies expected through numerical simulation

Lead chalcogenide colloidal quantum dot solar cells (CQDSCs) have the potential to revolutionize the field of light-to-electricity conversion with their exceptional optoelectronic properties. Unfortunately, realizing their full potential has been hindered by persistent and poorly understood limitations in fill factor (FF) and open-circuit voltage (Voc) losses. In this study, we performed a systematic numerical analysis of practical PbS CQDSCs to identify the root causes of FF and Voc losses in the current development stage, and to provide a clear and feasible roadmap for achieving a PCE of more than 20% in future development stages. Our analysis revealed that the highly effective route for enhancing the current 10% device is to initially modify the internal resistances, resulting in a significant reduction in FF losses to 15%, followed by systematic optimization of surface recombination velocities in the absorber layer and the absorber/hole transfer layer (HTL) interface, which can generate a Voc improvement of 3.76%, ultimately leading to a near-15% PCE. To further elevate PCE to unprecedented heights, we identified the precise regulation of surface excess charge densities at the absorber/HTL interface and the HTL/back contact interface as critical factors. By finely tuning these performance-limiting factors, we demonstrated the feasibility of achieving over 20% PCE, with minimal Voc loss of 318.10 mV and almost negligible FF loss of 6.08% in PbS CQDSCs. Our investigation provides crucial insights into the causes of FF and Voc losses in PbS CQDSCs and offers a clear pathway for future progress in this rapidly evolving field.

Metalloids (B, Si) and non-metal (N, P, S) doped graphene nanosheet as a supercapacitor electrode: A density functional theory study

Metalloids [Boron (B), Silicon (Si)] and Non -metals [Nitrogen (N), Phosphorus (P), Sulfur (S)] doped graphene nanosheets were considered for alternative lightweight electrode materials in energy storage device applications. The density functional theory studies were performed to investigate the structural stability, charge density distribution, excessive surface charge density, and quantum capacitance of doped graphene nanosheets. It is found that the structures are stable with negative formation energy, and the graphene nanosheet doped with P and S shows protrusion forming a pyramidal shape along the planar graphene nanosheet to maintain stability. Further, the doping of atoms into the graphene nanosheet introduced a minimal bandgap with a shift in the Fermi level, either into the conduction band or valence band, depending on the dopant type. This appearance of bandgap is attributed to the breaking of the symmetry in the graphene sublattice. Meanwhile, based on the type and concentration of dopant, localized and delocalized states are formed near the Fermi level. It is also found that the formation of a localized state near the Fermi level has profoundly improved the excessive surface charge density and quantum capacitance. The S – doped graphene nanosheet was observed to exhibit an excellent quantum capacitance of 38.88 μFcm−2 compared to all other structures and it can be used as a suitable light-weight electrode for asymmetric supercapacitors.

Understanding the degradation mechanism of TTA-based blue fluorescent OLEDs by exciton dynamics and transient electroluminescence measurements.

The lifetime of blue organic light-emitting diodes (OLEDs) has always been a big challenge in practical applications. Blue OLEDs based on triplet-triplet annihilation (TTA) up-conversion materials have potential to achieve long lifetimes due to fusing two triplet excitons to one radiative singlet exciton, but there is a lack of an in-depth understanding of exciton dynamics on degradation mechanisms. In this work, we established a numerical model of exciton dynamics to study the impact factors in the stability of doped blue OLEDs based on TTA up-conversion hosts. By performing transient electroluminescence experiments, the intrinsic parameters related to the TTA up-conversion process of aging devices were determined. By combining the change of excess charge density in the emitting layer (EML) with aging time, it is concluded that the TTA materials are damaged by the excess electrons in the EML during ageing, which is the main degradation mechanism of OLEDs. This work provides a theoretical basis for preparing long-lifetime blue fluorescent OLEDs.

Ab – initio study on the stability and electronic property of graphene nanosheets: Applications to batteries

AbstractThe aim of this work is to improve the electrochemical performance of graphene nanosheets for its potential applications as electrode materials in supercapacitors. In order to achieve this, we have carried out detailed ab – initio based density functional theory calculations on pristine and functionalized graphene nanosheets (containing 8, 18, and 32 carbon atoms) with different functional groups. We considered graphene nanosheets functionalized with groups such as ether, lactone, ketone, and carboxylate in addition to previously studied epoxy and hydroxyl. From the structural optimization, we observed variations in the transverse displacement of carbon atoms, changes in CC and CO bond length, and bond angles. In particular, we noticed when functionalized with lactone CC and CO bonds contracts more which results in excessive surface charge density, and quantum capacitance, This suggest that C32 – functionalized with lactone would be a better candidate for battery electrodes with relatively high and values.

Modeling the Frequency‐Dependent Effective Excess Charge Density in Partially Saturated Porous Media

AbstractIn the context of seismoelectric and self‐potential surveying, the effective excess charge density and the electrokinetic coupling coefficient are key parameters relating the measured electrical potential and the hydraulic characteristics of the explored porous media. In this work, we present a novel flux averaging approach that permits to estimate the frequency‐dependent effective excess charge density in partially saturated porous media. For this, we conceptualize the porous medium as a partially saturated bundle of capillary tubes under oscillatory flux conditions. We account for the pore size distribution (PSD) to determine the capillary‐pressure saturation relationship of the corresponding medium, which, in turn, permits to determine the pore scale saturation. We then solve the Navier‐Stokes equations within the saturated capillaries and, by means of a flux‐averaging procedure, obtain upscaled expressions for: (a) the effective excess charge density, (b) the effective permeability, and (c) the electrokinetic coupling coefficient, which are functions of the saturation and the probing frequency. We analyze and explain the characteristics of these functions for three different PSDs: fractal, lognormal, and double lognormal. It is shown that the PSD characteristics have a strong effect on the corresponding electrokinetic response. The proposed flux‐averaging approach has an excellent capability for reproducing experimental measurements and models in the literature, which are otherwise based on well‐known empirical relationships. The results of this work constitute a useful framework for the interpretation of electrokinetic signals in partially saturated media.

Piezoelectricity across 2D Phase Boundaries.

Piezoelectricity in low-dimensional materials and metal-semiconductor junctions has attracted recent attention. Herein, a 2D in-plane metal-semiconductor junction made of multilayer 2H and 1T' phases of molybdenum(IV) telluride (MoTe2 ) is investigated. Strong piezoelectric response is observed using piezoresponse force microscopy at the 2H-1T' junction, despite that the multilayers of each individual phase are weakly piezoelectric. The experimental results and density functional theory calculations suggest that the amplified piezoelectric response observed at the junction is due to the charge transfer across the semiconducting and metallic junctions resulting in the formation of dipoles and excess charge density, allowing the engineering of piezoelectric response in atomically thin materials.

The Cation Role in Ion Transport Selectivity of Gold-Plated Nanotubes

Ion permselectivity is an important ionic transport property exhibited in nanopores and nanotubes. Permselectivity develops due to the strong interactions between ions in solution and the nanopore/nanotube surfaces. Here, we study the ion permselectivity of gold-plated nanotube membranes. Gold-plated membranes were obtained by using an electroless gold plating method to deposit gold nanotubes into the pores and on the faces of track-etched polycarbonate membranes. These membranes have the potential to display cation permselectivity due to the excess surface charge density present on the membrane from chemisorbed Cl- anions. The cation permselectivity of membranes with 9.9 + 0.6 nm diameter nanotubes was studied potentiometrically by using a concentration cell. A new Debye-sphere based model was presented here to describe the extent of permselectivity. However, some ion specific effects with the gold-plated membrane are observed that cannot be interpreted by Debye theory. These ion-specific surface interactions lead to a reduction in the negative surface charge, causing no permselectivity for some cations as demonstrated by their lower than ideal cation transference numbers. Quantification of the surface charge density by XPS indicated the gold-plated membranes are highly charged due to Cl- chemisorption with a surface charge density of ~ 5.3 uC per cm2 corresponding to 3.3 x 1013 Cl--ions per cm2.

A Fractal Model for Effective Excess Charge Density in Variably Saturated Fractured Rocks

AbstractEstimating hydraulic properties and monitoring water flow in fractured rocks using self‐potential observations essentially relies on our ability to model streaming potential. One of the most promising approaches for modeling electrokinetic couplings is based on the macroscopic quantification of the excess charge which is effectively transported by pore water flow. In this study, we derive a fractal model to predict the effective excess charge density for fully and partially water saturated fractured media. Fractures are conceptualized as parallel plates with a fractal pattern described by the Sierpinski carpet. From the calculation of the excess charge in a single fracture and a flux averaging upscaling procedure, we obtain closed‐form expressions for the effective excess charge density. This new analytical model explicitly depends on the fracture water ionic concentration, interface properties, water saturation, porosity and permeability. Model predictions under saturated conditions are compared to published data measured in laboratory during hydraulic fracturing. The model development also shows the independence of the excess charge from the pore shapes: when expressed in terms of hydrological parameters, one can find an expression identical to recently published models for sedimentary porous media using capillary tubes. These results extend the validity of the existing models to fractured rocks and highlight the importance of hydraulic parameters for an accurate modeling of electrokinetic couplings.

Influence of carbon on electrochemical characteristics of the molten iron/slag interface

Interfacial properties between molten iron and slag play important roles in many steelmaking processes but very little electrochemical features are known. In this work, the influence of carbon (1 to 4.5 wt%) on electrochemical interfacial properties between molten iron and slag was investigated at 1600 °C. Impedance spectroscopy was performed at various direct current biases to measure ohmic-corrected differential capacitance. Single and double integration of the latter was used to obtain excess charge density and electrocapillary curves. All alloys displayed potentials of zero charge cathodic to the rest potential, indicating the metal side of the electric double layer carries a positive charge at the rest potential. Anodic to the potential of zero charge, carbon causes a large capacitance peak, increases excess charge density, and steepens electrocapillary curves. This behaviour is characteristic of specific (chemical) adsorption at the metal/slag interface, as opposed to electrostatic (physical) adsorption. This was verified by observation of the Esin and Markov coefficient where carbon systematically shifted potentials of zero charge towards more negative values. Measurement of the Esin and Markov coefficient showed the charge number of carbon in molten iron to be +5.9 ± 2.6. Hence, carbon carries a net positive charge while dissolved in molten iron, brings excess charge density to the interface that increases capacitance, causes attraction between metal/slag, and reduces interfacial tension. While it is well known carbon is not surface active at the iron/gas interface, results show carbon is capillary active at the iron/slag interface.

Dual-Modality Poly-l-histidine Nanoparticles to Deliver Peptide Nucleic Acids and Paclitaxel for In Vivo Cancer Therapy.

Cationic polymeric nanoformulations have been explored to increase the transfection efficiency of small molecules and nucleic acid-based drugs. However, an excessive positive charge density often leads to severe cell and tissue-based toxicity that restricts the clinical translation of cationic polymeric nanoformulations. Herein, we investigate a series of cationic poly(lactic-co-glycolic acid) (PLGA)-histidine-based nanoformulations for enhanced cytoplasmic delivery with minimal toxicity. PLGA/poly-l-histidine nanoparticles show promising physico-biochemical features and transfection efficiency in a series of in vitro and cell culture-based studies. Further, the use of acetone/dichloromethane as a solvent mixture during the formulation process significantly improves the morphology and size distribution of PLGA/poly-l-histidine nanoparticles. PLGA/poly-l-histidine nanoformulations undergo clathrin-mediated endocytosis. A contrast-matched small-angle neutron scattering experiment confirmed poly-l-histidine's distribution on the PLGA nanoformulations. PLGA/poly-l-histidine formulations containing paclitaxel as a small molecule-based drug and peptide nucleic acids targeting microRNA-155 as nucleic acid analog are efficacious in in vitro and in vivo studies. PLGA/poly-l-histidine NPs significantly decrease tumor growth in PNA-155 (∼6 fold) and paclitaxel (∼6.5 fold) treatment groups in a lymphoma cell line derived xenograft mice model without inducing any toxicity. Hence, PLGA/poly-l-histidine nanoformulations exhibit substantial transfection efficiency and are safe to deliver reagents ranging from small molecules to synthetic nucleic acid analogs and can serve as a novel platform for drug delivery.

Predicting the frequency-dependent effective excess charge density: A new upscaling approach for seismoelectric modeling

The seismoelectric method is based on the capacity of seismic waves to generate measurable modifications of the electrical field in porous media. Even though it combines the advantages of seismic and geoelectrical methods, it remains largely underused in hydrogeophysics. Its signal results from an electrokinetic coupling that can be modeled using either the coupling coefficient or the effective excess charge density. The traditional approach is based on the frequency-dependent coupling coefficient, which relates the pressure drop with the change in the electrical potential. A more recent approach consists of describing the excess charge that is effectively dragged by water flowing within the pores. We have developed a new model for the frequency-dependent effective excess charge density. For this, we make use of a mechanistic upscaling of the electrokinetic coupling in a capillary. This novel approach introduces inertial effects arising within the pore space in the flux-averaging procedure to explain the frequency dependence of the effective excess charge density. The presented model is successfully compared to previous models and published data. This new frequency-dependent upscaling approach has the potential of fundamentally improving our current understanding of the seismoelectrical signal in more complex environments, such as partially saturated and fractured media.

Electrochemical characteristics of molten iron electrodes in slag and electrochemical properties of their interface

Kinetic characteristics of molten iron/slag reactions and interfacial properties between molten iron/slag are of profound importance in steelmaking but quantitative electrochemical descriptions are lacking. Therefore, a detailed electrochemical investigation of pure (carbon-free) molten iron in slag was performed in the present work, using mostly impedance spectroscopy. Measurements were made between 1600–1700 °C at the rest potential and also at direct current biases to elucidate changes in interfacial properties when metal/slag reactions take place. Various fundamental physiochemical properties were measured for the first time including exchange currents, standard heterogeneous rate constants, Nernst diffusion layer thicknesses in slag, differential capacitance curves, potentials of zero charge, excess charge density curves, and electrocapillary curves. Results and discussion inform about the electric double layer formed between molten iron and slag.

Photophysics of Ruthenium(II) Complexes with Thiazole π-Extended Dipyridophenazine Ligands.

Transition-metal-based donor-acceptor systems can produce long-lived excited charge-transfer states by visible-light irradiation. The novel ruthenium(II) polypyridyl type complexes Ru1 and Ru2 based on the dipyridophenazine ligand (L0) directly linked to 4-hydroxythiazoles of different donor strengths were synthesized and photophysically characterized. The excited-state dynamics were investigated by femtosecond-to-nanosecond transient absorption and nanosecond emission spectroscopy complemented by time-dependent density functional theory calculations. These results indicate that photoexcitation in the visible region leads to the population of both metal-to-ligand charge-transfer (1MLCT) and thiazole (tz)-induced intraligand charge-transfer (1ILCT) states. Thus, the excited-state dynamics is described by two excited-state branches, namely, the population of (i) a comparably short-lived phenazine-centered 3MLCT state (τ ≈ 150-400 ps) and (ii) a long-lived 3ILCT state (τ ≈ 40-300 ns) with excess charge density localized on the phenazine and tz moieties. Notably, the ruthenium(II) complexes feature long-lived dual emission with lifetimes in the ranges τEm,1 ≈ 40-300 ns and τEm,2 ≈ 100-200 ns, which are attributed to emission from the 3ILCT and 3MLCT manifolds, respectively.