Chemical Potential Difference Research Articles

Quantifying the Driving Force of Silver Crystallization by Chemical Potential Difference

Quantifying the Driving Force of Silver Crystallization by Chemical Potential Difference

On the Thermodynamic Origin of the Formation of Li-Dendrites in an Electrochemical Cell

The direction of growth of neutral species in batteries and electrolyzers differs significantly. In a battery, dendrites can be formed during the charging process and are perpendicular to the interface between electrode and electrolyte. The aim of this manuscript is to address the origin of the growth orientation of the neutral metal and elucidate the factors that govern the dendrite growth by using the concept of chemical potential of neutral lithium and the electronic current in the electrolyte. With the consideration of the electronic conductivity in the ionic conductive phases, the chemical potential difference of lithium could be calculated across the cell, and predicts lithium deposition in the solid-electrolyte interphase (SEI) layer. The electronically conducting metal precipitate could work as a part of electrode and allow further growth along the current direction, resulting in the formation of dendrites. During growth, the ionic conductivity and the thickness distribution of the SEI layer determine the growth kinetics and the dendrite shape. A lower ionic conductivity and a nonuniform SEI layer lead to a sharp lithium dendrite. On the other hand, a low electronic conductivity and a high ionic conductivity of the electrode/electrolyte interface are in favor of suppressing the formation of a neutral species.

Diffusion processes in germanium and silicon films grown on Si3N4 substrates

In this article, the results of investigation of processes occurring during the molecular-beam deposition of germanium layers on Si$_3$N$_4$ dielectric substrates within a wide range of the Ge film growth temperatures (30 to 600{\deg}C) are presented. The intensity of the IR absorption bands related to the vibrations of the N$-$H and Si$-$N bonds are established to decrease with the increase of the Ge deposition temperature. It appears that this phenomenon cannot be explained only as a thermally activated process. Simultaneously, the peak corresponding to the Ge$-$N vibration bonds emerges in the X-ray photoelectron spectra. We suppose that the deposition of germanium layers on Si3N4 dielectric substrates containing hydrogen atoms causes the diffusion of hydrogen atoms from the dielectric layer into the growing film. The experimental results may be interpreted in terms of a model, according to which the migration of hydrogen atoms from the Si$_3$N$_4$ layer into the growing germanium film is due to the difference in chemical potentials of hydrogen atoms in the dielectric layer and the germanium film. This process initiates the diffusion of germanium atoms in the opposite direction, into the Si$_3$N$_4$ layer, where they connect to free bonds of nitrogen atoms arising due to the escape of hydrogen atoms. The analogous processes occur during the deposition of silicon layers on Si$_3$N$_4$ substrates.

A Drive towards Thermodynamic Efficiency for Dissipative Structures in Chemical Reaction Networks.

Dissipative accounts of structure formation show that the self-organisation of complex structures is thermodynamically favoured, whenever these structures dissipate free energy that could not be accessed otherwise. These structures therefore open transition channels for the state of the universe to move from a frustrated, metastable state to another metastable state of higher entropy. However, these accounts apply as well to relatively simple, dissipative systems, such as convection cells, hurricanes, candle flames, lightning strikes, or mechanical cracks, as they do to complex biological systems. Conversely, interesting computational properties—that characterize complex biological systems, such as efficient, predictive representations of environmental dynamics—can be linked to the thermodynamic efficiency of underlying physical processes. However, the potential mechanisms that underwrite the selection of dissipative structures with thermodynamically efficient subprocesses is not completely understood. We address these mechanisms by explaining how bifurcation-based, work-harvesting processes—required to sustain complex dissipative structures—might be driven towards thermodynamic efficiency. We first demonstrate a simple mechanism that leads to self-selection of efficient dissipative structures in a stochastic chemical reaction network, when the dissipated driving chemical potential difference is decreased. We then discuss how such a drive can emerge naturally in a hierarchy of self-similar dissipative structures, each feeding on the dissipative structures of a previous level, when moving away from the initial, driving disequilibrium.

Ferromagnetic percolation transition in a multiorbital flat band assisted by Hund's coupling

By connecting Hund's physics with flat band physics, we establish an exact result for studying ferromagnetism in a multiorbital system. We consider a two-layer model consisting of a ${p}_{x}, {p}_{y}$-orbital honeycomb lattice layer and an $f$-orbital triangular lattice layer with sites aligned with the centers of the honeycomb plaquettes. The system features a flat band that admits a percolation representation for an appropriate chemical potential difference between the two layers. In this representation, the ground-state space is spanned by maximum-spin clusters of localized single-particle states, and averaging over the ground states yields a correlated percolation problem with weights due to the spin degeneracy of the clusters. A paramagnetic-ferromagnetic transition occurs as the band approaches half filling and the ground states become dominated by states with a large maximum-spin cluster, as shown by Monte Carlo simulation.

Database-driven semigrand canonical Monte Carlo method: Application to segregation isotherm on defects in alloys.

The application of existing semigrand canonical ensemble Monte Carlo algorithms to alloys requires the chemical potential difference values between pairs of atomic species in the alloys as inputs. However, finding the appropriate values for a target system at a desired temperature and bulk composition is a time-consuming task consisting of multiple test runs to determine the chemical potential differences. This problem becomes more serious when dealing with systems containing three or more atomic species, such as medium- and high-entropy alloys, due to the increase of the number of chemical potential differences that need to be calculated. Here we propose a method for sampling from the semigrand canonical ensemble that relies on energy databases acting as an external atomic reservoir at the desired temperature and composition. Given these energy databases, the desired bulk composition and corresponding chemical potential differences can be satisfied in a "single" Monte Carlo simulation. Moreover, the energy databases shed light on the underlying energetics of alloys, reflecting their local chemical ordering. We demonstrate the validity of this method using analyses of segregation isotherms at grain boundaries and dislocations in two alloy systems: Fe-1-at.-%-Si and NiCoCr medium-entropy alloy. We also discuss the possibly relevant information contained in such energy databases.

Detailed explanations for the occurrence and nature of interfacial phenomena in liquid–liquid systems on the basis of the theory of spontaneous surface convection

The occurrence of unidirectional ejection phenomena (both continuous & intermittent), during mass transfer in binary and ternary systems respectively; reported earlier, have been explained on the basis of the theory of spontaneous surface convection (SSC). Also, intermittent jerking of the interface followed by emulsification coupled with profuse streaming action in the extract phase of two ternary systems has been explained by the same theory. In addition, intermittent circulatory motion in the extract phase only, in a ternary system has been explained on the basis of vertical and/or angular ejections’ restrained motion due to high viscosity of the extract phase. The theory of reversible adsorption and desorption phenomena for the transfer of surface-active solutes in ternary systems have been taken to help in justifying the occurrence of SSC during initial contacting of two phase. In most of the ternary systems reported earlier, vigorous density convection in the form of mushroom type density eddies observed are due to larger unstable density gradient. This is caused by high rates of mass transfer during SSC. SSC in the form of continuous circulatory motion in the extract phase only has been observed during the transfer of a surface inactive solute. Such phenomena occurred in aqueous to organic direction of transfer. The circulatory motion is due to ejections being against gravity. Surface inactive solute’s transfer also caused oscillatory motion of the interface as a whole in a particular system. The nature of most of the phenomena observed in binary and ternary systems appears to be due to molecular motions. The theory of SSC states that if specific energy of driving force of mass transfer is greater than free energy of the interface, interfacial instability occurs. It is probably a simplified version of a concept suggested here that can be explained by the kinetic theory as follows. It states that chemical potential difference of a solute between the two phases, if greater than the interfacial barrier plus molecular energy of the solute (in raffinate phase) then interfacial instability occurs. Thus, cluster of solute molecules in the form of ejections of bulk mass have been found to occur from raffinate to extract phase indicating high rates of mass transfer.

Orbital and spin polarizations induced by current through a helical atomic chain

Current-induced spin and orbital polarizations are theoretically studied in a helical atomic chain with ${p}_{x}, {p}_{y}$, and ${p}_{z}$ orbitals in each atom in the linear response to the chemical-potential difference between source and drain electrodes. It is shown that these polarizations are parallel to the helix axis and proportional to the curvature of the cylinder surface defined by the helix in the small curvature region. This proportionality suggests that the curvature generates the coupling between the current and the atomic orbital angular momentum and therefore influences the magnitude of induced spin polarization through the $LS$ coupling. It is also found that current-induced polarizations are nonzero even when the pitch is enforced to vanish. This suggests the possibility that nonchiral structures with curvature can produce current-induced polarizations. With this possibility in mind, it is proposed that the chirality in the current, rather than that in the structure, determines the existence of such current-induced polarizations.

Principles of reverse electrodialysis and development of integrated-based system for power generation and water treatment: a review

Abstract Reverse electrodialysis (RED) is among the evolving membrane-based processes available for energy harvesting by mixing water with different salinities. The chemical potential difference causes the movement of cations and anions in opposite directions that can then be transformed into the electrical current at the electrodes by redox reactions. Although several works have shown the possibilities of achieving high power densities through the RED system, the transformation to the industrial-scale stacks remains a challenge particularly in understanding the correlation between ion-exchange membranes (IEMs) and the operating conditions. This work provides an overview of the RED system including its development and modifications of IEM utilized in the RED system. The effects of modified membranes particularly on the psychochemical properties of the membranes and the effects of numerous operating variables are discussed. The prospects of combining the RED system with other technologies such as reverse osmosis, electrodialysis, membrane distillation, heat engine, microbial fuel cell), and flow battery have been summarized based on open-loop and closed-loop configurations. This review attempts to explain the development and prospect of RED technology for salinity gradient power production and further elucidate the integrated RED system as a promising way to harvest energy while reducing the impact of liquid waste disposal on the environment.

Classical nucleation theory of ice nucleation: Second-order corrections to thermodynamic parameters.

Accurately estimating the nucleation rate is crucial in studying ice nucleation and ice-promoting and anti-freeze strategies. In classical nucleation theory, estimates of the ice nucleation rate are very sensitive to thermodynamic parameters, such as the chemical potential difference between water and ice Δμ and the ice-water interfacial free energy γ. However, even today, there are still many contradictions and approximations when estimating these thermodynamic parameters, introducing a large uncertainty in any estimate of the ice nucleation rate. Starting from basic concepts for a general solid-liquid crystallization system, we expand the Gibbs-Thomson equation to second order and derive second-order analytical formulas for Δμ, γ, and the nucleation barrier ΔG*, which are used in molecular dynamics simulations. These formulas describe well the temperature dependence of these thermodynamic parameters. This may be a new method of estimating Δμ, γ, and ΔG*.

Estimation of the equilibrium free energy for glasses using the Jarzynski equality.

The free energy of glasses cannot be estimated using thermodynamic integration as glasses are intrinsically not in equilibrium. We present numerical simulations showing that, in contrast, plausible free-energy estimates of a Kob-Andersen glass can be obtained using the Jarzynski relation. Using the Jarzynski relation, we also compute the chemical potential difference of the two components of this system and find that, in the glassy regime, the Jarzynski estimate matches well with the extrapolated value of the supercooled liquid. Our findings are of broader interest as they show that the Jarzynski method can be used under conditions where the thermodynamic integration approach, which is normally more accurate, breaks down completely. Systems where such an approach might be useful are gels and jammed glassy structures formed by compression.

On the Optimization of Core-Shell Hybrid Cathode Materials for Extreme Fast-Charging: First Principles Computational Insights

Core-shell and core-gradient hybrid cathode materials for lithium-ion batteries display enhanced rate capability over their homogeneous counterparts. The apparent enhancement of transport is shown to arise from advective flow of Li+ from the higher free-energy core towards the lower free-energy shell compositions. First-principles analysis of a planar model of these hybrid structures concludes that the inbuilt free-energy gradient enhances the Li+ de-intercalation process by reducing the average overpotential during extreme fast-charging. Analysis of representative LiNi0.8Co0.1Mn0.1O2||LiNi0.4Co0.2Mn0.4O2 core/shell reveals: (i) an optimal components ratio exists that maximizes storage capacity during fast-charging and (ii) components should be selected with appreciably large chemical potential difference between the core and shell to further exploit the free-energy gradient effects provided volume ratios are optimized against the potential gradient. In the case of NCM811||NCM424 studied herein, a balanced (ca. 40/60 vol.%) structure appears optimal. This finding indicates that the shell must not necessarily be confined to a thin chemically-protective coating; higher relative volumes of the lower free-energy shell may provide performance benefits at high-rates. The presented insights will serve towards optimizing and developing high capacity, more rate capable core-shell particles for extreme fast charging batteries. Figure 1

Evolution of a low-alloy steel/nickel superalloy dissimilar metal weld during post-weld heat treatment

The design of the dissimilar metal weld investigated here is aimed at applications in the steam generator of a sodium-cooled nuclear reactor, with a multi-decade lifespan in demanding operational conditions. It consists in a narrow-gap joint between 2.25Cr-1Mo low-alloy steel and an austenitic alloy using a nickel-based alloy 82 as filler material. This study focuses on understanding the microstructural and micromechanical evolution in the near fusion boundary region between the low-alloy steel and the nickel alloy filler metal during post-weld heat treatment, using notably electron probe micro-analysis and nano-indentation. The difference in matrix phase and chemical composition between the two alloys leads to a large difference in chemical potential for carbon, which is mobile at the post-weld heat treatment temperature. A number of fine-scale characterization techniques were used to assess the gradient of composition, hardness, and microstructures across the fusion boundary, both as-welded and after post-weld heat treatment. This complete analysis permits to highlight and understand the main microstructural and micromechanical changes occurring during post-weld heat treatment and opens the way to their long term study in service conditions.

Magnetic charge propagation upon a 3D artificial spin-ice

Magnetic charge propagation in spin-ice materials has yielded a paradigm-shift in science, allowing the symmetry between electricity and magnetism to be studied. Recent work is now suggesting the spin-ice surface may be important in mediating the ordering and associated phase space in such materials. Here, we detail a 3D artificial spin-ice, which captures the exact geometry of bulk systems, allowing magnetic charge dynamics to be directly visualized upon the surface. Using magnetic force microscopy, we observe vastly different magnetic charge dynamics along two principal directions. For a field applied along the surface termination, local energetics force magnetic charges to nucleate over a larger characteristic distance, reducing their magnetic Coulomb interaction and producing uncorrelated monopoles. In contrast, applying a field transverse to the surface termination yields highly correlated monopole-antimonopole pairs. Detailed simulations suggest it is the difference in effective chemical potential as well as the energy landscape experienced during dynamics that yields the striking differences in monopole transport.

Relations between absorption, emission, and excited state chemical potentials from nanocrystal 2D spectra.

For quantum-confined nanomaterials, size dispersion causes a static broadening of spectra that has been difficult to measure and invalidates all-optical methods for determining the maximum photovoltage that an excited state can generate. Using femtosecond two-dimensional (2D) spectroscopy to separate size dispersion broadening of absorption and emission spectra allows a test of single-molecule generalized Einstein relations between such spectra for colloidal PbS quantum dots. We show that 2D spectra and these relations determine the thermodynamic standard chemical potential difference between the lowest excited and ground electronic states, which gives the maximum photovoltage. Further, we find that the static line broadening from many slightly different quantum dot structures allows single-molecule generalized Einstein relations to determine the average single-molecule linewidth from Stokes' frequency shift between ensemble absorption and emission spectra.

The Extended Eighth-Shell method for periodic boundary conditions with rotational symmetry.

The Eighth-Shell method for parallelization of molecular dynamics simulations has previously been shown to be the most optimal for efficiency at large process counts. However, in its current formulation only the P1 space group is supported for periodic boundary conditions (PBC) and thus reflection and/or rotational crystal symmetries are not supported. In this work, we outline the development and implementation of the Extended Eighth-Shell (EES) method that allows rotational symmetry by using an extended import region compared to the ES method. It simulates only the asymmetric unit and communicates coordinates and forces with images that correspond to P21 PBC. The P21 PBC has application in lipid bilayer simulations as it can be used to allow lipids to switch leaftlets, thus rapidly balancing the chemical potential difference between the two layers. Our results show that the EES method scales efficiently over large number of processes and can be used for simulations with P21 symmetry in an orthorhombic crystal.

Dynamic structure factors of a strongly interacting Fermi superfluid near an orbital Feshbach resonance across the phase transition from BCS to Sarma superfluid

We theoretically investigate dynamic structure factors of a strongly interacting Fermi superfluid near an orbital Feshbach resonance with random phase approximation, and find their dynamical characters during the phase transition between a balanced conventional Bardeen-Cooper-Schrieffer superfluid and a polarized Sarma superfluid by continuously varying the chemical potential difference of two spin components. In a BEC-like regime of the BCS superfluid, dynamic structure factors can do help to distinguish the in-phase ground state from the out-of-phase metastable state by the relative location of molecular excitation and Leggett mode, or the minimum energy to break a Cooper pair. In the phase transition between BCS and Sarma superfluid, we find the dynamic structure factor of Sarma superfluid has its own specific gapless excitation at a small transferred momentum which is mixed with the collective phonon excitation, and also a relatively strong atomic excitation at a large transferred momentum because of the existence of unpaired Fermi atoms, these signals can be used to differentiate Sarma superfluid from BCS superfluid.

The Economic Infeasibility of Salinity Gradient Energy via Pressure Retarded Osmosis

Pressure retarded osmosis (PRO) harvests the chemical potential difference between water sources of two different salinities and has been widely researched as a source of low carbon energy. This study identifies the cost-optimal design and operation using a nonlinear programming model to minimize the levelized cost of electricity (LCOE) of a PRO system for specified process and financial parameters. Our model includes a detailed finite difference module-scale model that considers the pressure drop along the module, nonconstant solution properties, local mass transfer coefficients, and equipment inefficiencies that previous analyses lacked. Under realistic case specifications and present-day costs, the expected median LCOE ranges from $2.37/kWh (seawater draw) to $0.11/kWh (Dead Sea draw). The optimistic case specifications, which assume significant improvements in process performance with no additional increase in cost, lower these median costs to $1.00/kWh (seawater draw) and $0.05/kWh (Dead Sea draw). These estimates exclude variable pretreatment costs and are likely to underestimate the actual LCOE. Membrane costs and maintenance are the primary cost components for all cases. Comparing the LCOE and capacity factor of PRO to other low carbon energy sources suggests that reductions in PRO component costs are unlikely to make PRO cost competitive with renewable energy technologies.

Modeling and Performance Optimization of Double-Resonance Electronic Cooling Device with Three Electron Reservoirs

Abstract In this paper, a new model of the three-electron reservoir energy selective electronic cooling device applying double-resonance energy filters is proposed by using finite time thermodynamics. The analytical formulas of the main performance parameters for the double-resonance three-electron reservoir cooling device are derived. The optimal cooling load and coefficient of performance of the cooling device varying with major structure design parameters are explored and the optimal operation regions are further determined. Moreover, detailed analyses are conducted to reveal the influences of center energy level difference, chemical potential difference, energy level width, energy spacing and the phonon transmission induced heat leakage on the optimal performance characteristics of the cooling device. Finally, a performance comparison is made between the double-resonance and single-resonance three-electron reservoir electronic cooling devices. It is shown that through reasonable structure design, the optimal performance characteristics of the double-resonance device can be controlled to be much higher than those of the single-resonance cooling device.

Novel insights into gel layer fouling in forward osmosis process based on thermodynamic analysis: Role of reverse salt diffusion

Membrane fouling in forward osmosis (FO) process is more complicated than pressure-driven membrane process due to the phenomenon of reverse salt diffusion. Gel layer fouling due to reverse salt diffusion of three draw solutions (NaCl, MgCl2 and CaCl2) were investigated from the thermodynamic view in FO process. The reverse-diffused Mg2+/Ca2+ caused more serious gel fouling and flux decline than Na+ at permeate volume of 500 mL. Non-invasive inverted phase-contrast microscope observed that reverse-diffused Mg2+/Ca2+ induced the formation and cross-linking of long sodium alginate chains. Thermogravimetric analysis (TGA) revealed that Mg2+/Ca2+ enhanced the binding ability of bound water to gel chains. From the thermodynamic view, the above changes caused by Mg2+/Ca2+ resulted in that a higher driving force (osmosis pressure difference) was consumed to overcome the chemical potential difference between gel and permeate during FO process, which gave rise to the less driving force and the worse performance. This study provided a new perspective and insight to explain gel fouling in FO process.