Double Layer Effects Research Articles

Recent advances in sensing and biosensing with arrays of nanoelectrodes

This review deals with recent advances in the field of electrochemical sensing and biosensing with nanoelectrode ensembles (NEEs) and nanoelectrode arrays (NEAs), focusing mainly on articles published since 2015. At first, a brief introduction on the properties and possible advantages which characterize electroanalytical signals at the NEE/NEA is presented, followed by an overview on the most recent theoretical advances concerning the modeling of relevant electrochemical signals. Novel nanofabrication methods and nanoelectrode materials are discussed together with original (bio)funtionalization procedures, suitable to obtain more sensitive and reliable sensors. Advanced applications of NEE/NEA-based sensors in the biological and biomedical field are presented, including their integration with living cells and application for neurochemical studies. Advances, present limits, and prospects for research in the area are finally discussed. As far as future research trends are concerned, on the one hand, there is a need for development of theoretical models which take into account specific effects that can rule electrochemistry with arrays of nanosized electrodes, such as double layer and quantum mechanical effects. On the other hand, frontier studies concerning the application of the NEE/NEA to the biomedical and neurochemical fields can open new tracks both to fundamental knowledge and application.

Potential-Induced Acid-Base Chemistry of Adsorbed Species

In a recent paper, Martinez-Hincapie et al.1 reported in situ reflection-absorption Fourier transform infrared spectra for a Pt(111) electrode in CO2 -saturated KClO4/HClO4 aqueous solutions over the pH range 1.10 - 3.10. As clearly shown by their data, significant changes in the relative ratios of the spectral features ascribed to adsorbed bicarbonate, HCO3 -(ads), and carbonate, CO3 2-(ads), were observed as the applied potential was increased in a region in which the total coverage of HCO3 -(ads) and CO3 2-(ads) attained a fairly constant value. The presence of these species in solutions of such low pH, as well as the changes in the extent of ionization induced by the applied potential represent a new phenomenon not as yet been fully explained. To the best our knowledge, the report of Martinez-Hincapie et al.1 represent the first illustration aimed at determining spectroscopically the extent of deprotonation as a function of the applied potential in this type of systems. This presentation will describe a model based largely on that reported by Smith and White2 decades ago, which predicted interfacial capacity vs potential plots displaying features attributed to the acid-base chemistry of self-assembled alkyl chain monolayers bearing carboxylic groups in contact with an aqueous electrolyte. Shortly thereafter, Fawcett et al. further refined this theory by introducing discreteness of charge effects.3 Application of this model to the adsorbed HCO3 -/CO3 2- layer on Pt(111) can account for the potential dependence of the relative ratios of the two species as a function of pH, for relatively reasonable values of the parameters involved. Particularly striking is the much lower pKa value for HCO3 -(ads) compared to that in bulk aqueous solutions, which we tentatively ascribe to the bonding of the adsorbate to the surface and thus to changes in its electronic structure. The starting point of our analysis regards the HCO3 -(ads)/CO3 2-(ads) layer, in this case, as attached to the surface through a bidentate type bond with the proton in HCO3 - (ads) bonded to the oxygen facing the electrolyte, which defines the so-called plane of acid dissociation (PAD) (see Fig. 1). Based on Smith and White’s formalism, the problem so stated reduces to finding solutions of a system of five non-linear algebraic equations with five unknowns, shown in Scheme I, where σM is the charge density on the electrode (C/cm2), CF is the capacitance of the adsorbed molecular film (F/cm2), Epcz is the potential of zero charge of the interface devoid of the adsorbate and σPAD is the charge density at the PAD, (C/cm2). Furthermore, the symbols and , represent the potential differences between the regions specified in Fig. 1, where ϕi is the electrostatic potential for i = metallic electrode, M; plane of acid dissociation, PAD; and electrolyte solution, S; f, the fraction of CO3 2-(ads), pH refers to the value of the bulk solution and pKa is the acidity constant of the adsorbed layer. The third equation represents the neutral character of the interface where is right hand side is σS, the charge density of the diffuse double layer (C/cm2) written in terms of DVs, the Debye length, k and the dielectric constants of vacuum and the electrolyte solution, eo and es, respectively. The system of equations was solved using Mathematica 11.3 for each of the log[f/(1-f)], E, data points collected from the spectroelectrochemical measurements at the three pH values examined. Shown in Figure 2 are plots of σM, σPAD, ΔVF , ΔVS , Cd, and pKa as a function of the rational potential, i.e. E - Epzc. As indicated, the value of pKa determined based on all the data collected is about 2.7, much lower than that of solution bicarbonate, 10.3. We tentatively ascribe this phenomenon to the bonding of the adsorbate to the surface and thus to changes in its electronic structure. Literature Cited 1. Martinez-Hincapie, R.; Berna, A.; Rodes, A.; Climent, V.; Feliu, J. M., Surface Acid-Base Properties of Anion-Adsorbed Species at Pt(111) Electrode Surfaces in Contact with CO2-Containing Perchloric Acid Solutions. Journal of Physical Chemistry C 2016, 120 (29), 16191-16199.Smith, C. P.; White, H. S., Voltammetry of Molecular Films Containing Acid-Base Groups. Langmuir 1993, 9 (1), 1-3.(a) Andreu, R.; Fawcett, W. R., Discreteness-of-Charge Effects at Molecular Films Containing Acid/Base Groups. J. Phys. Chem. 1994, 98 (48), 12753-12758; (b) Fawcett, W. R.; Fedurco, M.; Kovacova, Z., Double-Layer Effects at Molecular Films Containing Acid-Base Groups. Langmuir 1994, 10 (7), 2403-2408. Figure 1

(Invited) Sensing, Measuring and Imaging Surface Charge with Nanoscale Pipettes

Charge is a fundamental interfacial property that governs physical and chemical interactions at surfaces. The workings of catalysts, sensors, separation devices, biological interfaces, and colloidal systems, are well known to be strongly influenced by surface charge, typically present in the form of protonated or deprotonated chemical moieties. Directly measuring and sensing charge in situ, especially for small (micro/nanoscale), heterogeneous charge distributions presents an interesting and important challenge for electroanalytical chemistry. Here, recent studies in mapping interfacial charge with scanning ion conductance microscopy (SICM) and the influence of electrolyte concentration on the charge sensing mechanism will be described. We have validated a SICM method that utilizes current‐voltage relationships that can be intuitively understood for surface charge detection. The effect of electrical doublelayer (EDL) thickness on signal generation on chemically modified surfaces will be demonstrated. The differential measurement approach used here allows visualization of individual domains of surface charge. EDL effects are modeled with finite element simulations, and extension of our studies to sensing at biological samples and mineral samples will be demonstrated.

Facile preparation and capacitive properties of low-cost carbon nanofibers with ZnO derived from lignin and pitch as supercapacitor electrodes

To develop economical and high-performance supercapacitor electrodes in an aqueous electrolyte, polyacrylonitrile (PAN)/pitch/lignin-based carbon nanofibers (CNFs) with ZnO (PPL-Zn) are successfully fabricated by one-step electrospinning of PAN, pitch, lignin, and zinc acetate. The oxygen-rich lignin in the PPL-Zn electrodes induces porosity on the fiber surface by eliminating many functional groups such carboxylic, carbonyl, hydroxyl and ketone and organic moieties in the simple heat treatment without any activation agent/activation process. Moreover, the many aromatic components, high carbon content, and low glass transition temperature of lignin are excellent precursors to CNF composites. In addition to lignin, pitch is used as a precursor to CNF to reduce the cost and increase the carbon yield and electrical conductivity of the CNFs. These characteristics afford PPL-Zn(5) (5 wt% of zinc acetate relative to PAN and lignin) with good capacitive behavior for application as supercapacitor electrodes with a maximum specific capacitance of 165 Fg-1 at 1 mAcm−2 with a capacitance retention of 88%, high energy densities of 22–18 Whkg−1 in the power density range of 400 to 10,000 Wkg-1, and excellent cycling performance reduced by only ∼6% after 3000 cycles of charge/discharge due to the synergistic effect of the electrical double layer and the pseudocapacitive effect.

Equivalent circuit model modified for free-standing bilayer lipid membranes beyond 1 TΩ

A cell is the basic functional unit of living organisms. Bilayer lipid membranes (BLMs), which form cell membranes can be assembled by using artificial methods. The electrochemical characteristics of BLMs are normally investigated using electrochemical impedance spectroscopy (EIS); however, the equivalent circuit need to be modified by the experimental conditions. In this study, we formed plain BLMs to determine the underlying equivalent circuit model of free-standing BLMs, and we measured the electrical characteristics using EIS. To analyze the results of EIS, we proposed equivalent circuit models including electrical double layer (EDL) effects on both sides of a BLM. We also extracted and evaluated the electrochemical parameters; the aperture-suspended BLMs using an Si chip having tapered edge recorded TΩ-order membrane resistances, which were one order higher than those reported in most previous studies. Regarding the capacitances of EDL, we compared the extracted values and the calculated results.

Electrophoretic deposition of RGO-NiO core-shell nanostructures driven by heterocoagulation method with high electrochemical performance

A heterocoagulation route is proposed to prepare Reduced Graphene Oxide-Nickel Oxide (RGO/NiO) hybrid structures for their application as supercapacitor electrodes. The RGO intercalation among the NiO nanoplatelets was carried out by electrostatic interactions of the synthetized particles which were previously dispersed and stabilized in aqueous media to improve the assembly between both materials forming core-shell structures. The electrophoretic deposition (EPD) was used to shape the composite onto 3D collector (Ni foams) controlling their growth and homogeneity. Electrodes were thermal treated at 325 °C during 1 h to improve the electrochemical response since the formation of ceramic necks among NiO semiconductor nanoparticles preserves the microstructural integrity to enhance their connectivity avoiding the employment of binders, while RGO contributes with the electrochemical double layer effect to step up the specific capacitance by reducing the charge transfer resistance. FESEM results confirmed that RGO nanosheets were full-covered by the NiO nanoplatelets and suggested that ∼1 mg of the electroactive composite homogeneously covers the Ni foam and it is the optimum among of electroactive material to avoid microstructural defects that produce ohmic drops limiting the capacitance. The electrochemical characterization of the resulting binder-free RGO/NiO electrodes was compared with the bare-NiO electrode. The hybrid composite exhibited excellent performance with a high specific capacitance of 940 F g-1 at 2 Ag-1 and a higher rate capability.

Double Interfacial Layers Effect on Optical Third-order Nonlinear Susceptibility, Refraction Index, and Absorption Coefficient of a Metal/ Dielectric Composite

We investigate the way of enhancing the optical third order susceptibility, the refractive index, and absorption coefficient of a composite media in which identical nonlinear nanospheres having double interfacial layer randomly embedded in the linear host medium. We observe two maxima peaks of the nonlinear properties. We also show that the effect of double interfacial layers on the third order susceptibility, the refractive index, and absorption coefficient depends on the volume fraction metal/ dielectric nanosphers and the nature of the double interfacial layers. Under appropriate condition (nature of the two interfacial layer) we found two maximum peaks of the nonlinear properties. We also compare with the same composite without interfacial layer and in the presence of single interfacial layer and our finding shows that because of additional interfacial layer the effective medium exhibit a better third-order susceptibility, refractive index, and absorption coefficient.

A fractal study for the effective electrolyte diffusion through charged porous media

Electrolyte diffusion in electrolyte solutions exists in various areas including rechargeable batteries, soil physics and chemical engineering. In this paper, a fractal model based on the capillary model and fractal theory of porous media is proposed to quantify the effective electrolyte diffusivity in porous media with consideration of the electrical double layer (EDL) effects. The present model explicitly relates to the micro-structural parameters of porous media and electrokinetic parameters. To validate this model, a comparison is carried out with experimental data and semi-analytical model results, and yields satisfying agreement. Besides, the influences of the parameters (the porosity, equivalent particle diameter, ratio of the minimum pore radius to the maximum pore radius, molar concentration, zeta potential, and dimensionless parameter β) are discussed in details.

Study on pore size effect of low permeability clay seepage

Low-permeability clays are characterized by a large amount of clay minerals and a special distribution of pore sizes, so their seepage behavior shows an obvious pore size effect. Therefore, conventional seepage theories show deviations in describing the seepage behavior of low-permeability clays. This paper analyzes two reasons for the pore size effect in low-permeability clay seepage: the pore distribution property and the electric double layer effect of the clay surface. Considering these two factors, the seepage theory of the pore size effect based on the microscale seepage of the circular tube model is proposed. The rationality of this theory is tested by the seepage experiments of natural undisturbed clay and artificial clay, and from these experiments, three beneficial conclusions are drawn: (1) The results of the pore size effect seepage theory are in good agreement with the experimental results and are better than the modified Kozeny-Carman equation; (2) The properties of the electric double layer have a certain regular influence on the seepage behavior of the clay; (3) Considering the properties of the soil pore size distribution, the results obtained by using the pore size effect theory are much closer to the experimental results than the results calculated using the average pore diameter of the clay.

Diffusiophoresis of a Highly Charged Porous Particle Induced by Diffusion Potential

Diffusiophoresis, the motion of a colloidal particle in response to the concentration gradient of solutes in the suspending medium, is investigated theoretically on the basis of numerical computations in this study for charged porous particles, especially highly or extremely porous ones, focusing on the electrophoresis component induced by diffusion potential, which is generated spontaneously in a binary electrolyte solution where the diffusivities of the two ionic species are distinct. A benchmark carbonic acid solution of H(aq)+ and HCO3(aq)- is chosen to be the major suspending medium, as its large diffusion potential and remarkable performance in practical applications have been reported recently in the literature. More than 3 orders of magnitude increase in particle diffusiophoretic mobility is predicted under some circumstances, should the permeability of the particle increase 10-fold. Nonlinear effects such as the motion-deterring double-layer polarization effect pertinent to highly charged particles and the counterion condensation or shielding/screening effect pertinent to porous particles are investigated in particular for their impact on the particle motion, among other electrokinetic parameters examined. A visual demonstration of the nonlinear double-layer polarization is provided. Moreover, both the chemiphoresis and the electrophoresis components are explored and analyzed in detail. The results presented here can be applied in biochemical and biomedical fields involving DNAs and proteins, which can be modeled excellently as charged porous particles in their electrokinetic motion.

Effects of Double Interfacial Layers on the Local Field Enhancement Factor and Optical Induced Bistability of a Small Spherical Metal/Dielectric Composites

We propose the way of enhancing the enhancement factor of local field, and increasing the input domain threshold of the optical induced bistability of a spherical metal/dielectric composites within a linear host matrixes. The local field enhancement factor of a metal particles with dielectric core in the presence of double interfacial layers shows two maxima at two different frequencies. By introducing double interfacial layers, we calculate the enhancement factor of the local field. Also using the cubic equation the optical induced bistability of the composite material is calculated. Because of the double interfacial layers, we observe an increasing of the input domain threshold of the optical induced bistability. In comparison with the same composite without interfacial layer and with having single interfacial layer, our finding shows that, introducing additional interfacial layer makes the composite having a better enhancement factor and much better input domain threshold of the optical induced bistability.

Standalone interferometry-based calibration of convex lens-induced confinement microscopy with nanoscale accuracy.

Strongly confined environments (confined dimensions between 1-100 nm) represent unique challenges and opportunities for understanding and manipulating molecular behavior due to the significant effects of electric double layers, high surface-area to volume ratios, and other phenomena at the nanoscale. Convex Lens-induced Confinement (CLiC) can be used to analyze the dynamics of individual molecules or particles confined in a planar slit geometry with continuously varying gap thickness. We describe an interferometry-based method for precise measurement of the slit pore geometry. Specifically, this approach permitted accurate characterization of separation distances as small as 5 nm, with 1 nm precision, without a priori knowledge or assumptions about the contact geometry, as well as a greatly simplified experimental setup that required only a lens, coverslip, and inverted microscope. The interferometry-based measurement of gap height offered a distinct advantage over conventional fluorescent dye-based methods; e.g., accurate interferometric height measurements were made at low gap heights regardless of solution conditions, while the concentration of fluorescent dye was significantly impacted by solution conditions such as ionic strength or pH. The accuracy of the interferometric measurements was demonstrated by comparing the experimentally measured concentration of a charged fluorescent dye as a function of gap thickness with dye concentration profiles calculated using Debye-Hückel theory. Accurate characterization of nanoscale gap thickness will enable researchers to study a variety of practical and biologically relevant systems within the CLiC geometry.

Optimized Nickel-Cobalt and Nickel-Iron Oxide Catalysts for the Hydrogen Evolution Reaction in Alkaline Water Electrolysis

Ni and Ni-doped with transition metals (TM) such as Fe and Co represent the most suitable electrodes for hydrogen evolution reaction (HER) in alkaline media. Various compositions of co-precipitated Ni1 + xFe2 − xO4 and Ni1 + yCo2 − yO4 nanoparticles were investigated. The intrinsic HER catalytic activity is the same for all the catalysts, which we relate to similar values of the iso-electric point (IEP). However, the mass catalytic activity of the catalysts changes through a modification of the electrochemical surface area. Fractional reaction orders for hydrogen evolution revealed in all catalyst compositions are due to double layer effects and surface acid-base equilibria. Reaction order and Tafel slope of the catalysts are compatible with electrochemical adsorption as the rate-determining step for the HER. Tafel slopes were also evaluated independently from impedance spectroscopy, in good agreement with the polarization curves. Electrodes prepared from catalyst inks containing an anion-exchange ionomer displayed inferior catalytic activity for the HER as compared to electrodes prepared with Nafion in the ink. Chronoamperometry confirmed the sustained superior hydrogen kinetics over time of NiFe2O4 and NiCo2O4 composition over that of NiO.

Proton Discharge on a Gold Electrode from Triethylammonium in Acetonitrile: Theoretical Modeling of Potential-Dependent Kinetic Isotope Effects.

The discharge of protons on electrode surfaces, known as the Volmer reaction, is a ubiquitous reaction in heterogeneous electrocatalysis and plays an important role in renewable energy technologies. Recent experiments with triethylammonium (TEAH+) donating the proton to a gold electrode in acetonitrile demonstrate significantly different Tafel slopes for TEAH+ and its deuterated counterpart, TEAD+. As a result, the kinetic isotope effect (KIE) for the hydrogen evolution reaction changes considerably as a function of applied potential. Herein a vibronically nonadiabatic approach for proton-coupled electron transfer (PCET) at an electrode interface is extended to heterogeneous electrochemical processes and is applied to this system. This approach accounts for the key effects of the electrical double layer and spans the electronically adiabatic and nonadiabatic regimes, as found to be necessary for this reaction. The experimental Tafel plots for TEAH+ and TEAD+ are reproduced using physically reasonable parameters within this model. The potential-dependent KIE or, equivalently, isotope-dependent Tafel slope is found to be a consequence of contributions from excited electron-proton vibronic states that depend on both isotope and applied potential. Specifically, the contributions from excited reactant vibronic states are greater for TEAD+ than for TEAH+. Thus, the two reactions proceed by the same fundamental mechanism yet exhibit significantly different Tafel slopes. This theoretical approach may be applicable to a wide range of other heterogeneous electrochemical PCET reactions.

Quantitative Assessment of Molecular Transport through Sub-3 nm Silica Nanochannels by Scanning Electrochemical Microscopy.

Scanning electrochemical microscopy (SECM) has been proved to be a powerful technique to study molecular transport across ionic channels in biomembranes and artificial nanoporous membranes. In this work SECM was used to study the dynamics of molecular transport across the ultrathin silica nanoporous membrane consisting of sub-3 nm diameter perpendicular channels. We focused on the quantitative assessment of permselectivity and permeability of the membrane and the effect of radial electrical double layer (EDL) on them. By SECM imaging, it was phenomenologically observed that the membrane with negatively charged surface exhibited permselectivity to anionic molecule, for instance hexacyanoruthenate(II) (Ru(CN)64-). And the permselective transport of Ru(CN)64- was obviously more favored at a higher concentration of KCl. Precise membrane permeability to Ru(CN)64- was quantitatively determined by overlapping experimental SECM approach curves with the ones generated by finite element simulations. The high permeability up to 35 μm s-1 was ascribed to the straight channel structure and ultrahigh channel density of 4 × 1012 cm-2. Moreover, the permeability was varied from 35 μm s-1 to 2.5 μm s-1 when decreasing the concentration of KCl from 1.0 to 0.01 M, corroborating the electrostatic origin of membrane permselectivity. On the other hand, the simulated concentration profiles at both sides of the membrane suggested that the molecular transport across the membrane was mainly driven by the large transmembrane concentration gradient while the tip-induced transport was relatively negligible. These results help to quantitatively understand the molecular transport selectivity and dynamics across nanoporous membranes and to rationally design artificial molecular sieving membranes.

Mathematical modelling of surface tension of nanoparticles in electrolyte solutions

Nanoparticles (NPs) have been successfully applied to reservoirs for enhanced oil recovery and fines migration mitigation at laboratory scale. Despite the successful implementation at laboratory scale, it is rarely applied at field scale. One of the major reasons for the delay in implementation is the lack of an appropriate model to predict the fluid-particles behaviour in the reservoir. An accurate prediction of the surface tension of the fluid system is particularly important in field design and development in the petroleum sector.The surface tension of NPs in deionized water increases with increase in concentration of NPs. This study exploits the Debye-Hückel constants to calculate the mean activity coefficients of NPs in solution combined with the equation proposed by Li and Lu (2001) for single electrolyte solutions to estimate the change in surface tension.However, NPs behaviour in brine (electrolyte solution) is different from the behaviour of mixture of different electrolytes. In deionized water, the surface tension of the fluid increases with increase in the NPs concentration, but NPs in electrolyte solutions behave as surface active agent decreasing the surface tension with increase in NPs concentration. This work includes the dipole-dipole interaction and structural effects along with the equation developed by Borwankar and Wasan (1988) for surface excess adsorption. This surface excess adsorption is applied to Li and Lu's equation for mixed electrolyte solutions to estimate the change in surface tension.This study is able to model the surface tension of NPs with or without electrolyte. Here, the molecular interaction of NPs in deionized water and electrolyte solutions is considered to predict the fluid-surface tension. The free energy at the interface is affected by the intermolecular interaction of the NPs. This intermolecular interaction includes electrical double layer, dipole-dipole interaction, and structural effects. The proposed model shows a good agreement with the experimental data from previous studies.

Effect of electrical double layer and ion exchange on low salinity EOR in a pH controlled system

Wettability of an oil/brine/sandstone system is an important petro-physical parameter, governing subsurface multi-phase flow and residual oil saturations. While how edge-charged clays (e.g., kaolinite) contribute to low salinity effect has been extensively investigated, few work have been done on basal-charged clays (e.g., illite, smectite, and chlorite), and few have look beyond the application of the low salinity effect in reservoirs bearing basal-charged clays. We thus integrated atomic force microscopy (AFM) (at a given pH = 7), disjoining pressure calculations, together with surface complexation modelling to understand the importance of basal-charged clays during low salinity water flooding in sandstone reservoirs. We found that low salinity effect can take place without pH increase, confirming that electrical double layer is at least one of the mechanisms to yield low salinity effect, which can be interpreted using disjoining pressure isotherm, whereas ion exchange between oil and basal charged clays leads to an opposite effect at a given pH. However, ion exchange likely favors low salinity effect without controlling pH due to the chemical reaction: >Na + H+ = >H + Na+, which in return decreasing the electrostatic bridges between NH+/clays, COOCa+/clays. Knowing the contribution of EDL and ion exchange on oil/brine/basal-charged clays interaction, the potential of low salinity effect in sandstone reservoirs can be quantified.

Multiscale modeling of ion diffusion in cement paste: electrical double layer effects

Understanding the mechanism of ion diffusion in hardened cement paste is of great importance for predicting long-term durability of concrete structures. Gel pores in calcium silicate hydrate (CSH) phase forms dominant pathway for transport in cement paste with low w/c ratios where the electrical double layer effects play an important role. Experimental results suggest that the effective diffusivity of chloride ions is similar as that of tritiated water (HTO) and higher than the sodium ions. This difference can be attributed to the electrical double layer near the charged CSH surfaces. In order to understand species transport processes in CSH and to quantify its effective diffusivity, a multiscale modeling technique has been proposed to combine atomic-scale and pore-scale modeling. At the pore scale, the lattice Boltzmann method is used to solve a modified Nernst Planck equation to model transport of ions in gel pores. The modified Nernst Planck equation accounts for steric and ion-ion correlation effects by using correction term for excess chemical potential computed through the results from the grand canonical Monte Carlo scheme at atomic scale and in turn bridges atomic scale model with pore scale model. Quantitative analysis of pore size influence on effective diffusivity carried out by this multiscale model shows that the contribution of the Stern layer to ion transport is not negligible for pores with diameter less than 10 nm. The developed model is able to reproduce qualitatively the trends of the diffusivity of different ions reported in literature.

Understanding the Reaction Interface in Lithium‐Oxygen Batteries

AbstractThe presented review article recapitulates the current state of the art in understanding three fundamental issues relevant to the reaction interface in lithium‐oxygen batteries; i) charge transport across lithium peroxide, ii) morphological evolution and identification of reactive sites, and iii) mechanisms of the involved oxygen reactions. Except of the discharge reaction mechanism, there is still a lack of a complete mechanistic picture for these fundamental issues. However, we are standing at the brink of connecting the single dots to draw the overall image. Neglect of double layer effects and nonlinearities has led us to stray from the path towards correct understanding of the charge transport. The current status of reaction sites reminds us of the parable of the blind and the elephant. Multiple in‐situ, cross‐validated methods and multiple working hypotheses are essential for a comprehensive understanding. More efforts, especially on identifying the reaction intermediates, are required to portray a unifying mechanistic scheme for the charge reaction mechanism.

Dispersion of charged solute in charged micro- and nanochannel with reversible sorption.

We study dispersion of a charged solute in a charged micro- and nanochannel with reversible sorption and derive an analytical solution for mass fraction in the fluid, transport velocity and dispersion coefficient. Electrical double layer formed on the charged surface gives rise to a charge-dependent solute transport by modifying the transverse distribution of the solute. We discuss the effect of sorption and electrical double layer on solute transport and show that the coupling between sorption and electrical double layer gives rise to charge-dependent transport even for a thin double layer. However, in this case, it can be reduced to a simple non-charge-dependent case by introducing the intrinsic sorption equilibrium constant.