Revisiting the Charging Mechanism of α-MnO2 in Mildly Acidic Aqueous Zinc Electrolytes.

In recent years, there have been extensive debates regarding the charging mechanism of MnO2 cathodes in aqueous Zn electrolytes. The discussion centered on several key aspects including the identity of the charge carriers contributing to the overall capacity, the nature of the electrochemical process, and the role of the zinc hydroxy films that are reversibly formed during the charging/discharging. Intense studies are also devoted to understanding the effect of the Mn2+ additive on the performance of the cathodes. Nevertheless, it seems that a consistent explanation of the α-MnO2 charging mechanism is still lacking. To address this, a step-by-step analysis of the MnO2 cathodes is conducted. Valuable information is obtained by using in situ electrochemical quartz crystal microbalance with dissipation (EQCM-D) monitoring, supplemented by solid-state nuclear magnetic resonance (NMR), X-ray diffraction (XRD) in Characterization of Materials, and pH measurements. The findings indicate that the charging mechanism is dominated by the insertion of H3O+ ions, while no evidence of Zn2+ intercalation is found. The role of the Mn2+ additive in promoting the generation of protons by forming MnOOH, enhancing the stability of Zn/α-MnO2 batteries is thoroughly investigated. This work provides a comprehensive overview on the electrochemical and the chemical reactions associated with the α-MnO2 electrodes, and will pave the way for further development of aqueous cathodes for Zn-ion batteries.

Is "Water in Salt" Electrolytes the Ultimate Solution? Achieving High Stability of Organic Anodes in Diluted Electrolyte Solutions Via a Wise Anions Selection.

The introduction of the water-in-salt (WIS) electrolytes concept to prevent water splitting and widen the electrochemical stability window, has spurred extensive research efforts toward development of improved aqueous batteries. The successful implementation of these electrolyte solutions in many electrochemical systems shifts the focus from diluted to WIS electrolyte solutions. Considering the high costs and the tendency of these nearly saturated solutions to crystallize, this trend can be carefully re-evaluated. Herein we show that the stability of organic electrodes comprising the active material perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), is strongly influenced by the solvation character of the anions rather than the concentration of the electrolyte solution. Even though the charging process of PTCDA involves solely insertion of cations (i.e., principal counter-ions), surprisingly, the dominant factor influencing its electrochemical performance, including long-term electrode stability, is the type of the co-ions (i.e., electrolytic anions). Using systematic electrochemical analysis combined with theoretical simulations, we show that the selection of kosmotropic anions results in fast fading of the PTCDA anodes, while a selection of chaotropic anions leads to excellent stability, even at electrolytes concentrations as low as 0.2 M. These findings provide a new conceptual approach for designing advanced electrolyte solutions for aqueous batteries.

Polyimide Compounds For Post-Lithium Energy Storage Applications.

The exploration of cathode and anode materials that enable reversible storage of mono and multivalent cations has driven extensive research on organic compounds. In this regard, polyimide (PI)-based electrodes have emerged as a promising avenue for the development of post-lithium energy storage systems. This review article provides a comprehensive summary of the syntheses, characterizations, and applications of PI compounds as electrode materials capable of hosting a wide range of cations. Furthermore, the review also delves into the advancements in PI based solid state batteries, PI-based separators, current collectors, and their effectiveness as polymeric binders. By highlighting the key findings in these areas, this review aims at contributing to the understanding and advancement of PI-based structures paving the way for the next generation of energy storage systems.

Unique Mechanisms of Ion Storage in Polyaniline Electrodes for Pseudocapacitive Energy Storage Devices Unraveled by EQCM-D Analysis.

The optimal performance of organic electrodes for aqueous batteries requires their full compatibility with selected electrolyte solutions. Electrode materials having 1-3-dimensional structures of variable rigidity possess a confined space in their structure filled with water and electrolyte solutions. Depending on the rigidity and confined space geometry, insertion and extraction of ions into electrode structures are often coupled with incorporation/withdrawal of water molecules. Aside from the scientific interest in understanding the charging mechanism of such systems, co-insertion of solvent molecules affects strongly the charge storage capability of the electrodes for energy storage devices. We present herein in situ electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) investigations of polyaniline (PANI) electrodes operating in various aqueous Na+-containing electrolytes, namely, Na2SO4, NaClO4, NaBF4, and NaPF6. Careful analysis of the EQCM-D results provides a dynamic snapshot of the mixed anionic/protonic fluxes and the accompanying water molecules' insertion/extraction to/from the PANI electrodes. Based on our observations, it was found that the charging mechanism, as well as the capacity values, strictly depends on the electrolyte pH, the chaotropic/kosmotropic character of the anionic dopants, and the amount of the extracted water molecules. This study demonstrates the effectiveness of analysis by EQCM-D in selecting electrolytes for batteries comprising organic electrodes.

Can Anions Be Inserted into MXene?

Despite the continuous progress in the research and development of Ti3C2Tx (MXene) electrodes for high-power batteries and supercapacitor applications, the role of the anions in the electrochemical energy storage and their ability to intercalate between the MXene sheets upon application of positive voltage have not been clarified. A decade after the discovery of MXenes, the information about the possibility of anion insertion into the restacked MXene electrode is still being questioned. Since the positive potential stability range in diluted aqueous electrolytes is severely limited by anodic oxidation of the Ti, the possibility of anion insertion was evaluated in concentrated aqueous electrolyte solutions and aprotic electrolytes as well. To address this issue, we have conducted in situ gravimetric electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) measurements in highly concentrated LiCl and LiBr electrolytes, which enable a significant extension of the operation range of the MXene electrodes toward positive potentials. Also, halogens are among the smallest anions and should be easier to intercalate between MXene layers, in comparison to multiatomic anions. On the basis of mass change variations in the positive voltage range and complementary density functional theory calculations, it was demonstrated that insertion of anionic species into MXene, within the range of potentials of interest for capacitive energy storage, is not likely to occur. This can be explained by the strong negative charge on Ti3C2Tx sheets terminated by functional groups.

Quantification of porosity in extensively nanoporous thin films in contact with gases and liquids.

Nanoporous layers are widely spread in nature and among artificial devices. However, complex characterization of extensively nanoporous thin films showing porosity-dependent softening lacks consistency and reliability when using different analytical techniques. We introduce herein, a facile and precise method of such complex characterization by multi-harmonic QCM-D (Quartz Crystal Microbalance with Dissipation Monitoring) measurements performed both in the air and liquids (Au-Zn alloy was used as a typical example). The porosity values determined by QCM-D in air and different liquids are entirely consistent with that obtained from parallel RBS (Rutherford Backscattering Spectroscopy) and GISAXS (Grazing-Incidence Small-Angle Scattering) characterizations. This ensures precise quantification of the nanolayer porosity simultaneously with tracking their viscoelastic properties in liquids, significantly increasing sensitivity of the viscoelastic detection (viscoelastic contrast principle). Our approach is in high demand for quantifying potential-induced changes in nanoporous layers of complex architectures fabricated for various electrocatalytic energy storage and analytical devices.

Direct Assessment of Nanoconfined Water in 2D Ti3C2 Electrode Interspaces by a Surface Acoustic Technique.

Although significant progress has been achieved in understanding of ion-exchange mechanisms in the new family of 2D transition metal carbides and nitrides known as MXenes, direct gravimetric assessment of water insertion into the MXene interlayer spaces and mesopores has not been reported so far. Concurrently, the latest research on MXene and Birnessite electrodes shows that nanoconfined water dramatically improves their gravimetric capacity and rate capability. Hence, quantification of the amount of confined water in solvated electrodes is becoming an important goal of energy-related research. Using the recently developed and highly sensitive method of in situ hydrodynamic spectroscopy (based on surface-acoustic probing of solvated interfaces), we provide clear evidence that typical cosmotropic cations (Li+, Mg2+, and Al3+) are inserted into the MXene interspaces in their partially hydrated form, in contrast to the insertion of chaotropic cations (Cs+ and TEA+), which effectively dehydrate the MXene. These new findings provide important information about the charge-storage mechanisms in layered materials by direct quantification and efficient control (management) over the amount of confined fluid in a variety of solvated battery/supercapacitor electrodes. We believe that the proposed monitoring of water content as a function of the nature of ions can be equally applied to solvated biointerfaces, such as the ion channels of membrane proteins.

In Situ Real-Time Mechanical and Morphological Characterization of Electrodes for Electrochemical Energy Storage and Conversion by Electrochemical Quartz Crystal Microbalance with Dissipation Monitoring.

Quartz crystal microbalance with dissipation monitoring (QCM-D) generates surface-acoustic waves in quartz crystal plates that can effectively probe the structure of films, particulate composite electrodes of complex geometry rigidly attached to quartz crystal surface on one side and contacting a gas or liquid phase on the other side. The output QCM-D characteristics consist of the resonance frequency (MHz frequency range) and resonance bandwidth measured with extra-ordinary precision of a few tenths of Hz. Depending on the electrodes stiffness/softness, QCM-D operates either as a gravimetric or complex mechanical probe of their intrinsic structure. For at least 20 years, QCM-D has been successfully used in biochemical and environmental science and technology for its ability to probe the structure of soft solvated interfaces. Practical battery and supercapacitor electrodes appear frequently as porous solids with their stiffness changing due to interactions with electrolyte solutions or as a result of ion intercalation/adsorption and long-term electrode cycling. Unfortunately, most QCM measurements with electrochemical systems are carried out based on a single (fundamental) frequency and, as such, provided that the resonance bandwidth remains constant, are suitable for only gravimetric sensing. The multiharmonic measurements have been carried out mainly on conducting/redox polymer films rather than on typical composite battery/supercapacitor electrodes. Here, we summarize the most recent publications devoted to the development of electrochemical QCM-D (EQCM-D)-based methodology for systematic characterization of mechanical properties of operating battery/supercapacitor electrodes. By varying the electrodes' composition and structure (thin/thick layers, small/large particles, binders with different mechanical properties, etc.), nature of the electrolyte solutions and charging/cycling conditions, the method is shown to be operated in different application modes. A variety of useful electrode-material properties are assessed noninvasively, in situ, and in real time frames of ion intercalation into the electrodes of interest. A detailed algorithm for the mechanical characterization of battery electrodes kept in the gas phase and immersed into the electrolyte solutions has been developed for fast recognition of stiff and viscoelastic materials in terms of EQCM-D signatures treated by the hydrodynamic and viscoelastic models. Working examples of the use of in situ hydrodynamic spectroscopy to characterize stiff rough/porous solids of complex geometry and viscoelastic characterization of soft electrodes are presented. The most demonstrative example relates to the formation of solid electrolyte interphase on Li4Ti5O12 electrodes in the presence of different electrolyte solutions and additives: only a few cycles (an experiment during ∼30 min) were required for screening the electrolyte systems for their ability to form high-quality surface films in experimental EQCM-D cells as compared to 100 cycles (200 h cycling) in conventional coin cells. Thin/small-mass electrodes required for the EQCM-D analysis enable accelerated cycling tests for ultrafast mechanical characterization of these electrodes in different electrolyte solutions. Hence, this methodology can be easily implemented as a highly effective in situ analytical tool in the field of energy storage and conversion.

In situ real-time gravimetric and viscoelastic probing of surface films formation on lithium batteries electrodes.

It is generally accepted that solid-electrolyte interphase formed on the surface of lithium-battery electrodes play a key role in controlling their cycling performance. Although a large variety of surface-sensitive spectroscopies and microscopies were used for their characterization, the focus was on surface species nature rather than on the mechanical properties of the surface films. Here we report a highly sensitive method of gravimetric and viscoelastic probing of the formation of surface films on composite Li4Ti5O12 electrode coupled with lithium ions intercalation into this electrode. Electrochemical quartz-crystal microbalance with dissipation monitoring measurements were performed with LiTFSI, LiPF6, and LiPF6 + 2% vinylene carbonate solutions from which structural parameters of the surface films were returned by fitting to a multilayer viscoelastic model. Only a few fast cycles are required to qualify surface films on Li4Ti5O12 anode improving in the sequence LiPF6 < LiPF6 + 2% vinylene carbonate << LiTFSI.

In Situ Multilength-Scale Tracking of Dimensional and Viscoelastic Changes in Composite Battery Electrodes.

Intercalation-induced dimensional changes in a composite battery electrode (comprising a polymeric binder) are one of the major factors limiting electrode cycling performance. Since electrode performance is expressed by the quantities averaged over its entire surface area (e.g., capacity retention, Faradaic efficiency, rate capability), significant efforts have been made to develop a methodology allowing its facile mechanical diagnostics at the same areal scale. Herein we introduce such a generic methodology for a highly sensitive in situ monitoring of intrinsic mechanical properties of composite battery electrodes. The gravimetric, dimensional, viscoelastic, and adhesive changes in the composite electrodes caused by Li-ions intercalation are assessed noninvasively and in real time by electrochemical quartz-crystal microbalance with dissipation monitoring (EQCM-D). Multiharmonic acoustic waves generated by EQCM-D penetrate into thin porous electrodes comprising either rigid or a soft binder resulting in frequency and dissipation changes quantified by analytical acoustic load impedance models. As a first demonstration, we used a composite LiFePO4 (LFP) electrode containing either polyvinylidene dichloride (PVdF) or Na carboximethyl cellulose (NaCMC) as rigid and viscoelastic binders, respectively, in aqueous electrolytes. The intercalation-induced volume changes of LFP electrode were evaluated from a hydrodynamic correction to the mass effect of the intercalated ions for PVdF, and both components of the effective complex shear modulus (i.e., storage and loss moduli) in case of NaCMC binder have been extracted. The sliding friction coefficients for large particles bound at their bottom to the quartz crystal surface (a measure of the adhesion strength of binders) has also been evaluated. Tracking the mechanical properties of the composite electrodes in different environments and charging/cycling conditions in a self-consistent manner provides all necessary conditions for an optimal selection of the polymeric binders resistant to intercalation-induced volume changes of intercalation particles.

Understanding the influence of Mg doping for the stabilization of capacity and higher discharge voltage of Li- and Mn-rich cathodes for Li-ion batteries.

Although Li- and Mn-rich layered cathodes exhibit high specific capacity, the cathode materials of the general formula Li1+x[NiyMnzCow]O2 (x + y + z + w = 1) suffer from capacity fading and discharge-voltage decay during prolonged cycling, due to the layered-to-spinel transformation upon cycling to potentials higher than 4.5 V vs. Li. In this paper, we study the effect of Mg doping (by partial replacement of Mn ions) on the electrochemical performance of Li- and Mn-rich cathodes in terms of specific capacity, capacity retention and discharge voltage upon cycling. Mg-doped Li- and Mn-rich Li1.2Ni0.16Mn0.54Mg0.02Co0.08O2 and Li1.2Ni0.16Mn0.51Mg0.05Co0.08O2 cathode materials were synthesized by a self-combustion reaction (SCR), and their electrochemical performance in Li-ion batteries was tested. The replacement of a small amount of Mn ions by Mg ions in these materials results in a decrease in their specific capacity. The doping of a small amount of Mg (x = 0.02) resulted only in the stabilization of the capacity, whereas a greater amount (x = 0.05) resulted in improved capacity retention and discharge voltage upon cycling. Li1.2Ni0.16Mn0.51Mg0.05Co0.08O2 exhibits a low specific capacity of about 160 mA h g-1, which increases and then stabilizes at about 230 mA h g-1, and finally decreases to 210 mA h g-1 during 100 cycles. The substitution of Mg for Mn (x = 0.05) results in a higher discharge voltage than the other two cathode materials examined in this study. Structural analysis of the cycled electrodes suggests that Mg suppresses the activation of Li2MnO3 during the initial cycling, and hence, partially prevents layered-to-spinel transformation, resulting in a better electrochemical performance of the Mg-doped cathode material as compared to the undoped material.

Remarkably Improved Electrochemical Performance of Li- and Mn-Rich Cathodes upon Substitution of Mn with Ni.

Li- and Mn-rich transition-metal oxides of layered structure are promising cathodes for Li-ion batteries because of their high capacity values, ≥250 mAh g-1. These cathodes suffer from capacity fading and discharge voltage decay upon prolonged cycling to potential higher than 4.5 V. Most of these Li- and Mn-rich cathodes contain Ni in a 2+ oxidation state. The fine details of the composition of these materials may be critically important in determining their performance. In the present study, we used Li1.2Ni0.13Mn0.54Co0.13O2 as the reference cathode composition in which Mn ions are substituted by Ni ions so that their average oxidation state in Li1.2Ni0.27Mn0.4Co0.13O2 could change from 2+ to 3+. Upon substitution of Mn with Ni, the specific capacity decreases but, in turn, an impressive stability was gained, about 95% capacity retention after 150 cycles, compared to 77% capacity retention for Li1.2Ni0.13Mn0.54Co0.13O2 cathodes when cycled at a C/5 rate. Also, a higher average discharge voltage of 3.7 V is obtained for Li1.2Ni0.27Mn0.4Co0.13O2 cathodes, which decreases to 3.5 V after 150 cycles, while the voltage fading of cathodes comprising the reference material is more pronounced. The Li1.2Ni0.27Mn0.4Co0.13O2 cathodes also demonstrate higher rate capability compared to the reference Li1.2Ni0.13Mn0.54Co0.13O2 cathodes. These results clearly indicate the importance of the fine composition of cathode materials containing the five elements Li, Mn, Ni, Co, and O. The present study should encourage rigorous optimization efforts related to the fine composition of these cathode materials, before external means such as doping and coating are applied.

Electrochemical Quartz Crystal Microbalance with Dissipation Real-Time Hydrodynamic Spectroscopy of Porous Solids in Contact with Liquids.

Using multiharmonic electrochemical quartz crystal microbalance with dissipation (EQCM-D) monitoring, a new method of characterization of porous solids in contact with liquids has been developed. The dynamic gravimetric information on the growing, dissolving, or stationary stored solid deposits is supplemented by their precise in-operando porous structure characterization on a mesoscopic scale. We present a very powerful method of quartz-crystal admittance modeling of hydrodynamic solid-liquid interactions in order to extract the porous structure parameters of solids during their formation in real time, using different deposition modes. The unique hydrodynamic spectroscopic characterization of electrolytic and rf-sputtered solid Cu coatings that we use for our "proof of concept" provides a new strategy for probing various electrochemically active thin and thick solid deposits, thereby offering inexpensive, noninvasive, and highly efficient quantitative control over their properties. A broad spectrum of applications of our method is proposed, from various metal electroplating and finishing technologies to deeper insight into dynamic build-up and subsequent development of solid-electrolyte interfaces in the operation of Li-battery electrodes, as well as monitoring hydrodynamic consequences of metal corrosion, and growth of biomass coatings (biofouling) on different solid surfaces in seawater.

High-Capacity Layered-Spinel Cathodes for Li-Ion Batteries.

Li and Mn-rich layered oxides with the general structure x Li2 MnO3 ⋅(1-x) LiMO2 (M=Ni, Mn, Co) are promising cathode materials for Li-ion batteries because of their high specific capacity, which may be greater than 250 mA h g(-1) . However, these materials suffer from high first-cycle irreversible capacity, gradual capacity fading, limited rate capability and discharge voltage decay upon cycling, which prevent their commercialization. The decrease in average discharge voltage is a major issue, which is ascribed to a structural layered-to-spinel transformation upon cycling of these oxide cathodes in wide potential ranges with an upper limit higher than 4.5 V and a lower limit below 3 V versus Li. By using four elements systems (Li, Mn, Ni, O) with appropriate stoichiometry, it is possible to prepare high capacity composite cathode materials that contain LiMn1.5 Ni0.5 O4 and Lix Mny Niz O2 components. The Li and Mn-rich layered-spinel cathode materials studied herein exhibit a high specific capacity (≥200 mA h g(-1) ) with good capacity retention upon cycling in a wide potential domain (2.4-4.9 V). The effect of constituent phases on their electrochemical performance, such as specific capacity, cycling stability, average discharge voltage, and rate capability, are explored here. This family of materials can provide high specific capacity, high rate capability, and promising cycle life. Using Co-free cathode materials is also an obvious advantage of these systems.

In situ hydrodynamic spectroscopy for structure characterization of porous energy storage electrodes.

A primary atomic-scale effect accompanying Li-ion insertion into rechargeable battery electrodes is a significant intercalation-induced change of the unit cell volume of the crystalline material. This generates a variety of secondary multiscale dimensional changes and causes a deterioration in the energy storage performance stability. Although traditional in situ height-sensing techniques (atomic force microscopy or electrochemical dilatometry) are able to sense electrode thickness changes at a nanometre scale, they are much less informative concerning intercalation-induced changes of the porous electrode structure at a mesoscopic scale. Based on a electrochemical quartz-crystal microbalance with dissipation monitoring on multiple overtone orders, herein we introduce an in situ hydrodynamic spectroscopic method for porous electrode structure characterization. This new method will enable future developments and applications in the fields of battery and supercapacitor research, especially for diagnostics of viscoelastic properties of binders for composite electrodes and probing the micromechanical stability of their internal electrode porous structure and interfaces.

Novel in situ multiharmonic EQCM-D approach to characterize complex carbon pore architectures for capacitive deionization of brackish water.

Multiharmonic analysis by electrochemical quartz-crystal microbalance with dissipation monitoring (EQCM-D) is introduced as an excellent tool for quantitative studying electrosorption of ions from aqueous solution in mesoporous (BP-880) or mixed micro-mesoporous (BP-2000) carbon electrodes. Finding the optimal conditions for gravimetric analysis of the ionic content in the charged carbon electrodes, we propose a novel approach to modeling the charge-dependent gravimetric characteristics by incorporation of Gouy-Chapman-Stern electric double layer model for ions electrosorption into meso- and micro-mesoporous carbon electrodes. All three parameters of the gravimetric equation evaluated by fitting it to the experimental mass changes curves were validated using supplementary nitrogen gas sorption analysis and complementing atomic force microscopy. Important overlap between gravimetric EQCM-D analysis of the ionic content of porous carbon electrodes and the classical capacitive deionization models has been established. The necessity and usefulness of non-gravimetric EQCM-D characterizations of complex carbon architectures, providing insight into their unique viscoelastic behavior and porous structure changes, have been discussed in detail.

Non-invasive in†situ dynamic monitoring of elastic properties of composite battery electrodes by EQCM-D.

Reversible Li-ion intercalation into composite Li-ion battery (LIB) electrodes is often accompanied by significant dimensional electrode changes (deformation) resulting in significant deterioration of the cycling performance. Viscoelastic properties of polymeric binders affected by intercalation-induced deformation of composite LIB electrodes have never been probed in situ on operating electrochemical cells. Here, we introduce a newly developed noninvasive method, namely electrochemical quartz-crystal microbalance with dissipation monitoring (EQCM-D), for in situ monitoring of elastic properties of polymeric binders during charging of LIB electrodes. As such, we find EQCM-D as a uniquely suitable tool to track the binder's structural rigidity/softness in composite Li insertion electrodes in real-time by the characteristic increase/decrease of the dissipation factor during the charging-discharging process. The binders partially swollen in aprotic solutions demonstrate intermediate viscoelastic charge-rate-dependent behavior, revealing rigid/soft behavior at high/low charging rates, respectively. The method can be adjusted for continuous monitoring of elastic properties of the polymeric binders over the entire LIB electrodes cycling life.

Quartz crystal impedance response of nonhomogenous composite electrodes in contact with liquids.

A new model of quartz-crystal impedance (QCI) of nonuniform layers composed of bumps of carbon particles (either porous or nonporous) and a polymeric binder layer has been proposed. The solid particles are modeled by semispherical and oblate semispheroid bumps embedded into the "sea" of a polymeric binder layer. On the basis of this model and elaborating on the principles of hydrodynamic spectroscopy of composite electrode materials, the geometric and porous structure parameters of nanoporous carbon and nonporous graphite composite electrodes in contact with liquids have been reliably determined. This work is believed to create a solid theoretical background for both advanced studies and optimized formulations of the composite electrodes suited to practical electrochemical devices and for the interpretation of the processes of ions and solvent insertion into nanoporous carbon electrodes uniquely probed by the QCI method (supercapacitive cells, desalination membranes).

The effect of specific adsorption of cations and their size on the charge-compensation mechanism in carbon micropores: the role of anion desorption.

Combined application of cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) technique reveals a complicated interplay between the adsorption of ammonium and lower molecular weight tetraalkyl ammonium cations and desorption of Cl(-) anions inside carbon micropores at low surface charge densities, which results in failure of their permselectivity. Higher negative surface charge densities induce complete exclusion (desorption) of the Cl(-) co-ions, which imparts purely permselective behavior on the carbon micropores. The second fundamental effect discovered herein relates to the dominant role of anion desorption (as compared to cation adsorption), that is, overwhelming failure of permselectivity extends to high negative charge densities of the electrode in the presence of bulky tetraalkyl ammonium cations, which tend to be confined in the micropores of the carbon. The results obtained are important for advancement of high power density carbon-based supercapacitors, nanofiltration technologies with porous carbon membranes, and studies of ionic transport across biological membranes.