Enhanced Ion Mobility Research Articles

Facile sulfur chemistry assisted carbon reconfiguration for efficient potassium ion electrochemical storage

Carbon-based materials are commonly used as anodes for potassium-ion batteries due to their high conductivity and stable cycling performance. However, their practical application is greatly hindered by their low capacity. Herein, we introduce facile sulfur chemistry including thioether bonds and CoS₂ into a nitrogen-oxygen co-doped partially graphitized carbon skeleton (NOGC), while the extra reconfiguration process of carbon assists forming the CoS₂@R-NOGC composites. The reconfigured NOGC (R-NOGC), enriched with highly electronegative elements (N, O, S), significantly enhances the reversible potassium ion storage capacity. The ordered carbon structure provides more efficient ionic transport pathways, thereby improving K⁺ transport efficiency. Moreover, layered CoS₂ acts as additional ion transport channels and active sites, further enhancing ion mobility and storage capacity. R-NOGC also promotes the reconstruction and repair of the solid electrolyte interface (SEI) layer to form a more robust interface. As a result of the synergistic effect between R-NOGC and CoS₂, it exhibits excellent anode performance, including a high reversible capacity (314.0 mAh/g at 0.1 A/g) and long-term stability (250.3 mAh/g at 0.5 A/g after 1,000 cycles). This work presents a novel strategy for designing and synthesizing high-performance anode materials for potassium-ion batteries, significantly enhancing both capacity and cycling stability.

Optimization of electrochromic Mo doping WO3 films: A study on dual-phase stacked structures for energy-efficient smart windows

Amorphous tungsten trioxide (a-WO3) films were prepared on ITO conductive glass via electrodeposition and subsequently crystallized to obtain crystalline WO3 (c-WO3) films by heating a-WO3. A dual-phase stacked WO3 film was fabricated by covering Mo-a-WO3 film onto c-WO3/ITO substrate using electrodeposition and thermal-assisted electrodeposition methods, respectively. Optimization of electrochromic performance was achieved by varying Mo doping levels (0∼5 atom%). Results demonstrate that appropriate Mo doping (3 atom%) enhances the electrochromic properties of a-WO3 films. Mo doping introduced structural distortions that reduced energy barriers and enhanced ion mobility, leading to improved electrochemical and electrochromic properties. The intermediate c-WO3 layer improves adhesion between a-WO3 top film and ITO glass substrate, while the porous structure of a-WO3 layer increases the number of active sites for electrochromic reactions. Mo3-a-WO3/c-WO3 dual-phase stacked film with doping 3 atom% Mo shows an optical modulation range of 83.4 % at 633 nm, a coloration efficiency of 74.3 cm2/C, rapid response time (bleaching/coloration: 3.4 s/6.1 s), and 86.6 % retention of its maximum current density after 2000 cycles, respectively. The high oxidation ion diffusion coefficient (3.53 × 10−10 cm2/s) and reduction diffusion coefficient (1.55 × 10−10 cm2/s) were also observed. This dual-phase stacked film shows significant improvements in electrochromic performance due to the synergistic effects between the dual phases and Mo-doping. Electrochromic device (ECD) assembled with Mo3-a-WO3/c-WO3 dual-phase films as the working electrode, ITO glass as the counter electrode, and 1 mol/L LiClO4/PC solution as the electrolyte exhibited an optical modulation range of 74.2 % and response time (bleaching/ coloring) of 6.8 s/3.7 s. These findings confirm that ECD with Mo-a-WO3/c-WO3 dual-phase films offer excellent electrochromic performance.

Blue energy conversion utilizing smart ionic nanotransistors

The use of concentration gradients across nanofluidic membranes for energy generation presents a novel and sustainable approach to power production. This study investigates the impact of ion nanotransistor configurations on ion transport and energy generation. Two types of cylindrical symmetrical nanotransistors, PNP and NPN, were tested. Using the finite element method, the Poisson-Nernst-Planck and Navier-Stokes equations were solved to evaluate how the configuration of soft layers, concentration ratios, and charge density influence energy output. Results show that the NPN configuration consistently outperforms the PNP setup in energy production, with energy generation ranging from 40pW to 56pW, compared to 35pW to 43pW for the PNP structure, when soft layer charge density increase from 25mol/m3 to 100mol/m3. The superior performance of the NPN arrangement is attributed to its higher electrostatic potential and enhanced ion mobility. These findings underscore the potential of NPN nanotransistor configurations for optimizing energy generation as well as water desalination in nanofluidic systems.

Influence of graphene nanoplatelet on carboxymethyl cellulose for enhanced electrochemical performance

Renewable and bio-based polymers are favored over conventional synthetic polymers because of their low-cost, abundance and sustainability, but due to their average electrochemical performance, sometimes their application is limited as battery material. This study investigates the electrochemical properties of nanocomposites composed of carboxymethyl cellulose (CMC) and graphene nanoplatelets (GNP) at varying GNP ratios. Four samples with GNP weight ratios ranging from 0 to 0.33 wt.% were subjected to analysis using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy. The sample containing 0.33% GNP exhibited the most favorable electrochemical behavior, demonstrating an ionic conductivity of approximately 2.54 × 10−5 S/cm at 25 °C. Cyclic Voltammogram and Nyquist plots indicated an electrochemical process governed by diffusion processes, particularly evident with 0.33% GNP. This sample displayed the highest specific capacitance at 4.290 F/g, representing an 83.07% improvement over the Pure CMC sample, along with a favorable electrochemical window at 375 mV. Bode plot analysis underscored the influence of diffusion and charge transfer on resistance and conductivity, highlighting enhanced ion mobility in this sample. SEM micrographs revealed improved GNP dispersion in the CMC matrix at higher GNP concentrations, enhancing contact. FTIR analysis confirmed effective CMC–GNP interaction, characterized by a specific peak at 1589 cm−1. These findings provide valuable insights into the electrochemical potential of CMC–GNP composites, offering prospects for their application in diverse electrochemical devices.

Thermal-Sensitive Supramolecular Coordination Complex Formed by Orthogonal Metal Coordination and Host-Guest Interactions for an Electrical Thermometer.

Supramolecular coordination complexes (SCCs) are popular for their structural diversity and functional adaptability, which make them suitable for a wide range of applications. Photophysical and mechanical performance of SCCs are the most attractive characteristics, yet their ionically conductive behavior and potential in electrical sensing have been rarely investigated. This study reports a well-designed SCC that integrates orthogonal metal coordination and host-guest interactions to achieve sensitive electrical thermal sensing. Owing to the thermodynamic nature of the host-guest interaction, the SCC encounters thermally induced disassembly, leading to significantly enhanced ion mobility and thus allowing for the precise detection of minor temperature variation. The SCC-based thermometer is then fabricated with the assistance of 3D printing and demonstrates good accuracy and reliability in monitoring human skin temperature and real-time temperature changes of mouse during the whole anesthesia and recovery process. Our findings provide an innovative strategy for developing electrical thermometers and expand the current application scope of SCCs in electrical sensing.

Influence of defects on enhancing lithium diffusivity in crystalline silicon anodes for fast charging lithium-ion batteries

The energy storage sector requires high capacity, long cycling life batteries. Silicon (Si) arises as a pivotal anode material for next-generation lithium-ion batteries owing to its exceptional capacity. However, challenges arise from lithium interactions, causing volumetric expansion and structural concerns like cracking. Si anodes also exhibit diverse phenomena during lithiation, influenced by crystal orientations. A thorough comprehension of the (de)lithiation process is essential to address challenges, despite existing gaps in knowledge, with strategic design and complementary materials, offering potential solutions by enhancing ion mobility and minimizing diffusion barriers. Here we have developed and applied first-principles simulations to offer fundamental insights into atomic interactions, providing a realistic atomistic representation of lithiation processes. Our simulations systematically incorporate Li+ into Si and Si- nitrogen vacancies (NV) orientations, and evaluation between Si and Si-NV (110) indicates a more favorable behavior in ionic diffusion for Si-NV(110), with a range of 2.55 × 10−3 to 1.64 × 10−2 (cm2/s) and a 15 % decrease in volume expansion. Our results explain the ternary Si–Li–N electrode materials and the identification of optimal site disorders to maximize the rate of Li+ diffusion in crystalline Si anodes.

Key Experimental Considerations When Evaluating Functional Ionic Liquids for Combined Capture and Electrochemical Conversion of CO2.

Ionic liquids (ILs) are considered functional electrolytes for the electrocatalytic reduction of CO2 (ECO2R) due to their role in the double-layer structure formation and increased CO2 availability at the electrode surface, which reduces the voltage requirement. However, not all ILs are the same, considering the purity and degree of the functionality of the IL. Further, there are critical experimental factors that impact the evaluation of ILs for ECO2R including the reference electrode, working electrode construction, cosolvent selection, cell geometry, and whether the electrochemical cell is a single compartment or a divided cell. Here, we describe improved synthesis methods of imidazolium cyanopyrrolide IL for electrochemical studies in consideration of precursor composition and reaction time. We explored how IL with cosolvents (i.e. acetonitrile, dimethylformamide, dimethyl sulfoxide, propylene carbonate, and n-methyl-2-pyrrolidone) affects conductivity, CO2 mass transport, and ECO2R activation overpotential together with the effects of electrode materials (Sn, Ag, Au, and glassy carbon). Acetonitrile was found to be the best solvent for lowering the onset potential and increasing the catalytic current density for the production of CO owing to the enhanced ion mobility in combination with the silver electrode. Further, the ECO2R activity of molecular catalysts Ni(cyclam)Cl2 and iron tetraphenylsulfonato porphyrin (FeTPPS) on the carbon cloth electrode maintained high Faradaic efficiencies for CO in the presence of the IL. This study presents best practices for examining nontraditional multifunctional electrolytes amenable to integrated CO2 capture and conversion technologies for homogeneous and heterogeneous ECO2R.

Enhancing Ion Mobility in Solids with Physics-Informed and AI-Driven Descriptors

The field of sustainable energy storage and conversion has witnessed increasing interest in ionic conductors due to their potential applications in electrochemical devices such as electrodes and solid electrolytes. In this study, we employed a combination of density functional theory investigations and artificial intelligence techniques to develop a robust descriptor for ion mobility [1,2]. Our descriptor incorporates factors like structural distortions, electronegativity, ionic radii, and oxidation states. By investigating various charge carrier chemistries and the anion and cation chemistries of the host lattice, we discovered that migration barriers are interconnected through linear scaling relations. Building upon this descriptor, we conducted a comprehensive study that employed both theoretical and experimental approaches to identify cathode materials with enhanced mobility for Mg-ions. Our focus was on oxide spinels, and we employed periodic density functional theory calculations to analyze the migration of Mg2+ ions and evaluate the electronic, geometrical, and stability properties of different transition metals within the spinel structures. Our findings reveal that electronegative transition metals, such as Rh, facilitate high mobility of Mg-ions and promote favorable cathode functionality within oxide spinel frameworks [3]. Based on these insights, we identified MgRh2O4 as a promising candidate and proceeded to prepare and characterize it structurally. This study opens up new possibilities for utilizing functional cathode materials with improved transport properties in battery-related applications. [1] M. Sotoudeh and A. Groß JACS Au 2022, 2, 463–471.[2] M. Sotoudeh, M. Dillenz, A. Groß, Adv. Energy Sustainability Res. 2021, 2, 2100113. [3] M. Sotoudeh, M. Dillenz, J. Döhn, J. Hansen, S. Dsoke, A. Groß, Chem. Mater. 2023, 35, 4786–4797.

Enhancing ion mobility spectrometry performance through a programmable ion swarm shaping method based on Bradbury-Nielsen gates

The ion gate is a critical element in drift tube ion mobility spectrometry (IMS) as it directly influences the resolving power and sensitivity of the system. However, the conventional Bradbury-Nielsen gate (BNG) often leads to deformation of the ion swarm shape, resulting in reduced resolving power and significant discrimination effects. To address these limitations, we propose a novel method that incorporates a cutting phase following the gate opening. This approach effectively reduces trailing edge deformation, resulting in a maximum resolving power of over 100 and increased signal intensity. Additionally, this method maintains high resolving power even during longer gate opening times. Remarkably, this method not only significantly reduces the mobility discrimination effect but also enables the achievement of reverse discrimination by adjusting the duration of the cutting phase. Consequently, it demonstrates the potential to selectively amplify the peak height of target ions. Our method offers straightforward implementation across all IMS systems utilizing the BNG, thereby significantly improving system performance.

Rapid structural characterization of human milk oligosaccharides and distinction of their isomers using trapped ion mobility spectrometry time-of-flight mass spectrometry.

Oligosaccharides have multiple functions essential for health. Derived from the condensation of two to several monosaccharides, they are structurally diverse with many co-occurring structural isomer families, which make their characterization difficult. Thanks to its ability to separate small molecules based on their mass, size, shape, and charge, ion mobility-mass spectrometry (IM-MS) has emerged as a powerful tool for separating glycan isomers. Here, the potential of such a technique for the rapid characterization of main human milk oligosaccharides (HMOs) was investigated. Our study focused on 18 HMO standards. The IM-MS analysis enabled to distinguish almost all the HMOs studied, in particular thanks to the single ion mobility monitoring acquisition using the trapped ion mobility spectrometry device, providing high ion mobility resolution and enhanced ion mobility separation. Alternatively, the combination of IM-MS separation with MS/MS experiments has proven to increase performance in identifying HMOs and especially isomers poorly separated by ion mobility alone. Finally, collision cross-section values are provided for each species generated from the 18 HMOs standards, which can serve as an additional identifier to characterize HMOs.

Low Energy and Analog Memristor Enabled by Regulation of Ru ion Motion for High Precision Neuromorphic Computing

AbstractMobile species and matrix materials in ion motion‐mediated memristors predominantly determine the switching characteristics and device performance. As a result of exploring a new type of mobile species, a Ru ion‐mediated electrochemical metallization‐like memristor with an amorphous oxide matrix is recently suggested to achieve a low switching current, voltage, and good retention simultaneously. Although the ion migration of Ru in the oxide matrix is previously confirmed, no in‐depth study on how the crystallinity of the oxide matrix influences the Ru ion motion and switching characteristics has not been reported. Therefore, in this study, the crystallinity‐dependent resistive switching behavior of the Pt/HfO2/Ru structure device is investigated. With the crystallized HfO2 layer, the preferred Ru ion migration through the grain boundaries occurs owing to the enhanced ion mobility, resulting in a high switching current (≈100 µA) with continuous metallic Ru conducting filaments. The discontinuous conducting filaments with amorphous HfO2 exhibit a low switching current. In addition, highly linear and symmetric conductance modulation properties are achieved, and over 91.5% accuracy in the Mixed National Institute of Standards and Technology (MNIST) pattern recognition test is demonstrated.

Fluoride-Assisted Preparation of Plasmonic Oxygen-Deficient MoO3−x Nanowires for Dual-Band Electrochromic Smart Windows

Electrochromic materials are vital to the development of dual-band smart windows, which enable the individual control of visible and near-infrared (NIR) light transmittance. In this paper, we propose a novel single-component MoO3−x nanowire fabricated using a simplified preparation method via a fluoride-assisted route. The incorporation of oxygen vacancies into MoO3−x nanowire in the presence of fluoride anions has not been attempted before. Spectroscopic measurements confirm enhanced ion mobility in the MoO3−x conduction band through the Mo6+ substitution of Mo5+ cations as the origin of localized surface plasmon resonance (LSPR). Oxygen vacancies greatly improve Li+ diffusion in the MoO3−x host while providing near-infrared selective modulation due to tunable LSPR absorbance in the NIR region. The MoO3−x nanowire demonstrates excellent dual-band electrochromic performance in terms of switching speed (12.4 s and 5.4 s for coloration and bleaching between 1.0 V and 3.5 V), coloration efficiency (232.8 cm2·C−1 at 1080 nm and 211.7 cm2·C−1 at 450 nm), and electrochemical stability (91.8% at 1080 nm after 1,000 cycles). This suggests that MoO3−x nanowire with oxygen vacancy is a promising new electrochromic material for dual-band smart windows.

Enhanced ion mobility resolution of Abeta isomers from human brain using high-resolution demultiplexing software.

Isomerization of aspartic acid (Asp) residues in long-lived proteins is a key feature associated with neurodegenerative proteinopathies such as Alzheimer's disease (AD). Recently, using ultra high-performance liquid chromatography (UHPLC) coupled with drift tube ion mobility mass spectrometry (DTIMS-MS), we documented the extensive Asp isomerization in amyloid-beta (Aβ) peptides depositing in the extracellular cortical plaques (senile plaques) of the AD brain. Aβ1-15 was estimated to be ~ 85% isomerized, while Aβ4-15 another major constituent of these senile plaques was ~ 50% isomerized in AD brain. Low resolution on the standard demultiplexed ion mobility resulted in poor separation of these N-truncated Aβ isomers in the ion mobility domain. Here, using the same ion multiplexed dataset, we applied new post-acquisition data reconstruction technique, high-resolution demultiplexing (HRdm), to improve the resolution of these Aβ isomers in the ion mobility dimension. We demonstrate that for the complex proteomic AD brain digests, HRdm could successfully resolve three out of four major Asp isomers of Aβ1-15. For Aβ2-15 and Aβ4-15, the significant resolution enhancement in the HRdm data resulted in baseline peak separation of the respective Asp isomers. An analysis of two-peak resolution (Rpp) and peak-to-peak separation (ΔP) indicated twofold enhancement for the Asp-isomerized Aβ species. HRdm performed with an effective resolving power (Rp) of between 150 and 160 for the highest deconvolution settings in comparison to ~ 40 to 65 in the standard settings. These major resolution improvements in the ion mobility domain for the endogenous Aβ isomers demonstrate the feasibility of in situ measurement of peptide isomers and their role in the mechanism of amyloid plaque formation in AD.

Enhanced Ion Mobility Separation and Characterization of Isomeric Phosphatidylcholines Using Absorption Mode Fourier Transform Multiplexing and Ultraviolet Photodissociation Mass Spectrometry.

The structural diversity of phospholipids plays a critical role in cellular membrane dynamics, energy storage, and cellular signaling. Despite its importance, the extent of this diversity has only recently come into focus, largely owing to advances in separation science and mass spectrometry methodology and instrumentation. Characterization of glycerophospholipid (GP) isomers differing only in their acyl chain configurations and locations of carbon-carbon double bonds (C═C) remains challenging due to the need for both effective separation of isomers and advanced tandem mass spectrometry (MS/MS) technologies capable of double-bond localization. Drift tube ion mobility spectrometry (DTIMS) coupled with MS can provide both fast separation and accurate determination of collision cross section (CCS) of molecules but typically lacks the resolving power needed to separate phospholipid isomers. Ultraviolet photodissociation (UVPD) can provide unambiguous double-bond localization but is challenging to implement on the timescales of modern commercial drift tube time-of-flight mass spectrometers. Here, we present a novel method for coupling DTIMS with a UVPD-enabled Orbitrap mass spectrometer using absorption mode Fourier transform multiplexing that affords simultaneous localization of double bonds and accurate CCS measurements even when isomers cannot be fully resolved in the mobility dimension. This method is demonstrated on two- and three-component mixtures and shown to provide CCS measurements that differ from those obtained by individual analysis of each component by less than 1%.

A Preprocessing Tool for Enhanced Ion Mobility-Mass Spectrometry-Based Omics Workflows.

The ability to improve the data quality of ion mobility-mass spectrometry (IM-MS) measurements is of great importance for enabling modular and efficient computational workflows and gaining better qualitative and quantitative insights from complex biological and environmental samples. We developed the PNNL PreProcessor, a standalone and user-friendly software housing various algorithmic implementations to generate new MS-files with enhanced signal quality and in the same instrument format. Different experimental approaches are supported for IM-MS based on Drift-Tube (DT) and Structures for Lossless Ion Manipulations (SLIM), including liquid chromatography (LC) and infusion analyses. The algorithms extend the dynamic range of the detection system, while reducing file sizes for faster and memory-efficient downstream processing. Specifically, multidimensional smoothing improves peak shapes of poorly defined low-abundance signals, and saturation repair reconstructs the intensity profile of high-abundance peaks from various analyte types. Other functionalities are data compression and interpolation, IM demultiplexing, noise filtering by low intensity threshold and spike removal, and exporting of acquisition metadata. Several advantages of the tool are illustrated, including an increase of 19.4% in lipid annotations and a two-times faster processing of LC-DT IM-MS data-independent acquisition spectra from a complex lipid extract of a standard human plasma sample. The software is freely available at https://omics.pnl.gov/software/pnnl-preprocessor.

Mobility of Cu Ions in Cu-SSZ-13 Determines the Reactivity of Selective Catalytic Reduction of NOx with NH3

Selective catalytic reduction of NOx with NH3 (NH3-SCR) in Cu-SSZ-13 has been proposed to have a unique homogeneous-like mechanism governed by the spatial proximity of mobile Cu ions. Among factors that determine the proximity, the effect of ion density on the SCR reaction is well established; however, it has not been verified how the different mobility of the Cu ion influences the SCR reaction. Herein, we try to reveal the mobility-dependent SCR reaction by controlling the Cu species with different ion mobilities in Cu-SSZ-13. Since the reaction kinetics is governed by the diffusion of Cu ions, the Cu ion mobility determines the reactivity of the Cu-SSZ-13. In terms of this correlation, enhanced ion mobility leads to improved NH3-SCR activity. These findings help understand the behavior of Cu ions in Cu-SSZ-13 under a catalytic reaction and provide insights to design rational catalysts by tuning the ion mobility.

Volatile organic compounds sensing based on Bennet doubler-inspired triboelectric nanogenerator and machine learning-assisted ion mobility analysis

Ion mobility analysis is a well-known analytical technique for identifying gas-phase compounds in fast-response gas-monitoring systems. However, the conventional plasma discharge system is bulky, operates at a high temperature, and inappropriate for volatile organic compounds (VOCs) concentration detection. Therefore, we report a machine learning (ML)-enhanced ion mobility analyzer with a triboelectric-based ionizer, which offers good ion mobility selectivity and VOC recognition ability with a small-sized device and non-strict operating environment. Based on the charge accumulation mechanism, a multi-switched manipulation triboelectric nanogenerator (SM-TENG) can provide a direct current (DC) bias at the order of a few hundred, which can be further leveraged as the power source to obtain a unique and repeatable discharge characteristic of different VOCs, and their mixtures, with a special tip-plate electrode configuration. Aiming to tackle the grand challenge in the detection of multiple VOCs, the ML-enhanced ion mobility analysis method was successfully demonstrated by extracting specific features automatically from ion mobility spectrometry data with ML algorithms, which significantly enhance the detection ability of the SM-TENG based VOC analyzer, showing a portable real-time VOC monitoring solution with rapid response and low power consumption for future internet of things based environmental monitoring applications.

Temperature-depended ion concentration polarization in electrokinetic energy conversion

Previous studies on the electrokinetic energy conversion (EKEC) are limited to the isothermal condition at the environmental temperature. Here effects of temperature and membrane thermal conductivity are systematically investigated. Under isothermal conditions, elevated temperature can improve the electric power while the energy efficiency stays unchanged. Under non-isothermal conditions, at small membrane thermal conductivities, a negative temperature difference contributes to the electric power for dramatically enhanced streaming current as enhanced ion mobility along the streaming direction induces an internal ion concentration polarization (IICP) that generates a co-flow concentration gradient in the nanopore interior. At large membrane thermal conductivities, the positive temperature difference reverses the external ion concentration polarization (EICP) in the solution reservoirs due to the Soret effect, resulting in more obvious electric power improvement. Furthermore, a criterion to enhance the EKEC performance via employing asymmetric temperatures is proposed, and an alternative way to construct the tunable ionic current source is presented. Present study provides guidance for enhancing the EKEC performance by employing waste heat, and fabricating nanofluidic functional devices.

A new DMF-derived ionic liquid with ultra-high conductivity for high-capacitance electrolyte in electric double-layer capacitor

In this study, a new DMF-derived ionic liquid electrolyte [EDMF]BF4 was prepared, characterized and applied as a high-capacitance electrolyte for electric double-layer capacitors (EDLCs). [EDMF]BF4 was measured to have very high ionic conductivity and low viscosity (24.8 mS cm−1 and 21.6 mPa s at 25 °C), as well as a comparable electrochemical window (4.4 V, on a GC electrode) with [EMIm]BF4, which is one of the most widely studied ionic liquid electrolytes with high performance. Therefore, [EDMF]BF4 was used as a non-volatile electrolyte for activated carbon-based EDLCs. The [EDMF]BF4-based EDLCs are capable to operate stably over a voltage of 2.7 V, and the specific capacitance of activated carbon was determined to be 165 F g−1 (100th cycle at 1 mA cm−2 and 30 °C), which is much larger than in the case of [EMIm]BF4 (126 F g−1). Besides, [EDMF]BF4 showed lower ohmic resistance and double layer resistance than [EMIm]BF4 in EDLCs. The high performance of [EDMF]BF4 electrolyte should be related to the quasi-linear [EDMF] cation of moderate size, which is presumably more suitable for enhanced ion mobility and compact electric double layer.

Superionic UO2: A model anharmonic crystalline material.

Crystalline materials at elevated temperatures and pressures can exhibit properties more reminiscent of simple liquids than ideal crystalline materials. Superionic crystalline materials having a liquidlike conductivity σ are particularly interesting for battery, fuel cell, and other energy applications, and we study UO2 as a prototypical superionic material since this material is widely studied given its commercial importance as reactor fuel. Using molecular dynamics, we first investigate basic thermodynamic and structural properties. We then quantify structural relaxation, dynamic heterogeneity, and average ion mobility. We find that the non-Arrhenius diffusion and structural relaxation time of this prototypical superionic material can be described in terms of a generalized activated transport model ("string model") in which the activation energy varies with the average string length. Our transport data can also be described equally well by an Adam-Gibbs model in which the excess entropy density of the crystalline material is estimated from specific heat and thermal expansion data, consistent with the average scale of stringlike collective motion scaling inversely with the excess entropy of the crystal. Strong differences in the temperature dependence of the interfacial mobility from nonionic materials are observed, and we suggest that this difference is due to the relatively high cohesive interaction of ionic materials. In summary, the study of superionic UO2 provides insight into the role of cooperative motion in enhancing ion mobility in ionic materials and offers design principles for the development of new superionic materials for use in diverse energy applications.