Gel polymer electrolytes (GPEs) are effective candidates for developing long-lasting, high-energy-density lithium-ion batteries (LIBs). We present a crosslinked network polymer of poly(acrylonitrile-r-vinylidene diazide) with tethered tetrazolium rings (xPAN+) as highly stable and ion-selective GPEs for lithium-ion batteries. In concert with nitrile and azide groups from acrylonitrile and vinylidene blocks, these cationic rings play a crucial role in facilitating the movement of lithium-ions by interacting with both anions and solvent molecules, similar to single-ion conductors. This structure enables a remarkable lithium transference number (tLi+ = 0.9) and lithium-ion conductivity of 1.67 mS/cm at 30 degrees C. As a result, xPAN+ GPEs performed stable cycling performance over 2000 h in lithium plating and stripping behavior and maintained discharge capacity retention of 92.15 % in LiFePO4 paired half-cell (141.18 mAh/g at 0.5C over 230 cycles). This work demonstrates a straightforward approach for fabricating ionic polymer-based GPEs that promote superior ion transport and ensure stable electrochemical performance in LIBs.

Nafion membrane activation, or pretreatment, involves immersion in a hot sulfuric acid solution to improve proton conductivity by replacing non-proton X+ ions in-SO3X groups with H+ ions. This study demonstrates that nonacidic-CF2H terminal groups, formed during the thermal degradation of Nafion membranes, can also be converted to acidic-CF2SO3H groups through sulfuric acid treatment. The-CF2H signals were quantitatively measured using 1H magic angle spinning nuclear magnetic resonance spectroscopy to estimate the degree of-SO3H group detachment and the extent of its recovery. The disappearance of these signals directly correlated with the recovery of the proton conductivity, the spin-lattice relaxation time of 1H signals, X-ray photoelectron spectroscopy, ion exchange capacity, and water uptake data. These findings indicate that-SO3H groups can be regenerated by substituting the nonacidic hydrogen in terminal groups such as-CF2H with-SO3H groups, and that simple immersion in an H2SO4 solution at 80 degrees C is an effective method for restoring thermally degraded perfluorosulfonic acid membranes. Single-cell polymer electrolyte membrane fuel cell measurements showed that the electrochemical performance of thermally degraded membranes was largely restored after sulfuric acid treatment, and further indicated that this treatment is effective even for chemically degraded membranes.

Abstract Polymer electrolyte membranes (PEMs), such as Nafion, have been widely employed as separators between the anode and cathode electrodes in various fuel cells and electrolyzers due to their excellent ionic conductivity and durability. However, several critical aspects of PEMs, including the mechanisms of proton conduction, remain poorly understood. Moreover, the native, degraded, and regenerated states of PEMs require further investigation to enhance their performance. Consequently, comprehensive integrated analyses, particularly those integrating multiscale and multiple time-scale techniques, are essential not only for understanding the behavior of PEMs but also for improving their functional properties. In this context, we briefly overview various analytical methods used for structural and dynamical characterization of PEMs, including the self-diffusion and translational dynamics of ions. The application of solid-state nuclear magnetic resonance spectroscopy to the study of PEMs is also reviewed. In addition, in-situ/operando analyses and the integration of artificial intelligence (AI) or machine learning with accumulated analytical data are discussed as emerging strategies for developing new design concepts for PEMs.

Most NMR samples are cylindrical, which is ideal for obtaining high-resolution NMR spectra, especially in superconducting magnets with a vertical bore. However, expanding NMR applicability to samples that are not necessarily cylindrical requires a new approach. In this study, we introduce a method for obtaining solution NMR signals from flat samples, such as flat containers or layered structures like a fuel cell. A flat rectangular NMR coil was developed for RF application and sensitive signal detection, while biplanar shim coils were designed using Bfieldtools and manufactured on multilayered printed circuit boards to improve NMR resolution. Water and ethanol molecules in flat rectangular and flat circular containers, as well as in a direct ethanol fuel cell, were observed with narrow NMR linewidths. We believe that our spectrometer design will enable NMR analysis of samples that need to be contained in flat structures and support in-situ analysis of various devices.

Improving the energy density and safety of the conversion/storage systems such as fuel cells and batteries is essential because the systems have profoundly impacted the modern lifestyles, enhancing the mobility and convenience of portable electronics and electric vehicles. In such systems, electrochemical reactions and dynamics of chemical species play key roles and understanding them is necessary for developing constituent materials with improved performance. In this respect, NMR spectroscopy has advantage to observe specific nuclei with high selectivity and to obtain quantitative information without discrimination over light atoms or disordered structures. Investigation without damaging samples is additional advantage. Herein representative results will be introduced such as the reaction mechanism of direct alcohol fuel cells investigated by in situ & ex situ techniques and detection on degradation/deformation of polymer electrolyte membranes. In addition, the results of postmortem 7Li NMR spectroscopic analyses will be presented: an ordinary magic angle spinning probe was used to evaluate the reversibility of lithium metal electrodes and the behavior of Li+ in the lithium metal batteries.

Although the water content in polymer electrolyte membranes (PEMs) is a very important parameter for controlling their performance, measuring it is difficult because strong acidic groups such as sulfonic acid in PEMs make them very hygroscopic. In this study, we demonstrate that the proton magic-angle-spinning nuclear magnetic resonance spectroscopic data of a Nafion PEM accompanied by weight data measured for two different water contents can be used to determine the water content of dry as well as swollen PEM. The advantages of this method are that completely dry-PEM weight can be obtained without perfectly removing water from the PEM and no specific drying condition is required. Further, the advantages and disadvantages of the proposed method and calibration curve methods are discussed. The proposed method can be applied to various PEMs provided accurate equivalent-weight values for the PEMs are available.

Despite the proficiency of lithium (Li)-7 NMR spectroscopy in delineating the physical and chemical states of Li metal electrodes, challenges in specimen preparation and interpretation impede its progress. In this study, we conducted a comprehensive postmortem analysis utilizing 7Li NMR, employing a standard magic angle spinning probe to examine protective-layer coated Li metal electrodes and LiAg alloy electrodes against bare Li metal electrodes within Li metal batteries (LMBs). Our investigation explores the effects of sample burrs, alignment with the magnetic field, the existence of liquid electrolytes, and precycling on the 7Li NMR signals. Through contrasting NMR spectra before and after cycling, we identified alterations in Li0 and Li+ signals attributable to the degradation of the Li metal electrode. Our NMR analyses decisively demonstrate the efficacy of the protective layer in mitigating dendrite and the solid electrolyte interphase formation. Moreover, we noted that Li+ ions near the Li metal surface exhibit magnetic susceptibility anisotropy, revealing a novel approach to studying diamagnetic species on Li metal electrodes in LMBs. This study provides valuable insights and practical guidelines for characterizing distinct lithium states within LMBs.

Perfluorosulfonic acid (PFSA) polymer electrolyte membranes (PEMs) used in fuel cells undergo chemical degradation when exposed to radicals formed during electrochemical reactions. One of the products or intermediates formed during the degradation was reported to be proton-exchangeable groups such as CF2OH and COOH. However, the 1H magic angle spinning nuclear magnetic resonance (MAS NMR) spectra of Nafion PEMs degraded chemically through the Fenton reaction revealed that CF2H was generated. Furthermore, the accompanying depletion of SO3H in the Nafion PEMs reduced the water contents of Nafion PEMs even under water saturation conditions. Our results are consistent with recent thermal degradation results of CF2H generation via SO3H substitution with H. While very simple, the 1H MAS NMR spectroscopic analysis was demonstrated to be a powerful technique for determining degradation of PFSA membrane such as Naion and Aquivion when other techniques, such as 19F MAS NMR spectroscopy, failed to show any degradation evidence. Hence, this method is potentially useful for investigating various PFSA PEMs for initial degradation evidence before analyzing their in-depth degradation mechanisms.

Understanding the electrochemical reaction mechanisms of energy conversion and storage systems is essential for improving their performance. Nuclear magnetic resonance (NMR) spectroscopy is excellent for probing electrochemical reactions due to its capability to provide quantitative and qualitative information. For the in situ simultaneous acquisition of the anode and cathode exhaust spectra of direct alcohol fuel cells such as a direct methanol fuel cell (DMFC) or direct ethanol fuel cell (DEFC), real-time flow-NMR spectroscopy using a toroid cavity detector was developed in our laboratory. In the cathode exhaust of DMFC, the CD3OH crossed over from the anode as well as HOD was observed. Ex situ NMR spectroscopy cannot detect gas products because they are lost during sample preparation. On the other hand, the amount of CO2 gas detected in the anode exhaust using our in situ detection method was proportional to the HOD amount. It was also proportional to the cell current generated. This explains differences in the fuel cell performance by identifying generated and consumed chemicals and their pathways in the cells at respective conditions. Analyses of DEFC exhausts showed various reaction products such as acetic acid and acetaldehyde but CO2 gas detected was negligible. Our results show that this in situ real-time analysis could identify and quantify the exhaust components, including the gaseous products. Therefore, our results demonstrate that this in situ real-time analysis is appropriate to study the reaction mechanisms of diverse other liquid-flowing electrochemical systems in addition to fuel cells. Furthermore, it may be applicable to designing advanced materials for the systems.

Low-field nuclear magnetic resonance (NMR) spectroscopy, conducted at or below a few millitesla, provides only limited spectral information due to its inability to resolve chemical shifts. Thus, chemical analysis based on this technique remains challenging. One potential solution to overcome this limitation is the use of isotopically labeled molecules. However, such compounds, particularly their use in two-dimensional (2D) NMR techniques, have rarely been studied. This study presents the results of both experimental and simulated correlation spectroscopy (COSY) on 1-13C-ethanol at 34.38 μT. The strong heteronuclear coupling in this molecule breaks the magnetic equivalence, causing all J-couplings, including homonuclear coupling, to split the 1H spectrum. The obtained COSY spectrum clearly shows the spectral details. Furthermore, we observed that homonuclear coupling between 1H spins generated cross-peaks only when the associated 1H spins were coupled to identical 13C spin states. Our findings demonstrate that a low-field 2D spectrum, even with a moderate spectral line width, can reveal the J-coupling networks of isotopically labeled molecules.

Understanding the electrochemical reaction mechanisms of energy conversion and storage systems is essential for improving their performance. Nuclear magnetic resonance (NMR) spectroscopy is an excellent quantitative and qualitative analysis method for investigating electrochemical reactions. We developed in situ real-time 2H flow NMR spectroscopy using a toroid cavity detector to simultaneously acquire the spectra of the anode and cathode exhausts of a direct methanol fuel cell. We used deuterium-enriched methanol (CD3OH) as fuel in order to obtain background-free spectra. Besides HOD, the CD3OH crossed over from the anode was observed in the cathode exhaust. The amount of CO2 gas, which is impossible to detect with ex situ NMR spectroscopy, was proportional to the HOD amount and current generated during the cell operation at a given potential. Therefore, in situ real-time analysis enabled us to identify and quantify the anode and cathode exhaust chemical components, including the gaseous products, such as CO2, of a fuel cell. This explains differences in the fuel cell performance by identifying generated and consumed chemicals and their pathways in the cells at respective conditions. Hence, our results demonstrate that this in situ real-time flow NMR method is applicable to studying the reaction mechanism of various other liquid-flowing chemical reaction systems besides fuel cells. Furthermore, it may open a new door for designing advanced materials.

Carbonation of calcium hydroxide (Ca(OH)2) is an indispensable process with applications in the stable storage of CO2, geological disposal of radioactive waste, and cement manufacture for the construction industry. In the carbonation reaction of Ca(OH)2, water plays an important role in the conversion of CO2 and increases the thermodynamic stability of calcium carbonate. Therefore, understanding the interaction between water and Ca (OH)2 is essential for controlling the kinetics and thermodynamics of the carbonation reaction of Ca(OH)2. In this study, changes in the physical and chemical properties of Ca(OH)2 that appear before the carbonation of hydrated Ca(OH)2 were observed through XRD and NMR analyses. Through XRD analysis, the interplanar distance of hydrated Ca(OH)2 increased by approximately 0.39% compared to that of the pristine Ca(OH)2. Furthermore, we quantified the intercalated water through NMR analysis based on water signal appearing around 0.9 ppm, which was approximately 3.0-7.0 wt% of Ca(OH)2. Through theoretical calculations, the hydrated Ca(OH)2 formed a stable structure with intercalated water molecules, resulting in lower reaction barrier and heat of reaction of the Ca(OH)2 carbonation. For the first time, the intercalation of water between the Ca(OH)2 interlayers is observed, and its importance in the carbonation reaction is established.

Field-stepped NMR spectroscopy at up to 36 T using the series-connected hybrid (SCH) magnet at the US National High Magnetic Field Laboratory is demonstrated for acquiring ultra-wideline powder spectra of nuclei with very large quadrupolar interactions. Historically, NMR evolved from the continuous-wave (cw) field-swept method in the early days to the pulsed Fourier-transform method in the modern era. Spectra acquired using field-sweeping are generally considered to be equivalent to those acquired using the pulsed method. Here, it is shown that field-stepped wideline spectra of half-integer spin quadrupolar nuclei acquired using WURST/CPMG methods can be significantly different from those acquired with the frequency-stepped method commonly used with superconducting magnets. The inequivalence arises from magnetic field-dependent NMR interactions such as the anisotropic chemical shift and second-order quadrupolar interactions; the latter is often the main interaction leading to ultra-wideline powder patterns of half-integer spin quadrupolar nuclei. This inequivalence needs be taken into account to accurately and correctly determine the quadrupolar coupling and chemical shift parameters. A simulation protocol is developed for spectral fitting to facilitate analysis of field-stepped ultra-wideline NMR spectra acquired using powered magnets. A MATLAB program which implements this protocol is available on request.

The ionic conductivity of polymer electrolyte membranes (PEMs) is an essential parameter for their device applications. In water-swollen PEMs, protons and other ions are transferred through hydrophilic channels of a few nanometers in diameter at most. Thus, optimizing the chemical and physical properties of the channels can enhance the conductivity of PEMs. However, the factors controlling the conductivity have not been completely clarified. Here, we report that measurements taken near the channel walls by a special nuclear magnetic resonance technique with ≤1 nm spatial resolution showed the largest water diffusivity when ∼80% of hydrophilic sulfonic acid groups were blocked, but the proton conductivity was low. The water diffusivity was much less affected by differences in water content. Our results provide a concept for changing the properties of PEMs and a challenge to implement the improved diffusivity in a way that enhances net ion conductivity.

We report the characteristic magnetic behaviors of nonemissive (N416) and green emissive (G416) Cs4PbBr6 perovskite crystals. N416 exhibits a diamagnetic behavior, while G416 shows an additional su...

Histidine, inspired by vanadium bromoperoxidase enzyme, has been applied as a homogeneous electrocatalyst to the positive electrolyte of vanadium redox flow battery (VRFB) to improve the performance and stability of VRFB at elevated temperatures. The histidine-containing electrolyte is found to significantly improve the performance of VRFB in terms of thermal stability estimated by the remaining amount of VO2+ in the electrolyte (61 vs 43% of a pristine one), energy efficiency at a high current density of 150 mA cm(-2) (78.7 vs 71.2%), and capacity retention (73.2 vs 27.7%) at 60 degrees C. The mechanism of the catalytic functions of histidine with the chemical species in the electrolyte has been investigated for the first time by multinuclear NMR spectroscopy and first-principles calculations. The analyzed data reveal that histidine improves the kinetics of both charge and discharge reactions through different affinity toward the reactants and products as well as suppresses the precipitation of VO2+ by impeding the polymerization of vanadium ions. These findings are in good agreement with the improved chemical and electrochemical performance of the histidine-containing VRFB. Our results show a new type of chemical/electrochemical mechanism in the improved redox flow battery performance that may be essential in a new research arena for better performance of electrochemical systems.

The development of electrocatalysts has emerged as an important aspect of rechargeable lithium-oxygen (Li-O-2) batteries due to the fact that they facilitate the formation and decomposition of discharge products, leading to a higher capacity and cyclability. Herein, we demonstrate that ruthenium oxide (RuO2) inverse opal (IO), which possesses a three-dimensionally ordered porous network, has been developed and applied to the Li-O-2 battery as a cathode. The RuO2 JO cathode contributes to the reduction of charge overpotential by up to similar to 120mV in lithium nitrate/dimethyl sulfoxide (LiNO3/DMSO), which corresponds to an similar to 670 mV decrease as compared with that of a carbon cathode, Ketjen black (KB). Differential electrochemical mass spectrometer (DEMS) monitoring and magic angle spinning nuclear magnetic resonance (MAS NMR) measurement reveal the origin of the extremely low charge overpotential obtained from the RuO2 JO cathode by confirming the formation of lithium hydroxide (LiOH) as the main discharge product. The incorporation of RuO2 also remarkably reduces the formation of byproducts such as lithium carbonate (Li2CO3) by substantially lowering the charge overpotential. A mechanistic explanation of the device operation is provided in this study as well.

Low energy density of a vanadium redox flow battery (VRFB) due to limited solubility and stability of vanadium ions constrains its wide spread applications and this issue becomes more critical by low active surface areas of electrodes and mass transport limitations of active species on the electrodes that lead to low electrolyte utilization. In this study the issue of low energy density is addressed by improving the electrode performance through modifying the surface properties and morphology of thin (0.19 mm thick) carbon paper electrodes instead of commonly used several millimeters thick carbon felts. Surface functionalization and pore formation of carbon paper are carried out using a catalytic etching method at high temperaturewhere the diameters of nanopores are controlled by tuning the etching conditions. The synergistic effects of thin, nanoporous and functionalized carbon paper result in more effective electrode/electrolyte interaction and the less mass transport resistance. Therefore, the zero-gap VRFB cell employing the nanoporous electrodes displays remarkable performance improvement in terms of electrolyte utilization by 110%, discharge energy density by 155% and energy efficiency by 29% as compared to the one using pristine electrodes at a current density of 50 mA cm(-2). The results imply that the more energy can be harvested by employing nanoporous and functionalized carbon paper electrodes having larger active surface areas.

Electromagnetic interference (EMI) shielding is an important issue in modern daily life due to the increasing prevalence of electronic devices and their compact design. This study estimated EMI-shielding effect (EMI-SE) of small (8-14x17 mm) Hanji (Korean traditional paper) doped with carbon nanotubes (CNTs) and compared to Hanji without CNT using H-2 (92.1 MHz) and Na-23 (158.7 MHz) nuclear magnetic resonance (NMR) peak area data obtained from 1 M NaCl in D2O samples in capillary tubes that were wrapped in the Hanji samples. The simpler method of using the variation of reflected power and tuning frequency by inserting the sample into an NMR coil was also tested at 242.9, 158.7, and 92.1 MHz. Overall, EMI shielding was relatively more effective at the higher frequencies. Our results validated that NMR methods to be useful to evaluate EMI-SE, particularly for small, flexible shielding materials, and demonstrated that EMI shielding by absorption is dominant in Hanji mixed with CNT.