Open Access

One (re-)emerging research field of porous carbons, especially, so-called hard carbons (HCs), focusses on their ability to store sodium metal ions.[1] Recent results show that closed pores can reversibly store large amounts of sodium, whereas open pores contribute significantly to irreversible capacity losses due to the formation of the solid electrolyte interphase (SEI) during initial sodium insertion.[2] Nevertheless, correlating the specific surface area (SSA) obtained from gas physisorption measurements of HCs with electrochemical performance remains inconclusive, as large irreversible capacities are also observed in samples with experimentally determined low SSAs.[3] Apparently, SSA measurements using small probe molecules such as N₂ and CO₂ are not fully reliable for HCs. Therefore, a distinction between pores accessible only to Na and those also accessible to the electrolyte would be highly desirable, allowing the derivation of accurate structure–performance relationships. Herein, the main approach is to test dynamic vapor sorption (DVS) with diethyl carbonate (DEC), a representative battery electrolyte solvent molecule, as alternative technique to quantify the interface between the solid carbon and the liquid electrolyte. The study primarily focuses on our recently developed synthetic core–shell carbon materials consisting of a highly microporous carbon core coated via chemical vapor deposition (CVD) with a semi-permeable, non-graphitic carbon shell.[4] Gas physisorption measurements of the core and the core-shell material reveal that the CVD-coating successfully blocks N2-penetration at 77 K, however, still allows penetration by CO2 at 298 K. Moreover, small angle X-ray scattering measurements show that ca. 94% of the core’s porosity are retained after coating. According to DVS measurements at 298 K, the core carbon shows a DEC uptake of 670 mg g⁻¹ at 90% relative pressure, which is drastically reduced to 12 mg g⁻¹ for the core–shell material (Fig. 1a). Calculating SSA from these isotherms requires the molecular cross-sectional area. Therefore, we carried out grand canonical Monte Carlo simulations of DEC adsorption on monolayer graphene, yielding a SSA of 1896 m² g⁻¹ and 13 m² g⁻¹ for the core and the core–shell material, respectively. It appears that DEC is too large to penetrate the shell, thereby establishing electrolyte DVS as a promising technique for quantifying the liquid–solid interface in hard carbons. Moreover, the DVS-results can be nicely linked to the electrochemical performance, revealing a significant reduction of 1st-cycle-losses after CVD-coating (Fig. 1b). Apparently, the SEI-formation on such core-shell particles is forced to the external surface (shell). Thus, irreversible losses should be proportional to the SSA of the material, as it is the case for graphite anodes in lithium-ion batteries.[5] The relationship between the liquid-solid interfacial area, determined by battery electrolyte vapor sorption, and the loss during the initial sodiation will be discussed for both commercial and designed carbon materials. Overall, the present work introduces DEC sorption analysis as a more suitable tool than N2- or CO2-sorption to relate the liquid-solid interface to initial losses. The markedly lower DEC uptake of the core–shell carbon corresponds to a higher initial Coulomb efficiency, showing that solvent vapor sorption with battery electrolytes is a very powerful to predict first-cycle performance.

One (re-)emerging research field is the ability of hard carbons (HCs) to reversibly store sodium metal ions. Hard carbons are derived from pyrolysis of a non-graphitizing precursor, commonly specific carbonizable biomass. However, HCs often exhibit large irreversible capacity losses, mainly due to the formation of the solid electrolyte interphase (SEI) during initial sodium insertion, even in samples with low specific surface area.[1,2] Recent results show that closed pores allow to reversibly store large amounts of sodium (especially at low potentials), while open pores contribute to the irreversible capacity loss.[3] While some researchers consider pores open if they are accessible to probe gases used in gas sorption porosimetry or pycnometry,[3] other researchers use the size of the pore necks as descriptor, arguing with the accessibility of electrolyte to the pores.[4] Moreover, the chemical structure of the carbon is related to the sloping capacity.[3] A separate view on pores that are only accessible to Na and those also accessible to electrolyte would be desirable. This would allow to derive accurate structure–performance relationships in order to increase the reversible Na storage capacity and predict the theoretical limits of hard carbon anodes. Herein, we develop a strategy to tackle this challenge by creating core–shell carbon materials with a highly porous core and a semi-permeable shell.[6] For the core, two strategies are pursued: A) microporous carbon materials with varied porosity, however, similar composition, and B) microporous carbons with tuneable composition, but similar porosity. Approach A involves the selection of commercially available activated carbons (ACs).[6] Strategy B is based on the modification of the chemical composition (i.e., amount and type of N-sites) of zeolitic imidazolate framework (ZIF-8) derived carbons.[7] In both cases, the shell is formed via chemical vapor deposition (CVD). Different analytical methods, e.g., powder XRD, gas physisorption (N2, Ar, CO2), XPS, and SAXS are used to thoroughly characterize morphological and chemical features of the core as well as of the core-shell carbons. These features are linked to the electrochemical characteristics of the materials. After CVD-coating, all materials show a significant reduction in detectable surface area (up to a factor of up to 190x) by N2-physisorption. The coating technique is successfully applied to a range of AC-materials, enabling to link porosity features to Na-storage behavior.[6] Ex-situ and operando NMR-measurements are performed to link the porosity of the core to possible Na cluster formation. For the best performing AC-based material, the reversible capacity is increased from ~140 mAhg 1 to ~400 mAhg-1 while irreversible capacity is decreased from ~640 mAhg-1 to ~90 mAhg-1 (see Figure 1). The results of the coated ZIF-derived carbon reveal that a higher nitrogen content leads to a greater capacity in the sloping region, but to a lower capacity in the plateau region of the voltage profile.[7] Moreover, diethyl carbonate sorption (DEC) analysis is introduced as a more suitable tool than N2- or CO2-sorption to relate the liquid–solid interphase to initial losses. The markedly lower DEC uptake of core–shell carbons corresponds to higher initial coulombic efficiency, allowing this method to predict first-cycle performance. Generally, core-shell carbon anodes promise to enable high capacities accompanied with low irreversible losses.

Pore size analysis is essential for understanding and optimizing structure-performance relations of functional carbon-basedmaterials including activated carbons, supercapacitor electrodes and atomically dispersed metal-nitrogen-doped carbon (M-N-C) catalysts. Pore size distribution (PSD) plots based on gas sorption porosimetry often show narrow micropores that are relatedto the adsorptive properties of named materials, which must be considered as artefacts arising from approximations in classicaldensity functional theory (cDFT) models. By selectively preparing specific in-plane functionalities using pyrolytic template-ion(salt templating) reactions, we herein show that those apparent pores can be explained by preferential adsorption of the adsorbatemolecules to specific in-plane functionalities. Tetrapyrrolic Zn-N 4 sites are present in ZIF-8 derived carbons, which are convertedby Zn-extraction into nitrogen-doped carbons (NDC) comprising tetrapyrrolic H 2 N4 sites. DFT-based calculation of adsorptionenergies allows the conclusive assignment of corresponding adsorption phenomena in comparative N 2 vs. CO2 vs. Ar adsorptionmeasurements additionally using Langmuir analysis. While the assignment of artefacts may improve the discussion of porosity,the determination of specific adsorption sites may be utilized as a valuable tool in materials science. Advanced models for theimportant material classes may allow accelerated progress in important energy-related research fields.

Hydrogen refueling station (HRS) requires continuous safety monitoring, yet conventional management relies largely on periodic inspection and manual oversight, limiting proactive risk mitigation. This study presents a data-driven intelligent analysis platform for real-time monitoring and anomaly detection of HRS safety data, including pressure, temperature, and flow-rate measurements from compressors, storage tanks, and dispensers. The platform integrates data collection adapters, a time-series database, and machine learning-based diagnostic modules (regression, clustering, and classification) into a unified reference software framework. For anomaly detection, an unsupervised LSTM-Variational Autoencoder trained on normal operating data is combined with DBSCAN-based clustering and a Mann–Kendall trend test to jointly identify point anomalies and pattern-level drifts, addressing the scarcity of labeled abnormal data in HRS environments. A continual learning mechanism further adapts detection thresholds to gradual and abrupt pattern changes without full retraining. The system was deployed and validated at BAM’s demonstration hydrogen refueling station in Germany, integrated with a remote safety-monitoring system and confirmed through performance testing, demonstrating reliable, proactive hydrogen safety management.

A reliable stress analysis of a cask for radioactive materials under dynamic load conditions requires a qualified numerical model. For this purpose, the cask is typically discretized using a mesh of finite elements. Certain parts of the mesh usually require a refinement to accurately determine the stresses and strains. Other parts of the mesh may not be of interest with respect to stresses and strains. In such parts, a coarse mesh is sufficient. The mesh density can vary considerably within a cask model. Transitions between regions with different mesh densities can be achieved either by gradually changing the element size or by using tie contact conditions. Such mesh transitions can sometimes lead to complications. In general, a finer mesh can transmit higher-frequency signals than a coarser mesh. The propagation of stress waves through the model may be influenced by the transition zone or by any artificially introduced interface. Stress waves arising within the fine mesh can be partially confined by the surrounding coarse mesh. Poor mesh transitions can therefore cause stress waves to be partially reflected or to change their shape. A thin rod is examined to demonstrate the effects. It is modeled with a varying number of elements or varying size of elements respectively. A stress pulse is applied to one end of the rod, while the opposite end remains free. The generated stress wave is observed at various locations along the rod, and its shape and amplitude are analyzed in relation to the mesh density. Inappropriate meshing can lead to incorrect simulation results without the finite element code issuing warnings or error messages. Such problems are often not obvious. As a result, when using finite element meshing, the maximum size of the finite elements required to model the expected stress wave propagation should not be exceeded. In other words, the correct modeling of stress wave propagation determines the minimum number of finite elements required to mesh a cask component. This study illustrates the ASME Guidance Document “Use of Explicit Finite Element Analysis for the Evaluation of Radioactive Material Transport Packages and Storage Casks in Energy-Limited Impact Events”.