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Rising demand for sustainable energy storage has renewed interest in sodium-ion batteries (SIBs) as alternative to lithium-ion batteries. Although hard carbon and related materials are common SIB-anodes, the correlation between its structure and ion storage mechanism remains unclear.[1] As shown recently, the pore design is essential to block the formation of excessive solid electrolyte interphase (SEI) and allows the formation of pseudo-metallic clusters inside the pores.[2,3] Adjusting the diameter of the pore entrance, enables a reversible low-potential plateau (< 0.1 V), which significantly enhances the capacity (potentially up to 450-500 mAh/g) compared to graphite (Qtheo = 372 mAh/g) in Li-ion batteries.[2]
Activated carbon (AC) is a low-cost material with abundant micropores and high surface area, making it a promising anode candidate for SIBs. However, its performance is often hindered by structural disorder and excessive SEI-formation. Hence, mitigating active-species loss is essential to achieve high specific capacities (> 300 mAh g-1).[3] The aim herein was to investigate the relationship between the properties of the AC and the CVD-conditions required to achieve an efficient SIB-anode.
This study introduces an optimized chemical vapor deposition (CVD) method to modify various, highly porous commercial ACs aiming towards core-shell carbons, consisting of a porous core and a non-graphitic CVD-shell.[3] The ACs were treated via CVD and characterized using a range of techniques including gas physisorption, small-angle x-ray scattering and X-ray diffraction. The electrochemical properties of the different materials, prior and after CVD-coating, were analysed in half cells vs. Na-metal.
After coating, gas physisorption confirmed a significantly lower surface area for the materials. Depending on the porosity of the material, a longer CVD-time was necessary to fully coat the particles. The successful formation of core-shell carbons enables separation of the storage mechanism from SEI-formation. The CVD-process enables precise control over the microstructure of the carbon material, allowing to enhance the reversible Na-storage capacity, e.g., from 107 mAh g-1 to 353 mAh g-1 while significantly reducing initial Coulombic losses by 73%.
The greatly increased low-potential capacity verifies the formation of an electrolyte-tight CVD shell enabling Na-storage in the porosity of the core. The established link between porosity, CVD-parameters, and performance guides optimization for future materials.
The German National Hydrogen Strategy (NWS) envisions a transition towards a hydrogen-based energy grid. However, due to the material incompatibility of existing pipeline infrastructure for amounts of hydrogen higher than 10 cmol/mol, many system components of the existing grid must be replaced with significant costs and considerable time investments. Given these constraints, the admixture of hydrogen into natural gas (NG) to create a hydrogen-enriched NG blend has been designated as a transitional technology. The NWS supports this approach on a regional and time-limited basis, but clearly states that it is not intended as a permanent solution.
Nevertheless, the conversion to a fully hydrogen-based grid is expected to take several decades. During this transitional phase, precise process analytical monitoring of hydrogen amounts in the NG blend is essential to ensure both energy efficiency via calorific value control and operational safety. These procedures require cost-effective, robust, and reliable sensor technologies capable of real-time, in situ/on-site quantification of hydrogen amounts in NG.
In response to this need, we have advanced a physical sensing approach utilizing an oscillating cantilever in collaboration with Truedyne Sensor AG. This sensor system enables quantification of hydrogen amounts, direct calorific value determination as well as display of beneficial gas properties, like density, viscosity, and thermal conductivity. Moreover, the enhanced cantilever system enables direct physical sensing and can also be operated in a quasi-binary mode.
We performed comparative evaluations against two benchmark sensor systems to validate the developed technology. One utilizes chemical sensing, and the other operates on thermal conductivity measurements for hydrogen quantification. Through standardized testing, we demonstrated that the cantilever-based sensor offers both high effectiveness and competitive performance compared to current state-of-the-art technologies for accurate hydrogen detection in natural gas and precise determination of its calorific value.
In dem Vortrag wurde der Einfluss ausgewählter Fertigungsparameter auf die Sicherheit von Composite-Druckbehältern diskutiert. Die Inhalte stammen aus einem Projekt im Rahmen des BTU-BAM Graduiertenkollegs "Trustworthy Hydrogen". Darüber hinaus umfasst der Foliensatz eine Kurzvorstellung der Aktivitäten des Fachbereichs 3.5 im Bereich der Wasserstofftechnologien.
Pseudocapacitance-type transition metal oxides have been extensively investigated as anodes for lithium-ion batteries (LIBs). Currently, they are also gaining attention for sodium-ion batteries (SIBs) due to their low volume change and safety. However, their performance in sodium storage remains limited, primarily due to the larger Na+ ion radius. Here, for the first time, an iron niobate is reported with a columbite structure as a high-Performance sodium storage anode. The presence of iron triggers the loss of long-rangeorder through disorder of the FeO6 octahedra local structure, subsequentlyallowing reversible sodium storage in an amorphous phase. Simultaneously, the formation of short-range ordered zigzag-chain structures within the NbO6 planes creates a “skeleton” that offers abundant active sites forpseudocapacitive ion storage and enhanced ion diffusion pathways. These characteristics of FeNb2O6 make it an effective intercalation host, offering high capacity along with fast Na+ kinetics, as demonstrated through operando and ex situ characterizations. It leads to an applicable reversible capacity (>300 mAh g−1) with a favorable average voltage of ≈0.6 V and excellent rate capability (180.4 mAh g−1 at a current density of 2 A g−1). This study provides insights into the development of intrinsically active transition metal oxides for Na+-ion intercalation.
Pseudocapacitance-type transition metal oxides have been extensively investigated as anodes for lithium-ion batteries (LIBs). Currently, they are also gaining attention for sodium-ion batteries (SIBs) due to their low volume change and safety. However, their performance in sodium storage remains limited, primarily due to the larger Na+ ion radius. Here, for the first time, an iron niobate is reported with a columbite structure as a high-performance sodium storage anode. The presence of iron triggers the loss of long-range order through disorder of the FeO6 octahedra local structure, subsequently allowing reversible sodium storage in an amorphous phase. Simultaneously, the formation of short-range ordered zigzag-chain structures within the NbO6 planes creates a “skeleton” that offers abundant active sites for pseudocapacitive ion storage and enhanced ion diffusion pathways. These characteristics of FeNb2O6 make it an effective intercalation host, offering high capacity along with fast Na+ kinetics, as demonstrated through operando and ex situ characterizations. It leads to an applicable reversible capacity (>300 mAh g−1) with a favorable average voltage of ≈0.6 V and excellent rate capability (180.4 mAh g−1 at a current density of 2 A g−1). This study provides insights into the development of intrinsically active transition metal oxides for Na+-ion intercalation.
The N2 + CO2 co-electrolysis to urea synthesis has become a promising alternative to the energy intensive traditional processes for urea production. However, there are still challenges in this approach, especially due to the competition with HER (Hydrogen Evolution Reaction) leading to low efficiency. Electrochemistry assisted by localized surface plasmon resonance (LSPR) using metal nanoparticles has been reported to enhance different electrochemical reactions. Here we report an electrochemical LSPR assisted urea synthesis using Ag nanoparticles (NPs) supported on BiVO4/BiFeO3 catalyst mechanochemically synthesized. The electrochemical experiments were performed under dark and upon plasmon excitation at the LSPR region of Ag NPs. Our results demonstrated that exciting in the LSPR range, urea yield rate and Faradic efficiency were considerably improved with reduced overpotential, 19.2 μmol h− 1 g− 1 and FE 24.4% at +0.1 V vs RHE compared to 9.6 μmol h− 1 g− 1 and FE 9.4% at − 0.2 V vs RHE under dark conditions. Further in situ FTIR-RAS experiments for mechanism investigation revealed the presence of N-H and C-N intermediates and the real effect of Ag plasmon excitation on HER and N2 + CO2 co-electrolysis. Theoretical calculations confirm the energy of the species involved in C-N coupling as well the role of the complex catalytic sites, which agrees with XAS measurements.
Two carbon fiber reinforced type IV pressure vessels are subjected to step-wise pressurization until burst, while monitored using acoustic emissions (AE). Unlike most prior studies, AE data is collected throughout the entire damage progression. The vessels, manufactured with differing parameters, failed in distinct composite layers – A-type in the hoop layers and B-type in the helical layers. The AE signals are evaluated to study material degradation and identify fiber breaks as signs of critical damage accumulation. The signals are distributed randomly across the surface, with localized accumulation only minutes before rupture, close to the rupture plane. The difference in manufacturing parameters did not result in any clear difference in the AE activity. Felicity and Shelby ratios show consistent decline with increasing pressure, suggesting potential for damage assessment and burst prediction. It is discussed how these ratios are affected by coupling quality of the AE sensors, the shape of the pressurization profile and prior loadings. Different signal features based on the amplitude and the frequency content are extracted for a classification into failure mechanisms. Based on previous studies, AE signals corresponding to fiber breaks have a characteristic high-frequency spectrum and show a delay in occurrence, with an increase in the number of breaking fibers towards the end of the experiment. Indeed, high frequency signals tend to occur later and signals in specific peak-frequency ranges (350 – 400 kHz, 500 kHz) somewhat resemble the expected behavior. However, the dataset is too variable and too incongruent for any clear interpretations. Likely reasons are signal propagation effects, the complex composite structure, simultaneous occurrence of signals and measurement uncertainties. A review of relevant studies is provided to show that similar issues affect also previous works. Successfully identifying fiber breaks in large-scale, complex composite structures based on AE data, and turning this into an applicable health-monitoring technique, therefore remains a challenge.
Liquefied Hydrogen is a promising energy carrier for the flexible import of energy to Europe. But, tanks in the relevant scale of 40 000 to 200 000 m³ do not exist yet. The upscaling of liquid hydrogen (LH2) storage tanks from the current largest tank of 4700 m³ requires a new concept for thermal insulation. NICOLHy studies novel concepts based on multiple layers of vacuum insulation panels (VIPs). Current LH2 tanks rely on the intactness of a single vacuum layer that covers the whole tank. The multilayered VIP systems offer redundancy and improve manufacturability. The Article describes the progress within the project.
Based on the UBA report “Advanced materials for energy transition” by Xenia Knigge and Jörg Radnik the role of critical raw materials is discussed. Critical raw materials are needed in main fields of the energy transition, like photovoltaic, fuel cells, wind energy, and batteries. For the optimisation of the use of these materials different scenarios are discussed like (i) decreasing the needed amount of raw materials, (ii) searching for alternatives, (iii) using technologies which do not require critical raw materials, (iv) increasing the recycling rates, and (v) expanding the raw material sources.