Anode-free aqueous zinc metal batteries (AZMBs) offer significant potential for energy storage due to their low cost and environmental benefits. Ti₃C₂T_x MXene provides several advantages over traditional metallic current collectors like Cu and Ti, including better Zn plating affinity, lightweight, and flexibility. However, self-freestanding MXene current collectors in AZMBs remain underexplored, likely due to challenges with Zn deposition reversibility. This study investigates the combination of a Ti₃C₂T_x self-freestanding film with advanced electrolyte engineering, specifically examining the effects of Li-salt and propylene carbonate (PC) as additives on Zn plating reversibility. While using Li⁺ ions as an additive alone facilitates uniform Zn deposition on bulk metals through the electrostatic shielding effect, the addition of Li-salt negatively impacts Zn plating uniformity on Ti₃C₂T_x. Meanwhile, using PC additive alone forms an organic SEI layer on Ti₃C₂T_x and causes Zn agglomeration. The use of both additives together results in a ZnF₂-containing hybrid SEI layer with improved interfacial kinetics, promoting more uniform Zn deposition. This approach achieves an average Coulombic efficiency (CE) of 96.8% over 150 cycles (a maximum CE of 97.8%). The study highlights the strategic difference in electrolyte design, emphasizing the need for tailored approaches to optimize Zn deposition on MXenes, contrasting with traditional metallic current collectors.

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Optical hydrogen sensors have the power to reliably detect hydrogen in an inherently safe way, which is crucial to ensure safe operation and prevent emissions of hydrogen as an indirect greenhouse gas. These sensors rely on metal hydride material that can reversibly absorb hydrogen when it is present in the environment, and as a result, change their optical properties. To apply this technology along hydrogen infrastructure, in hydrogen-powered planes and other vehicles, it is crucial that these sensors can operate down to −60 °C, a challenge so far unaddressed. Here, it is showed that metal hydride hydrogen sensing materials can be used to detect hydrogen optically down to −60 °C in just a couple of seconds and across a hydrogen concentration range of 0.02–100% with a 1% change in transmission per order of magnitude change in hydrogen concentration. The in-situ X-ray diffraction and optical transmission measurements show that Ta, Ta₈₈Pd₁₂, Ta₈₈Ru₁₂, and Pd₆₀Au₄₀ can gradually, reversibly and hysteresis-free absorb hydrogen while providing sufficient optical contrast. Specifically, Ta₈₈Ru₁₂ possesses the largest optical contrast and the swiftest response down to 6 s at −60 °C. These results confirm the operational viability and foretell new applications of metal hydride hydrogen sensing in cold conditions.

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Optical hydrogen sensors based on metal hydrides have distinct advantages over other types of hydrogen sensors as they can be made small, do not require the presence of oxygen, and have a large sensing range. The working principle is based on the fact that when exposed to an atmosphere containing hydrogen, a metal hydride absorbs hydrogen, which in turn changes the optical properties. In a micro-mirror configuration, this change in optical properties can be measured by measuring the reflectivity of light. Tantalum alloys have been identified as suitable sensing material owing to their large sensing range, hysteresis-free response and fast response times. Here, we rationally develop a micro-mirror hydrogen sensor based on a tantalum-alloy as sensing layer. We first study the optical contrast of Ta_0.88Pd_0.12 thin films with a Pd_0.6Au_0.4 catalyst layer deposited on substrates with various catalyst and sensing layer thicknesses in reflection. Modeling the experimental results shows that the total optical contrast, that is the change of the reflectivity with a changing hydrogen concentration, is a strong interplay of wavelength and hydrogen-concentration dependent reflection, attenuation and amplification coefficients of both the Ta_0.88Pd_0.12 thin films with a Pd_0.6Au_0.4 catalyst layer. These effects may either constructively or destructively contribute to the overall signal, making carefully choosing the wavelength and layer thicknesses essential. Using optimal values of the wavelength and layer thicknesses, we successfully construct and test a micro-mirror sensor that can detect hydrogen over at least 5 orders of magnitude in hydrogen concentration without any hysteresis.

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We have designed and realized a temperature and pressure controlled cell for Neutron Reflectometry (NR) and Small Angle Neutron Scattering (SANS) that is compatible with simultaneous optical transmission and resistivity measurements. The cell can accommodate samples up to 102 mm (4 inch) in diameter, can be pressurized from vacuum up to 10 bar gas pressure and the sample temperature can be controlled up to 350°C. The four single crystal quartz windows ensure both a good neutron and optical transmission and hence can be used in combination with in-situ optical transmission measurements. We present the cell and illustrate its performance with a series of neutron reflectometry experiments performed on Ta based thin films under a hydrogen containing atmosphere.

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Hydrogen, which serves as a major driver of sustainable aviation, requires precise sensing methods. This study focuses on the development of a metal hydride-coated tilted fibre Bragg grating (TFBG) based sensor for hydrogen detection, with tantalum as a novel sensing material for fibre optic hydrogen sensing. Magnetron sputtering has been employed to deposit nanometer-scale metal films onto the optical fibre surface of the TFBG structure. In this proof of concept work, changes in both amplitude and the centre wavelength of cladding resonances of the TFBG transmission spectrum were observed in the hydrogen concentration range from 0.01% to 4% at room temperature.

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Additives are commonly used to increase the performance of metal-halide perovskite solar cells, but detailed information on the origin of the beneficial outcome is often lacking. Herein, the effect of glycine hydrochloride is investigated when used as an additive during solution processing of narrow-bandgap mixed Pb–Sn perovskites. By combining the characterization of the photovoltaic performance and stability under illumination, with determining the quasi-Fermi level splitting, time-resolved microwave conductivity (TRMC), and morphological and elemental analysis a comprehensive insight is obtained. Glycine hydrochloride is able to retard the oxidation of Sn2+ in the precursor solution, and at low concentrations (1–2 mol%) it improves the grain size distribution and crystallization of the perovskite, causing a smoother and more compact layer, reducing non-radiative recombination, and enhancing the lifetime of photogenerated charges. These improve the photovoltaic performance and have a positive effect on stability. By determining the quasi-Fermi level splitting on perovskite layers without and with charge transport layers it is found that glycine hydrochloride primarily improves the bulk of the perovskite layer and does not contribute significantly to passivation of the interfaces of the perovskite with either the hole or electron transport layer (ETL).@en

Mixed Sn-Pb halide perovskites are promising absorber materials for solar cells due to the possibility of tuning the bandgap energy down to 1.2-1.3 eV. However, tin-containing perovskites are susceptible to oxidation affecting the optoelectronic properties. In this work, we investigated qualitatively and quantitatively metastable oxygen-induced doping in isolated ASn_xPb_1-xI₃ (where A is methylammonium or a mixture of formamidinium and cesium) perovskite thin films by means of microwave conductivity, structural and optical characterization techniques. We observe that longer oxygen exposure times lead to progressively higher dark conductivities, which slowly decay back to their original levels over days. Here oxygen acts as an electron acceptor, leading to tin oxidation from Sn²⁺ to Sn⁴⁺ and creation of free holes. The metastable oxygen-induced doping is enhanced by exposing the perovskite simultaneously to oxygen and light. Next, we show that doping not only leads to the reduction in the photoconductivity signal but also induces long-term effects even after loss of doping, which is thought to derive from consecutive oxidation reactions leading to the formation of defect states. On prolonged exposure to oxygen and light, optical and structural changes can be observed and related to the formation of SnO_x and loss of iodide near the surface. Our work highlights that even a short-term exposure to oxygen immediately impairs the charge carrier dynamics of the perovskite, while structural perovskite degradation is only noticeable upon long-term exposure and accumulation of oxidation products. Hence, for efficient solar cells, exposure of mixed Sn-Pb perovskites to oxygen during production and operation should be rigorously blocked.

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Lithium metal with its high theoretical capacity and low negative potential is considered one of the most important candidates to raise the energy density of all-solid-state batteries. However, lithium filament growth and its induced solid electrolyte decomposition pose severe challenges to realize a long cycle life. Here, dendrite growth in solid-state Li metal batteries is alleviated by introducing a high dielectric material, barium titanate, as a filler that removes the electric field gradients that catalyze dendrite formation. In symmetrical Li-metal cells, this results in a very small over-potential of only 48 mV at a relatively high current density of 1 mA cm⁻², when cycling a capacity of 2 mA h cm⁻² during 1700 h. The high dielectric filler improves the Coulombic efficiency and cycle life of full cells and suppresses electrolyte decomposition as indicated by solid-state nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) measurements. This indicates that the high dielectric filler can suppress dendrite formation, thereby reducing solid electrolyte decomposition reactions, resulting in the observed low overpotentials and improved cycling efficiency.

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The thermal stability of an equilibrium phase may be tuned due to lattice strain and distortion induced by nanosizing. We apply these effects to destabilize magnesium hydride, a promising hydrogen storage material owing to its high gravimetric hydrogen density but with a too high operating temperature/low supply pressure of hydrogen for most practical applications. The destabilization is attempted with MgH₂ in contact with high entropy alloy (HEA), in which multiple metal atoms lead to lattice strain and distortion. Here, two HEAs, CrMnFeCoNi with a face centered cubic (fcc) structure and TiVZrNbHf with a body centered cubic (bcc) structure, were prepared. Subsequently, they were cosputtered with Mg to synthesize Mg−HEA thin films, respectively. Although, in the Mg−CrMnFeCoNi thin films, miscible metals with Mg as Co and Ni may hamper the formation of independent Mg domains, a small proportion of Mg atoms form destabilized MgH₂. In contrast, Mg and TiVZrNbHf domains are chemically segregated at the nanoscale in the Mg−TiVZrNbHf thin films. The formation of nanometer-sized Mg domains is promoted by atomic rearrangement following the structural change of TiVZrNbHf from a bcc to an fcc structure upon hydrogenation, resulting in distorted and destabilized MgH₂. Our strategy to use HEAs and the structural change upon hydrogenation for the formation of destabilized MgH₂ is effective and opens up the possibility for the development of advanced and low-cost hydrogen storage and supply systems.

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Metal hydrides have been widely studied as hydrogen sensing materials and applied to various optical sensor configurations. With the increasing interest in using hydrogen as an energy source across sectors involving combustion processes, there is a growing demand for reliable hydrogen sensors operating at temperatures above 100 °C. Therefore, it is necessary to evaluate the performance of potential hydrogen sensing materials at elevated temperatures. We conducted experiments to observe the optical response and structural characteristics of palladium, palladium–gold, tantalum, and tantalum-alloy thin films with respect to varying hydrogen concentrations from 28 °C to 270 °C. Our results demonstrate that the optical response of palladium and palladium–gold diminish at 270 °C. However, tantalum provides a remarkable optical response to hydrogen concentrations below 1% for all the observed temperatures and a stable response at 270 °C for 350 cycles. Our measurement results show that tantalum is the most suitable material for detecting hydrogen within the range of 0.01% to 100% at temperatures ranging from 28 °C to 270 °C.

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This paper studies the structural and optical properties of tantalum–iron-, tantalum–cobalt-, and tantalum–nickel-sputtered thin films both ex situ and while being exposed to various hydrogen pressures/concentrations, with a focus on optical hydrogen sensing applications. Optical hydrogen sensors require sensing materials that absorb hydrogen when exposed to a hydrogen-containing environment. In turn, the absorption of hydrogen causes a change in the optical properties that can be used to create a sensor. Here, we take tantalum as a starting material and alloy it with Fe, Co, or Ni with the aim to tune the optical hydrogen sensing properties. The rationale is that alloying with a smaller element would compress the unit cell, reduce the amount of hydrogen absorbed, and shift the pressure composition isotherm to higher pressures. X-ray diffraction shows that no lattice compression is realized for the crystalline Ta body-centered cubic phase when Ta is alloyed with Fe, Co, or Ni, but that phase segregation occurs where the crystalline body-centered cubic phase coexists with another phase, as for example an X-ray amorphous one or fine-grained intermetallic compounds. The fraction of this phase increases with increasing alloyant concentration up until the point that no more body-centered cubic phase is observed for 20% alloyant concentration. Neutron reflectometry indicates only a limited reduction of the hydrogen content with alloying. As such, the ability to tune the sensing performance of these materials by alloying with Fe, Co, and/or Ni is relatively small and less effective than substitution with previously studied Pd or Ru, which do allow for a tuning of the size of the unit cell, and consequently tunable hydrogen sensing properties. Despite this, optical transmission measurements show that a reversible, stable, and hysteresis-free optical response to hydrogen is achieved over a wide range of hydrogen pressures/concentrations for Ta–Fe, Ta–Co, or Ta–Ni alloys which would allow them to be used in optical hydrogen sensors@en

Palladium thin films have been studied as hydrogen sensing materials and applied to variety of optical hydrogen sensors. Recently, tantalum has emerged as an attractive option for hydrogen sensing materials due to its broad sensing range and flexibility in tuning the sensing range by modifying the alloying composition or elements. Following the demand for optical hydrogen sensors for aerospace applications, testing the performance of hydrogen sensing materials is of interest. This work examines the optical response in respect to changing hydrogen concentrations and thermal expansion of palladium-gold (Pd_0.65Au_0.35) and tantalum-ruthenium (Ta_0.97Ru_0.03 and Ta_0.91Ru_0.09) thin films at temperatures similar to a hydrogen combustion engine. Our results suggest that tantalum-ruthenium alloys are suitable for sensing hydrogen from ambient temperatures up to 270^◦C because its low detection limit (0.01% of hydrogen in the atmosphere) is well below the explosive limit of hydrogen (4% of hydrogen in the atmosphere).

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Here, we study the structural and optical properties of tetragonal β-tantalum-sputtered thin films both ex situ and when exposed to hydrogen, with a focus on optical hydrogen sensing applications. Using optical transmission measurements, out-of-plane and in-plane X-ray diffraction, and X-ray and neutron reflectometry, we show that thin film β-tantalum gradually, reversibly, and hysteresis-freely absorbs hydrogen with an increasing hydrogen pressure/concentration. The gradual absorption of hydrogen with increasing hydrogen concentrations induces a change in the optical transmission and reflection. These quantities change reversibly and are hysteresis-free over at least 5 orders of magnitude in hydrogen pressure/concentration, making β-tantalum a suitable hydrogen sensing material. At all partial hydrogen pressures studied, we observe that the volumetric expansion, hydrogen-to-metal ratio, and lattice expansion are substantially smaller than for body-centered cubic α-tantalum.

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Full-area passivating contacts based on SiOx/poly-Si stacks are key for the new generation of industrial silicon solar cells substituting the passivated emitter and rear cell (PERC) technology. Demonstrating a potential efficiency increase of 1 to 2% compared to PERC, the utilization of n-type wafers with an n-type contact at the back and a p-type diffused boron emitter has become the industry standard in 2024. In this work, variations of this technology are explored, considering p-type passivating contacts on p-type Si wafers formed via a rapid thermal processing (RTP) step. These contacts could be useful in conjunction with n-type contacts for realizing solar cells with passivating contacts on both sides. Here, a particular focus is set on investigating the influence of the applied thermal treatment on the interfacial silicon oxide (SiOx) layer. Thin SiOx layers formed via ultraviolet (UV)–O3 exposure are compared with layers obtained through a plasma treatment with nitrous oxide (N2O). This process is performed in the same plasma enhanced chemical vapor deposition (PECVD) chamber used to grow the Si-based passivating layer, resulting in a streamlined process flow. For both oxide types, the influence of the RTP thermal budget on passivation quality and contact resistivity is investigated. Whereas the UV–O3 oxide shows a pronounced degradation when using high thermal budget annealing (T > 860 °C), the N2O–plasma oxide exhibits instead an excellent passivation quality under these conditions. Simultaneously, the contact resistivity achieved with the N2O-plasma oxide layer is comparable to that yielded by UV–O3-grown oxides. To unravel the mechanisms behind the improved performance obtained with the N2O-plasma oxide at high thermal budget, characterization by high-resolution (scanning) transmission electron microscopy (HR-(S)TEM), X-ray reflectometry (XRR) and X-ray photoelectron spectroscopy (XPS) is conducted on layer stacks featuring both N2O and UV–O3 oxides after RTP. A breakup of the UV–O3 oxide at high thermal budget is observed, whereas the N2O oxide is found to maintain its structural integrity along the interface. Furthermore, chemical analysis reveals that the N2O oxide is richer in oxygen and contains a higher amount of nitrogen compared to the UV–O3 oxide. These distinguishing characteristics can be directly linked to the enhanced stability exhibited by the N2O oxide under higher annealing temperatures and extended dwell times.@en

Hydrogen, crucial in industrial and environmental realms, demands precise sensing methods. This study focuses on the design of a metal hydride-coated tilted fibre Bragg grating (TFBG) based sensor for hydrogen detection, introducing tantalum as a novel sensing material for fibre optic hydrogen sensor development. To facilitate the ellipsometry inspection of optical constants, magnetron sputtering technique has been employed to deposit nanometer-scale metal films onto a glass substrate. Numerical modeling results are presented for mode analysis of the proposed sensor design, analyzing transverse mode behavior for sensor optimization. The study also provides insights into other TFBG sensor design considerations, suggesting potential hydrogen sensing applications, such as hydrogen-powered aviation and storage solutions.

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Formation cycling is a critical process aimed at improving the performance of lithium ion (Li-ion) batteries during subsequent use. Achieving highly reversible Li-metal anodes, which would boost battery energy density, is a formidable challenge. Here, formation cycling and its impact on the subsequent cycling are largely unexplored. Through solid-state nuclear magnetic resonance (ssNMR) spectroscopy experiments, we reveal the critical role of the Li-ion diffusion dynamics between the electrodeposited Li-metal (ED-Li) and the as-formed solid electrolyte interphase (SEI). The most stable cycling performance is realized after formation cycling at a relatively high current density, causing an optimum in Li-ion diffusion over the Li-metal-SEI interface. We can relate this to a specific balance in the SEI chemistry, explaining the lasting impact of formation cycling. Thereby, this work highlights the importance and opportunities of regulating initial electrochemical conditions for improving the stability and life cycle of lithium metal batteries.

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Achieving both high redox activity and rapid ion transport is a critical and pervasive challenge in electrochemical energy storage applications. This challenge is significantly magnified when using large-sized charge carriers, such as the sustainable ammonium ion (NH₄⁺). A self-assembled MXene/n-type conjugated polyelectrolyte (CPE) superlattice-like heterostructure that enables redox-active, fast, and reversible ammonium storage is reported. The superlattice-like structure persists as the CPE:MXene ratio increases, accompanied by a linear increase in the interlayer spacing of MXene flakes and a greater overlap of CPEs. Concurrently, the redox activity per unit of CPE unexpectedly intensifies, a phenomenon that can be explained by the enhanced de-solvation of ammonium due to the increased volume of 3 Å-sized pores, as indicated by molecular dynamic simulations. At the maximum CPE mass loading (MXene:CPE ratio = 2:1), the heterostructure demonstrates the strongest polymeric redox activity with a high ammonium storage capacity of 126.1 C g⁻¹ and a superior rate capability at 10 A g⁻¹. This work unveils an effective strategy for designing tunable superlattice-like heterostructures to enhance redox activity and achieve rapid charge transfer for ions beyond lithium.

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The growing demand for safe, cost-efficient, high-energy and high-power electrochemical energy storage devices has stimulated the development of aqueous-based supercapacitors with high capacitance, high rate capability, and high voltage. 2D titanium carbide MXene-based electrodes have shown excellent rate capability in various dilute aqueous electrolytes, yet their potential window is usually narrower than 1.2 V. In this study, we show that the potential window of Ti₃C₂T _x MXene can be efficiently widened to 1.5 V in a cost-effective and environmentally benign polyethylene glycol (PEG) containing molecular crowding electrolyte. Additionally, a pair of redox peaks at −0.25 V/−0.05 V vs. Ag (cathodic/anodic) emerged in cyclic voltammetry after the addition of PEG, yielding an additional 25% capacitance. Interestingly, we observed the co-insertion of the molecular crowding agent PEG-400 during the Li⁺ intercalation process based on in-situ x-ray diffraction analysis. As a result, Ti₃C₂T _x electrodes presented an interlayer space change of 4.7 Å during a complete charge/discharge cycle, which is the largest reversible interlayer space change reported so far for MXene-based electrodes. This work demonstrates the potential of adding molecular crowding agents to improve the performance of MXene electrodes in aqueous electrolytes and to enlarge the change of the interlayer spacing.

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Many electronic and electrochemical devices rely on the exchange of light elements such as hydrogen and oxygen with the environment. Understanding and tailoring the device functionality requires accurate information about the concentration and chemical bonding of such species inside a solid, which is particularly difficult if several species are exchanged. In LaNiO3 thin films in situ transport experiments reveal a re-entrant metal–insulator transition upon hydrogen exposure. The origin of this unusual behavior can be understood by combining information about the stoichiometry and chemical bonding of hydrogen and oxygen as determined by neutron reflectometry and x-ray absorption spectroscopy, respectively. In addition to the metallic parent phase, an insulating phase with composition LaNiO2.65 and a re-entrant metallic phase with composition LaNiO2.15(OH)0.5 are identified. They can be inter-converted by redox reactions in different external environments. The methodology employed offers new insights into the mechanisms underlying the influence of hydrogen in functional devices.@en