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Accelerating lattice oxygen kinetics of layered oxide cathodes via active facet modulation and robust mechanochemical interface construction for high energy density sodium ion batteries
No full textTriggering anionic redox reactions ARRs offers a powerful route to enhance the energy density of low cost manganese based layered oxides for rechargeable sodium ion batteries SIBs . However, the ARR process often results in irreversible lattice oxygen release, leading to significant structural distortions and rapid performance degradation. Herein, we propose a multifunctional tunnel interface engineering strategy that stabilizes P2 Na0.75Li0.25Mn0.75O2 NLMO by regulating active facets, suppressing lattice oxygen release, and enhancing air stability, thereby achieving desirable performance in terms of energy density and cycling stability. With protection of this tunnel layer, NLMO retains high anionic redox activity without irreversible oxygen release at high voltage, undergoing a simplified solid solution reaction with minimal structural mechanical stress, which was confirmed by a series of advanced synchrotron radiation based characterization methods as well as mechanical stress simulations. The tunnel modified NLMO cathode delivers a high energy density of 649.6 Wh kg amp; 8722;1 at 0.1 C within 1.5 4.4 V, and exhibits exceptional capacity retention 91.24 . Given the intrinsic advantages of the sophisticated tunnel interface and superior lattice matching, NLMO exhibits excellent Na diffusion kinetics and enhanced air stability, which further improves its practicality. The tunnel interface engineering in this work offers valuable insights into high voltage cathodes for SIBs, emphasizing lattice oxygen stabilization and robust interfacial stabilit
First experiments with ultrashort, circularly polarized soft x ray pulses at FLASH2
Full text linkTime resolved absorption spectroscopy and magnetic circular dichroism with circularly polarized soft x rays XAS and XMCD are powerful tools to probe electronic and magnetic dynamics in magnetic materials element and site selectively. By employing these methods, groundbreaking results have been obtained, for instance, for magnetic alloys, which helped to fundamentally advance the field of ultrafast magnetization dynamics. At the free electron laser facility FLASH, key capabilities for ultrafast XAS and XMCD experiments have recently improved. In an upgrade, an APPLE III helical afterburner undulator was installed at FLASH2 in September 2023. This installation allows for the generation of circularly polarized soft x ray pulses with a duration of a few tens of femtoseconds covering the L 3,L 2 edges of the important 3d transition metal elements with pulse energies of several mu J. Here, we present first experimental results with such ultrashort x ray pulses from the FL23 beamline employing XMCD at the L 3,L 2 edges of the 3d metals, Co, Fe, and Ni. We obtain significant dichroic difference signals indicating a degree of circular polarization close to 100 . With the pulse length preserving monochromator at beamline FL23 and an improved pump laser setup, FLASH can offer important and efficient experimental instrumentation for ultrafast demagnetization studies and other investigations of ultrafast spin dynamics in 3d transition metals, multilayers, and alloy
Combining X Ray Photoelectron and Absorption Spectroscopies for Determining Surface Chemistry and Composition of Ti3C2Tx MXene
Full text linkSurface chemistry and core composition of 2D MXenes play a major role in their interfacial properties, but the determination and quantification of their bonding environments remain challenging. X ray Photoelectron Spectroscopy XPS is a method of choice that is broadly utilized but is often hindered by large uncertainties and systematic bias due to adsorbed species such as adventitious carbon or etching residues. In this work, energy dependent XPS and depth profile modeling of the Ti3C2Tx MXene surface are employed to differentiate the contributions from the MXene and the adsorbed species, thereby increasing the accuracy of quantification. In comparison, uncorrected lab based XPS suffers from a systematic overestimation of Ti vacancies by 7 and an underestimation of terminal atoms, particularly F, by as much as 15 . Interestingly, it is found that a simple inelastic mean free path correction is sufficient to address the issue and reveals extremely low defects in Ti3C2Tx MXene synthesized using the HF HCl etching route. Soft X ray Absorption Spectroscopy XAS , supported by Density Functional Theory DFT calculations, also demonstrates a high chemical sensitivity of the surface terminations. This work provides novel insights into XPS quantification and the use of XAS for probing the carbide core and surface chemistry of Ti3C2Tx MXene
Magnetic field induced chiral soliton lattice in the bulk magnetoelectric helimagnet Cu2OSeO3
Full text linkChiral soliton lattices CSLs are anharmonic magnetic structures typically found in uniaxial chiral magnets. In this study, we report the observation of CSL in bulk Cu2OSeO3 , a chiral insulator known for its magnetoelectric properties. Using small angle neutron scattering SANS experiments, we demonstrate the formation of CSLs in Cu 2 OSeO3 at low temperatures, driven by the competition between cubic anisotropy and magnetic field. Our observations of higher harmonics in the SANS signal clearly indicate the anharmonic nature of the spiral. This finding underscores the complex interplay between magnetic interactions in Cu2OSeO3 , offering insights for potential applications of CSLs in electric field controlled spintronic device
Plasma activated copper alkanolamine precursor paste for printed flexible antenna formulation, mechanism, and performance evaluation
No full textCopper based pastes have attracted significant attention for printed electronic applications because of their low cost and high conductivity. Copper precursor pastes are easier to prepare, exhibit long term stability and do not have oxidation issues during preparation and storage, when compared to copper micro sized flakes and nanoparticle pastes. Up to now, copper precursor pastes activated by plasma have been rarely studied, and their activation mechanism is not clear. Furthermore, little attention has been paid to the application of these pastes in wireless electronic devices. In this paper, therefore, we formulated a plasma activated copper alkanolamine complex precursor paste for antenna applications. The paste was formulated only using copper II formate and excess 2 amino 2 methyl 1,2 propanediamine, which exhibited favorable flowability for screen printing. Copper films with good conductivity were produced on PET substrates by plasma sintering this paste. The effects of plasma sintering time on the properties of the copper film were explored and correlations between them were established. A possible plasma activation mechanism was proposed. Finally, a flexible ultra wideband antenna with notch properties was fabricated with the copper paste, demonstrating its feasibility in wireless electronics application
Stabilizing Wide Bandgap Perovskite with Nanoscale Inorganic Halide Barriers for Next Generation Tandem Technology
No full textWide bandgap WBG perovskite solar cells PSCs play a crucial role in advancing perovskite based tandem solar cells. In WBG perovskite films, grain boundary GB defects are the main contributors to open circuit voltage VOC deficits and performance degradation. This report presents an effective strategy for passivating GBs by incorporating an inorganic protective layer and reducing the density of GBs in perovskite films. This is achieved by integrating potassium thiocyanate KSCN into I Br mixed halide WBG perovskites. It is reported for the first time that the incorporation of KSCN creates band shaped barriers along the GBs. In addition, KSCN enlarges the grains of perovskite film. Elemental and structural analyses reveal that these barriers are composed of potassium lead halide. Incorporating KSCN significantly enhances the fill factor and VOC of WBG single junction PSCs by reducing trap density. This results in high power conversion efficiencies of 19.22 bandgap of 1.82 eV , 20.45 1.78 eV , and 21.54 1.70 eV with a C60 bathocuproine electron transport layer, and 18.51 1.82 eV with a C60 SnO2. Furthermore, both operational and shelf stabilities are significantly improved due to reduced light induced halide segregation. By using inorganic halide passivated WBG sub cells, a monolithic all perovskite tandem solar cell with an efficiency of 27.04 is demonstrate
Seasonal Effects on Outdoor Stability of Perovskite Solar Cells
Full text linkThe critical challenge for the commercialization of perovskite solar cells PSCs is their operational stability. PSCs outdoor operation exposes the cells to a combination of stress factors that are difficult to reproduce by indoor testing due to diurnal and seasonal variations. This highlights the need for outdoor testing under operational conditions. The effect of climate conditions on outdoor operational lifetime degradation of n i p PSCs is systematically studied herein. Their lifetime indicators are determined in different seasons, and correlated with the outdoor irradiance and temperatures measured simultaneously. Based on this outdoor measurement analysis and indoor light cycling stability tests, it is suggested that ambient temperatures induce a more significant effect than the irradiance on the PSC s lifetime degradation. The study also suggests different roles played by the temperatures during the diurnal light versus dark periods the day light time maximum temperatures have a more significant effect on the long term degradation. In contrast, minimum temperatures during the night dark cycles significantly affected the diurnal reversible degradation and the initial fast degradation. The results show that the commonly used lifetime indicators T80 and T50 are climate dependent, and their use for comparative purposes is valid only if measured in similar climatic condition
Toward Ultrawide Bandgap Engineering Physical Properties of an alpha TixGa1 x 2O3 Material Library
No full textDue to its high bandgap of 5.3 5.6 amp; 8201;eV and high predicted breakdown field of 10 amp; 8201;MV amp; 8201;cm amp; 8722;1, much attention is drawn to the ultrawide bandgap semiconductor amp; 945; Ga2O3 for applications in high power and solar blind optoelectronic devices. In contrast to the thermodynamically most stable amp; 946; phase of Ga2O3, various transition metal sesquioxides with rhombohedral crystal structure and similar lattice constants to amp; 945; Ga2O3 are available for bandgap engineering toward lower bandgap energies. Therefore the material system amp; 945; TixGa1 amp; 8722;x 2O3 in principle offers the possibility to tune the materials bandgap for wavelength selective optoelectronics over an extremely wide range from 5.6 amp; 8201;eV amp; 945; Ga2O3 down to 0.14 amp; 8201;eV amp; 945; Ti2O3 . In this work, high throughput combinatorial synthesis by pulsed laser deposition is employed to realize a spatially addressable material library covering almost the entire composition range within the ternary TixGa1 amp; 8722;x yOz solid solution. Phase pure growth of TixGa1 amp; 8722;x 2O3 up to x amp; 8201; amp; 8201;0.25 is reported, exceeding previously found miscibility limits by a factor of 5. The physical properties of the material system are investigated in relation to x and bandgap engineering within the rhombohedral amp; 945; TixGa1 amp; 8722;x 2O3 material system is demonstrated over an up to now unprecedented large spectral range from 4.4 to 5.3 amp; 8201;e
Evaluating the electronic structure and stability of epitaxially grown Sr doped LaFeO3 perovskite alkaline O2 evolution model electrocatalysts
No full textIn this work, we have investigated the relationships between surface stability, electronic structure and O2 evolution reaction OER activity for epitaxial thin film La1 amp; 8722;xSrxFeO3 x 0, 0.33, 0.8 model electrocatalysts before and after different electrochemical treatments. Cyclic voltammetry CV between 1.22 V and 1.92 V vs. RHE results in the continuous enhancement of OER performance of LaFeO3, while for La0.67Sr0.33FeO3 and La0.2Sr0.8FeO3 a gradual decrease of OER performance with increasing number of CV cycles was observed. A combination of atomic force microscopy, X ray diffraction and X ray reflectivity reveals that the surfaces of La1 amp; 8722;xSrxFeO3 x 0, 0.33, 0.8 undergo surface morphology changes during OER treatment. Synchrotron ex situ X ray photoemission spectroscopy data show a gradual down shift of the Fermi level EF of LaFeO3 with increasing number of CV cycles, while near edge X ray absorption fine structure spectroscopy NEXAFS at the Fe L edge and O K edge shows the presence of surface Fe4 species as well as new hole states near the conduction band minimum upon electrochemical treatment, leading to a further enhancement of the electrochemical activity of LaFeO3. The newly formed hole state in LaFeO3 that appeared after 3 CV cycles remained constant upon progressing OER treatment. On the contrary, the decrease of OER performance of La0.67Sr0.33FeO3 and La0.2Sr0.8FeO3 with increasing CV cycles is attributed to an up shift of EF along with a decrease of Fe4 and hole state content after OER treatment. Furthermore, we found that the stability of the OER performance of La1 amp; 8722;xSrxFeO3 is closely related to the leaching of Sr during OER, and the stability deteriorates with increasing Sr doping concentration in the pristine sample
Estimating the quasi Fermi level of holes at the surface of semiconductor photoanodes using outer sphere redox couples
Full text linkSemiconductor electrodes can catalyze photo induced redox reactions with light illumination. Photoexcitation produces excited carriers that subsequently transfer to the front and back contacts as determined by the bulk and surface properties of the photoelectrodes. This transfer defines the resultant quasi Fermi levels of the photo generated carriers at the photoelectrode surface, which, in turn, impacts the efficiency of surface photoelectrochemical reactions. However, determining such quasi Fermi levels is not a simple task. In this study, we introduce a method for estimating the quasi Fermi level of holes using outer sphere electron transfer reactions. The quasi Fermi level of holes is estimated by linking the oxidation photocurrent on photoanodes to the separately measured electrode potential on a stable metal electrode. Using this method, the quasi Fermi level of holes at the surface is monitored in response to variations in applied potential and light intensity. This approach effectively separates the photocurrents of the CdS model electrode between surface redox reaction and photocorrosion, while concurrently quantifying the dynamic quasi Fermi level at the surface. This work facilitates quantitative understanding of photoelectrochemical reactions on semiconductor electrodes to design green chemical transformation system