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Gradient Structural Design Inducing Rocksalt Interface and P2 and P3 Biphasic Bulk for Layered Oxide Cathode with Prolonged Sodium Ion Storage
No full textLayered transition metal oxides are the most promising cathode materials for sodium ion batteries SIBs , which unfortunately suffer from rapid capacity decay and sluggish Na ion kinetics due to irreversible phase transition and aggravated interface side reactions during de sodiation. Herein, a material with coherent gradient architecture ranging from rocksalt interface to P2 P3 layered bulk heterostructure is prepared via a precursor oriented driven reaction method. Such core shell structure design reduces the detrimental phase transition through the interlocking effect, which improves the structural integrity of resulting cathode. Specifically, the rocksalt surface is structurally robust, mitigating interfacial parasitic reactions and stabilizing surface oxygen. With this unique design, the resulting cathode delivers a discharge capacity of 94 mAh g amp; 8722;1 at 5C in the voltage range of 2.0 4.3 V and demonstrates excellent cycling stability with 76 capacity retention after 1000 cycles. Moreover, the precursor induced gradient structural design significantly enhances the thermal stability of the cathode, which is of additional advantage with respect to the safety of SIBs. This work offers future guidance toward designing high performance cathode materials for advanced SIB
Extrinsic and Intrinsic Factors Governing the Electrochemical Oxidation of Propylene in Aqueous Solutions
No full textThe electrochemical synthesis of commodity chemicals such as epoxides and glycols offers a sustainable alternative to conventional methods that involve hazardous chemicals. Efforts to improve the yield and selectivity of propylene oxidation using Pd based catalysts have been shown to be highly sensitive to applied potential, pH, and electrochemical cell design. Record efficiencies and yields were obtained by substitution of PdO by 4d or 5d transition metals, including Pt, with thus far little rationale regarding the origin for the improvement. Through electrochemical analysis, scanning transmission electron microscopy, X ray absorption spectroscopy, and surface enhanced infrared absorption spectroscopy, we investigated the mechanism of propylene oxidation on Pd based catalysts. We demonstrate that adsorbates forming on PdO, where Pd adopts a square planar coordination [PdO4], differ from that forming on the surface of oxidized metallic Pd catalysts with an oxo intermediate mediating propylene oxidation on PdO. We further show that Pt substitution in PdO does not modify this oxo intermediate. Varying pH, we found that the onset for propylene oxidation is pH independent, indicating a potential determining step where the proton is not involved in and similar reaction pathway in acidic and near neutral conditions. Finally, our work undoubtedly demonstrates that high Faradaic efficiency toward propylene glycol and propylene oxide formation, such as those previously reported in the literature, can be achieved by means of electrode engineering and mastery of mass transport and local pH. Notably, we achieved amp; 8776;100 faradaic efficiency for propylene glycol at 1.7 V vs RHE in acidic media using a Pt substituted PdO catalyst loaded onto a gas diffusion electrod
Triplet Metallovinylidenes of Palladium and Platinum Based on a Chelating P Diazoalkene Ligand
Full text linkTriplet carbenes featuring a metal adjacent to the carbene center metallocarbenes; R amp; 9472;C amp; 9472;M are an emerging class of diradicals within the field of reactive intermediates. Here, we report the synthesis of the first spectroscopically characterized triplet metallovinylidenes R amp; 9472;C amp; 8594;M; M Pt, Pd . The synthetic access is based on a rigid P C chelating diazoalkene ligand and its coordination to Pt and Pd. The C P chelating ligand geometrically constrains the R amp; 9472;C amp; 8594;M angle and inhibits free bending. Irradiation of the free diazoalkene ligand generates a triplet vinylidene, characterized by Q band electron paramagnetic resonance EPR spectroscopy. Irradiation of the metal coordination complexes Pt and Pd affords triplet metallovinylidenes, which were characterized at low temperatures including photochemically triggered in crystallo X ray diffraction. Combined FD FT THz EPR spectroscopy and SQUID measurements allowed the determination of the large triplet zero field splitting ZFS with D values of 124.5 cm amp; 8722;1 Pt and 8.0 cm amp; 8722;1 Pd in excellent agreement with the electronic structure obtained by high level quantum chemical calculation
Surface photovoltage spectroscopy for defect investigation of diamond
No full textDefect related transition energies and charge transfer along grain boundaries were studied in polycrystalline diamond by using a new type of mirrorless double prism monochromator based on fused silica and by introducing modulated transient surface photovoltage spectroscopy. Polycrystalline diamond served as a model system containing small crystallites at the seed and large crystallites at the growth sides. Illumination was performed between 0.4 and 7.3 eV for seed and growth side orientations of the sample which allowed for homogeneous excitation of defect related transitions across the sample and for variation of the penetration depth under fundamental absorption in diamond. Photogenerated electrons were separated towards the seed side independently of the defect related transition for excitation below the range of the bandgap of diamond. Under strong absorption, photogenerated electrons were preferentially separated towards the surface. We found that photogenerated electrons are transferred faster than photogenerated holes along grain boundaries and that photogenerated holes are preferentially trapped at defects in crystallites. The enhancement of electron transfer via grain boundaries also explains the observed preferential electron trapping at surface states of diamon
New insights into non contact reflectance IR mapping of teeth
No full textTeeth are made of highly mineralized tissues that withstand years of daily usage. Their mechanical properties have been studied at all length scales with ageing but manly small areas have been the focus of high sensitivity chemical property quantification. A comprehensive, spatially resolved examination across centimeter sized tooth specimens is needed to expand our comprehension of young versus aged teeth. Specular Reflectance Fourier Transform Infrared Spectroscopy srFTIR is a nondestructive microscopy technique that can be used to characterize the chemical composition of mineralized surfaces. This technique provides spatially resolved chemical absorption information, making it useful to study both organics and mineral in visibly accessible tooth tissues. Highly polished dehydrated cross sectional surfaces of bovine and human teeth were srFTIR imaged, and spectra were processed using a Kramers Kronig Transformation to generate absorbance like chemical maps. Results are comparable with the well established FTIR Transmission and Attenuated Total Reflection ATR methods. Maps of multiple amp; 120584;3 phosphate vibrations, amp; 120584;2 carbonate, and amide I reveal insights into structural and chemical variations across dentine. Young bovine teeth exhibited many chemical and structural similarities to old, partially sclerotic human teeth, affirming their use as proxies in dental research. This work highlights the capability of specular reflection infrared spectroscopy imaging to reveal spatial chemical information and expand our understanding of tooth microstructure and composition variation
A Low Ringing, High Bandwidth Button Beam Position Monitor for Bunch by Bunch Diagnostics in Advanced Storage Ring Operations
No full textModern electron storage rings that implement extreme operating modes require a high accuracy bunch bybunch beam position monitor BPM system capable of diagnosing and controlling individual bunches while remaining compatible with bunch selective feedback systems. Any signal ringing beyond a nanosecond in time is critical, as it can lead to the misinterpretation of beam position and current for subsequent bunches. This necessitates an improvement in the performance of BPM systems for bunch selective operations. In this study, we present an empirical evaluation of the existing button BPMs in the BESSY II storage ring and propose a new button BPM design featuring advanced capabilities, such as optimized impedance matching within the button structure and enhanced signal processing techniques. Our beam experiments demonstrate a significant improvement in signal fidelity and precision, paving the way for more effective beam diagnostics and control in high performance storage ring
Operando X ray Spectroscopy Study of Pd and Pd Au Laterally Condensed Catalysts during Selective Acetylene Hydrogenation The Role of Carbon
No full textTwo stage evolution of magnetic correlations in the spiral spin liquid material Ca10Cr7O28
No full textWe present an X band and tunable high frequency high field electron spin resonance HF ESR study of single crystalline Ca10Cr7O28, which constitutes alternating antiferromagnetic and ferromagnetic kagome bilayers. At high temperatures, a phonon assisted relaxation process is evoked to account for the pronounced increase of the linewidth in an exchange narrowing regime kBT gt; gt; J . In contrast, at low temperatures kBT lt; J , a power law behavior in line narrowing is observed. Our data reveal two distinct power law regimes for the linewidth which crossover at T amp; 8727; amp; 8776; 7.5K. Notably, the intriguing evolution of the ESR linewidth in this alternating kagome bilayer system with opposite sign of exchange interactions highlights distinct spin dynamics compared to those in a uniform kagome antiferromagne