Anion redox in lithium transition-metal oxides such as Li2RuO3 and Li2MnO3 has catalyzed intensive research efforts to find transition-metal oxides with anion redox that may boost the energy density ...of lithium-ion batteries. The physical origin of the observed anion redox remains debatable, and more direct experimental evidence is needed. In this work, we have shown electronic signatures of oxygen–oxygen coupling, direct evidence central to lattice oxygen redox (O2–/(O2) n−), in charged Li2–x RuO3 after Ru oxidation (Ru4+/Ru5+) upon first electron removal with lithium deintercalation. Experimental Ru L3-edge high-energy-resolution fluorescence-detected X-ray absorption spectra (HERFD-XAS), supported by ab initio simulations, revealed that the increased intensity in the high-energy shoulder upon lithium deintercalation resulted from increased O–O coupling, inducing (O–O) σ*-like states with π overlap with Ru d-manifolds, in agreement with O K-edge XAS spectra. Experimental and simulated O K-edge X-ray emission spectra further supported this observation with the broadening of the oxygen nonbonding feature upon charging, also originated from (O–O) σ* states. This lattice oxygen redox of Li2–x RuO3 was accompanied by a small amount of O2 evolution in the first charge from differential electrochemistry mass spectrometry but diminished in the subsequent cycles, in agreement with the more reduced states of Ru in later cycles from Ru L3-edge HERFD-XAS. These observations indicated that Ru redox contributed more to discharge capacities after the first cycle. This study has pinpointed the key spectral fingerprints related to lattice oxygen redox from a molecular level and constructed a transferrable framework to rationally interpret the spectroscopic features by combining advanced experiments and theoretical calculations to design materials for Li-ion batteries and electrocatalysis applications.
Anion redox in lithium transition metal oxides such as Li
RuO
and Li
MnO
has catalyzed intensive research efforts to find transition metal oxides with anion redox that may boost the energy density of ...lithium-ion batteries. The physical origin of observed anion redox remains debated, and more direct experimental evidence is needed. In this work, we have shown electronic signatures of oxygen-oxygen coupling, direct evidence central to lattice oxygen redox (O
/(O
)
), in charged Li
RuO
after Ru oxidation (Ru
/Ru
) upon first-electron removal with lithium de-intercalation. Experimental Ru L
-edge high-energy-resolution fluorescence detected X-ray absorption spectra (HERFD-XAS), supported by
simulations, revealed that the increased intensity in the high-energy shoulder upon lithium de-intercalation resulted from increased O-O coupling, inducing (O-O)
*-like states with
overlap with Ru
-manifolds, in agreement with O K-edge XAS spectra. Experimental and simulated O K-edge X-ray emission spectra (XES) further supported this observation with the broadening of the oxygen non-bonding feature upon charging, also originated from (O-O)
* states. This lattice oxygen redox of Li
RuO
was accompanied by a small amount of O
evolution in the first charge from differential electrochemistry mass spectrometry (DEMS) but diminished in the subsequent cycles, in agreement with the more reduced states of Ru in later cycles from Ru L
-edge HERFD-XAS. These observations indicated that Ru redox contributed more to discharge capacities after the first cycle. This study has pinpointed the key spectral fingerprints related to lattice oxygen redox from a molecular level and constructed a transferrable framework to rationally interpret the spectroscopic features by combining advanced experiments and theoretical calculations to design materials for Li-ion batteries and electrocatalysis applications.
The electronic structure and dynamics of ruthenium complexes are widely studied given their use in catalytic and light-harvesting materials. Here we investigate three model Ru complexes, ...RuIII(NH3)63+, RuII(bpy)32+, and RuII(CN)64–, with L3-edge 2p3d resonant inelastic X-ray scattering (RIXS) to probe unoccupied 4d valence orbitals and occupied 3d orbitals and to gain insight into the interactions between these levels. The 2p3d RIXS maps contain a higher level of spectral information than the L3 X-ray absorption near edge structure (XANES). This study provides a direct measure of the 3d spin–orbit splittings of 4.3, 4.0, and 4.1 eV between the 3d5/2 and 3d3/2 orbitals of the RuIII(NH3)63+, RuII(bpy)32+, and RuII(CN)64– complexes, respectively.
Multiplexed ion beam imaging by time-of-flight (MIBI-TOF) is a form of mass spectrometry imaging that uses metal labeled antibodies and secondary ion mass spectrometry to image dozens of proteins ...simultaneously in the same tissue section. Working with the National Cancer Institute's (NCI) Cancer Immune Monitoring and Analysis Centers (CIMAC), we undertook a validation study, assessing concordance across a dozen serial sections of a tissue microarray of 21 samples that were independently processed and imaged by MIBI-TOF or single-plex immunohistochemistry (IHC) over 12 days. Pixel-level features were highly concordant across all 16 targets assessed in both staining intensity (R
= 0.94 ± 0.04) and frequency (R
= 0.95 ± 0.04). Comparison to digitized, single-plex IHC on adjacent serial sections revealed similar concordance (R
= 0.85 ± 0.08) as well. Lastly, automated segmentation and clustering of eight cell populations found that cell frequencies between serial sections yielded an average correlation of R
= 0.94 ± 0.05. Taken together, we demonstrate that MIBI-TOF, with well-vetted reagents and automated analysis, can generate consistent and quantitative annotations of clinically relevant cell states in archival human tissue, and more broadly, present a scalable framework for benchmarking multiplexed IHC approaches.
To limit further rising levels in methane emissions from stationary and mobile sources and to enable promising technologies based on methane, the development of efficient combustion catalysts that ...completely oxidize CH4 to CO2 and H2O at low temperatures in the presence of high steam concentrations is required. Palladium is widely considered as one of the most promising materials for this reaction, and a better understanding of the factors affecting its activity and stability is crucial to design even more improved catalysts that efficiently utilize this precious metal. Here we report a study of the effect of three important variables (particle size, support, and reaction conditions including water) on the activity of supported Pd catalysts. We use uniform palladium nanocrystals as catalyst precursors to prepare a library of well-defined catalysts to systematically describe structure–property relationships with help from theory and in situ X-ray absorption spectroscopy. With this approach, we confirm that PdO is the most active phase and that small differences in reaction rates as a function of size are likely due to variations in the surface crystal structure. We further demonstrate that the support exerts a limited influence on the PdO activity, with inert (SiO2), acidic (Al2O3), and redox-active (Ce0.8Zr0.2O2) supports providing similar rates, while basic (MgO) supports show remarkably lower activity. Finally, we show that the introduction of steam leads to a considerable decrease in rates that is due to coverage effects, rather than structural and/or phase changes. Altogether, the data suggest that to further increase the activity and stability of Pd-based catalysts for methane combustion, increasing the surface area of supported PdO phases while avoiding strong adsorption of water on the catalytic surfaces is required. This study clarifies contrasting reports in the literature about the active phase and stability of Pd-based materials for methane combustion.
The electronic structure of phosphorus, sulfur, and chlorine in compounds with T d and C 3v local symmetries was studied with high-resolution Kβ X-ray emission spectroscopy (XES) in the tender X-ray ...range. Measured spectra are compared to the results of ab initio quantum chemical calculations based on density functional theory (DFT). The spectral structure is reproduced by the model spectra of isolated XO4 n– and XO3 n– (X = P, S, or Cl) anions incorporating only the first coordination sphere around the central atom. The main spectral components can be explained by the molecular orbital theory. Finally, the potential of XES spectroscopy combined with DFT calculations to study the electronic structure of third-row elements in a slightly larger molecule is investigated.
Total reflection X‐ray fluorescence (TXRF) analysis is extensively used by the semiconductor industry for measuring trace metal contamination on silicon surfaces. In addition to determining the ...quantity of impurities on a surface, TXRF can reveal information about the vertical distribution of contaminants by measuring the fluorescence signal as a function of the angle of incidence. In this study, two samples were intentionally contaminated with copper in non‐deoxygenated and deoxygenated ultrapure water (UPW) resulting in impurity profiles that were either atomically dispersed in a thin film or particle‐like, respectively. The concentration profile of the samples immersed into deoxygenated UPW was calculated using a theoretical concentration profile representative of particles, yielding a mean particle height of 16.1 nm. However, the resulting theoretical profile suggested that a distribution of particle heights exists on the surface. The fit of the angular distribution data was further refined by minimizing the residual error of a least‐squares fit employing a model with a Gaussian distribution of particle heights about the mean height. The presence of a height distribution was also confirmed with atomic force microscopy measurements.
The angular distribution of the total reflection X‐ray fluorescence signal can suggest a distribution of particle heights deposited on a surface. This height distribution can be deduced by fitting theoretical concentration profiles representative of particles.
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