Lattice oxygen redox yields anomalous capacity and can significantly increase the energy density of layered Li‐rich transition metal oxide cathodes, garnering tremendous interest. However, the mechanism behind O redox in these cathode materials is still under debate, in part due to the challenges in directly observing O and following associated changes upon electrochemical cycling. Here, with17O NMR as a direct probe of O activities, it is demonstrated that stacking faults enhance O redox participation compared with Li2MnO3domains without stacking faults. This work is concluded by combining both ex situ and in situ17O NMR to investigate the evolution of O at 4i, 8j sites from monoclinic
The detailed information on the surface structure and binding sites of oxide nanomaterials is crucial to understand the adsorption and catalytic processes and thus the key to develop better materials for related applications. However, experimental methods to reveal this information remain scarce. Here we show that17O solid-state nuclear magnetic resonance (NMR) spectroscopy can be used to identify specific surface sites active for CO2adsorption on MgO nanosheets. Two 3-coordinated bare surface oxygen sites, resonating at 39 and 42 ppm, are observed, but only the latter is involved in CO2adsorption. Double resonance NMR and density functional theory (DFT) calculations results prove that the difference between the two species is the close proximity to H, and CO2does not bind to the oxygen ions with a shorter O···H distance of approx. 3.0 Å. Extensions of this approach to explore adsorption processes on other oxide materials can be readily envisaged.
more » « less- NSF-PAR ID:
- 10362268
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 13
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract C2/m and 6c(1), 6c(2), 6c(3) sites from the stacking faults (P3112). These measurements are further corroborated and explained by first‐principles calculations finding a stabilization effect of stacking faults in delithiated Li2MnO3. In situ17O NMR tracks O activities with temporal resolution and provides a quantitative determination of reversible O redox versus irreversible processes that form short covalent OO bonds. This work provides valuable insights into the O redox reactions in Li‐excess layered cathodes, which may inspire new material design for cathodes with high specific capacity. -
more » « less
Abstract Beta gallium oxide (β‐Ga2O3) has emerged as a highly promising semiconductor material with an ultrawide bandgap ranging from 4.5 to 4.9 eV for future applications in power electronics, optoelectronics, as well as gas and ultraviolet (UV) radiation sensors. Here, surface adsorption and air damping behavior of doubly clamped β‐Ga2O3nanomechanical resonators are probed and systemically studied by measuring the resonance characteristics under different gas and pressure conditions. High responsivities of resonance to pressure are obtained by heating the devices up to 300 °C to induce an accelerated adsorption–desorption process. The initial surface conditions of the β‐Ga2O3thin film play important roles in affecting the resonant behavior. UV ozone treatment proves effective in altering the initial surface conditions of β‐Ga2O3nanosheets by eliminating physisorbed contaminants and filling oxygen vacancy defects residing on the surface, resulting in a consequential and discernible modification of the resonance behavior of β‐Ga2O3nanomechanical resonators. The surface adsorption and desorption processes in β‐Ga2O3demonstrate clear reversibility by exposing the UV treated β‐Ga2O3to air. This study attains first‐hand information on how the surface conditions of β‐Ga2O3affect its mechanical properties, and helps guide future development of transducers via β‐Ga2O3nanoelectromechanical systems (NEMS) for pressure sensing applications, especially in harsh environments.
-
more » « less
Abstract Solid‐state NMR measurements coupled with density functional theory (DFT) calculations demonstrate how hydrogen positions can be refined in a crystalline system. The precision afforded by rotational‐echo double‐resonance (REDOR) NMR to interrogate13C–1H distances is exploited along with DFT determinations of the13C tensor of carbonates (CO32−). Nearby1H nuclei perturb the axial symmetry of the carbonate sites in the hydrated carbonate mineral, hydromagnesite [4 MgCO3⋅Mg(OH)2⋅4 H2O]. A match between the calculated structure and solid‐state NMR was found by testing multiple semi‐local and dispersion‐corrected DFT functionals and applying them to optimize atom positions, starting from X‐ray diffraction (XRD)‐determined atomic coordinates. This was validated by comparing calculated to experimental13C{1H} REDOR and13C chemical shift anisotropy (CSA) tensor values. The results show that the combination of solid‐state NMR, XRD, and DFT can improve structure refinement for hydrated materials.
-
more » « less
Abstract Solid‐state NMR measurements coupled with density functional theory (DFT) calculations demonstrate how hydrogen positions can be refined in a crystalline system. The precision afforded by rotational‐echo double‐resonance (REDOR) NMR to interrogate13C–1H distances is exploited along with DFT determinations of the13C tensor of carbonates (CO32−). Nearby1H nuclei perturb the axial symmetry of the carbonate sites in the hydrated carbonate mineral, hydromagnesite [4 MgCO3⋅Mg(OH)2⋅4 H2O]. A match between the calculated structure and solid‐state NMR was found by testing multiple semi‐local and dispersion‐corrected DFT functionals and applying them to optimize atom positions, starting from X‐ray diffraction (XRD)‐determined atomic coordinates. This was validated by comparing calculated to experimental13C{1H} REDOR and13C chemical shift anisotropy (CSA) tensor values. The results show that the combination of solid‐state NMR, XRD, and DFT can improve structure refinement for hydrated materials.
-
more » « less
Abstract The structures of glasses in the lithium–bismuth orthoborate composition range deviate significantly from the short‐range order structure of the two crystalline end‐members. Although binary Li3BO3and BiBO3are solely of comprised trigonal orthoborate anions, all glasses formed by their combination contain four‐coordinated borate tetrahedra. We analyze the structure of (75−1.5
x )Li2O–x Bi2O3–(25+0.5x )B2O3glasses in increments ofx = 5, with11B magic‐angle spinning nuclear magnetic resonance (NMR), infrared (IR), and Raman spectroscopy. For the full series, the oxygen‐to‐boron ratio remains constant at O/B = 3:1. NMR quantifies an increase in the fraction of tetrahedral boron with increasing bismuth oxide content. Evolution of the mid‐IR profile suggests multiple types of tetrahedral boron sites. Raman spectroscopy reveals that Bi2O3tends to cluster within the lithium borate matrix when initially introduced and that this behavior transforms into a bismuthate network with increasing bismuth oxide content. In all cases, mixed Bi–O–B linkages are observed. The dual role of bismuth as network modifier and network former is likewise observed in the far IR. The glass transition temperature continuously increases with bismuth oxide content; however, the glass stability displays a maximum in the multicomponent glass ofx = 40.
