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Voltage fade has been a major barrier to the commercialization of a series of high-energy-density battery electrodes for more than a decade. It is now re-examined with advanced characterization techniques, which find its origin is correlated to oxygen activities.
Determination of the local configuration of interacting defects in a crystalline, periodic solid is problematic because defects typically do not have a long-range periodicity. Uranium dioxide, the primary fuel for fission reactors, exists in hyperstoichiometric form, UO2+x. Those excess oxygen atoms occur as interstitial defects, and these defects are not random but rather partially ordered. The widely-accepted model to date, the Willis cluster based on neutron diffraction, cannot be reconciled with the first-principles molecular dynamics simulations present here. We demonstrate that the Willis cluster is a fair representation of the numerical ratio of different interstitial O atoms; however, the model does not represent the actual local configuration. The simulations show that the average structure of UO2+x involves a combination of defect structures including split di-interstitial, di-interstitial, mono-interstitial, and the Willis cluster, and the latter is a transition state that provides for the fast diffusion of the defect cluster. The results provide new insights in differentiating the average structure from the local configuration of defects in a solid and the transport properties of UO2+x.
Controllable doping of TiO 2 nanowires with cobalt using sol-flame method, which achieves significantly enhanced electrocatalytic activity for oxygen evolution reactions.
Here, a simple and scalable method has been developed for the synthesis of Co 3 O 4 -coated N- and B-doped graphene hollow spheres (Co 3 O 4 /NBGHSs). These Co 3 O 4 /NBGHSs are highly active for both oxygen reduction and evolution reactions and can exhibit higher electrocatalytic activities and better durability than commercial Pt/C and RuO 2 /C, respectively, demonstrating them to be efficient bi-functional electrocatalysts. In-depth analysis shows that the coupling between Co 3 O 4 and NBGHSs, strong interaction with adsorbed O 2 , high electric conductivity, and the specific hollow structure play important roles in imparting the higher electrocatalytic activities to the Co 3 O 4 /NBGHSs. When tested as cathode catalysts for Zn–air batteries, the Co 3 O 4 /NBGHSs exhibit better performance and higher stability than the Pt/C catalyst and other catalysts reported previously. Lastly, this strongly suggests that the Co 3 O 4 /NBGHSs could be used as efficient electrocatalysts for metal–air batteries with great potential to replace precious metal/carbon based materials.
Intermetallic nanocrystals are currently receiving extensive attentions due to their well- defined crystal structures, highly ordered atomic distribution and superior structural stability that endow them with optimized catalytic activities, stabilities and high selectivity as electrocatalysts for fuel cells. Here, for the first time, we reported the facile synthesis of intermetallic Pd3Pb nanowire networks (IM-Pd3Pb NNs) with a one-step wet-chemical strategy at a relatively low temperature (i.e. 170 °C) in 1 h. The as-prepared IM-Pd3Pb NNs exhibited superior bifunctional catalytic performances toward oxygen reduction reaction (ORR) and ethanol oxidation reaction (EtOR) compared to commercial Pt/C and Pd black, respectively. Significantly, IM-Pd3Pb NNs also showed excellent methanol- and CO-tolerant ability as ORR cathode and EtOR anode electrocatalysts, respectively. The electrochemical active surface area and mass activity of IM-Pd3Pb NNs are about 3.4 times and 2 times higher than Pd black toward EtOR, respectively. As the Pt-free bifunctional electrocatalysts, 3D IM-Pd3Pb architectures with exceptional catalytic performances hold great promise in various applica-tions of energy conversion and storage devices, sensors, electronics, optics and so on.
High-valent iron-oxo complexes are key intermediates in C–H functionalization reactions. Herein, we report the generation of a (TAML)Fe-oxo species (TAML = tetraamido macrocyclic ligand) via electrochemical proton-coupled oxidation of the corresponding (TAML)Fe III –OH 2 complex. Cyclic voltammetry (CV) and spectroelectrochemical studies are used to elucidate the relevant (TAML)Fe redox processes and determine the predominant (TAML)Fe species present in solution during bulk electrolysis. Evidence for iron( IV ) and iron( V ) species is presented, and these species are used in the electrochemical oxygenation of benzylic C–H bonds and dehydrogenation of alcohols to ketones.
The mechanism for oxygen release and uptake is influenced by crystal field effects in the solid solution YbMn x Fe 2− x O 4 .
A novel oxygen octahedral tilt engineering is used to design a new NaNbO 3 -based lead-free piezoceramic with thermal insensitive high piezoresponse.
Here, we report the synthesis and oxygen-atom transfer (OAT) photochemistry of [Cu(tpa)BrO 3 ]ClO 4 . In situ spectroscopy and in crystallo experiments indicate OAT proceeds from a Cu–O fragment generated by sequential Cu–O bond cleavage and OAT from BrO x to [Cu(tpa)] + . Furthermore, these results highlight synthetic opportunities in M–O photochemistry and demonstrate the utility of in crystallo experiments to evaluating photochemical reaction mechanisms.
Kinetic studies of aldol condensation of mixtures on TiO 2 reveal strong suppression of acetone self-condensation in the presence of acetaldehyde.
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Here, we use density-functional theory to investigate the bulk and surface properties of MgB 2 . The unique bonding structure of MgB 2 is investigated by Bader's atoms-in-molecules, charge density difference, and occupancy projected band structure analyses. Oxygen adsorption on the charge-depleted surfaces of MgB 2 is studied by a surface potential energy mapping method, reporting a complete map including low-symmetry binding sites. The B-terminated MgB 2 (0001) demonstrates reconstruction of the graphenelike B layer, and the reconstructed geometry exposes a threefold site of the subsurface Mg, making it accessible from the surface. Detailed reconstruction mechanisms are studied by simulated annealing method based on ab initio molecular dynamics and nudged elastic band calculations. The surface clustering of B atoms significantly modifies the B 2p states to occupy low energy valence states. The present paper emphasizes that a thorough understanding of the surface phase may explain an apparent inconsistency in the experimental surface characterization of MgB 2 . Furthermore, these results suggest that the surface passivation can be an important technical challenge when it comes to development of a superconducting device using MgB 2 .
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We derive and compute effective valence-space shell-model interactions from ab initio coupled-cluster theory and apply them to open-shell and neutron-rich oxygen and carbon isotopes. Our shell-model interactions are based on nucleon-nucleon and three-nucleon forces from chiral effective-field theory. We compute the energies of ground and low-lying states, and find good agreement with experiment. In particular, our computed 2 + states are consistent with N=14,16 shell closures in 22,24 O, and a weaker N=14 shell closure in 20 C. We find good agreement between our coupled-cluster effective-interaction results with those obtained from standard single-reference coupled-cluster calculations for up to eight valence neutrons.
We demonstrate a widely applicable technique to absolutely calibrate the energy scale of x-ray spectra with experimentally well-known and accurately calculable transitions of highly charged ions, allowing us to measure the K-shell Rydberg spectrum of molecular O 2 with 8 meV uncertainty. Here, we reveal a systematic ~450 meV shift from previous literature values, and settle an extraordinary discrepancy between astrophysical and laboratory measurements of neutral atomic oxygen, the latter being calibrated against the aforementioned O 2 literature values. Because of the widespread use of such, now deprecated, references, our method impacts on many branches of x-ray absorption spectroscopy. Moreover, it potentially reduces absolute uncertainties there to below the meV level.
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