Oxidation Induced Doping of Nanoparticles Revealed by in Situ X-ray Absorption Studies

Doping is a well-known approach to modulate the electronic and optical properties of nanoparticles (NPs). However, doping at nanoscale is still very challenging, and the reasons for that are not well understood. We studied the formation and doping process of iron and iron oxide NPs in real time by in situ synchrotron X-ray absorption spectroscopy. Our study revealed that the mass flow of the iron triggered by oxidation is responsible for the internalization of the dopant (molybdenum) adsorbed at the surface of the host iron NPs. The oxidation induced doping allows controlling the doping levels by varying the amount of dopant precursor. Our in situ studies also revealed that the dopant precursor substantially changes the reaction kinetics of formation of iron and iron oxide NPs. Thus, in the presence of dopant precursor we observed significantly faster decomposition rate of iron precursors and substantially higher stability of iron NPs against oxidation. The same doping mechanism and higher stability of host metal NPs against oxidation was observed for cobalt-based systems. Since the internalization of the adsorbed dopant at the surface of the host NPs is driven by the mass transport of the host, this mechanism can be potentially applied to introduce dopants into different oxidized forms of metal and metal alloy NPs providing the extra degree of compositional control in material design.Fil: Kwon, Soon Gu. Argonne National Laboratory; Estados UnidosFil: Chattopadhyay, Soma. Argonne National Laboratory; Estados Unidos. Illinois Institute of Technology; Estados UnidosFil: Koo, Bonil. Argonne National Laboratory; Estados UnidosFil: Dos Santos Claro, Paula Cecilia. Argonne National Laboratory; Estados UnidosFil: Shibata, Tomohiro. Argonne National Laboratory; Estados UnidosFil: Requejo, Felix Gregorio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Giovanetti, Lisandro Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Liu, Yuzi. Argonne National Laboratory; Estados UnidosFil: Johnson, Christopher. Argonne National Laboratory; Estados UnidosFil: Prakapenka, Vitali. University of Chicago; Estados UnidosFil: Lee, Byeongdu. Argonne National Laboratory; Estados UnidosFil: Shevchenko, Elena V.. Argonne National Laboratory; Estados Unido

Surface functionalization of semiconductor and oxide nanocrystals with small inorganic oxoanions (e.g., PO43-, MoO42-, OCN-) and polyoxometalate ligands

ISSN:1936-0851ISSN:1936-086

Toward Lithium Ion Batteries with Enhanced Thermal Conductivity

As batteries become more powerful and utilized in diverse applications, thermal management becomes one of the central problems in their application. We report the results on thermal properties of a set of different Li-ion battery electrodes enhanced with multiwalled carbon nanotubes. Our measurements reveal that the highest in-plane and cross-plane thermal conductivities achieved in the carbon-nanotube-enhanced electrodes reached up to 141 and 3.6 W/mK, respectively. The values for in-plane thermal conductivity are up to 2 orders of magnitude higher than those for conventional electrodes based on carbon black. The electrodes were synthesized via an inexpensive scalable filtration method, and we demonstrate that our approach can be extended to commercial electrode-active materials. The best performing electrodes contained a layer of γ-Fe2O3 nanoparticles on carbon nanotubes sandwiched between two layers of carbon nanotubes and had in-plane and cross-plane thermal conductivities of ∼50 and 3 W/mK, respectively, at room temperature. The obtained results are important for thermal management in Li-ion and other high-power-density batteries.Fil: Koo, Bonil. Argonne National Laboratory; Estados UnidosFil: Goli, Pradyumna. University of California; Estados UnidosFil: Sumant, Anirudha V.. Argonne National Laboratory; Estados UnidosFil: Dos Santos Claro, Paula Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Argonne National Laboratory; Estados UnidosFil: Rajh, Tijana. Argonne National Laboratory; Estados UnidosFil: Johnson, Christopher S.. Argonne National Laboratory; Estados UnidosFil: Balandin, Alexander A.. University of California; Estados UnidosFil: Shevchenko, Elena V.. Argonne National Laboratory; Estados Unido

Surface Functionalization of Semiconductor and Oxide Nanocrystals with Small Inorganic Oxoanions (PO₄^3–, MoO₄^2–) and Polyoxometalate Ligands

In this work, we study the functionalization of the nanocrystal (NC) surface with inorganic oxo ligands, which bring a new set of functionalities to all-inorganic colloidal nanomaterials. We show that simple inorganic oxoanions, such as PO₄^3– and MoO₄^2–, exhibit strong binding affinity to the surface of various II–VI and III–V semiconductor and metal oxide NCs. ζ-Potential titration offered a useful tool to differentiate the binding affinities of inorganic ligands toward different NCs. Direct comparison of the binding affinity of oxo and chalcogenidometallate ligands revealed that the former ligands form a stronger bond with oxide NCs (<i>e.g.</i>, Fe₂O₃, ZnO, and TiO₂), while the latter prefer binding to metal chalcogenide NCs (<i>e.g.</i>, CdSe). The binding between NCs and oxo ligands strengthens when moving from small oxoanions to polyoxometallates (POMs). We also show that small oxo ligands and POMs make it possible to tailor NC properties. For example, we observed improved stability upon Li⁺-ion intercalation into the films of Fe₂O₃ hollow NCs when capped with MoO₄^2– ligands. We also observed lower overpotential and enhanced exchange current density for water oxidation using Fe₂O₃ NCs capped with [P₂Mo₁₈O₆₂]^6– ligands and even more so for [{Ru₄O₄(OH)₂(H₂O)₄}(γ-SiW₁₀O₃₆)₂] with POM as the capping ligand

Intercalation of Sodium Ions into Hollow Iron Oxide Nanoparticles

Cation vacancies in hollow γ-Fe₂O₃ nanoparticles are utilized for efficient sodium ion transport. As a result, fast rechargeable cathodes can be assembled from Earth-abundant elements such as iron oxide and sodium. We monitored in situ structural and electronic transformations of hollow iron oxide nanoparticles by synchrotron X-ray adsorption and diffraction techniques. Our results revealed that the cation vacancies in hollow γ-Fe₂O₃ nanoparticles can serve as hosts for sodium ions in high voltage range (4.0–1.1 V), allowing utilization of γ-Fe₂O₃ nanoparticles as a cathode material with high capacity (up to 189 mAh/g), excellent Coulombic efficiency (99.0%), good capacity retention, and superior rate performance (up to 99 mAh/g at 3000 mA/g (50 C)). The appearance of the capacity at high voltage in iron oxide that is a typical anode and the fact that this capacity is comparable with the capacities observed in typical cathodes emphasize the importance of the proper understanding of the structure–properties correlation. In addition to that, encapsulation of hollow γ-Fe₂O₃ nanoparticles between two layers of carbon nanotubes allows fabrication of lightweight, binder-free, flexible, and stable electrodes. We also discuss the effect of electrolyte salts such as NaClO₄ and NaPF₆ on the Coulombic efficiency at different cycling rates

How “Hollow” Are Hollow Nanoparticles?

Diamond anvil cell (DAC), synchrotron X-ray diffraction (XRD), and small-angle X-ray scattering (SAXS) techniques are used to probe the composition inside hollow γ-Fe₃O₄ nanoparticles (NPs). SAXS experiments on 5.2, 13.3, and 13.8 nm hollow-shell γ-Fe₃O₄ NPs, and 6 nm core/14.8 nm hollow-shell Au/Fe₃O₄ NPs, reveal the significantly high (higher than solvent) electron density of the void inside the hollow shell. In high-pressure DAC experiments using Ne as pressure-transmitting medium, formation of nanocrystalline Ne inside hollow NPs is not detected by XRD, indicating that the oxide shell is impenetrable. Also, FTIR analysis on solutions of hollow-shell γ-Fe₃O₄ NPs fragmented upon refluxing shows no evidence of organic molecules from the void inside, excluding the possibility that organic molecules get through the iron oxide shell during synthesis. High-pressure DAC experiments on Au/Fe₃O₄ core/hollow-shell NPs show good transmittance of the external pressure to the gold core, indicating the presence of the pressure-transmitting medium in the gap between the core and the hollow shell. Overall, our data reveal the presence of most likely small fragments of iron and/or iron oxide in the void of the hollow NPs. The iron oxide shell seems to be non-porous and impenetrable by gases and liquids

Hollow Iron Oxide Nanoparticles for Application in Lithium Ion Batteries

Material design in terms of their morphologies other than solid nanoparticles can lead to more advanced properties. At the example of iron oxide, we explored the electrochemical properties of hollow nanoparticles with an application as a cathode and anode. Such nanoparticles contain very high concentration of cation vacancies that can be efficiently utilized for reversible Li ion intercalation without structural change. Cycling in high voltage range results in high capacity (∼132 mAh/g at 2.5 V), 99.7% Coulombic efficiency, superior rate performance (133 mAh/g at 3000 mA/g) and excellent stability (no fading at fast rate during more than 500 cycles). Cation vacancies in hollow iron oxide nanoparticles are also found to be responsible for the enhanced capacity in the conversion reactions. We monitored in situ structural transformation of hollow iron oxide nanoparticles by synchrotron X-ray absorption and diffraction techniques that provided us clear understanding of the lithium intercalation processes during electrochemical cycling

A multifaceted educational intervention shortened time to antibiotic administration in children with severe sepsis and septic shock: ABISS Edusepsis pediatric study.

info:eu-repo/semantics/publishedVersio

Self-Improving Anode for Lithium-Ion Batteries Based on Amorphous to Cubic Phase Transition in TiO₂ Nanotubes

We report an electrochemically driven transformation of amorphous TiO₂ nanotubes for Li-ion battery anodes into a face-centered-cubic crystalline phase that self-improves as the cycling proceeds. The intercalation/deintercalation processes of Li ions in the electrochemically grown TiO₂ nanotubes were studied by synchrotron X-ray diffraction and absorption spectroscopies along with advanced computational methods. These techniques confirm spontaneous development of a long-range order in amorphous TiO₂ in the presence of high concentration of Li ions (>75%). The adopted cubic structure shows long-term reversibility, enhanced power with capacity approaching the stochiometry of Li₂Ti₂O₄. The anode shows also superior stability over 600 cycles and exhibits high specific energy (∼200 W h kg_electrode^–1) delivered at a specific power of ∼30 kW kg_electrode^–1. The TiO₂ anode in a full Li-ion cell with a LiNi_0.5Mn_1.5O₄ cathode operates at 2.8 V and demonstrates the highest (∼310 mA h/g) reversible specific capacity reported to date. Our conceptually new approach fosters the ability of amorphous nanoscale electrodes to maximize their capacity in <i>operando</i>, opening a new avenue for synthesis of safe and durable high-power/high-capacity batteries