Narayanan M.,Energy Systems Division |
Tong S.,Energy Systems Division |
Koritala R.,Argonne National Laboratory |
Ma B.,Energy Systems Division |
And 3 more authors.
Chemistry of Materials | Year: 2011
A facile solution chemistry is demonstrated to fabricate high-quality polycrystalline strontium ruthenium oxide (SrRuO3) thin film electrodes on silicon substrates suppressing the formation of undesired ruthenium oxide (RuO2) for the deposition of dielectric and ferroelectric materials like lead lanthanum zirconate titanate (PLZT). The robust, highly crystalline SrRuO3 film fabrication process does not favor the formation of RuO2 because of molecular level modification of the precursors possessing analogous melting points, yielding homogeneous films. This chemistry is further understood and complemented by kinetic and thermodynamic analysis of the DTA data under nonisothermal conditions, with which the activation energies to form RuO2 and SrRuO3 were calculated to be 156 ' 17 and 96 ' 10 kJ/mol, respectively. The room-temperature resistivity of the SrRuO3 film was measured to be ∼850 ' 50 ?Ω cm on silicon (100) substrates. The dielectric properties of sol?gel-derived PLZT thin film capacitors on polycrystalline SrRuO 3 electrodes were also measured to illustrate the high quality of the formed SrRuO3 bottom electrode. These results have broad implications for the expanded use of these conductive oxide electrodes in many applications that require low thermal budgets. The PLZT (8/52/48) films exhibited well-defined hysteresis loops with remanent polarization of ∼10.5 ?C/cm2, dielectric constant of >1450, dielectric loss of <0.06, and leakage current density of ∼3.8 - 10?8 A/cm2. These dielectric properties are similar to those of PLZT on platinized silicon, indicating the high quality of the bottom conductive oxide layer. In addition, the PLZT capacitors were essentially fatigue free for >1 - 109 cycles when deposited over an oxide electrode. © 2010 American Chemical Society.
Xia Z.,University of Science and Technology Beijing |
Liu G.,Chemical science and Engineering Division |
Wen J.,Center for Nanoscale Materials |
Mei Z.,Argonne National Laboratory |
And 7 more authors.
Journal of the American Chemical Society | Year: 2016
Controlled photoluminescence tuning is important for the optimization and modification of phosphor materials. Herein we report an isostructural solid solution of (CaMg)x(NaSc)1-xSi2O6 (0 < x < 1) in which cation nanosegregation leads to the presence of two dilute Eu2+ centers. The distinct nanodomains of isostructural (CaMg)Si2O6 and (NaSc)Si2O6 contain a proportional number of Eu2+ ions with unique, independent spectroscopic signatures. Density functional theory calculations provided a theoretical understanding of the nanosegregation and indicated that the homogeneous solid solution is energetically unstable. It is shown that nanosegregation allows predictive control of color rendering and therefore provides a new method of phosphor development. © 2016 American Chemical Society.
Lin C.-K.,Chemical science and Engineering Division |
Piao Y.,Chemical science and Engineering Division |
Piao Y.,Jilin University |
Kan Y.,Chemical science and Engineering Division |
And 6 more authors.
ACS Applied Materials and Interfaces | Year: 2014
Safety of lithium-ion batteries has been a major barrier to large-scale applications. For better understanding the failure mechanism of battery materials under thermal abuse, the decomposition of a delithiated high energy cathode material, Li1.2-xNi0.15Mn0.55Co 0.1O2, in the stainless-steel high pressure capsules was investigated by in situ high energy X-ray diffraction. The data revealed that the thermally induced decomposition of the delithiated transition metal (TM) oxide was strongly influenced by the presence of electrolyte components. When there was no electrolyte, the layered structure for the delithiated TM oxide was changed to a disordered Li1-xM2O4-type spinel, which started at ca. 266 °C. The disordered Li1-xM 2O4-type spinel was decomposed to a disordered M 3O4-type spinel phase, which started at ca. 327 °C. In the presence of organic solvent, the layered structure was decomposed to a disordered M3O4-type spinel phase, and the onset temperature of the decomposition was ca. 216 °C. When the LiPF6 salt was also present, the onset temperature of the decomposition was changed to ca. 249 °C with the formation of MnF2 phase. The results suggest that a proper optimization of the electrolyte component, that is, the organic solvent and the lithium salt, can alter the decomposition pathway of delithiated cathodes, leading to improved safety of lithium-ion batteries. © 2014 American Chemical Society.
Barkholtz H.M.,Northern Illinois University |
Gallagher J.R.,Chemical Science and Engineering Division |
Li T.,Argonne National Laboratory |
Liu Y.,Argonne National Laboratory |
And 5 more authors.
Chemistry of Materials | Year: 2016
We report new fundamental chemistry involved in the synthesis of bimetallic nanoalloys via dissolving the pure bulk transition metals in molten lithium. It is revealed at the atomic level that when two pure bulk transition metals such as Pd and Pt are placed in molten lithium (∼200°C), they undergo a dissolution process in which the metal-metal bonds in pure bulk transition metals are completely ruptured, which results in the existence of individual Pd and Pt atoms surrounded by lithium atoms, as is evident by synchrotron X-ray adsorption techniques. Then, upon the conversion of metal lithium to LiOH in humid air, the Pd and Pt atoms undergo an alloying process to aggregate into nanoalloys. This method was further expanded to include PdZn, which is notoriously difficult to prepare via traditional nanoalloy synthesis methods due to the easily oxidizable Zn component. The constantly reducing environment of metallic Li allowed for preparation of PdZn nanoalloys with minimal Zn oxidation via dissolution-alloying of individual bulk transition metals in molten lithium. Additionally, this lithium assisted "dissolution-alloying" method bypasses many complications intrinsic to conventional ion reduction-based nanoalloy synthesis including the necessity of ligated metal ions, the use of proper reducing agents and dispersing surfactants, and the presence of segregated phases due to different reduction potentials of the constituent metal ions. © 2016 American Chemical Society.
Lipson A.L.,Chemical science and Engineering Division |
Lipson A.L.,Argonne National Laboratory |
Pan B.,Chemical science and Engineering Division |
Pan B.,Argonne National Laboratory |
And 7 more authors.
Chemistry of Materials | Year: 2015
As new uses for larger scale energy storage systems are realized, new chemistries that are less expensive or have higher energy density are needed. While lithium-ion systems have been well studied, the availability of new energy storage chemistries opens up the possibilities for more diverse strategies and uses. One potential path to achieving this goal is to explore chemistries where a multivalent ion such as Ca2+ or Mg2+ is the active species. Herein, we demonstrate this concept for a Ca-ion system utilizing manganese hexacyanoferrate (MFCN) as the cathode to intercalate Ca reversibly in a dry nonaqueous electrolyte. Through characterization via X-ray absorption near-edge spectroscopy, it is determined that only the manganese changes oxidation state during cycling with Ca. X-ray diffraction indicates the MFCN maintains its crystallinity during cycling, with only minor structural changes associated with expansion and contraction. Furthermore, we have demonstrated the first rechargeable Ca-ion battery utilizing MFCN as the cathode and elemental tin as the anode. © 2015 American Chemical Society.
Chen L.X.,Chemical science and Engineering Division |
Chen L.X.,Northwestern University |
Zhang X.,X ray Science Division |
Wasinger E.C.,Chemical science and Engineering Division |
And 7 more authors.
Chemical Science | Year: 2010
Axial ligation mechanisms of a metalloporphyrin, nickel(ii) tetramesitylporphyrin (NiTMP), were investigated by static and transient X-ray absorption spectroscopy at Ni K-edge (8.333 keV). A surprisingly broad (i.e. ∼1.4 eV) linewidth for the 1s → 3dx2-y2 transition in the ground state was attributed to strong geometry dependent 3d molecular orbital (MO) energies due to coexisting conformers in solution. The broad distribution of 3d MO energy levels enables transient degeneracy of the 3dz2 and 3dx2-y2 MOs to produce a temporary vacancy in the 3dz2 MO which favors axial ligation. Photoexcitation also induces the vacancy in the 3dz2 MO, leading to a more than two-fold enhancement in the axial ligated species. Therefore, a unified axial ligation mechanism for both the ground and excited state is proposed based on the elucidation of the excited state structural dynamics, which will have a broad impact in understanding and controlling axial ligation in enzymatic reactions and molecular catalysis involving transient axial ligation. © 2010 The Royal Society of Chemistry.
Ji Z.,Ohio State University |
Natu G.,Ohio State University |
Huang Z.,Ohio State University |
Kokhan O.,Chemical science and Engineering Division |
And 2 more authors.
Journal of Physical Chemistry C | Year: 2012
We report the first application of cyclometalated ruthenium complexes of the type Ru[(N ̂N) 2(C ̂N)] + as sensitizers for p-type NiO dye-sensitized solar cells (NiO p-DSCs). These dyes exhibit broad absorption in the visible region. The carboxylic anchoring group is attached to the phenylpyridine ligand, which results in efficient hole injection. Moreover, the distance between the Ru[(N ̂N) 2(C ̂N)] + core and the carboxylic anchoring group is systematically varied by inserting rigid phenylene linkers. Femtosecond transient absorption (TA) studies reveal that the interfacial charge recombination rate between reduced sensitizers and holes in the valence band of NiO decreases as the number of phenylene linkers increases across the series. As a result, the solar cell made of the dye with the longest spacer (O12) exhibits the highest efficiency with both increased short-circuit current (J sc) and open-circuit voltage (V oc). The incident photon-to-current conversion efficiency (IPCE) spectra match well with the absorption spectra of sensitizers, suggesting the observed cathodic current is generated from the dye sensitization. In addition, the absorbed photon-to-current conversion efficiencies (APCEs) display an increment across the series. We further studied the interfacial charge recombination of our solar cells by electrochemical impedance spectroscopy (EIS). The results reveal an enhanced hole lifetime as the number of phenylene linkers increases. This study opens up opportunities of using cyclometalated Ru complexes for p-DSCs. © 2012 American Chemical Society.
Huang J.,Chemical science and Engineering Division |
Cheng L.,Argonne National Laboratory |
Assary R.S.,Argonne National Laboratory |
Wang P.,Chemical science and Engineering Division |
And 4 more authors.
Advanced Energy Materials | Year: 2015
A series of dimethoxybenzene-based catholyte molecules, which are electrochemically reversible at high potential (4.0 V vs Li/Li+) and in the form of liquid, is developed. The liquid nature offers the molecules the possibility of being a solo or co-solvent for nonaqueous redox flow batteries. This could dramatically improve the energy density. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Wang H.,Chemical science and Engineering Division |
Wang H.,University of Saskatchewan |
Lu J.,Argonne National Laboratory |
Marshall C.L.,Chemical science and Engineering Division |
And 8 more authors.
Catalysis Today | Year: 2014
A catalyst of Pt nanoparticles was prepared by atomic layer deposition on SrTiO3nanocuboids andtested for methanol decomposition and partial oxidation. The catalyst had uniform nanoparticle size of1.58 ± 0.37 nm and a Pt (1 1 1) surface. In situ X-ray absorption near-edge spectroscopy (XANES) measuredin a temperature-programmed reduction showed that the Pt particles were easily reduced. However, theas-received catalyst, a reduced catalyst, and an oxidized catalyst all had catalytic activity, differing slightly in methanol conversion and product selectivity. In situ XANES also revealed that CO adsorbed on the Pt sites was the only observed surface species during both methanol decomposition and partial oxidation. It seemed that the breakage of CH and OH bonds overwhelmingly occurred once methanol was adsorbed,forming H2 and adsorbed CO. The latter was then released from the catalyst surface or was oxidized toCO2 when O2 was present. © 2014 Elsevier B.V. All rights reserved.
Mara M.W.,Northwestern University |
Bowman D.N.,North Carolina State University |
Buyukcakir O.,Korea Advanced Institute of Science and Technology |
Shelby M.L.,Northwestern University |
And 9 more authors.
Journal of the American Chemical Society | Year: 2015
Copper(I) diimine complexes have emerged as low cost replacements for ruthenium complexes as light sensitizers and electron donors, but their shorter metal-to-ligand-charge-transfer (MLCT) states lifetimes and lability of transient Cu(II) species impede their intended functions. Two carboxylated Cu(I) bis-2,9-diphenylphenanthroline (dpp) complexes [Cu(I)(dpp-O(CH2CH2O)5)(dpp-(COOH)2)]+ and [Cu(I)(dpp-O(CH2CH2O)5)(dpp-(φ-COOH)2)]+ (φ = tolyl) with different linker lengths were synthesized in which the MLCT-state solvent quenching pathways are effectively blocked, the lifetime of the singlet MLCT state is prolonged, and the transient Cu(II) ligands are stabilized. Aiming at understanding the mechanisms of structural influence to the interfacial charge transfer in the dye-sensitized solar cell mimics, electronic and geometric structures as well as dynamics for the MLCT state of these complexes and their hybrid with TiO2 nanoparticles were investigated using optical transient spectroscopy, X-ray transient absorption spectroscopy, time-dependent density functional theory, and quantum dynamics simulations. The combined results show that these complexes exhibit strong absorption throughout the visible spectrum due to the severely flattened ground state, and a long-lived charge-separated Cu(II) has been achieved via ultrafast electron injection (<300 fs) from the 1MLCT state into TiO2 nanoparticles. The results also indicate that the TiO2-phen distance in these systems does not have significant effect on the efficiency of the interfacial electron-transfer process. The mechanisms for electron transfer in these systems are discussed and used to develop new strategies in optimizing copper(I) diimine complexes in solar energy conversion devices. © 2015 American Chemical Society.