E. Andrew Payzant

Anomalous High Ionic Conductivity of Nanoporous β-Li3PS4

Lithium-ion-conducting solid electrolytes hold promise for enabling high-energy battery chemistries and circumventing safety issues of conventional lithium batteries. Achieving the combination of high ionic conductivity and a broad electrochemical window in solid electrolytes is a grand challenge for the synthesis of battery materials. Herein we show an enhancement of the room-temperature lithium-ion conductivity by 3 orders of magnitude through the creation of nanostructured Li(3)PS(4). This material has a wide electrochemical window (5 V) and superior chemical stability against lithium metal. The nanoporous structure of Li(3)PS(4) reconciles two vital effects that enhance the ionic conductivity: (1) the reduction of the dimensions to a nanometer-sized framework stabilizes the high-conduction β phase that occurs at elevated temperatures, and (2) the high surface-to-bulk ratio of nanoporous β-Li(3)PS(4) promotes surface conduction. Manipulating the ionic conductivity of solid electrolytes has far-reaching implications for materials design and synthesis in a broad range of applications, including batteries, fuel cells, sensors, photovoltaic systems, and so forth.

Template-removal-associated microstructural development of porous-ceramic-supported MFI zeolite membranes

Defect-free thin MFI zeolite films were synthesized on porous α-alumina and yttria-doped zirconia (YZ) substrates by an in situ crystallization method using tetrapropylammonium hydroxide (TPAOH) as a template. The microstructure evolution of the supported zeolite films during calcination for template removal was studied by high-temperature X-ray diffraction and in situ gas permeance. Removal of the template from the zeolite films occurs at 350–500°C and is accompanied by a substantial shrinkage in the zeolite framework. After the template is removed from the zeolite at high temperatures, the zeolite crystals expand on cooling while the support shrinks. A compressive stress develops in the zeolite film during the cooling process when the zeolite crystallites are bound to the support after template removal. Without annealing prior to template removal, this stress induces cracks in the YZ-supported MFI films. High-quality MFI membranes were obtained on both α-alumina and YZ supports by using a suitable calcination temperature program. Removal of the template can either create or enlarge intercrystalline gaps as the zeolite crystallites decrease in size and draw away from adjacent crystallites. These gaps constitute the microporous non-zeolitic pores affecting the permselectivity of single-gas permeation for H2 and SF6. Both alumina- and YZ-supported MFI membranes show very good separation properties for hydrogen and n-butane mixtures, although the YZ-supported MFI films appear to have larger non-zeolitic pores than the alumina-supported membranes.

Wet-chemical synthesis of monodispersed barium titanate particles : hydrothermal conversion of TiO2 microspheres to nanocrystalline BaTiO3

Abstract A low-temperature hydrothermal reaction scheme has been developed to produce pure, ultrafine, uniform-sized, nanocrystalline barium titanate (BaTiO 3 ) microspheres from two inorganic precursors: synthesized titania microspheres and barium hydroxide solutions. The size and morphology of titania (TiO 2 ) microspheres were controlled using isopropanol to fine-tune the dielectric constant of the isopropanol–water mixed solvent system. Monodispersed titania microspheres approximately 0.1–1 μm in diameter were successfully synthesized for the further conversion to barium titanate. Barium titanate and titania microspheres were characterized by scanning electron microscopy (SEM) and room-temperature X-ray diffraction (RTXRD). High-temperature XRD (HTXRD) was also utilized for in situ study of the phase transformations and changes of crystallite size with calcination temperatures. The titania microspheres were predominant in the anatase (plus some brookite) phase at room temperature and were converted to the rutile phase when the calcination temperature was increased from 650°C to 900°C. Monodispersed barium titanate microspheres were successfully synthesized from optimized titania via a hydrothermal reaction (≤100°C) in barium hydroxide solutions. The size and morphology of the barium titanate particles remained the same as the precursor titania particles, indicating a “shrinking-core” diffusion–reaction mechanism. Barium carbonate in the form of witherite was also found along with the formation of barium titanate, especially under conditions with higher Ba/Ti ratios, but a formic acid washing procedure effectively removed this impurity phase from the barium titanate samples. The as-prepared barium titanate was in the cubic nanocrystalline form and did not change when the temperature was increased from room temperature to as high as 750°C. The cubic phase was also stable at high temperatures for over 5 h.

Investigating phase transformation in the Li1.2Co0.1Mn0.55Ni0.15O2 lithium-ion battery cathode during high-voltage hold (4.5 V) via magnetic, X-ray diffraction and electron microscopy studies

This study is the first that provides evidence of phase transformation in a Li-rich Li1.2Co0.1Mn0.55Ni0.15O2 cathode material for lithium-ion batteries (LIBs) during constant voltage charging. Diffraction and magnetic measurement techniques were successfully implemented to investigate the structural transformation in this cathode material during holding a half-cell at 4.5 V in a charged state. The results from X-ray diffraction showed a decrease in c-lattice parameters during high-voltage hold. Magnetic data revealed an increase in average effective magnetic moments of transition metal (TM) ions at constant voltage corresponding to a change in electronic states of TM ions. Analysis showed the reduction of Ni4+ to Ni2+, which was attributed to charge compensation due to oxygen loss. The appearance of the strong {100} forbidden reflection in the single-crystal selected area electron diffraction (SAED) data was attributed to migration of transition metal ions to the octahedral vacancy sites in the lithium layer during high-voltage hold, which was in agreement with the magnetization results. After prolonged hold at 4.5 V, high-resolution transmission electron microscopy (TEM) images along with SAED results showed the presence of spinel phases in the particles, indicating a layered to spinel like phase transformation at constant voltage in agreement with the magnetic data. The results obtained from these magnetic and diffraction studies furnish the fundamental understanding of the structural transformation pathways in Li-rich cathodes at constant voltage and will be instrumental for modifying the parent structure to achieve greater stability.

Synthesis of silica supported AuCu nanoparticle catalysts and the effects of pretreatment conditions for the CO oxidation reaction

Supported gold nanoparticles have generated an immense interest in the field of catalysis due to their extremely high reactivity and selectivity. Recently, alloy nanoparticles of gold have received a lot of attention due to their enhanced catalytic properties. Here we report the synthesis of silica supported AuCu nanoparticles through the conversion of supported Au nanoparticles in a solution of Cu(C(2)H(3)O(2))(2) at 300 °C. The AuCu alloy structure was confirmed through powder XRD (which indicated a weakly ordered alloy phase), XANES, and EXAFS. It was also shown that heating the AuCu/SiO(2) in an O(2) atmosphere segregated the catalyst into a Au-CuO(x) heterostructure between 150 °C to 240 °C. Heating the catalyst in H(2) at 300 °C reduced the CuO(x) back to Cu(0) to reform the AuCu alloy phase. It was found that the AuCu/SiO(2) catalysts were inactive for CO oxidation. However, various pretreatment conditions were required to form a highly active and stable Au-CuO(x)/SiO(2) catalyst to achieve 100% CO conversion below room-temperature. This is explained by the in situ FTIR result, which shows that CO molecules can be chemisorbed and activated only on the Au-CuO(x)/SiO(2) catalyst but not on the AuCu/SiO(2) catalyst.

Correlating cation ordering and voltage fade in a lithium–manganese-rich lithium-ion battery cathode oxide: a joint magnetic susceptibility and TEM study

Structure-electrochemical property correlation is presented for lithium-manganese-rich layered-layered nickel manganese cobalt oxide (LMR-NMC) having composition Li1.2Co0.1Mn0.55Ni0.15O2 (TODA HE5050) in order to examine the possible reasons for voltage fade during short-to-mid-term electrochemical cycling. The Li1.2Co0.1Mn0.55Ni0.15O2 based cathodes were cycled at two different upper cutoff voltages (UCV), 4.2 V and 4.8 V, for 1, 10, and 125 cycles; voltage fade was observed after 10 and 125 cycles only when the UCV was 4.8 V. Magnetic susceptibility and selected-area electron diffraction data showed the presence of cation ordering in the pristine material, which remained after 125 cycles when the UCV was 4.2 V. When cycled at 4.8 V, the magnetic susceptibility results showed the suppression of cation ordering after one cycle; the cation ordering diminished upon further cycling and was not observed after 125 cycles. Selected-area electron diffraction data from oxides oriented towards the [0001] zone axis revealed a decrease in the intensity of cation-ordering reflections after one cycle and an introduction of spinel-type reflections after 10 cycles at 4.8 V; after 125 cycles, only the spinel-type reflections and the fundamental O3 layered oxide reflections were observed. A significant decrease in the effective magnetic moment of the compound after one cycle at 4.8 V indicated the presence of lithium and/or oxygen vacancies; analysis showed a reduction of Mn(4+) (high spin/low spin) in the pristine oxide to Mn(3+) (low spin) after one cycle. The effective magnetic moment was higher after 10 and 125 cycles at 4.8 V, suggesting the presence of Mn(3+) in a high spin state, which is believed to originate from distorted spinel (Li2Mn2O4) and/or spinel (LiMn2O4) compounds. The increase in effective magnetic moments was not observed when the oxide was cycled at 4.2 V, indicating the stability of the structure under these conditions. This study shows that structural rearrangements in the LMR-NMC oxide happen only at higher potentials (4.8 V, for example) and provides evidence of a direct correlation between cation ordering and voltage fade.

An Oxide Ion and Proton Co-Ion Conducting Sn0.9In0.1P2O7 Electrolyte for Intermediate-Temperature Fuel Cells

The ionic conductivity of Sn 009 In 0.1 P 2 O 7 ceramic was investigated under various atmospheres within the temperature range of 130-230°C. Similar to mixed-conductive perovskite oxides at high temperatures (such as SrCe 0.95 Yb 0.05 O 3-α, La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3-α at 600-1000°C), Sn 0.9 In 0.1 P 2 O 7 can conduct both protons and oxide ions at low temperatures (130-230°C). The conductivity of Sn 0.9 In 0.1 P 2 O 7 reaches 0.019 S/cm at 200°C in wet nitrogen. Its transport numbers determined by steam concentration cells are around 0.76 for a proton and 0.12 for an oxide ion. The performance of direct methanol fuel cells at 170°C using mixed-ion conductive Sn 0.9 In 0.1 P 2 O 7 electrolyte is higher than that at 235°C using pure proton conductive CsH 2 PO 4 electrolyte. This is attributed to direct oxidation of CO at the anode by the oxide ions generated at the cathode and moved through the Sn 0.9 In0.1P 2 O 7 electrolyte.

Preparation of the negative thermal expansion material cubic ZrMo2O8

The negative thermal expansion material cubic ZrMo2O8 can be prepared by the carefully controlled dehydration of ZrMo2O7(OH)2·2H2O. The quality of the end product is dependent upon the route used to prepare the ZrMo2O7(OH)2·2H2O. The influence of both the Zr∶Mo ratio in the solution used to prepare the hydrate and the type of acid used in its preparation (HCl, H2SO4, CH3CO2H, HNO3 and HClO4) are examined. Not all acids provide media suitable for the preparation of ZrMo2O7(OH)2·2H2O. Cubic ZrMo2O8 could only be obtained from precipitates containing the hydrate. Starting solutions with a Zr∶Mo ratio in excess of 1∶2 were necessary to avoid coprecipitation of amorphous MoO3. The nature of the acid used in the hydrate synthesis affects the morphology of both the hydrate precursor and the cubic ZrMo2O8 particles. Many of the syntheses examined led to cubic ZrMo2O8 contaminated with amorphous impurities. Highly crystalline pure material could be obtained by using a perchloric acid medium for the synthesis of the hydrate precursor.

Enhanced performance of room-temperature-grown epitaxial thin films of vanadium dioxide

Vanadium dioxide (VO2) in bulk, thin-film, and nanostructured forms exhibits an insulator-to-metal transition accompanied by structural reorganization, induced by temperature, light, electric fields, doping, or strain. We have grown epitaxial films of VO2 on c-cut (0001) sapphire following two different procedures: (1) room-temperature growth followed by annealing and (2) direct high-temperature growth. We find that variations in strain at the film-substrate interface in the two protocols leads to differences in morphologies and transition characteristics. Our results show that room-temperature-grown epitaxial films have smoother morphologies and better switching contrast, analogous to the enhanced performance of epitaxially grown compound semiconductors.

Solvent quality-induced nucleation and growth of parallelepiped nanorods in dilute poly(3-hexylthiophene) (P3HT) solution and the impact on the crystalline morphology of solution-cast thin film

Understanding the chain conformation of conjugated polymers in casting solutions and its impact on the crystalline morphology of solution-cast thin films is crucial for many electronic applications. Using small-angle neutron scattering, we show that well-dissolved poly(3-hexyl thiophene) (P3HT) chains in good solvent (chloroform) form long rectangular parallelepipeds (RPs) via nucleation and growth processes upon increasing the volume fraction of poor solvent (hexane) above a certain critical point. The growth of the RPs is due to the π–π stacking of the P3HT main backbone occurring along the long axis of the RPs. P3HT solutions prepared with different poor solvent volume fractions were drop-cast onto Si-wafers to prepare thin films, which were examined using 2D grazing-incidence X-ray scattering and 1D X-ray diffraction. The results indicate that the RPs grown in solution preferentially orient on the substrate with their two longer axes parallel to the surface after solvent evaporation, and give rise to much improved crystallinity and crystal orientation compared to the disordered chains.