Nominal Formula Research Articles

Phase-Controlled Synthesis of High-Bi-Ratio Ternary Sulfide Nanocrystals of Cu1.57 Bi4.57 S8 and Cu2.93 Bi4.89 S9.

High Bi-ratio ternary sulfides have been recently reported as superior thermoelectric materials. However, the synthesis of high Bi-ratio Cu-Bi-S nanocrystal remains a challenge. Reported here are the synthesis and characterization of three-phase Cu-Bi-S nanocrystals with the nominal chemical formulae of Cu1.57 Bi4.57 S8 , Cu2.93 Bi4.89 S9 and Cu3 BiS3 . The samples were prepared using a Bi2 S3 precursor by varying the amount and type of Cu2-x S (i. e. Cu2 S or Cu7.2 S4 ) reactants. TEM images reveal that two new samples crystalized having nanorod morphology with radii of approximately 50 nm and lengths of 200 nm. XPS results indicate that the valence states of Bi in both the two new phases are +3 with viable oxidation states for Cu. UV-Vis-NIR absorption spectroscopy reveals that narrow direct bandgaps are 1.12 and 1.27 eV for Cu1.57 Bi4.57 S8 and Cu2.93 Bi4.89 S9 , respectively. Besides, this method could also be applied to synthesize the Cu3 BiS3 phase with a new nanoplate morphology. The as-synthesized Cu-Bi-S samples show Cu/Bi ratio-dependent photoresponsive properties. This study not only reports the structure and bandgap of two ternary sulfides, which have only been discovered in the mineral previously, but also provides an efficient method for synthesizing Bi-rich ternary chalcogenide nanocrystals.

Europium containing red light-emitting fibers made by electrohydrodynamic casting

Red light-emitting polymeric micro- and nanofibers were made by electrohydrodynamic co-casting of two fluids. One fluid contains a 10 wt% concentration europium (III) complex dissolved in a dimethylformamide (DMF) solvent. The europium complex, an Eu3+ compound with the nominal formula of Eu(BA)3phen/PAN, consists of polyacrylonitrile (PAN), 1,10-phenanthroline (phen), and benzoic acid (BA). The other fluid consists of iron metal oxide nanoparticles dispersed in a solution containing 10 wt% polyacrylonitrile polymer in DMF solvent. The two fluids were electrohydrodynamically co-cast onto a soft tissue paper using a stainless steel coaxial nozzle. The intensity of the electric field used for the co-casting was 1.5 kV/cm. Scanning electron microscopic observation on the fibers obtained from the co-casting was made. The size of the fibers ranges from several hundreds of nanometers to several microns. Energy dispersive X-ray spectroscopic analysis of the fibers confirmed that the major elements included C, O, Fe, and Eu. The fluorescence of the two types of fibers was tested under the excitation of a UV light source. It was found that when the europium complex-containing solution was the sheath fluid and the iron-containing solution was the core, the prepared fibers showed red light-emitting behavior under ultraviolet light. Time-dependent fluorescence shows the two-stage decaying behavior. The first stage lasts about 2000 s and the intensity of fluorescence decreases linearly. The second stage reveals the slow decaying behavior and it lasts longer than 3 h. Based on the bi-exponential data fitting using a processing MATLAB code, the fluorescence-related constants were extracted. A bi-exponential formula was proposed to describe the time-dependent fluorescence behavior of the fiber made by the europium complex-containing solution as the sheath fluid. The decaying in the fluorescence shows two different stages. The first stage lasts about 2000 s and it is characterized by a fast decaying model. The intensity of fluorescence decreases linearly. The second stage has a slow decaying feature. It takes over 3 h for the fluorescence to die out completely. Bi-exponential data fitting shows that the time constant for the decay of fluorescence is about 10,000 s.

Structural and spectroscopic investigations on the crystallization of uranium brannerite phases in glass

AbstractBrannerite‐based glass‐ceramics with relatively high actinide waste loadings are potential waste forms for the immobilization of actinide‐rich radioactive wastes containing process chemicals. In this work, the crystallization of pentavalent uranium brannerite phases in glass with the incorporation of yttrium/cerium/europium has been investigated. The formation of brannerite phases in glass has been confirmed with X‐ray diffraction and Raman spectroscopy. The evolution of microstructures and the development of micro pores in brannerite phases have been revealed by scanning electron microscopy with the nominal formula, Y0.51U0.49Ti2O6, Ce0.65U0.35Ti2O6, and Eu0.53U0.47Ti2O6, being determined with energy‐dispersive spectroscopy. The presence of dominant U5+ species has been proven with both diffuse reflectance spectroscopy and X‐ray absorption near‐edge spectroscopy. In addition, the systematic Raman band shifts with the mean cation radius in the studied brannerite series have been observed and discussed.

Structural investigation and giant dielectric response of CaCu3Ti4O12 ceramic by Nd/Zr co-doping for energy storage applications

High performance dielectric materials are highly required for practical application for energy storage technologies. In this work, high-k pristine and modified calcium copper titanate having nominal formula Ca0.95Nd0.05Cu3Ti4−xZrxO12 (x = 0.01, 0.03 & 0.10) were synthesized and characterized for structural and dielectric properties. Single phase formation of the synthesized compositions was confirmed by X-ray diffraction patterns and further analysed using Rietveld refinement technique. Phase purity of the synthesized ceramics was further confirmed by Energy-dispersive X-ray Spectroscopy (EDX) analysis. SEM images demonstrated that grain size of the modified CCTO ceramics was controlled by Zr4+ ions due to solute drag effect. Impedance spectroscopy was employed to understand the grain, grain boundaries and electrode contribution to the dielectric response. Nyquist plots were fitted with a 2R-CPE model which confirms the non-ideality of the system. Substitution of specific concentration of Nd and Zr improved the dielectric properties of high dielectric permittivity (e′ ~ 16,902) and minimal tanδ (≤ 0.10) over a wide frequency range. The giant e′ of the investigated system was attributed to internal barrier layer capacitance (IBLC) effect and reduced tanδ accredited to enhanced grain boundaries resistance due to substitution of Zr4+ ions at Ti4+ site.

Surface Chemistry Mechanism of Ultra-Low Interfacial Resistance in the Solid-State Electrolyte Li7La3Zr2O12

The garnet-type solid-state electrolyte, based on the nominal formula Li7La3Zr2O12 (LLZO), is unique in that it is a fast Li-ion conductor, exhibits sufficient mechanical properties, and is also chemically and electrochemically stable against metallic Li. Despite these promising attributes, additional challenges must be overcome before solid-state batteries based on LLZO are viable. Demonstrating low Li–LLZO interfacial resistance (R Li–LLZO) is a critical milestone along the path to commercialization. While several studies have characterized R Li–LLZO, nearly all report values significantly higher than conventional LIBs employing liquid electrolytes. Thus, strategies to reduce R Li–LLZO to values comparable to, or lower than, LIBs are needed [1]. In this study, the impact of surface chemistry on the interfacial resistance between the LLZO solid-state electrolyte and a metallic Li electrode is revealed [1]. Control of surface chemistry allows the interfacial resistance to be reduced to 2 Ω cm2, lower than that of liquid electrolytes, without the need for interlayer coatings. A mechanistic understanding of the origins of ultra-low resistance is provided by quantitatively evaluating the linkages between interfacial chemistry, Li wettability, and electrochemical phenomena. A combination of Li contact angle measurements, X-ray photoelectron spectroscopy (XPS), first-principles calculations, and impedance spectroscopy demonstrates that the presence of common LLZO surface contaminants, Li2CO3 and LiOH, result in poor wettability by Li and high interfacial resistance. On the basis of this mechanism, a simple procedure for removing these surface layers is demonstrated, which results in a dramatic increase in Li wetting and the elimination of nearly all interfacial resistance. The low interfacial resistance is maintained over one-hundred cycles and suggests a straightforward pathway to achieving high energy and power density solid-state batteries. [1] A. Sharafi, E. Kazyak, A. L. Davis, S. Yu, T Thompson, D. J. Siegel, N. P. Dasgupta, J. Sakamoto, Chem. Mater. 29, 7961(2017)

Effects of sintering atmospheres on thermoelectric properties, phase, microstructure and lattice parameters c/a ratio of Al, Ga dual doped ZnO ceramics sintered at high temperature

Thermoelectric properties, phase and microstructural investigation of (Zn1−x−yAlxGay)O, where x = 0.02, y = 0.04, 0.05 and x = 0.03, y = 0.01, 0.02 are studied at a high temperature of 1450 °C in this article. We have focused on the effects of sintering atmospheres on thermoelectric properties, phase, and microstructure in the air as well in the argon atmosphere. The Seebeck coefficient (S) and electrical resistivities (ρ) measured in air and argon atmospheres have an evidential large difference. The air sintered Al, Ga co-doped ZnO has higher power factor (S2σ) of the order 720.9 µW K− 2 m− 1 and lower electrical resistivity (ρ) of 5.803 mΩ cm for the nominal formula (Zn1− x−yAlxGay)O, with x = 0.03, y = 0.01 as compared to the power factor 543.6 µW K− 2 m− 1 and electrical resistivity of the order 1.550 mΩ cm at 692.2 °C sintered in the argon atmosphere at the same temperature i.e. 1450 °C. The power factor of the air sintered sample with x = 0.03, y = 0.01 is 1.4 times higher than the argon sintered sample with the same composition. The difference in power factors and electrical resistivities are linked to sintering atmospheres. We will investigate the effects of sintering atmospheres of the co-doped ZnO and will study thermoelectric properties, phase, and microstructures of the co-doped ZnO.

Investigating the electrical conduction and relaxation phenomena in rare earth erbium doped lead free 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 by impedance spectroscopy

Rare earth erbium (Er3+) doped 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (NBT-6BT) was prepared via a solid state synthesis route as per the nominal formula 0.94Na0.5Bi0.5-xErxTiO3-0.06BaTiO3 (0 ≤ x ≤ 0.05). Detailed impedance spectroscopy studies, invoking complex impedance and modulus formalisms, were carried out in order to investigate the influence of erbium doping on the long range electrical conduction and localized relaxation in the system. Our results suggest that a low concentration (x = 0.005) of rare earth doping significantly reduces the long range ionic conductivity (with respect to the undoped NBT-6BT value) and decreases the local relaxation, making the system electrically homogeneous. At a higher doping concentration (x ≥ 0.01), enhancement in the electrical conductivity occurs and local relaxation increases in the system. Observed trends are rationalized on the basis of a model, which hypothesizes phase segregation at a higher concentration of Er-doping. Such segregation leads to the formation of pure NBT-6BT regions and Er-saturated phase with probable dissimilar polar symmetry compared to that of NBT-6BT. A possible correlation between grain size, electrical conductivity, activation energy of conductivity, and local relaxation is indicated.

Atomic Layer Deposition of Nickel Carbide from a Nickel Amidinate Precursor and Hydrogen Plasma.

A new atomic layer deposition (ALD) process for depositing nickel carbide (Ni3C x) thin films is reported, using bis( N, N'-di- tert-butylacetamidinato)nickel(II) and H2 plasma. The process shows a good layer-by-layer film growth behavior with a saturated film growth rate of 0.039 nm/cycle for a fairly wide process temperature window from 75 to 250 °C. Comprehensive material characterizations are performed on the Ni3C x films deposited at 95 °C with various H2 plasma pulse lengths from 5 to 12 s, and no appreciable difference is found with the change of the plasma pulse length. The deposited Ni3C x films are fairly pure, smooth, and conductive, and the x in the nominal formula of Ni3C x is approximately 0.7. The ALD Ni3C x films are polycrystalline with a rhombohedral Ni3C crystal structure, and the films are free of nanocrystalline graphite or amorphous carbon. Last, we demonstrate that, by using this ALD process, highly uniform Ni3C x films can be conformally deposited into deep narrow trenches with an aspect ratio as high as 20:1, which thereby highlights the broad and promising applicability of this process for conformal Ni3C x film coatings on complex high-aspect-ratio 3D architectures in general.

Preparation and characterization of mechanically alloyed AB3-type based material LaMg2Ni5Al4 and its solid-gaz hydrogen storage reaction

We developed in the present paper the synthesis of a new AB3-type compound LaMg2Ni5Al4 by mechanical alloying (MA) process. ​​X-ray diffraction analysis (XRD) was used to determine the structural properties and the phase evolution of the powder mixtures. Two different synthesis pathways have been investigated. The first starting from elemental metals and the second from a mixture of two binary compounds LaNi5 (CaCu5-type structure, P6/mmm space group) and Al(Mg) solid solution (cubic Fm-3 m space group). The results show multiphase alloys which contain LaMg2Ni5Al4 main phase with hexagonal PuNi3-type structure (R-3 m space group). Rietveld analysis shows that using a planetary ball mill, we obtain a good yield of LaMg2Ni5Al4 compound after 5 h of mechanical alloying for both synthesis pathways. TEM analysis confirmed XRD results. SEM-EDX analysis of the final product was in agreement with the nominal chemical formula. A setup of possible solid-gaz hydrogenation reaction will be described so far at the end of this work. Electrochemical results demonstrate evidence on hydrogen absorption in the AB3 material and the discharge capacity was equal to 5.9 H/f.u.

Effect of annealing atmosphere on the structure and dielectric properties of unfilled tungsten bronze ceramics Ba4PrFe0.5Nb9.5O30

Unfilled tungsten bronze ceramics with the nominal formula Ba4PrFe0.5Nb9.5O30 were synthesized via the standard solid-state sintering route, and the effects of oxygen vacancies on the dielectric and electrical properties were investigated in addition to the structure. Room-temperature X-ray diffraction showed that the N2-annealed sample had the largest cell volume. Low-temperature spectrum showed that N2 annealing rendered the dielectric constant and dielectric loss more frequency dispersive, whereas O2 annealing inhibited the frequency dispersion. The dc conductivity of all the samples originated from the electrons produced in the second ionization of oxygen vacancies and was most likely controlled by a mixed conduction mechanism of the electron and oxygen-vacancy ions. The N2-annealed sample has the highest dc conductivity owing to its high concentration of oxygen vacancies. The broadening of the Raman lines and the decrease of Raman intensity for the N2-annealed sample originated from a significant structural disorder. X-ray photoelectron spectra demonstrated that the increased oxygen vacancies caused by the change of valences of Fe and Pr ions contributed to the structural disorder.

Photomechanical photochromism in a cetyltrimethylammonium isopolytungstate.

The photochromic properties of a hybrid compound comprised of the surfactant cation cetyltrimethylammonium [(C16H33)N(CH3)3]+ (CTA+) and the isopolytungstate anion [H2W12O40]6− is investigated. The compound, which has the nominal formula (CTA)7[H2W12O40]Cl·2H2O, changes from white to blue when exposed to UV radiation. The sample returns to the bleached state if stored in the dark-ambient. Application of XPS indicates that the coloring species are WV and WIV. The CTA+ component is found by XPS and FTIR to undergo progressive and irreversible oxidation during this cycle. Examination of FTIR suggests that the changes occur at multiple sites across the amphiphile. Surprisingly, the photochromic cycle is correlated with changes in the X-ray diffraction pattern, indicating partially reversible changes in the ordering of the Keggin ions and their spacing. In particular, application of the UV radiation causes the progressive accumulation of strain in the [001] direction. This is due to permanent oxidative changes in the CTA+ accumulating from cycle to cycle, resulting in an increase in interlamellar-distance due to less interdigitation of the chains. This provides a controllable photomechanical response.

Exploring and Monitoring of Methane Hydrate Deposits

Relatively recently, in the last 20 years, it was discovered that methane hydrate (MH) deposits are globally distributed in the permafrost and oceans. Before 1965 when first deposits were discovered in nature, it was believed that MH can occur only in laboratory conditions or in vast parts of the Universe. Presently it is presumed that this solid crystalline compounds in which CH4 molecules occupies the water ice lattices (nominal chemical formula of MH is C4H62O23) can serve as an energy source favorably to the all of the world remaining conventional hydrocarbon sources. The worldwide estimates of MH deposits range from 2x1014 m3 to 3.053x1018 cubic meters. This uncertainty partly results from our limitations in geological understanding of the MH deposits, which is due to the relatively bad quality of data obtained by presently available seismic and electromagnetic techniques. Moreover, MH deposits can become vulnerable to climate changes, which were already occurring in geological past whit tremendous consequences for the global life on Earth. Thus, further development of advanced techniques is needed to enhance our abilities to better characterize, quantify and monitor the MH deposits. In the work presented 14 MeV neutrons and associated alpha particle imaging (API) where used to quantify the amount of MH in the sample. Samples were prepared from sea sediment, quartz sand and MH simulant. MH simulant with chemical formula C4H46O23 was made from sucrose (25 % by mass) and water. MH quantity was measured by measuring the carbon content in the sample [1-8].

Thermoelectric Properties, Phase Analysis, Microstructure Investigation and Lattice Parameters c/a Ratio of Al3+ and In3+ Substituted ZnO Sintered at High Temperature under Argon Atmosphere

Al2O3 and In2O3 co-doped Zinc oxide (ZnO) system have been studied for enhancing thermoelectric properties of ZnO. Al2O3 and In2O3 are doped with ZnO via solid-state solution method. The compositions were sintered at 1400°C in Argon atmosphere. The thermal and electrical properties of the system are investigated. The power factor of the order 481.8 μWK-2m-1 at 692.3°C and Seebeck coefficient of the order -133.99 μVK-1 at 691.4°C was obtained for the nominal formula (Zn1-x-yAlxIny)O, with x=0.02, y=0.05. It has been studied that power factor is a function of c/a ratio which is further a function of dopant concentration. The resistivities of all the compositions have been tuned and the lowest resistivity of the order 1.997 mΩ.cm at 692.3°C has been observed for the nominal formula (Zn1-x-yAlxIny) with x=0.02, y=0.01. These tuned resistivities will be helpful for future thermoelectric devices.

Dielectric relaxation and conduction mechanism of complex perovskite Ca0.90Sr0.10Cu3Ti3.95Zn0.05O12 ceramic

In this work, Sr and Zn co-doped calcium copper titanate having nominal formula Ca0.90Sr0.10Cu3Ti3.95Zn0.05O12 has been synthesized and systematically studied for structure, dielectric and electrical properties. The phase purity of the prepared composition has been confirmed by X-ray diffraction (XRD) pattern and various structural parameters are presented here with Rietveld refinement data. The Scanning electron microscopy (SEM) image revealed the presence of homogeneous fine-grained microstructure investigated in the prepared ceramic. The impedance data well fitted with 2 R-CPE model confirmed the non-ideality of the system. Dielectric studies have shown the existence of two relaxation processes in low and high frequency domains. Low frequency dielectric response proposed as a combination of Maxwell-Wagner relaxation and intrinsic defect (Vo++) while high frequency behavior has been interpreted in terms of polaronic relaxation caused by hopping process of an electron between Ti3+ and Ti4+ states. The frequency dependent behavior of conductivity has been well fitted to Dong’s model and interpreted in term of Overlapping Large Polaron Tunneling (OLPT) mechanism. The various parameters; relaxation angular frequency (ω1) of Debye process, ionic hopping frequency (ω2), dc conductivity (σo), cole- cole parameter (α) and frequency exponent (s) have been determined by Dong’s Model fitting.

Effect of lanthanum-deficiency on structural, magnetic and magnetocaloric properties of $${\text{L}}{{\text{a}}_{0.5}}{\text{S}}{{\text{r}}_{0.5}}{\text{Co}}{{\text{O}}_3}$$ L a 0.5 S r 0.5 Co O 3

Lanthanum-deficient mixed-valence cobaltite of nominal formula $${\text{La}}_{{0.5 - x}} \Box_{x} {\text{Sr}}_{{0.5}} {\text{CoO}}_{3};(0 \le x \le 0.2)$$ has been investigated for its structural, magnetic, and magnetocaloric properties. Our samples were synthesized using the sol–gel method. X-ray diffraction analysis showed that all samples crystallized in the rhombohedral symmetry with $$R\bar {3}c$$ space group. Magnetization measurements versus temperature under different magnetic fields indicate that the samples undergo a paramagnetic to ferromagnetic phase transition. The Curie temperature seems to decrease with increasing lanthanum vacancy, but is still higher than that of the stoichiometric compound. Under a magnetic field of 5 T, the magnetic entropy change maximum $$\left| {\Delta S_{M}^{{{max} }}} \right|$$ reaches a value of 1.63 J kg−1 K−1 for x = 0.2, which corresponds to a value of 139 J kg−1 for the relative cooling power. Furthermore, the magnetic entropy change sensitivity to the magnetic field was checked using the local exponent $$n\left( {T,{\text{ }}{\mu_0}H} \right).$$

Dielectric properties of unfilled tetragonal tungsten bronze Ba4PrFe0.5Nb9.5O30 ceramics

In order to found new dielectrics ceramics in tungsten bronze structure, unfilled tungsten bronze (TB) ceramics with nominal formula Ba4PrFe0.5Nb9.5O30 were prepared by the solid state reaction method. The microstructure and dielectric properties were studied using powder X-ray diffraction, field emission scanning electron microscope, and variable temperature dielectric test system. The results show that the ceramics have a single phase and belong to the space group of P4bm with the cell of a = b = 12.4839(3) A, c = 3.9409(5) A, V = 614.192(2) A3. The frequency dependent dielectrics properties show that the ceramics have a Debye-like relaxation at room temperature, while the temperature dependent dielectrics properties indicate that the ceramics are a relaxor and the relaxation is due to the nanopolars and oxygen vacancies. The ceramics have a potential application in electronic ceramics as temperature-stable multilayer ceramic capacitors.

Characterisation of amorphous molybdenum silicide (MoSi) superconducting thin films and nanowires

We report on the optimisation of amorphous molybdenum silicide thin film growth for superconducting nanowire single-photon detector (SNSPD) applications. Molybdenum silicide was deposited via co-sputtering from Mo and Si targets in an Ar atmosphere. The superconducting transition temperature (Tc) and sheet resistance (Rs) were measured as a function of thickness and compared to several theoretical models for disordered superconducting films. Superconducting and optical properties of amorphous materials are very sensitive to short- (up to 1 nm) and medium-range order (∼1–3 nm) in the atomic structure. Fluctuation electron microscopy studies showed that the films assumed an A15-like medium-range order. Electron energy loss spectroscopy indicates that the film stoichiometry was close to Mo83Si17, which is consistent with reports that many other A15 structures with the nominal formula A3B show a significant non-stoichiometry with A:B > 3:1. Optical properties from ultraviolet (270 nm) to infrared (2200 nm) wavelengths were measured via spectroscopic ellipsometry for 5 nm thick MoSi films indicating high long wavelength absorption. We also measured the current density as a function of temperature for nanowires patterned from a 10 nm thick MoSi film. The current density at 3.6 K is 3.6 × 105 A cm−2 for the widest wire studied (2003 nm), falling to 2 × 105 A cm−2 for the narrowest (173 nm). This investigation confirms the excellent suitability of MoSi for SNSPD applications and gives fresh insight into the properties of the underlying materials.

Revisiting Hollandites: Channels Filling by Main-Group Elements Together with Transition Metals in Bi2–yVyV8O16

Starting from the nominal BixV8O16 formula, we have performed a state-of-the-art transmission electron microscopy investigation to propose a new Bi2–yVyV8O16 chemical formula for this hollandite structure. This results from the filling of the channels by main-group elements together with vanadium (V5+) species, with a variable content of Bi and V inside the channels. The influence of the Bi content and of this local disorder on the magnetic and transport properties has been investigated in polycrystalline samples of BixV8O16 with nominal x = 1.6 and x = 1.8 compositions. The rather x-independent electrical resistivity (≈5 mΩ cm) and Seebeck coefficient at high T (−35 μV K–1 at 900 K) are discussed in terms of an unchanged V oxidation state resulting from the filling of the wide channels with Bi and V. It is proposed that this local disorder hinders the charge/orbital setting below 60 K on the V ions of the V8O16 framework. Hollandites exhibit complex electronic and magnetic properties and have potential applications in the fields of batteries, photocatalysis, and nuclear waste storage, and these results show that a careful and detailed investigation of the nature and content of the cations inside the channels is crucial for improving our understanding of the impact of doping and disorder on their properties.

High Performance All-Solid State Lithium-Air Batteries Employing Aluminum-Substituted Lithium Lanthanum Titanate Solid Electrolyte

Recently, lithium(Li)-air battery has attracted much attention due to its extremely high theoretical specific energy density as 11,680 Wh kg-1 Li, which can be even comparable to that of gasoline. Despite potential of Li-air battery, the commercialization of the battery is a great challenge, since it can suffer from plenty of problems majorly associated with the use of liquid electrolytes and metallic Li anode; leakage, flammability, electrochemical instability under reduced oxygen environment and uncontrollable dendritic growth of Li. In this study, to address these issues, all-solid state Li-air battery has been proposed. By using a stable solid electrolyte with proper Li+ conductivity, the risks of leakage, short-circuit and fire/explosion can be successfully addressed. Moreover, the solid electrolyte can act as a barrier to protect Li metal from harmful gases such as O2, CO2 and moisture diffusing from outside air. In this study, we used aluminum-substituted lithium lanthanum titanate (A-LLTO) ceramic as a main ceramic solid electrolyte for all-solid state Li-air batteries. Herein, A-LLTO ceramic with a nominal formula of (Li0.33La0.56)1.005Ti0.99Al0.01O3 was prepared using citrate-gel method. In particular, the air electrode was specially designed by engaging a thin layer solid electrolyte to form an integrated cathode structure. The integrated cathode consisted of a dense ~20-µm-thick A-LLTO solid electrolyte layer adhering to the 500-µm-thick pellet of porous cathode. Moreover, CoO catalyst particles were directly deposited on the surface of A-LLTO cathode backbone. Further, due to instability of A-LLTO solid electrolyte against Li metal anode, an interlayer of composite gel polymer electrolyte (CGPE) was inserted between A-LLTO and Li metal. The interlayer CGPE was stabilized by the addition of small amount of an ionic liquid. After cell assembly, the solid-state Li-air cell was cycled at the current density of 0.3 mA cm-2 in pure O2 gas atmosphere at 50 oC. Under the limited capacity mode of 500 mAh g-1, the cell exhibited the cycle life of 132 cycles. During the cycling process, the discharge potential of the cell almost remained. Meanwhile, the charge cell potential appeared to increase significantly. By using SEM, XPS and Raman spectra analysis, the formation of reaction products on the cathode surface after cycling test was identified. With the increase in cycle number of discharge-charge, the amount of reaction products was found to increase. This demonstrates the degradation of catalytic activity of CoO catalyst. Because Li2O2 possesses the low Li ionic conductivity of 4×10-19 S cm-1 and low electrical conductivity of 5×10-20 S cm-1, it hinders the transportation of electrons and Li+ ions in the cathode. Accordingly, the degree of polarization for the cell increased gradually with cycle. Although the solid state Li-air cell developed in this work could prevent the problems which can happen when liquid electrolyte is used, its life span was not still satisfactory. Therefore, the factors such as operation temperature, catalyst type, which can enhance the kinetics for the reaction process, needs to be investigated further.

Tuning the Electrocatalytic Activity of Perovskite Electrocatalysts for Water Oxidation By Active Site Variation

Perovskites are a family of complex oxides with the nominal formula AMO3, where A is lathanide or alkali earth and M is typically a transition metal. They are of great interest as replacements for precious metals and oxides used in the oxygen evolution reaction (OER). Perovskite electrocatalysts have been shown to have greater specific activities than precious metals and their oxides, but high mass activities have not yet been realized due to the complex nature of perovskite oxide surfaces and inadequate synthesis techniques which often result in unwanted phase impurities and micron-scale materials. In this presentation we demonstrate the precise control over the chemical composition and structure of a series of perovskite and Ruddlesden-Popper electrocatalysts that are highly active for OER. The reaction pathways are perturbed by the direct modification of the perovskite structure by selective cation replacement and by promotion of catalyst-carbon support-interactions. Specifically the synthesis and electrochemical evaluation of a series of Ruddlesden-Popper (RP) La0.5Sr1.5Ni1-xFexO4+δ will be reported that describe the highest catalytic activities reported for RP/perovskite matierials to date. These results will be described in the context of benchmarking to IrO2 and Pd and definition of the structure, electronic configuration and catalytic pathways. Electroanalytical techniques such as rotating disk electrochemistry and cyclic voltammetry are used in conjunction with materials characterization enabled by dynamic light scattering, electron microscopy, nitrogen sorption, X-ray photoelectron spectroscopy and X-ray diffraction. It will be demonstrated that these highly active perovskite catalysts are an emerging replacement for the precious metal catalysts.