Mixture Of La0 Research Articles

Enhancement of capacitance of waterproof supercapacitors by controlling the thickness of their composite electrodes (graphene/ La0.2Gd1.8Zr2O7: La0.7Sr0.3MnO3)

We report the electrochemical performance of wrinkled/washable graphene-based supercapacitors (SCs). Sustainable graphene electrodes were fabricated by printing graphene microplates on recycled plastics (taken from wasted chip-packets), which provided flexibility to the SCs. The devices made with only graphene electrodes had an energy-density/specific-capacitance of 8.8 Wh kg−1/99.1 F g−1. To enhance the electrochemical properties of the SCs, a mixture of La0.2Gd1.8Zr2O7 (LGZ) and La0.7Sr0.3MnO3 (LSM) perovskites (redox materials) were added on their electrodes. After this, the energy-density/capacitance was enhanced to 53.1 Wh kg−1/596.90 F g−1, that is, an improvement of 503/502%, respectively. Subsequently, the solid state SCs were completely rolled or wrinkled, in consequence, the capacitance decreased by 12.1 and 35.6%, respectively. Even more, the SCs were immersed in water or subjected to washing/drying cycles using a washing-machine and the capacitance barely decreased by ⁓14.2%. Additionally, the thickness of the SC electrodes was varied in the range of 65–400 μm and obtained the maximum capacitance for a thickness of 330 μm. Overall, we demonstrated that incorporating the LGZ/LSM perovskite on the SC electrodes provided extra redox centers, which incremented the capacitance of the devices. The SCs reported here are waterproof and wrinkled, thus, they could provide energy to wearable devices.

Reversible Solid Oxide Cells: Cycling and Long-Term Durability of Air Electrodes

Introduction Reversible solid oxide cell (r-SOC) enables both power generation and electrolysis, when the cell can be operated as a solid oxide fuel cell (SOFC) and as a solid oxide electrolysis cell (SOEC). Many studies are being conducted to improve their performance and durability (1,2).Lanthanum strontium cobalt ferrite (LSCF) is an air electrode material with a perovskite-type crystal structure which exhibits high electronic and ionic conductivity, oxygen diffusivity, and electrocatalytic activity (3). However, performance and durability of the cells with Sr-containing oxide air electrodes have to be carefully analyzed, as Sr ions tend to easily diffuse during sintering and in long-term operation, reacting with Zr ions from the solid electrolyte to form a highly resistance reaction layer such as SrZrO3 (4-6). While the performance and durability of LSCF-based air electrodes and the Sr diffusion in SOFC operation have been studied, there are still limited number of studies on the SOEC operation, and especially on the r-SOC operation. The diffusion of constituent ions such as Co and Fe may not be negligible in SOCs.Here in this study, we fabricate YSZ electrolyte-supported r-SOCs and conduct durability studies in both SOFC and SOEC modes. STEM-EDS observation of the air electrode materials is also made to investigate the durability and diffusion of various elements in the LSCF-based air electrode of r-SOCs. Experimental R-SOCs with yttria stabilized zirconia electrolytes (YSZ, 200 µm thick) were prepared. Ni-GDC co-impregnated fuel electrode was prepared, where a mixture of La0.1Sr0.9TiO3 (LST) and Gd0.1Ce0.9O2 (GDC) at a volume ratio of 50:50 was used as the porous electrode backbone, onto which Ni-containing solution of 1 µL was impregnated for Ni loading of 0.167 mg cm-2 (7). Gd0.1Ce0.9O2 (GDC) buffer layer was prepared between the electrolyte and the air electrode to prevent elemental diffusion (8). La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) was used for the air electrode. In addition, a Pt reference electrode was deposited onto the electrolyte on the fuel electrode side. The voltage measurement terminals of the electrochemical measurement setup were connected between the reference electrode and the air electrode to evaluate the air electrode potential. 50%-humidified hydrogen (100 ml min-1) was supplied to the fuel electrode, and air (150 ml min-1) was supplied to the air electrode. Negative current density means the value in the SOEC mode, while positive current density in the SOFC mode. Results and discussion As shown in Fig. 2 describing one cycle, current density was varied at 800°C for the 1000-cycle durability tests in the r-SOC operation. The range of current density was between -0.2 A cm-2 and 0.2 A cm-2. The air electrode potential at different current densities and the electrode impedance in every 100 cycles were measured. For the 1000-hour electrolysis durability test in the SOEC mode, current density of -0.2 A cm-2 was applied for 1000 hours at 800°C. The air electrode potential and the impedance in every 100 hours were measured (9). It has been found that a gradual degradation of the r-SOCs associated with an increase in air electrode potential in the SOEC mode and a decrease in the potential in the SOFC mode could be distinguished. However, such degradation tended to be stabilized with the number of cycles.STEM-EDS observations were performed to analyze the elemental distribution around the air electrode and the electrolyte in the cell. It was found that such elemental diffusion could occur during sintering and durability experiments.AcknowledgmentsA part of this study was supported by “Research and Development Program for Promoting Innovative Clean Energy Technologies Through International Collaboration” of the New Energy and Industrial Technology Development Organization (NEDO) (Project No. JPNP20005). Collaborative support by Prof. H. L. Tuller, and Prof. B. Yildiz at Massachusetts Institute of Technology (MIT) for their continuous support is gratefully acknowledged. Figure 1

Green synthesis and characterisation of nanocrystalline NiO-GDC powders with low activation energy for solid oxide fuel cells

This work reports the preparation of nanocrystalline Ni-Gd0.1Ce0.9O1.95 (NiO-GDC) anode powders using a novel single-step co-precipitation synthesis method (carboxylate route) based on ammonium tartrate as a low-cost green precipitant. The thermogravimetric analysis (TGA) of the synthesised powder showed the complete calcination/crystallisation of the resultant precipitates to take place at 500 °C. The prepared NiO-GDC powder was coated on a GDC electrolyte disc and co-sintered at 1300 °C. A mixture of La0.6Sr0.4Co0.2Fe0.8O3−δ and GDC was used as the cathode material and subsequently coated onto the anode-electrolyte bilayer, resulting in the fabrication of a NiO-GDC|GDC|La0.6Sr0.4Co0.2Fe0.8O3−δ-GDC cell. The crystallite size of both NiO and CeO2 phases were estimated using the X-ray powder diffraction (XRD) profiles and were calculated to be ~14 nm. Applied H2 temperature-programmed reduction (H2-TPR) analysis indicated a synergetic effect among different anode composites' constituents, where an intense interaction between the dispersed NiO nanocrystalline particles and the GDC crystallite phase had weakened the metal-oxygen bonds in the synthesised anode composites, resulting in a strikingly high catalytic activity at temperatures as low as 300 °C. The electrochemical impedance spectroscopy (EIS) and the electrochemical performance of the fabricated cells were measured over a broad range of operating temperatures (500–750 °C) and H2/Ar-ratios of the anode fuel (e.g. 100%–15%). Quantitative analysis from the EIS data and the application of the distribution of relaxation times (DRT) method allowed for the estimation of the activation energies of the anodic high and intermediate frequency processes that were 0.45 eV and 0.76 eV, respectively. This is the first report of a NiO-GDC synthesis, where a considerable improvement in activation energy is observed at the low-temperature region. Such low activation energies were later associated with the adsorption/desorption process of water molecules at the surface of NiO-GDC composite, indicating a high activity towards hydrogen oxidation.

Synthesis and electrochemical characterization of La0.6Sr0.4Co0.2Fe0.8O3–δ / Ce0.9Gd0.1O1.95 co-electrospun nanofiber cathodes for intermediate-temperature solid oxide fuel cells

Synthesis and electrochemical characterization of composite cathodes, formed from a mixture of La0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF) and Ce0.9Gd0.1O1.95 (GDC) nanofibers, is reported. The electrodes are obtained by simultaneous electrospinning of the two precursor solutions, using apparatus equipped with two spinnerets working in parallel. Results of electrochemical testing carried out through electrochemical impedance spectroscopy (EIS) are presented and discussed. The results suggest that the electrochemical reaction takes place in an electrode region close to the electrode/current collector interface and that the oxygen ions then flow along the ionic conducting path of the GDC fibers. At 650 °C, the polarization resistance is Rp = 5.6 Ω cm−2, in line with literature values reported for other IT-SOFC cathodes.

Measurement and augmentation of effective thermal conductivity of La0.8Ce0.2Ni5 hydride bed

An experimental set up for measuring Effective Thermal Conductivity (ETC) of Metal Hydride (MH) beds was fabricated using one-dimensional steady-state radial heat transfer absolute method. La0.8Ce0.2Ni5 alloy powder and its hydride were considered in the present study. Two types of compacts were fabricated for ETC augmentation of MH bed. First type was made from the mixture of 6 wt% graphite flakes with the La0.8Ce0.2Ni5 alloy powder. A three dimensional structure, having six radial fins, uniformly distributed around the outer periphery of a hollow cylinder, made with copper wire mesh, was integrated with the mixture of La0.8Ce0.2Ni5 powder and 6 wt% graphite flakes to make the second type of compacts. The ETC of the three types of beds namely loose metal powder bed (LMP), bed of compacts of metal alloy powder mixed with graphite flakes (CMPGF) and bed of compacts of metal alloy powder mixed with graphite flakes and embedded with copper wire mesh structure (CMPGFCu) were measured and compared at different argon and hydrogen pressures, hydrogen concentrations and average bed temperatures. The maximum values of effective thermal conductivity for the bed configurations of LMP/CMPGF/CMPGFCu were 1.3/4.7/6.8 W m−1 K−1. These values of effective thermal conductivity were obtained at 70 bar hydrogen gas pressure and 60 °C average bed temperature. The decrease in mass fraction of hydrogen absorbed by the La0.8Ce0.2Ni5 hydride, as a result of implementation of ETC augmentation techniques, was nominal (around 5.7% in case of CMPGF and 4.5% in case of CMPGFCu) when compared to the respective powder bed configurations.

Effect of heat transfer enhancement on the performance of metal hydride based hydrogen compressor

A single stage metal hydride based hydrogen compressor has been developed using La0.8Ce0.2Ni5 hydride. The performance of the hydrogen compressor was evaluated in three different configurations to determine the effect of heat transfer augmentation. Two different types of metal hydride pellets were developed. Graphite flakes were mixed with La0.8Ce0.2Ni5 hydride for the first type of pellets. While in the second type, an augmentation structure made with copper wire mesh was embedded with the mixture of La0.8Ce0.2Ni5 hydride and graphite flakes. All the three types of La0.8Ce0.2Ni5 hydride beds namely, with loose MH powder (LMHP), pellets of MH powder and graphite fibres (PMHGF), and pellets of MH, graphite fibres with embedded copper wire mesh structure (PMHGFCu) were tested for a wide range of pressure and temperature conditions and their performances were compared. As expected, the heat transfer enhancement of La0.8Ce0.2Ni5 hydride bed resulted in enhancement of kinetics of hydrogenation/dehydrogenation and performance of hydrogen compressor. The maximum pressure ratio, maximum cycle efficiency, minimum time to reach saturation stage during absorption in cases of LMHP/PMHGF/PMHGFCu were 4.18/5.04/5.2, 5.1%/5.94%/6.07%, 400 s/250 s/220 s respectively. The highest increase in compression ratio and efficiency in case of pellets bed compared to those for powder bed were 76.51% and 29.3% respectively.

Preparation and Characterization of Rare Earth Composite Catalytic Materials for Conversion of Exhaust from Natural Gas Automobiles

A series of rare-earth composite catalytic material LZ1,LZ2 and LZ3 that contains mixture of La0.9Sr0.1Co0.5Mn0.5O3and Ce0.7Zr0.3O2in different proportion (3:7, 5:5, 7:3) were prepared by a sol-gel method and characterized by X-ray diffraction (XRD), specific surface analysis (BET) , Transmission electron microscopy (TEM) and temperature programmed reduction (TPR). The results indicated that in LZ3, a perfect crystal structure of perovskite and a cubic fluorite structure were formed. Besides LZ3 presented scattered spherical granules with a particle size of about 30 nm and a specific surface area of 20.9870 m2/g. The temperature of reduction peak was lowest (490°C) and peak area was larger, so it had the best catalytic activity for methane combustion.

Behavior of High Temperature SOFC Materials Subjected to Thermal Cycles

In order to evaluate the thermal stress of high temperature SOFC materials, four different square bars of materials were examined under four different thermal cycles. Materials composed of a Ni-YSZ anode in H2 and 5%H2-N2, a YSZ electrolyte, and a (La,Sr)(Cr,Co)O3 interconnect were unaffected by the thermal cycles. However, a Ni-YSZ anode in N2 purge gas and a (La,Sr)MnO3+d cathode in air were affected by the thermal cycles strongly. Thus, by using 5%H2-N2, the anode can evade thermal cycle damage. The shrinkage characteristic of two cathode materials in air and N2 atmospheres were also evaluated. A reduction of thermal cycle induced shrinkage is made possible by a mixture of La0.6Sr0.4MnO3 and stabilized zirconia materials, and when the atmosphere of the temperature decrease phase of the thermal cycle is nitrogen, the behavior becomes independent of the atmosphere for the temperature increase portion of the cycle.

The Suppression of Discharge Area Shrinkage of the La0.5Sr0.5CoO3 Cathode by Use of Insulator

The La0.5Sr0.5CoO3 was used as a cathode for the first time when the plasma display panel was used on the handheld personal computer. It has favorable sputtering resistance characteristic and stable discharge characteristic in gases. A cathode made from the La0.5Sr0.5CoO3 has unique electrical characteristic in period of continual discharge. The discharge voltage and luminance of the La0.5Sr0.5CoO3 shift during an extended period of discharge, and the discharge voltage continue to increase in later period of continual discharge. It is presumed that the discharge voltage and luminance shift is caused by the discharge and luminescence area shift of the cathode surface, and that the current density shift is caused by the discharge area shrinkage phenomenon.This discharge area shrinkage phenomenon is reduced by use of a mixture of La0.5Sr0.5CoO3 and insulator, and the sputter rate is reduced, too. In this report, the discharge and luminescence area shift of the La0.5Sr0.5CoO3 are investigated through an analysis of the DC plasma panel that is made as prototype, and the discharge characteristic of the La0.5Sr0.5CoO3 cathode is compared with the cathode that is made from a mixture of La0.5Sr0.5CoO3 and insulator.