Unravelling the effects of calcium substitution in BaGd2CoO5 Haldane gap 1D material and its thermoelectric performance

Ecobenign and high-temperature-stable oxides are considered a promising alternative to traditional Bi2Te3-, Bi2Se3-, and PbTe-based thermoelectric materials. The quest for high-performing thermoelectric oxides is still open and, among other challenges, includes the screening of various materials systems for potentially promising electrical and thermal transport properties. In this work, a new family of acceptor-substituted Haldane gap 1D BaGd2CoO5 dense ceramic materials was characterized in this respect. The substitution of this material with calcium results in a general improvement of the electrical performance, contributed by an interplay between the charge carrier concentration and their mobility. Nevertheless, a relatively low electrical conductivity was measured, reaching ∼5 S/cm at 1175 K, resulting in a maximum power factor of ∼25 μW/(K × m2) at 1173 K for BaGd1.80Ca0.20CoO5. On the other hand, the unique anisotropic 1D structure of the prepared materials promotes efficient phonon scattering, leading to low thermal conductivities, rarely observed in oxide electroceramics. While the BaGd2–xCaxCoO5 materials show attractive Seebeck coefficient values in the range 210–440 μV/K, the resulting dimensionless figure of merit is still relatively low, reaching ∼0.02 at 1173 K. The substituted BaGd2–xCaxCoO5 ceramics show comparable thermoelectric performance in both inert and air atmospheres. These features highlight the potential relevance of this structure type for thermoelectric applications, with future emphasis placed on methods to improve conductivity.publishe

Bias polarization study of steam electrolysis by composite oxygen electrode Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ/BaCe_0.4Zr_0.4Y_0.2O_3-δ

The polarization behavior of Ba0.5Sr0.5Co0.8Fe0.2O3-δ-BaCe0.4Zr0.4Y0.2O3-δ (BSCF-BCZY) electrode under steam electrolysis conditions was studied in detail. The composite oxygen electrode supported by BCZY electrolyzer has been assessed as a function of temperature (T), water vapor partial pressures (pH2O), and bias polarization voltage for electrodes of comparable microstructure. The Electrochemical impedance spectra show two depressed arcs in general without bias polarization. And the electrode resistance became smaller with the increase of the bias polarization under the same water vapor partial pressures. The total resistance of the electrode was shown to be significantly affected by temperature, with the same level of pH2O and bias polarization voltage. This result highlights BSCF-BCZY as an effective oxygen electrode under moderate polarization and pH2O conditions.</p

Two step mechanochemical synthesis of Nb doped MgO rock salt nanoparticles and its application for hydrogen storage in MgH2

In the present study, we demonstrate two mechanochemical approaches suitable for the bulk scale synthesis of catalytically active Nb doped MgO rock salt nanoparticles. In the first method, Nb2O5 initially was reduced to NbO2 by MgH2 and then transformed to MgxNbyOx+y. In the second method, MgO and Nb2O5 were initially combined to make MgNb2O6 and then converted to MgxNbyOx+y. The DSC-TG and Sievert's volumetric analysis suggest that the end product, MgxNbyOx+y, is catalytically more active in comparison to all other oxide phases involved in the reaction, such as Nb2O5, NbO2 and MgNb2O6. (C) 2015 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved

Chemically transformed additive phases in Mg2TiO4 and MgTiO3 loaded hydrogen storage system MgH2

The present work deals with a comparative study of Mg2TiO4, MgTiO3 and titania additives incorporated MgH2. Hydrogen storage measurements suggest that all these additives improve the hydrogen desorption/absorption performance of MgH2. X-ray diffraction (XRD) and X ray photoelectron spectroscopy (XPS) studies highlight that rock salt phases consisting of highly reduced Ti exist in the samples. These results reiterate that in-situ formation of chemically reduced Ti containing active species is a critical step in the catalysis of TiO2/Mg2TiO4/MgTiO3 additives loaded MgH2

Hydrogen storage characteristics of magnesium impregnated on the porous channels of activated charcoal scaffold

Ball milled (30 h) MgH2 is impregnated on the pores/grooves of activated charcoal scaffold using a programmed heat treatment at 550 °C under 5 bar pure hydrogen ambient. The result obtained by this approach is better and more consistent than the materials prepared by metal infiltration at 650 °C or vacuum heated samples under 550 °C. The activation energy value (88 kJ/mol) obtained in the case of impregnated catalyst free material is far better than the activation energy value of the unconfined material (149 kJ/mol). The impregnated material can absorb hydrogen almost closer to its actual capacity at ∼1 bar under 170 °C. The low temperature desorption characteristics and ab/desorption behaviors are extensively analyzed and described

Elucidating Evidence for the In Situ Reduction of Graphene Oxide by Magnesium Hydride and the Consequence of Reduction on Hydrogen Storage

The current study highlights important information regarding how graphene oxide (GO) additive interacts with magnesium hydride (MgH2) and transforms to reduced graphene oxide (rGO). A mild reduction occurs during mechanical milling itself, whereas a strong reduction of GO happens concurrently with the oxidation of Mg formed during the dehydrogenation of MgH2. Owing to the in situ transformation of GO to rGO, the dehydrogenation temperature of MgH2 reduces by about 60 °C, whereas the hydrogen ab/desorption reaction kinetics of MgH2 increases by two orders of magnitude and the dehydrogenation activation energy decreases by about 20 kJ/mol. We have thoroughly scrutinized the transformation of GO to rGO by differential scanning calorimetry (DSC), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) techniques. Interestingly, the GO to rGO transformation triggered by magnesium hydride in the current study further paves the way for the facile preparation of rGO- and MgO-decked rGO composites, which are important materials for energy storage applications