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

Hydrogen Storage Materials for Mobile and Stationary Applications: Current State of the Art

One of the limitations to the widespread use of hydrogen as an energy carrier is its storage in a safe and compact form. Herein, recent developments in effective high-capacity hydrogen storage materials are reviewed, with a special emphasis on light compounds, including those based on organic porous structures, boron, nitrogen, and aluminum. These elements and their related compounds hold the promise of high, reversible, and practical hydrogen storage capacity for mobile applications, including vehicles and portable power equipment, but also for the large scale and distributed storage of energy for stationary applications. Current understanding of the fundamental principles that govern the interaction of hydrogen with these light compounds is summarized, as well as basic strategies to meet practical targets of hydrogen uptake and release. The limitation of these strategies and current understanding is also discussed and new directions proposed

Cigarette butt-derived carbons have ultra-high surface area and unprecedented hydrogen storage capacity

Discarded cigarette filters, in the form of cigarette butts, are a major waste disposal and environmental pollution hazard due to mainly containing cellulose acetate which is nonbiodegradable; 5.8 trillion cigarettes are smoked worldwide per annum generating > 800 000 metric tons of cigarette butts. Apart from causing litter, cigarette butts contain contaminants such as toxic heavy metals, which can leach into waterways, potentially causing harm to both humans and wildlife. In an effort to turn dangerous waste into value products, this study explores the valorisation of discarded smoked cigarette filters/butts. We show that porous carbons derived from cigarette butts, via sequential benign hydrothermal carbonisation and activation, are super porous and have ultra-high surface area (4300 m2 g-1) and pore volume (2.09 cm3 g-1) arising almost entirely (> 90%) from micropores. The carbons also have uncharacteristically high oxygen content associated with O-containing functional groups (COOH, C-OH and C=O), and show anomalous behaviour with respect to the effect of activation temperature on porosity, the latter being ascribable to the chemical mix present in cigarette butts and their hydrochar products. Due to the combined effects of high surface area, high microporosity and an oxygen-rich nature, the carbons exhibit unprecedentedly high hydrogen storage capacity of 8.1 wt% excess uptake, and 9.4 wt% total uptake at -196 ºC and 20 bar, rising to total uptake of 10.4 wt% and 11.2 wt% at 30 and 40 bar, respectively. The hydrogen storage capacity is the highest reported to date for any porous carbons and attains new levels for porous materials in general. This work also raises the question on whether valorisation can solve the intractable cigarette butt problem

Formation of MgxNbyOx+y through the Mechanochemical Reaction of MgH2 and Nb2O5, and Its Effect on the Hydrogen-Storage Behavior of MgH2

The present study aims to understand the catalysis of the MgH2-Nb2O5 hydrogen storage system. To clarify the chemical interaction between MgH2 and Nb2O5, the mechanochemical reaction products of a composite mixture of MgH2+0.167Nb(2)O(5) was monitored at different time intervals (2, 5, 15, 30, and 45min, as well as 1, 2, 5, 10, 15, 20, 25, and 30h). The study confirms the formation of catalytically active Nb-doped MgO nanoparticles (typically MgxNbyOx+y, with a crystallite size of 4-8nm) by transforming reactants through an intermediate phase typified by Mgm-xNb2n-yO5n-(x+y). The initially formed MgxNbyOx+y product is shown to be Nb rich, with the concentration of Mg increasing upon increasing milling time. The nanoscale end-product MgxNbyOx+y closely resembles the crystallographic features of MgO, but with at least a 1-4% higher unit cell volume. Unlike MgO, which is known to passivate the surfaces in MgH2 system, the Nb-dissolved MgO effectively mediates the Mg-H-2 sorption reaction in the system. We believe that this observation will lead to new developments in the area of catalysis for metal-gas interactions