Promoting the ambient-condition stability of Zr-doped barium cerate: Toward robust solid oxide fuel cells and hydrogen separation in syngas

Increasing the stability of perovskite proton conductor against atmospheric CO2 and moisture attack at ambient conditions might be equally important as that at the elevated service temperatures. It can ease the transportation and storage of materials, potentially reducing the maintenance cost of the integral devices. In this work, we initially examined the surface degradation behaviors of various Zr-doped barium cerates (BaCe0.7Zr0.1Y0.1Me0.1O3) using XRD, SEM, STEM and electron energy loss spectroscopy. Though that the typical lanthanide (Y, Yb and Gd) and In incorporated Zr-doped cerates well resisted CO2-induced carbonation in air at elevated temperatures, they were unfortunately vulnerable at ambient conditions, suffering slow decompositions at the surface. Conversely, Sn doped samples (BCZYSn) were robust at both conditions yet showed high protonic conductivity. Thanks to that, the anode supported solid oxide fuel cells equipped with BCZYSn electrolyte delivered a maximum power density of 387 mW cm−2 at 600 °C in simulated coal-derived syngas. In the hydrogen permeation test using BCZYSn based membrane, the H2 flux reached 0.11 mL cm−2 min−1 at 850 °C when syngas was the feedstock. Both devices demonstrated excellent stability in the presence of CO2 in the syngas

Wire-arc additive manufactured nickel aluminum bronze with enhanced mechanical properties using heat treatments cycles

Wire-arc additive manufacturing (WAAM) technique was used to develop nickel aluminum bronze (NAB) components for naval applications. The microstructural changes were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS). As-built WAAM-NAB consists of κII (globular Fe3Al) and κIII (lamellar NiAl) phases in the interdendritic regions and fine Fe-rich κIV particles in the Cu-matrix. Along the build direction, the WAAM-NAB flat samples exhibited yield and ultimate tensile strength values of 380 and 708 MPa, respectively, and 34 % elongation. Furthermore, three different heat-treatments were performed on the samples in a view to evaluating their effect on mechanical properties. When heat-treated to 350 °C for 2 h (HT-1), there are no significant microstructural changes, and tensile properties along the build direction are similar to the as-built WAAM-NAB. Heat-treatment at 550 °C for 4 h (HT-2) produced a new needle-like κv phase in the α-matrix, coarsening of globular κII, partial spheroidization of lamellar κIII, and reduced amount of κIV precipitation. As compared to the WAAM-NAB, HT-2 samples exhibited a significant increase in yield strength (∼90 MPa), and ultimate tensile strength (∼60 MPa); however, tensile ductility was observed to drop by 20 %. After heat-treatment at 675 °C for 6 h (HT-3), globular κII and needle-like κv were coarsened, lamellar κIII was completely spheroidized, and the amount of κIV was significantly reduced. HT-3 samples showed better tensile strength (∼37 MPa) than the WAAM-NAB with marginal loss (6%) in the ductility. © 202

Generating C4 Alkenes in Solid Oxide Fuel Cells via Cofeeding H2 and n-Butane Using a Selective Anode Electrocatalyst

Solid oxide fuel cells (SOFCs) offer opportunities for the application as both power sources and chemical reactors. Yet, it remains a grand challenge to simultaneously achieve high efficiency of transforming higher hydrocarbons to value-added products and of generating electricity. To address it, we here present an ingenious approach of nanoengineering the triple-phase boundary of an SOFC anode, featuring abundant Co7W6@WOx core-shell nanoparticles dispersed on the surface of black La0.4Sr0.6TiO3. We also developed a cofeeding strategy, which is centered on concurrently feeding the SOFC anode with H2 and chemical feedstock. Such combined optimizations enable effective (electro)catalytic dehydrogenation of n-butane to butenes and 1,3-butadiene. The C4 alkene yield is higher than 50% while the peak power density of the SOFC reached 212 mW/cm2 at 650 ºC. In addition, coke formation is largely suppressed and little CO/CO2 is produced in this process. While this work shows new possibility of chemical-electricity coupling in SOFCs, it might also open bona fide avenues toward the electrocatalytic synthesis of chemicals at higher temperatures

Stable hydrogen storage cycling in magnesium hydride, in the range of room temperature to 300\ub0C, achieved using a new bimetallic Cr-V nanoscale catalyst

We created a bimetallic chromium vanadium hydrogen sorption catalyst for magnesium hydride (MgH 2). The catalyst allows for significant room-temperature hydrogen uptake, over 10 cycles, at absorption pressures as low as 2 bar. This is something that has never been previously achieved. The catalyst also allowed for ultrarapid and kinetically stable hydrogenation cycling (over 225 cycles) at 200 and at 300 \ub0C. Transmission electron microscopy analysis of the postcycled samples revealed a nanoscale dispersion of Cr-V nanocrystallites within the Mg or MgH 2 matrix. TEM analysis of the partially absorbed specimens revealed that even at a high absorption pressure, that is, a high driving force, relatively few hydride nuclei are formed at the surface of the pre-existing magnesium, ruling out the presence of any contracting volume (also termed contracting envelope or core shell) type growth. HRTEM of the cycled and desorbed powder sample demonstrated that the bcc Cr-V phase is crystalline and nanoscale. We experimentally demonstrated that the activation energy for hydrogen absorption is not constant but rather evolves with the driving force. This finding sheds new insight regarding the origins of the wide discrepancy in the literature - reported values of the hydrogenation activation energy in magnesium hydride and in related metal hydride systems. \ua9 2011 American Chemical Society.Peer reviewed: YesNRC publication: Ye

Laser powder bed fused Inconel 718 in stress-relieved and solution heat-treated conditions

Inconel 718 superalloy cylindrical rods were fabricated using the laser powder bed fusion (L-PBF) technology in the vertical orientation. The rods were stress-relieved at 980 °C for 15 min before cutting them from the build plate. The microstructure in this condition exhibited a significant amount of undesirable needle-like δ-phase precipitates and a small amount of interdendritic Laves phase that is finer in size. Differential Scanning Calorimetry (DSC) was used to determine the temperatures for solid-state phase transformations and appropriate temperature for solution-treatment. Solution-treatment was performed at 1065 °C for 1 h, followed by air cooling. The microstructures were characterized with specific reference to δ-phase and Nb segregation. Solution-treatment at 1065 °C was found to result in a significant elimination of micro-segregation (mainly Nb), complete dissolution of δ phase, considerable Laves dissolution, and partly undissolved carbide particles (few nm in size). Solution-treatment did not produce a significant change in the grain morphology (columnar dendritic) on a plane parallel to the build direction but more recrystallized and equiaxed grains were formed on a plane perpendicular to the build direction. The hardness of the solution-treated sample is comparable with wrought 718 alloys but lesser (115 HV) than in the stress-relieved condition attributing to the annihilation of dislocation tangles. © 202

Developing a Thermal- and Coking-Resistant Cobalt-Tungsten Bimetallic Anode Catalyst for Solid Oxide Fuel Cells

We report the development of a novel Co–W bimetallic anode catalyst for solid oxide fuel cells (SOFCs) via a facile infiltration-annealing process. Using various microscopic and spectroscopic measurements, we find that the formed intermetallic nanoparticles are highly thermally stable up to 900 °C and show good coking resistance in methane. In particular, a fuel cell fitted with Co3W anode shows comparable activity (relative to Co) in the electro-oxidation of hydrogen and methane at 900 °C without suffering significant degradation during a longevity test

Magnesium and magnesium-silicide coated silicon nanowire composite anodes for lithium-ion batteries

We synthesized composites consisting of silicon nanowires (SiNWs) coated with magnesium (Mg) and magnesium silicide (Mg2Si) for lithium-ion battery anodes and studied their electrochemical cycling stability and degradation mechanisms. Compared to bare SiNWs, both Mg- and Mg 2Si-coated materials show significant improvement in coulombic efficiency during cycling, with pure Mg coating being slightly superior by 3c1% in each cycle. XPS measurements on cycled nanowire forests gave quantitative information on the composition of the SEI layer and showed lower Li2CO3 and higher polyethylene oxide content for coated nanowires, thus revealing a passivating effect towards electrolyte decomposition. Extensive characterization of the microstructure before and after cycling was carried out by scanning- and transmission electron microscopy aided by focused ion beam cross-sectioning. The formation of large voids between the nanowire assembly and the substrate during cycling, causing the nanowires to lose electrical contact with the substrate, is identified as an important degradation mechanism. \ua9 2013 The Royal Society of Chemistry.Peer reviewed: YesNRC publication: Ye