On the Al-Al11Ce3 Eutectic Transformation in Aluminum-Cerium Binary Alloys.

The L ↔ Al + Al11Ce3 technologically important eutectic transformation in Al-Ce binary alloys, containing from 5 to 20 wt.% Ce and ranging from hypo- to hypereutectic compositions, was examined along with the microstructure and properties of its solidified product. A combination of thermal analysis and metallography determined the coordinates of the eutectic point at 644.5 ± 0.6 °C and 10.6 wt.% Ce, clarifying the existing literature ambiguity. Despite the high entropy of melting of the Al11Ce3 phase, in hypoeutectic alloys the eutectic was dominated by the regular morphology of periodically arranged lamellae, typical for non-faceted systems. In the lamellar eutectic, however, the faceting of Al11Ce3 was identified at the atomic scale. In contrast, for hypereutectic compositions, the Al11Ce3 eutectic phase exhibited complex morphology, influenced by the proeutectic Al11Ce3 phase. The Al11Ce3 eutectic phase lost its coherency with Al; it was deduced that a partial coherency was present only at early stages of lamellae growth. The orientation relationships between the Al11Ce3 and Al in the eutectic structure, leading to partial coherency, were determined to be Al ║ Al11Ce3 with Al ║ Al11Ce3 and Al ║ Al11Ce3 with Al ║ Al11Ce3. The Al11Ce3 phase with a hardness of 350 HV and Al matrix having 35 HV in their eutectic arrangement formed in situ composite, with the former playing a role of reinforcement. However, the coarse and mostly incoherent Al11Ce3 eutectic phase provided limited strengthening and the Al-Ce alloy consisting of 100% eutectic reached at room temperature a yield stress of just about 70 MPa.

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 °C. 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.

Thermodynamically destabilized hydride formation in "bulk" Mg-AlTi multilayers for hydrogen storage.

Thermodynamic destabilization of MgH2 formation through interfacial interactions in free-standing Mg-AlTi multilayers of overall "bulk" (0.5 µm) dimensions with a hydrogen capacity of up to 5.5 wt% is demonstrated. The interfacial energies of Mg-AlTi and Mg-Ti (examined as a baseline) are calculated to be 0.81 and 0.44 J m(-2). The enhanced interfacial energy of AlTi opens the possibility of creating ultrathin alloy interlayers that provide further thermodynamic improvements in metal hydrides.