Few-layer graphene (FLG) supported ruthenium nanoparticle catalysts were synthesized and used for the hydrogenation of levulinic acid (LA), one of the "top 10" biomass platform molecules derived from carbohydrates. FLG-supported ruthenium catalyst showed 99.7% conversion and 100% selectivity toward γvalerolactone (GVL) at room temperature in a batch reactor under high-pressure hydrogen. This catalyst showed 4 times higher activity and exceptional stability in comparison with traditional activated carbon supported ruthenium catalysts (Ru/C). X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) studies suggest that the superior catalytic properties of Ru nanoparticles supported on FLG in LA hydrogenation could be attributed to the greater metallic Ru content present in the Ru/FLG in comparison to that in Ru/C. ABSTRACT: Few-layer graphene (FLG) supported ruthenium nanoparticle catalysts were synthesized and used for the hydrogenation of levulinic acid (LA), one of the "top 10" biomass platform molecules derived from carbohydrates. FLG-supported ruthenium catalyst showed 99.7% conversion and 100% selectivity toward γ-valerolactone (GVL) at room temperature in a batch reactor under high-pressure hydrogen. This catalyst showed 4 times higher activity and exceptional stability in comparison with traditional activated carbon supported ruthenium catalysts (Ru/C). X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) studies suggest that the superior catalytic properties of Ru nanoparticles supported on FLG in LA hydrogenation could be attributed to the greater metallic Ru content present in the Ru/FLG in comparison to that in Ru/C. NotesThe authors declare no competing financial interest. ■ ACKNOWLEDGMENTSThis work was supported through funding from the Iowa Energy Center. We thank Iowa State University for startup funds. We also thank Gordon J. Miller for use of his XRD instrument and Igor I. Slowing for use of his ICP-AES instrument. The valuable discussion with Young-Jin Lee and Aaron J. Rossini is greatly appreciated.

Composite phases have been shown to improve both the thermoelectric efficiency and mechanical properties of materials. Here, we demonstrate an improved thermoelectric figure of merit, power factor, and mechanical properties for the high-temperature p-type Zintl phase Yb 14 MgSb 11 . Composites with 0, 1, 2, 3, 4, 6, and 8 vol % 6−10 μm reduced Fe powder were prepared via a fast, scalable, mechanical milling and spark plasma sintering procedure. Powder X-ray diffraction, scanning electron microscopy, and transmission electron microscopy show that Fe is not incorporated into the Yb 14 MgSb 11 structure. First-order reversal curves and scanning electron microscopy images show that the Fe inclusions are larger and closer together with increasing Fe content. Thermogravimetric and differential scanning calorimetry show that the composites are stable up to 1273 K. The elastic constants of the 8 vol % Fe composite were measured by resonant ultrasound spectroscopy and show that Yb 14 MgSb 11 becomes stiffer with increasing Fe volume % and SEM after indentations show crack arresting occurs at the Fe interface. Thermoelectric properties on dense pellets are measured from 300 K − 1273 K. The thermoelectric power factor (PF = S 2 /ρ) increases with increasing Fe content, with the 8 vol % Fe resulting in 40% higher PF than pristine Yb 14 MgSb 11 . The increase in PF is attributed to a systematic reduction in electrical resistivity. Peak thermoelectric figure of merit [zT = (S 2 T)/(κρ)] is observed at 3 vol % Fe, an 11% improvement in zT compared to Yb 14 MgSb 11 . Yb 14 MgSb 11 composites with Fe are compatible with Ce 0.9 Fe 3.5 Co 0.5 Sb 12 for thermoelectric generator couple segmentation. KEYWORDS: composite, thermoelectric, transport properties, Zintl phase, SPS synthesis, first-order reversal curves PFS 2 =ρ by band structure engineering, such as band convergence, tuning the electronic states with resonance levels, or simple substitutional alloying. There has also been significant research

The Zintl phases, Yb14MSb11 (M = Mn, Mg, Al, Zn), are now some of the highest thermoelectric efficiency p-type materials with stability above 873 K. Yb14MnSb11 gained prominence as the first p-type thermoelectric material to double the efficiency of SiGe alloy, the heritage material in radioisotope thermoelectric generators used to power NASA’s deep space exploration. This study investigates the solid solution of Yb14Mg1−xAlxSb11 (0 ≤ x ≤ 1), which enables a full mapping of the metal-to-semiconductor transition. Using a combined theoretical and experimental approach, we show that a second, high valley degeneracy (Nv = 8) band is responsible for the groundbreaking performance of Yb14MSb11. This multiband understanding of the properties provides insight into other thermoelectric systems (La3−xTe4, SnTe, Ag9AlSe6, and Eu9CdSb9), and the model predicts that an increase in carrier concentration can lead to zT > 1.5 in Yb14MSb11 systems.

Scalable programmable photonic integrated circuits (PICs) can potentially transform the current state of classical and quantum optical information processing. However, traditional means of programming, including thermo-optic, free carrier dispersion, and Pockels effect result in either large device footprints or high static energy consumptions, significantly limiting their scalability. While chalcogenide-based non-volatile phase-change materials (PCMs) could mitigate these problems thanks to their strong index modulation and zero static power consumption, they often suffer from large absorptive loss, low cyclability, and lack of multilevel operation. Here, we report a wide-bandgap PCM antimony sulfide (Sb2S3)-clad silicon photonic platform simultaneously achieving low loss (<1.0 dB), high extinction ratio (>10 dB), high cyclability (>1600 switching events), and 5-bit operation. These Sb2S3-based devices are programmed via on-chip silicon PIN diode heaters within sub-ms timescale, with a programming energy density of $$\sim 10\,{fJ}/n{m}^{3}$$ ~ 10 f J / n m 3 . Remarkably, Sb2S3 is programmed into fine intermediate states by applying multiple identical pulses, providing controllable multilevel operations. Through dynamic pulse control, we achieve 5-bit (32 levels) operations, rendering 0.50 ± 0.16 dB per step. Using this multilevel behavior, we further trim random phase error in a balanced Mach-Zehnder interferometer.

Type I clathrates of the composition K8E8Ge38 (E = Al, Ga, In) were prepared via the reaction of KH with E and Ge and thermoelectric properties measured in order to compare to K8Al8Si38, a promising thermoelectric material. The structures were confirmed with Rietveld refinement of powder diffraction patterns obtaining lattice parameters of 10.7729(2) Å, 10.7469(5) Å, and 10.9975(6) Å for E = Al, Ga, and In, respectively. Samples of K8E8Ge38 with E = Al and Ga were consolidated via spark plasma sintering for property measurements and determined to be 94.2% and 81.4% dense, respectively. K8In8Ge38 showed significant decomposition after sintering with both elemental In and Ge present in the powder diffraction pattern. The thermoelectric properties of K8E8Ge38 (E = Al, Ga) from 300–10 K were measured on sintered pellets. K8Al8Ge38 was found to have a Seebeck coefficient, electrical resistivity, and thermal conductivity of −35.8 μV/K, 2.56 mΩ·cm, 1.37 W/m·K at 300 K, respectively. K8Ga8Ge38 was found to be a compensated semiconductor with a Seebeck coefficient, electrical resistivity, and thermal conductivity of 4.19 μV/K, 1080 mΩ·cm, and 1.05 W/m·K at 300 K, respectively. The resistivity of K8Al8Ge38 is 46 times lower than K8Al8Si38 which has a Seebeck coefficient of −90.0 μV/K and thermal conductivity of 1.77 W/mK at 300 K, suggesting that a solid solution of K8Al8Si38‑xGe x has potential for optimal thermoelectric performance.