Structure and properties of Al2O3-bonded porous fibrous YSZ ceramics fabricated by aqueous gel-casting

To meet requirements for high porosity and high strength, novel aqueous gel-casting process has been successfully developed to fabricate Al2O3-bonded porous fibrous YSZ ceramics with ρ-Al2O3 and YSZ fibers as raw materials. Microstructure, phase composition, apparent porosity, bulk density, thermal conductivity, and compressive strength of fabricated porous ceramics were investigated, and effects of fiber content on properties were discussed. According to results, bird nest 3D mesh with interlaced YSZ fibers and Al2O3 binder was formed, ensuring the ability to obtain high performance, lightweight ceramics. An increase in the number of YSZ fibers led to more complex interlaced arrangement of fibers and denser network structure of porous ceramics at retaining their stability. Furthermore, their apparent porosity and bulk density increased, whereas thermal conductivity and compressive strength decreased with increasing the fiber content. In particular, comparatively high porosity (71.1–72.7%), low thermal conductivity (0.209–0.503 W/mK), and relatively high compressive strength (3.45–4.24 MPa) were obtained for as-prepared porous ceramics, making them promising for applications in filters, thermal insulation materials, and separation membranes

One-Dimensional Non-coplanar Nitrogen Chains in Manganese Tetranitride under High Pressure

Transition metal nitrides have great potential applications as incompressible and high energy density materials. Various polymeric nitrogen structures significantly affect their properties, contributing to their complex bonding modes and coordination conditions. Herein, we first report a new manganese polynitride MnN4 with bifacial trans–cis [N4]n chains by treating with high-pressure and high-temperature conditions in a diamond anvil cell. Our experiments reveal that MnN4 has a P-1 symmetry and could stabilize in the pressure range of 56–127 GPa. Detailed pressure–volume data and calculations of this phase indicate that MnN4 is a potential hard (255 GPa) and high energy density (2.97 kJ/g) material. The asymmetric interactions impel N1 and N4 atoms to hybridize to sp2–3, which causes distortions of [N4]n chains. This work discovers a new polynitride material, fills the gap for the study of manganese polynitride under high pressure, and offers some new insights into the formation of polymeric nitrogen structures

Solid-State Luminescence in Self-Assembled Chlorosalicylaldehyde-Modified Carbon Dots

Carbon dots (CDs) have excellent optical properties with broad potential applications. However, obtaining CDs with multicolor emission in the solid state remains a great challenge. Four chlorosalicylaldehyde-functionalized CDs with solid-state fluorescence were prepared here via molecular self-assembly. Their emission wavelengths were 456, 494, 556, and 584 nm, ranging from blue to yellow. Experimental results and theoretical calculations indicated that the different positions (para-, meta-, and ortho-position) of Cl on the aromatic core of chlorosalicylaldehyde affect the coplanarity and degree of conjugation of the CDs, thereby changing their molecular orbital energy levels and adjusting the emission. The self-assembly showed distinct isomeric effects: with changing positioning of the Cl, three-dimensional to one-dimensional self-assembled morphologies appeared in turn. The multicolor luminescence of the CDs makes them potentially useful in light-emitting diodes and fluorescent films. Their fat solubility and strong ultraviolet absorption characteristics allow them to be applied in fingerprint detection

Green synthesis of porous SiC ceramics using silicon kerf waste in different sintering atmospheres and pore structure optimization

This work reported the feasibility of using silicon kerf waste as raw material for the preparation of porous SiC ceramics, as well as effects of sintering atmospheres and additives on the properties of as-prepared ceramics. Samples sintered in Ar, N2, and carbon embedded atmospheres exhibited entirely different properties because of the formed bonding phases of SiCw, Si3N4/Si2N2O, and Si2N2O. Moreover, the apparent porosity and closed porosity of the samples were increased with the additions of feldspar and starch. Preferably, a series of porous SiC ceramics with apparent/closed porosity of 24.15%–59.59%/5.83%–14.77%, bulk density of 1.13–1.91 g cm−3, cold compressive strength of 34.73–249.89 MPa, and thermal shock resistance of 110–118 cycles was synthesized at 1500 °C in carbon embedded atmosphere. Therefore, a low-cost and facile synthesis strategy for preparing high-quality porous SiC ceramics from solid waste is proposed in present study

Synthesis and characterization of mullite-ZrO2 porous fibrous ceramic for highly efficient oil-water separation

This work aimed to proposing a new strategy for preparing the mullite-ZrO2 porous fibrous ceramic used as alternative matrix material for oil-water separation by the aqueous gel-casting method. The properties of the fabricated porous fibrous ceramics in terms of microstructure, phase composition, apparent porosity, bulk density and compressive strength were investigated and the separation behavior was predicted by analyzing the structural changes. It is demonstrated that the phase composition of green bodies consisted of bayerite, boehmite, ZrSiO4 and YSZ, and the sintered sample contained mullite, ZrO2 and YSZ. As the YSZ fibers increased, the porosity of the fabricated porous ceramic increased with the maximum value of 70.65% due to the formation of more pores caused by YSZ fibers. Moreover, a significant increase in compressive strength (up to 9.52–21.86 MPa) was observed with the increase of YSZ fibers. Therefore, the fabricated porous ceramics could be appropriative for advanced applications of separation membranes for oil-water separation

Oxygen Radical Coupling on Short-Range Ordered Ru Atom Arrays Enables Exceptional Activity and Stability for Acidic Water Oxidation

The discovery of efficient and stable electrocatalysts for oxygen evolution reaction (OER) in acid is vital for the commercialization of the proton-exchange membrane water electrolyzer. In this work, we demonstrate that short-range Ru atom arrays with near-ideal Ru–Ru interatomic distances and a unique Ru–O hybridization state can trigger direct O*–O* radical coupling to form an intermediate O*–O*-Ru configuration during acidic OER without generating OOH* species. Further, the Ru atom arrays suppress the participation of lattice oxygen in the OER and the dissolution of active Ru. Benefiting from these advantages, the as-designed Ru array-Co3O4 electrocatalyst breaks the activity/stability trade-off that plagues RuO2-based electrocatalysts, delivering an excellent OER overpotential of only 160 mV at 10 mA cm–2 in 0.5 M H2SO4 and outstanding durability during 1500 h operation, representing one of the best acid-stable OER electrocatalysts reported to date. 18O-labeled operando spectroscopic measurements together with theoretical investigations revealed that the short-range Ru atom arrays switched on an oxide path mechanism (OPM) during the OER. Our work not only guides the design of improved acidic OER catalysts but also encourages the pursuit of short-range metal atom array-based electrocatalysts for other electrocatalytic reactions

Electron Delocalization of Au Nanoclusters Triggered by Fe Single Atoms Boosts Alkaline Overall Water Splitting

The rational design and in-depth understanding of the structure–activity relationship (SAR) of hydrogen and oxygen evolution reaction (HER and OER) bifunctional electrocatalysts are vital to decreasing the energy consumption of hydrogen production by electrochemical water splitting. Herein, we report an inducing electron delocalization method where Fe single atoms as inducers are used to regulate the electron structure of Au nanoclusters by the M–Nx–C substrate to acquire satisfactory intrinsic HER activity. Meanwhile, Fe single atoms also serve as efficient OER active sites to construct bifunctional electrocatalysts. On account of the strong synergistic effect between Au nanoclusters and Fe single atoms, the hybrid catalyst Au-Fe1NC/NF performs an outstanding alkaline HER and OER activity. Only 35.6 mV, 246 mV, and 1.52 V are needed to reach 10 mA cm–2 for alkaline HER, OER, and two-electrode electrolytic cells, respectively. In addition, the bifunctional electrocatalysts also display excellent electrochemical stability. DFT calculations demonstrate that the strong synergistic effect can enhance the O–H bond activation ability of Au nanoclusters and upshift the d-band center of the Fe single atom to promote alkaline electrocatalytic water splitting. The strong synergistic effect is proven to arise from the electron delocalization of Au nanoclusters triggered by Fe single atoms

RuO₂–CeO₂ Lattice Matching Strategy Enables Robust Water Oxidation Electrocatalysis in Acidic Media via Two Distinct Oxygen Evolution Mechanisms

The discovery of acid-stable and highly active electrocatalysts for the oxygen evolution reaction (OER) is crucial in the quest for high-performance water-splitting technologies. Herein, a heterostructured RuO2–CeO2 electrocatalyst was constructed by using a lattice-matching strategy. The interfacial Ru–O–Ce bridge structure provided a channel for electron transfer between Ru and Ce, creating a lattice stress that distorts the local structure of RuO2. The resulting RuO2–CeO2 catalyst exhibited attractive stability with negligible decay after 1000 h of the OER in 0.5 M H2SO4, along with high activity with an overpotential of only 180 mV at 10 mA cm–2. In situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), in situ differential electrochemical mass spectrometry (DEMS), and density functional theory (DFT) calculations were used to reveal that the interface and noninterface RuO2 sites enabled an oxide path mechanism (OPM) and the enhanced adsorbate evolution mechanism (AEM-plus), respectively, during the OER. The simultaneous and independent OER pathways accessible by lattice matching guides improved electrocatalyst design for the OER in acidic media