Large-area reduced graphene oxide thin film with excellent thermal conductivity and electromagnetic interference shielding effectiveness

In this work, we fabricated reduced large-area graphene oxide (rLGO) with maximum surface area of 1592 μm² through a cost-effective chemical reduction process at low temperature. The product revealed large electrical conductivity of 243 ± 12 S cm⁻¹ and thermal conductivity of 1390 ± 65 W m⁻¹ K⁻¹, values much superior to those of a conventional reduced small-area graphene oxide (with electrical conductivity of 152 ± 7.5 S cm⁻¹ and thermal conductivity of 900 ± 45 W m⁻¹ K⁻¹). The rLGO thin film also exhibited not only excellent stiffness and flexibility with Young’s modulus of 6.3 GPa and tensile strength of 77.7 MPa, but also an efficient electromagnetic interference (EMI) shielding effectiveness of ∼20 dB at 1 GHz. The excellent performance of rLGO is attributed to the fact that the larger area LGO sheets include much fewer defects that are mostly caused by the damage of graphene sp² structure around edge boundaries, resulting in large electrical conductivity. The manufacturing process of rLGO is an economical and facile approach for the large scale production of highly thermally conducting graphene thin films with efficient EMI shielding properties, greatly desirable for future portable electronic devices.     

Synthesis,densification and oxidation study of lanthanum hexaboride

This paper presents the result of investigation carried out on the synthesis, densification and oxidation studies of LaB₆. LaB₆ was synthesized by boron carbide reduction of La₂O₃. Effect of temperature on product quality was investigated. Pure LaB₆ powder was obtained at 1500 °C, in vacuum. Pressureless sintering at 1950 °C of LaB₆ powder resulted in a density of only 85.1% of the theoretical value. Hot pressing resulted in near theoretical density at the same operating temperature. Hardness and fracture toughness of the dense LaB₆ was measured as 20 GPa and 3.02 MPa m^1/2 respectively. Oxidation study by thermogravimetry revealed that oxidation starts slowly at 500 °C and accelerates at 700 °C. Isothermal oxidation study revealed that protective oxide layer forms on LaB₆ surface on oxidation at 900 °C. The presence of protective continuous oxide layer on the surface was observed even after 64 h exposure in air atmosphere.     

Flexible and thermally stable SiC fiber mats derived from electrospun boron-doped polyaluminocarbosilane precursors

Polymer-derived SiC fibers are critical structural and functional materials for high-temperature applications, whose service performance can be further improved by introduction of certain heterogeneous elements. Herein, flexible and thermal stable SiC fiber mats were prepared from boron-doped polyaluminocarbosilane (PACS) precursor by electro-spinning, curing and pyrolysis. Two boron-containing compounds o-carborane (oCB) and phenylboronic acid (PBA) were used as the boron sources and their effects on the properties and structure of the SiC fiber mats were investigated. The introduced oCB and PBA had obviously improved the ceramic yield of the cured fiber mats and the flexibility of the SiC fiber mats. However, PBA introduced more boron, but also more oxygen, which leaded to formation of more amorphous SiC_xO_y phases. Although only a small amount of boron was introduced by oCB, a more significant improvement in the thermal stability of the SiC fiber mat was obtained. This work provided a practical approach for fabrication of flexible and thermally stable SiC fiber mats.     

Optimization of dielectric phenomenon in 0.8[(1-x)SrCoO2.29 + xCr2FeO4] + 0.2PZT tri-phase composites

Composite materials are emerging and have potential to revolutionize the modern technology. In this work, a series of tri-phase composite materials having the chemical formula; 0.8[(1-x) SrCoO_2.29+xCr₂FeO₄] + 0.2PZT, is synthesized to explore their energy storage capability. In this series, SrCoO_2.29 and Cr₂FeO₄ ceramics are synthesized by using a sol-gel auto-combustion process while PZT is prepared by the solid-state method. The XRD analysis confirmed the formation of cubic crystal structure of the SrCoO_2.29 and Cr₂FeO₄ and the rhombohedral phase of PZT. The SEM images exhibited an increase in average grain size with the incorporation and increasing contents of Cr₂FeO₄. The presence of all constituting elements with the exact stoichiometric ratio is validated through EDX analysis. Wide-range frequency-dependent dielectric behavior showed a dramatic fall in dielectric constant with increasing frequency. A same frequency dependent behaviour of ε'' and tanδ is witnessed as that of ε'. The investigation of electric modulus reveals that in the low-frequency region it possesses a trivial value which became significantly large with the increase of frequency. The presence of a relaxation peak in the plot of the imaginary part of the electric modulus plays a decisive role to distinguish the small and large range hopping mechanism. The complex impedance analysis revealed different electroactivity of composite material in the different frequency domains which made them viable for advanced energy storage devices working in the vast frequency range.     

Hydrogen storage and mobility determined by NMR to various organically functionalized porous silica synthetized by using the post-grafting method

The results of this study will help in guiding the future design of low-cost and highly performing functionalized mesoporous silica using cationic surfactants as directing agents. Indeed, by properly tuning surface interactions and the textural characteristics, the overall efficiency of H₂ capture processes could be improved. Among different synthetized samples, the experimental results show the better interaction with (3-Aminopropyl)triethoxysilane precursor. Furthermore, an NMR investigation aiming at clarifying the internal arrangement and diffusion properties of hydrogen molecules inside functionalized porous silica materials has been performed. The NMR spectral analysis and the T₁ relaxation times indicated two different “populations” for H₂ sorbate due to the molecules adsorbed in mesopores and in micropores. For the first time, the H₂ self-diffusion coefficient in functionalized silica has been experimentally measured by pulsed field gradient NMR. The spin-echo decay revealed two different diffusion mechanisms coexist in the functionalized mesoporous silica, except for the material functionalized with iodopropyl groups, which shows a single diffusion coefficient.     

Electrocatalyst of RuO2 decorating TiO2 nanowire arrays for acidic oxygen evolution

Oxygen evolution reaction (OER) at the anode limits the efficiency of hydrogen production from water electrolysis substantially. A novel electrocatalyst of RuO₂ decorating TiO₂ nanowire arrays for OER was successfully prepared using a cyclic voltammetric method with electrodeposition of RuO₂ nanoparticles on the TiO₂ nanowire (TNW) arrays synthesized hydrothermally. Even though the electrodes with the composite electrocatalyst have a lower loading of RuO₂, they have higher electrocatalytic activity and stability for acidic oxygen evolution than the Ti/RuO₂ electrode prepared by conventional thermal decomposition method. The core-shell structure of the TNW@RuO₂ electrocatalyst not only increases the specific surface area of the electrodes, but also inhibits the adverse effect of the poor conductivity of TiO₂. This novel OER electrocatalyst can improve the efficiency and reduce the cost of hydrogen production from electrolytic water splitting.     

Electronic Interpretation of Interlayer Energy Landscape in Layered Materials

The interlayer energy landscape of layered materials is essential to disassemble their structure–property relationships. However, a clear definition of interlayer electronic coupling that generally rules the interlayer energy landscape for their outstanding electronic and tribological properties, remains a matter of debate. Herein, diverse methods for electron coupling are evaluated to discriminate their feasibility to interpret interlayer sliding energy landscape for frictional sliding or stacking faults, by using density functional theory calculation of the layered models in the case of transition metal dichalcogenides (TMDs). It is discovered that the charge density evolution in dynamic stacking configurations dictates the interlayer energy landscape along the sliding pathway, challenging the prevailing belief that the energy corrugation arises from the nonuniform distribution of charge density or the charge density in the interface region. The present studies may open the way to disassemble the electron coupling principle underlying interlayer energy landscape for structure–property relationships as stacking faults, registry effects, even superlubric behavior in layered structures.     

Engineering Structural Janus MXene-nanofibrils Aerogels for Season-Adaptive Radiative Thermal Regulation

Aerogels have provided a significant platform for passive radiation-enabled thermal regulation, arousing extensive interest due to their capabilities of radiative cooling or heating. However, there still remains challenge of developing functionally integrated aerogels for sustainable thermal regulation in both hot and cold environment. Here, Janus structured MXene-nanofibrils aerogel (JMNA) is rationally designed via a facile and efficient way. The achieved aerogel presents the characteristic of high porosity (≈98.2%), good mechanical strength (tensile stress of ≈2 MPa, compressive stress of ≈115 kPa), and macroscopic shaping property. Based on the asymmetric structure, the JMNA with switchable functional layers can alternatively enable passive radiative heating and cooling in winter and summer, respectively. As a proof of concept, JMNA can function as a switchable thermal-regulated roof to effectively enable the inner house model to maintain >25 °C in winter and <30 °C in hot summer. This design of Janus structured aerogels with compatible and expandable capabilities is promising to widely benefit the low-energy thermal regulation in changeable climate.     

Microstructure evolution and bonding mechanisms of silica sol bonded coating at elevated temperatures

High emissivity coating plays a critical role in thermal protective system, which can radiate a large amount of aero-convective heat. Silica sol bonded MoSi₂-SiC-Al₂O₃ (S-MSA) coating was proved to be promising for mullite fibrous insulation. However, the bonding mechanisms of the coating at elevated temperatures are not clear. In this work, the S-MSA coatings were heat-treated at temperatures from 600 °C to 1500 °C to reveal the bonding mechanisms at elevated temperatures. The S-MSA coatings go through a relatively stable stage (600 °C–1000 °C), a crystallization stage (1100 °C–1200 °C), and a densification stage (1300 °C–1500 °C) at ever increasing temperatures. Results show that both the contact damage resistance and the bonding strength of the calcined coatings exhibit a decrease followed by an increase at elevated calcination temperatures, with the inflection point at 1200 °C, corresponding to the transition temperature of the bonding mechanisms from 600 °C to 1500 °C.