No abstract

No abstract

Hydrogen is believed to be one of the essential clean secondary energy sources in the energy structure revolution of both industry and daily life. Driven by renewable electricity such as solar and wind power, water electrolysis for hydrogen production is deemed as one of the main processes of green hydrogen production in the future by both academia and industry. Transition metal chalcogenides (TMCs) are promising candidates to replace noble metals as earth-abundant electrocatalysts for water splitting. However, it remains challenging to further improve the electrocatalytic activity and long-term stability of TMCs, especially in a practical water electrolyzer. This Review summarizes the recent advances and the strategies of optimizing the electrocatalytic activities of TMCs toward water splitting as well as the latest investigations on the surface reconstructions of TMCs during water electrolysis. The performances of TMCs in practical electrocatalytic water splitting cells are particularly discussed. Finally, a concluding remark and perspective is provided, and we hope to inspire future works in this area, narrowing the gap between material design and practical application.

Realizing high average thermoelectric figure of merit (ZTave) and power factor (PFave) has been the utmost task in thermoelectrics. Here the new strategy to independently improve constituent factors in ZT is reported, giving exceptionally high ZTave and PFave in n‐type PbSe. The nonstoichiometric, alloyed composition and resulting defect structures in new Pb1+xSe0.8Te0.2 (x = 0–0.125) system is key to this achievement. First, incorporating excess Pb unusually increases carrier mobility (µH) and concentration (nH) simultaneously in contrast to the general physics rule, thereby raising electrical conductivity (σ). Second, modifying charge scattering mechanism by the authors’ synthesis process boosts a magnitude of Seebeck coefficient (S) above theoretical expectations. Detouring the innate inverse proportionality between nH and µH; and σ and S enables independent control over them and change the typical trend of PF to temperature, giving remarkably high PFave ≈20 µW cm−1 K−2 from 300 to 823 K. The dual incorporation of Te and excess Pb generates unusual antisite Pb at the anionic site and displaced Pb from the ideal position, consequently suppressing lattice thermal conductivity. The best composition exhibits a ZTave of ≈1.2 from 400 to 823 K, one of the highest reported for all n‐type PbQ (Q = chalcogens) materials.

No abstract

Phase-change materials (PCMs) for efficient thermal energy harvesting has promising prospects for thermal energy storage and thermal management. However, the low intrinsic thermal conductivity (TC) of PCMs is a long-standing...

Highly oriented graphite-based composites have attracted great attention because of their high thermal conductivity (TC), but the low mechanical properties caused by the inhomogeneous distribution and discontinuity of reinforcements restrict the wide applications. Herein, continuous SiC ceramic skeleton reinforced highly oriented graphite flake (SiC/GF) composites were successfully prepared by combining vacuum filtration and spark plasma sintering. The effect of SiC concentration on the microstructure, flexural strength, and thermophysical properties of the composites was investigated. The GF grains in the composites exhibited high orientation with a Lotgering factor of > 88% when the SiC concentration was ⩽ 30 wt%, and the SiC skeleton became continuous with the SiC concentration reaching 20 wt%. The formation of continuous SiC skeleton improved the flexural strength of the composites effectively while keeping the TC in a high level. Especially, the composites with 30 wt% SiC exhibited the flexural strength up to 105 MPa, and the specific TC reaching 0.118 W·m2·K−1·kg·1. The composites with excellent flexural strength and thermophysical properties showed significant promise for thermal management applications.

Graphical Abstract:Highlight: Novel blue-emitting (SiC) x -(AlN) 1-x :yEu 2+ phosphors were synthesized by nitriding combustion reaction, and their luminescence properties, thermal stability and possible doping site of Eu 2+ in (SiC) x -(AlN) 1-x lattice were investigated. AbstractNovel blue-emitting phosphors with the chemical composition of (SiC) x -(AlN) 1-x :yEu 2+ (x=0.06-0.50, y=0.001-0.01) were synthesized by a nitriding combustion reaction route, and the crystal structure, luminescence properties and thermal stability of the (SiC) x -(AlN) 1-x :yEu 2+ phosphors were investigated by theoretical and experimental approaches. Fist-principles calculation results prove that the solid solution of SiC with AlN promotes the doping of Eu 2+ ions into the (SiC) x -(AlN) 1-x host lattice, and Eu 2+ ions tend to occupy Al sites of the host. The synthesized (SiC) x -(AlN) 1-x :yEu 2+ phosphors absorb light in the region of 250-425 nm and show a single and symmetric broadband emission centered at about 470 nm due to the 4f 6 5d-4f 7 transitions of Eu 2+ . The luminescence intensity increases with the SiC content and reaches its maximum at x=0.20. The critical quenching concentration of Eu 2+ in the (SiC) 0.20 -(AlN) 0.80 :yEu 2+ phosphor is about y=0.006. The composition-optimized (SiC) 0.20 -2 (AlN) 0.80 :0.006Eu 2+ phosphor shows a small thermal quenching, retaining the luminance of 91.1% at 150 °C. The CIE coordinates were measured as (0.135, 0.167) with high color purity.The above results indicate that (SiC) x -(AlN) 1-x :yEu 2+ is a promising candidate as a blue-emitting ultraviolet convertible phosphor for white LEDs, and the combustion reaction route is expected to be applicable to synthesis of the present and other kinds of nitride phosphors. IntroductionWhite light emitting diodes (LEDs) have attracted increasing attention as a promising light source for solid state lighting due to their long lifetime, high luminous efficiency, energy saving, and environmental friendly characteristics. 1-3 Typically, commercial white LEDs can be generated by the combination of a blue LED chip and the famous yellow phosphor, YAG:Ce 3+ . 4 However, the disadvantages of this method are a low color-rendering index (CRI) and high correlated color temperature (CCT) due to red emission deficiency in the visible spectrum.During the last several years, white LEDs fabricated by using ultraviolet (UV)/near-ultraviolet (n-UV) chips coupled with blue, green and red phosphors have attracted much attention because of the advantageous of color stability and excellent color rending. 5-7 Therefore, the exploration of novel phosphors with strong absorption, desirable emission/excitation, and high efficiency under UV/n-UV excitation plays an important role in the development of white LEDs.Furthermore, low fabrication cost, low thermal quenching as well as high chemical stability are also required for the phosphors.As a highly efficient activator with allowed 4f-5d transitions, Eu 2+ ion has been widely investigated for the rare-earth-doped phos...