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With the continuous advancements in electronics towards downsizing and integration, efficient thermal dissipation from chips has emerged as a critical factor affecting their lifespan and operational efficiency. The fan-less chip cooling system has two critical interfaces for thermal transport, which are the contact interface between the base and the chip dominated by thermal conduction, and the surface of the fins dominated by thermal radiation. The different thermal transfer modes of these two critical interfaces pose different requirements for thermal management materials. In the study, a novel approach was proposed by developing graphene thermal transport functional material whose morphology could be intentionally designed via reformed plasma-enhanced chemical vapor deposition (PECVD) methods to meet the diverse requirements of heat transfer properties. Specifically, graphene with multilevel branching structure of vertical graphene (BVG) was fabricated through the hydrogen-assisted PECVD (H2-PECVD) strategy, which contributed a high emissivity of ∼ 0.98. BVG was deposited on the fins' surface and functioned as the radiation enhanced layer to facilitate the rapid radiation of heat from the heat sinks into the surrounding air. Meanwhile, the well-oriented vertical graphene (OVG) was successfully prepared through the vertical electric field-assisted PECVD process (EF-PECVD), which showed a high directional thermal conductivity of ∼ 53.5 W·m−1·K−1. OVG was deposited on the contact interface and functioned as the thermal conduction enhanced layer, allowing for the quick transmission of heat from the chip to the heat sink. Utilizing this design concept, the two critical interfaces in the chip cooling system can be jointly enhanced, resulting in a remarkable cooling efficiency enhancement of ∼ 30.7%, demonstrating that this novel material possessed enormous potential for enhancing the performance of cooling systems. Therefore, this research not only provided new design concepts for the cooling system of electronic devices but also opened up new avenues for the application of graphene materials in thermal management. [ABSTRACT FROM AUTHOR]

S-scheme possesses superior redox capabilities compared with the II-scheme, providing an effective method to solve the innate defects of g-C3N4 (CN). In this study, S-doped g-C3N4/g-C3N4 (SCN-tm/CN) S-scheme homojunction was constructed by rationally integrating morphology control with interfacial engineering to enhance the photocatalytic hydrogen evolution performance. In-situ Kelvin probe force microscopy (KPFM) confirms the transport of photo-generated electrons from CN to SCN. Density functional theory (DFT) calculations reveal that the generation of a built-in electric field between SCN and CN enables the carrier separation to be more efficient and effective. Femtosecond transient absorption spectrum (fs-TAS) indicates prolonged lifetimes of SCN-tm/CN3 (τ1: 9.7, τ2: 110, and τ3: 1343.5 ps) in comparison to those of CN (τ1: 4.86, τ2: 55.2, and τ3: 927 ps), signifying that the construction of homojunction promotes the separation and transport of electron hole pairs, thus favoring the photocatalytic process. Under visible light irradiation, the optimized SCN-tm/CN3 exhibits excellent photocatalytic activity with the hydrogen evolution rate of 5407.3 µmol·g−1·h−1, which is 20.4 times higher than that of CN (265.7 µmol·g−1·h−1). Moreover, the homojunction also displays an apparent quantum efficiency of 26.8% at 435 nm as well as ultra-long and ultra-stable cycle ability. This work offers a new strategy to construct highly efficient photocatalysts based on the metal-free conjugated polymeric CN for realizing solar energy conversion. [ABSTRACT FROM AUTHOR]

The slot-die coating is recognized as the most compatible method for the roll-to-roll (R2R) processing of large-area flexible organic solar cells (OSCs). However, the photovoltaic performance of the large-area flexible all-polymer solar cells was significantly lagging behind that of polymer donors with small molecule non-fullerene acceptors devices. In this work, the 1 cm2 flexible device of an all-polymer system, PTQ10:PYF-T-o, fabricated by slot-die coating, achieves an excellent efficiency of 11.24% via controlling the coating temperatures. It is found that, compared with the donor, the crystallinity of PYF-T-o plays a crucial role in device performance. The all-polymer flexible devices show superior mechanical bending stability, maintaining an efficiency of over 95% of the initial value during a 1000-cycle bending test. [ABSTRACT FROM AUTHOR]

Microwave absorbing materials (MAMs) are playing an increasingly essential role in the development of wireless communications, high-power electronic devices, and advanced target detection technology. MAMs with a broad-bandwidth response are particularly important in the area of communication security, radiation prevention, electronic reliability, and military stealth. Although considerable progress has been made in the design and preparation of MAMs with a broad-bandwidth response, a number of challenges still remain, and the structure–function relationship of MAMs is still far from being completely understood. Herein, the advances in the design and research of MAMs with a broad-bandwidth response are outlined. The main strategies for expanding the effective absorption bandwidth of MAMs are comprehensively summarized considering three perspectives: the chemical combination strategy, morphological control strategy, and macrostructure control strategy. Several important results as well as design principles and absorption mechanisms are highlighted. A coherent explanation detailing the influence of the chemical composition and structure of various materials on the microwave absorption properties of MAMs is provided. The main challenges, new opportunities, and future perspectives in this promising field are also presented. [ABSTRACT FROM AUTHOR]

To achieve excellent electromagnetic wave (EMW) absorption properties, the microstructure design of the absorber is critical. In this work, six kinds of N-Ni/C nanostructures with different morphologies were prepared by one-step hydrothermal method and high temperature carbonization by adjusting the types of nickel salts and reaction solvents. The EMW absorption performance of six different morphologies of N-Ni/C nanostructures was compared and analyzed. Among them, it is found that the nanoflower-like N-Ni/C composite has excellent dielectric loss and magnetic loss synergistic effect due to its polycrystalline structure, and can obtain excellent EMW absorption performance. The minimum reflection loss value at a thickness of 1.9 mm is −59.56 dB at 16.88 GHz, and the effective absorption bandwidth value reaches 6.0 GHz at a thickness of 2.2 mm. Our research shows that different morphologies and multiple lattice structures of nanostructures with the same composition have a significant influence on EMW absorption performance, which provides new research ideas for developing high-performance EMW absorbing materials. [ABSTRACT FROM AUTHOR]

Lead-free bismuth-based halide perovskites and their analogues have attracted research interest for their high stability and optoelectronic properties. However, the morphology-controlled synthesis of bismuth-based perovskite nanocrystals has been rarely demonstrated. Herein, we report the colloidal synthesis of zero-dimensional (0D) Cs3BiCl6 nanosheets (NSs), Cs3Bi2Cl9 NSs/nanoplates (NPs) and Cs4MnBi2Cl12 NPs through a hot-injection method. We demonstrate that the Cs3BiCl6 NSs, as an initial product of Cs3Bi2Cl9 and Cs4MnBi2Cl12 NPs, can transform into Cs3Bi2Cl9 NSs or Cs4MnBi2Cl12 NPs via Cl-induced metal ion insertion reactions under the templating effect of Cs3BiCl6. This growth mechanism is also applicable for the synthesis of Cs4CdBi2Cl12 nanoplates. Furthermore, the alloying of Cd2+ into Cs4MnBi2Cl12 lattice could weaken the strong coupling effect between Mn and Mn, which leads to a prolonged photoluminescence lifetime and an enhanced photoluminescence quantum yield (PLQY). As a proof of concept, the alloyed Cs4MnxCd1−xBi2Cl12 NPs are used as a scintillator, which show a lowest detection limit of 134.5 nGy/s. The X-ray imaging results display a high spatial resolution of over 20 line pairs per millimeter (lp/mm). These results provide new insights in the synthesis of anisotropic bismuth-based perovskite nanocrystals and their applications in radiation detection. [ABSTRACT FROM AUTHOR]

The precise control of the crystal morphology of metal-organic frameworks (MOFs) enables optimization of its adsorptive properties, as well as enables better integration within functional devices. However, the influence of such modifications on the dynamic properties of flexible MOFs is poorly understood. Here, we report the synthesis of a series of Cu2(bdc)2(bpy) (bdc2− = 1,4-benzenedicarboxylate; bpy = 4,4′-bipyridine) crystals having an unusual picture frame-like morphology that results from a restriction in the quantity of bpy pillars added to the reaction mixture during the intercalation of the Cu2(bdc)2(MeOH)2 layers. The width of the frames is found to correlate with the quantity of bpy, and importantly, causes the dynamic properties of the resulting Cu2(bdc)2(bpy) material to vary between rigid, elastic, and shape memory modes. In all, the results demonstrate the potential for the properties of MOFs to be optimized via subtle manipulations in the crystal morphology rather than changes in the overall material composition. [ABSTRACT FROM AUTHOR]

Designing highly efficient and low-cost electrocatalysts for oxygen evolution reaction is important for many renewable energy applications. In particular, strain engineering has been demonstrated as a powerful strategy to enhance the electrochemical performance of catalysts; however, the required complex catalyst preparation process restricts the implementation of strain engineering. Herein, we report a simple self-template method to prepare hierarchical porous Co3O4 nanowires (PNWs) with tunable compressive strain via thermal-oxidation-transformation of easily prepared oxalic acid-cobalt nitrate (Co(NO3)2) composite nanowires. Based on the complementary theoretical and experimental studies, the selection of proper solvents in the catalyst preparation is not only vital for the hierarchical structural evolution of Co3O4 but also for regulating their compressive surface strain. Because of the rich surface active sites and optimized electronic Co d band centers, the PNWs exhibit the excellent activity and stability for oxygen evolution reaction, delivering a low overpotential of 319 mV at 10 mA·cm−2 in 1 M KOH with a mass loading 0.553 mg·cm−2, which is even better than the noble metal catalyst of RuO2. This work provides a cost-effective example of porous Co3O4 nanowire preparation as well as a promising method for modification of surface strain for the enhanced electrochemical performance. [ABSTRACT FROM AUTHOR]

We have sought to improve the electrocatalytic performance of tungsten nitride through synthetic control over chemical composition and morphology. In particular, we have generated a thermodynamically unstable but catalytically promising nitrogen-rich phase of tungsten via a hydrothermal generation of a tungsten oxide intermediate and subsequent annealing in ammonia. The net product consisted of three-dimensional (3D) micron-scale flower-like motifs of W2N3; this architecture not only evinced high structural stability but also incorporated the favorable properties of constituent two-dimensional nanosheets. From a performance perspective, as-prepared 3D W2N3 demonstrated promising hydrogen evolution reaction (HER) activities, especially in an acidic environment with a measured overpotential value of −101 mV at a current density of 10 mA/cm2. To further enhance the electrocatalytic activity, small amounts of precious metal nanoparticles (such as Pt and Au), consisting of variable sizes, were uniformly deposited onto the underlying 3D W2N3 motifs using a facile direct deposition method; these composites were applied towards the CO2 reduction reaction (CO2RR). A highlight of this series of experiments was that Au/W2N3 composites were found to be a much more active HER (as opposed to either a CO2RR or a methanol oxidation reaction (MOR)) catalyst. [ABSTRACT FROM AUTHOR]

The precise control of the crystal morphology of metal-organic frameworks (MOFs) enables optimization of its adsorptive properties, as well as enables better integration within functional devices. However, the influence of such modifications on the dynamic properties of flexible MOFs is poorly understood. Here, we report the synthesis of a series of Cu2(bdc)2(bpy) (bdc2− = 1,4-benzenedicarboxylate; bpy = 4,4′-bipyridine) crystals having an unusual picture frame-like morphology that results from a restriction in the quantity of bpy pillars added to the reaction mixture during the intercalation of the Cu2(bdc)2(MeOH)2 layers. The width of the frames is found to correlate with the quantity of bpy, and importantly, causes the dynamic properties of the resulting Cu2(bdc)2(bpy) material to vary between rigid, elastic, and shape memory modes. In all, the results demonstrate the potential for the properties of MOFs to be optimized via subtle manipulations in the crystal morphology rather than changes in the overall material composition. [ABSTRACT FROM AUTHOR]

Controlled synthesis of structurally anisotropic rhenium diselenide (ReSe2) with macroscopically uniform and strictly monolayer thickness as well as tunable domain shape/size is of great interest for electronics-, optoelectronics-, and electrocatalysis-related applications. Herein, we describe the controlled synthesis of uniform monolayer ReSe2 flakes with variable morphology (sunflower- or truncated-triangle-shaped) on SiO2/Si substrates using different ambient-pressure chemical vapor deposition (CVD) setups. The prepared polycrystalline ReSe2 flakes were transferred intact onto Au foil electrodes and tested for activity in the hydrogen evolution reaction (HER). Interestingly, compared to the compact truncated-triangle-shaped ReSe2 flakes, their edge-abundant sunflower-shaped counterparts exhibited superior electrocatalytic HER activity, featuring a relatively low Tafel slope of ∼76 mV/dec and an exchange current density of 10.5 μA/cm2. Thus, our work demonstrates that CVD-grown ReSe2 is a promising two-dimensional anisotropic material for applications in the electrocatalytic HER. [ABSTRACT FROM AUTHOR]

Bimetallic PtCu nanocrystals (NCs) with well-defined hexa-pod morphology were synthesized via a wet chemistry approach. The as-synthesized convex NCs with dimensions of around 20 nm show exposed low-index (111) facets on the seeds and various high-index facets on the pods. The growth mechanism involved preferred growth along the <100> crystallographic direction on cuboctahedral seeds. The synthetic protocol could be applied to the synthesis of PtCu NCs with various Cu/Pt ratios. The electro-catalytic activity of the hexa-pod PtxCuy NCs supported on carbon black towards the oxygen reduction reaction (ORR) was studied. The hexa-pod PtCu/C catalysts exhibit the highest specific activity (3.7 mA/cm) and mass activity (2.4 A/mg) reported to date for PtCu. Comparison with other morphological forms of PtCu indicated that the enhanced activity originated from morphological factors. The existence of high-index facets as well as abundant edges and steps on the pods could reasonably explain the enhanced catalytic activity. The hexa-pod PtCu/C catalysts also show high morphological stability and activity after accelerated durability tests. The as-synthesized hexa-pod PtCu NCs have high potential as cathode electro-catalysts for proton exchange membrane fuel cells. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

series of unique nanowire superstructures, Cu2O nanowire polyhedra, have been synthesized through a cost-effective hydrothermal route. Three types of nanowire polyhedra, namely octahedra, concave octahedra, and hexapods, were formed in high morphological yields (90%) by reducing cupric acetate with o-anisidine or o-phenetidine in the presence of carboxylic acids. The architectures of these CuO nanowire polyhedra were examined by electron microscopy, which revealed ordered, highly aligned CuO nanowires within the polyhedral outlines. The growth of the CuO nanowire polyhedra is controlled by the orientation and growth rates of the nanowire branches which are adjusted by addition of carboxylic acids. Compared to the CuO samples reported in the recent literature, the CuO nanowire octahedra exhibit notably enhanced photocatalytic activities for dye degradation in the presence of HO under visible light, probably due to the high-density charge carriers photoexcited from the branched nanowires with their special structures. Additionally, the discussion in the recent literature of the photocatalytic activity of CuO in the absence of HO for direct photodegradation of dyes seems questionable. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]