Metastable 1T'-phase transition metal dichalcogenides (1T'-TMDs) with semi-metallic natures have attracted increasing interest owing to their uniquely distorted structures and fascinating ...phase-dependent physicochemical properties. However, the synthesis of high-quality metastable 1T'-TMD crystals, especially for the group VIB TMDs, remains a challenge. Here, we report a general synthetic method for the large-scale preparation of metastable 1T'-phase group VIB TMDs, including WS
, WSe
, MoS
, MoSe
, WS
Se
and MoS
Se
. We solve the crystal structures of 1T'-WS
, -WSe
, -MoS
and -MoSe
with single-crystal X-ray diffraction. The as-prepared 1T'-WS
exhibits thickness-dependent intrinsic superconductivity, showing critical transition temperatures of 8.6 K for the thickness of 90.1 nm and 5.7 K for the single layer, which we attribute to the high intrinsic carrier concentration and the semi-metallic nature of 1T'-WS
. This synthesis method will allow a more systematic investigation of the intrinsic properties of metastable TMDs.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
Layered materials have garnered immense interest due to their unique electronic, mechanical, thermal, and optoelectronic properties. In these materials, atomically thin layers are held together by ...van der Waals (vdW) interactions, allowing single layers to be isolated and studied as 2D materials. New theoretical insights as well as novel experimental techniques have empowered recent developments in both thermoelectric physics and performance of 2D materials. In this Review, some of the key ideas are surveyed and open questions are discussed, laying out a vision for original discoveries in this still‐emerging field of applied physics. Here, graphene, transition metal dichalcogenides, black phosphorus, topological insulators as well as intercalated compounds are in focus. With these materials as a platform, how band structure, hydrodynamics, metal–insulator transitions, anisotropy, and surface states affect phonons and electrons and manifest in their thermoelectric properties is analyzed.
Thermoelectricity is a phenomenon that allows for the conversion between heat and electrical energy. In the past decade, two‐dimensional materials have emerged that provide a unique playground to explore both new physics and functionality. Here, the progress and ideas that will continue to push this field forward toward discoveries in the near future are reviewed.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Black phosphorus attracts enormous attention as a promising layered material for electronic, optoelectronic and thermoelectric applications. Here we report large anisotropy in in-plane thermal ...conductivity of single-crystal black phosphorus nanoribbons along the zigzag and armchair lattice directions at variable temperatures. Thermal conductivity measurements were carried out under the condition of steady-state longitudinal heat flow using suspended-pad micro-devices. We discovered increasing thermal conductivity anisotropy, up to a factor of two, with temperatures above 100 K. A size effect in thermal conductivity was also observed in which thinner nanoribbons show lower thermal conductivity. Analysed with the relaxation time approximation model using phonon dispersions obtained based on density function perturbation theory, the high anisotropy is attributed mainly to direction-dependent phonon dispersion and partially to phonon-phonon scattering. Our results revealing the intrinsic, orientation-dependent thermal conductivity of black phosphorus are useful for designing devices, as well as understanding fundamental physical properties of layered materials.
It is reported that electron doped n‐type SnSe2 nanoplates show promising thermoelectric performance at medium temperatures. After simultaneous introduction of Se deficiency and Cl doping, the Fermi ...level of SnSe2 shifts toward the conduction band, resulting in two orders of magnitude increase in carrier concentration and a transition to degenerate transport behavior. In addition, all‐scale hierarchical phonon scattering centers, such as point defects, nanograin boundaries, stacking faults, and the layered nanostructures, cooperate to produce very low lattice thermal conductivity. As a result, an enhanced in‐plane thermoelectric figure of merit ZTmax of 0.63 is achieved for a 1.5 at% Cl doped SnSe1.95 pellet at 673 K, which is much higher than the corresponding in‐plane ZT of pure SnSe2 (0.08).
A novel ecofriendly n‐type SnSe2 oriented‐nanoplate‐based thermoelectric material is demonstrated. A high power factor is achieved through defect chemistry and a low thermal conductivity is achieved by all‐scale hierarchical phonon scattering. Taken together, an enhanced in‐plane thermoelectric figure of merit ZTmax of 0.63 is achieved for a 1.5 at% Cl doped SnSe1.95 pellet at 673 K.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Polymers are widely used in daily life, but exhibit low strength and low thermal conductivity as compared to most structural materials. In this work, we develop crystalline polymer nanofibers that ...exhibit a superb combination of ultra-high strength (11 GPa) and thermal conductivity, exceeding any existing soft materials. Specifically, we demonstrate unique low-dimensionality phonon physics for thermal transport in the nanofibers by measuring their thermal conductivity in a broad temperature range from 20 to 320 K, where the thermal conductivity increases with increasing temperature following an unusual ~T
trend below 100 K and eventually peaks around 130-150 K reaching a metal-like value of 90 W m
K
, and then decays as 1/T. The polymer nanofibers are purely electrically insulating and bio-compatible. Combined with their remarkable lightweight-thermal-mechanical concurrent functionality, unique applications in electronics and biology emerge.
Recent progress in the currently available methods of producing black phosphorus bulk and phosphorene are presented. The effective passivation approaches toward improving the air stability of ...phosphorene are also discussed. Furthermore, the research efforts on the phosphorene and phosphorene‐based materials for potential applications in lithium ion batteries, sodium ion batteries, and thermoelectric devices are summarized and highlighted. Finally, the outlook including challenges and opportunities in these research fields are discussed.
Phosphorene and phosphorene‐based materials receive extensive attention for potential applications in energy storage and conversion devices. In this Review, the state‐of‐the‐art progress of phosphorene and phosphorene‐based materials for lithium ion batteries, sodium ion batteries, thermoelectric devices, and other energy storage devices are presented.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Developing low‐cost and efficient oxygen evolution electrocatalysts is key to decarbonization. A facile, surfactant‐free, and gram‐level biomass‐assisted fast heating and cooling synthesis method is ...reported for synthesizing a series of carbon‐encapsulated dense and uniform FeNi nanoalloys with a single‐phase face‐centered‐cubic solid‐solution crystalline structure and an average particle size of sub‐5 nm. This method also enables precise control of both size and composition. Electrochemical measurements show that among FexNi(1−x) nanoalloys, Fe0.5Ni0.5 has the best performance. Density functional theory calculations support the experimental findings and reveal that the optimally positioned d‐band center of O‐covered Fe0.5Ni0.5 renders a half‐filled antibonding state, resulting in moderate binding energies of key reaction intermediates. By increasing the total metal content from 25 to 60 wt%, the 60% Fe0.5Ni0.5/40% C shows an extraordinarily low overpotential of 219 mV at 10 mA cm−2 with a small Tafel slope of 23.2 mV dec−1 for the oxygen evolution reaction, which are much lower than most other FeNi‐based electrocatalysts and even the state‐of‐the‐art RuO2. It also shows robust durability in an alkaline environment for at least 50 h. The gram‐level fast heating and cooling synthesis method is extendable to a wide range of binary, ternary, quaternary nanoalloys, as well as quinary and denary high‐entropy‐alloy nanoparticles.
A facile, surfactant‐free, and gram‐level synthesis method is reported for synthesizing a wide range of nanoalloys. The relationships between the composition of FexNi(1−x) nanoalloy, its electronic structure, and the oxygen evolution reaction (OER) activity are studied and analyzed. By optimizing the composition and mass loading, FeNi nanoalloy shows an excellent OER activity, which outperforms the state‐of‐the‐art RuO2.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract
Bayesian optimization (BO) has been leveraged for guiding autonomous and high-throughput experiments in materials science. However, few have evaluated the efficiency of BO across a broad ...range of experimental materials domains. In this work, we quantify the performance of BO with a collection of surrogate model and acquisition function pairs across five diverse experimental materials systems. By defining acceleration and enhancement metrics for materials optimization objectives, we find that surrogate models such as Gaussian Process (GP) with anisotropic kernels and Random Forest (RF) have comparable performance in BO, and both outperform the commonly used GP with isotropic kernels. GP with anisotropic kernels has demonstrated the most robustness, yet RF is a close alternative and warrants more consideration because it is free from distribution assumptions, has smaller time complexity, and requires less effort in initial hyperparameter selection. We also raise awareness about the benefits of using GP with anisotropic kernels in future materials optimization campaigns.
Active heat flow control is essential for broad applications of heating, cooling, and energy conversion. Like electronic devices developed for the control of electric power, it is very desirable to ...develop advanced all-thermal solid-state devices that actively control heat flow without consuming other forms of energy. Here we demonstrate temperature-gated thermal rectification using vanadium dioxide beams in which the environmental temperature actively modulates asymmetric heat flow. In this three terminal device, there are two switchable states, which can be regulated by global heating. In the “Rectifier” state, we observe up to 28% thermal rectification. In the “Resistor” state, the thermal rectification is significantly suppressed (<1%). To the best of our knowledge, this is the first demonstration of solid-state active-thermal devices with a large rectification in the Rectifier state. This temperature-gated rectifier can have substantial implications ranging from autonomous thermal management of heating and cooling systems to efficient thermal energy conversion and storage.
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IJS, KILJ, NUK, PNG, UL, UM
Abstract
In materials science, the discovery of recipes that yield nanomaterials with defined optical properties is costly and time-consuming. In this study, we present a two-step framework for a ...machine learning-driven high-throughput microfluidic platform to rapidly produce silver nanoparticles with the desired absorbance spectrum. Combining a Gaussian process-based Bayesian optimization (BO) with a deep neural network (DNN), the algorithmic framework is able to converge towards the target spectrum after sampling 120 conditions. Once the dataset is large enough to train the DNN with sufficient accuracy in the region of the target spectrum, the DNN is used to predict the colour palette accessible with the reaction synthesis. While remaining interpretable by humans, the proposed framework efficiently optimizes the nanomaterial synthesis and can extract fundamental knowledge of the relationship between chemical composition and optical properties, such as the role of each reactant on the shape and amplitude of the absorbance spectrum.
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