Triazole‐phosphine‐copper complexes (TAP−Cu) have been synthesized and applied as tunable and efficient catalysts for the selective synthesis of fluoro‐substituted 2‐aryl‐1H‐benzodimidazole and ...1‐benzyl‐2‐aryl‐1H‐benzodimidazole derivatives from simple alcohols in only one step. TAP−Cu exhibited excellent and tunable catalytic activity for both dehydrogenation and borrowing hydrogen reactions with more than 80 examples being demonstrated for the first time. It was observed that the ligand played a critical role in catalyst activity. Mechanistic studies and deuterium labeling experiments indicated that the reactions proceeded by an initial and reversible alcohol dehydrogenation resulting in a copper hydride intermediate. This was also supported by the direct observation of a diagnostic copper hydride signal by solid‐state infrared spectroscopy. The TAP−Cu‐H complex showed absorptions at 912 cm−1 that could be assigned to copper−hydride stretches. Furthermore, the direct trapping of an intermediate bisimine was also successfully performed.
SnSe is challenging to use in thermoelectric devices due to difficulties in simultaneously optimizing its thermoelectric and mechanical properties. Here, the authors show a unique solvothermal ...synthetic environmental design to fabricate super‐large and micro/nanoporous Sn0.965Se microplates by using CrCl3. Cl− ions to trigger Sn‐vacancy formation and optimize the hole concentration to ≈3 × 1019 cm−3, while the as‐formed Cr(OH)3 colloidal precipitations act as “templates” to achieve micro/nanoporous features, leading to low lattice thermal conductivity of ≈0.2 W m−1 K−1 in the as‐sintered polycrystal, contributing to a high ZT of ≈2.4 at 823 K and an average ZT of ≈1.1. Of particular note, the polycrystal exhibits high hardness (≈2.26 GPa) and compression strength (≈109 MPa), strengthened by grain refinement and vacancy‐induced lattice distortions and dislocations; while a single‐leg device provides a stable output power (>100 mW) and conversion efficiency of ≈10% by a temperature difference of 425 K, indicating great potential for applying to practical thermoelectric devices.
A solvothermal synthetic environmental design to fabricate super‐large and micro/nanoporous Sn0.965Se microplates using CrCl3 is employed, and the mechanically robust polycrystals sintered from these microplates exhibit a high ZT of ≈2.4 at 823 K and an average ZT of ≈1.1, leading to a conversion efficiency of ≈10% by a temperature difference of 425 K in the single‐leg device.
Owing to high intrinsic figure‐of‐merit implemented by multi‐band valleytronics, GeTe‐based thermoelectric materials are promising for medium‐temperature applications. Transition metals are widely ...used as dopants for developing high‐performance GeTe thermoelectric materials. Herein, relevant work is critically reviewed to establish a correlation among transition metal doping, electronic quality factor, and figure‐of‐merit of GeTe. From first‐principle calculations, it is found that Ta, as an undiscovered dopant in GeTe, can effectively converge energy offset between light and heavy conduction band extrema to enhance effective mass at high temperature. Such manipulation is verified by the increased Seebeck coefficient of synthesized Ge1−x−yTaxSbyTe samples from 160 to 180 µV K−1 at 775 K upon doping Ta, then to 220 µV K−1 with further alloying Sb. Characterization using electron microscopy also reveals the unique herringbone structure associated with multi‐scale lattice defects induced by Ta doping, which greatly hinder phonon propagation to decrease thermal conductivity. As a result, a figure‐of‐merit of ≈2.0 is attained in the Ge0.88Ta0.02Sb0.10Te sample, reflecting a maximum heat‐to‐electricity efficiency up to 17.7% under a temperature gradient of 400 K. The rationalized beneficial effects stemming from Ta doping is an important observation that will stimulate new exploration toward high‐performance GeTe‐based thermoelectric materials.
The nexus between electronic quality factor and thermoelectric figure‐of‐merit in transition‐metal‐doped GeTe, which can serve as a facile yet efficient descriptor for high‐throughput screening of good thermoelectric materials, is explained. To clarify this point, Ta‐doped GeTe is designed with optimized electronic quality factor, rendering a figure‐of‐merit over 2.0 and a conceptional efficiency over 15%.
Owing to the moderate energy offset between light and heavy band edges of the rock‐salt structured GeTe, its figure‐of‐merit (ZT) can be enhanced by the rational manipulation of electronic band ...structures. In this study, density functional theory calculations are implemented to predict that V is an effective dopant for GeTe to enlarge the bandgap and converge the energy offset, which suppresses the bipolar conduction and increases the effective mass. Experimentally, V‐doped Ge1−xVxTe samples are demonstrated to have an enhanced Seebeck coefficient from ≈163 to ≈191 µV K−1. Extra alloying with Bi in Ge1−x−yVxBiyTe can optimize the carrier concentration to further enhance the Seebeck coefficient up to ≈252 µV K−1, plus an outstanding power factor of ≈43 µW cm−1 K−2. Comprehensive structural characterization results also verify the refinement of grain size by V‐doping, associated with highly dense grain boundaries, stacking faults, nanoprecipitates, and point defects, reinforcing the wide‐frequency phonon scattering and in turn, securing an ultralow thermal conductivity of ≈0.59 W m−1 K−1. As a result, the Ge0.9V0.02Bi0.08Te sample shows a peak ZT of >2.1 at 773 K, with an average plateaued average ZT of >2.0 from 623 and 773 K, which extends better thermoelectric behavior for GeTe over a wider temperature range. This study clarifies the multiple benefits of V‐doping in GeTe‐based derivatives and provides a framework for a new‐type of high‐performance middle‐temperature thermoelectric material.
The versatile benefits of Vanadium‐doping in a GeTe matrix are revealed, such as modulating the crystal symmetry, grain refining and band structure engineering, which enhance the power factor and suppress the thermal conductivity. With further Bi doping to tune carrier concentration, a high figure‐of‐merit of >2.1 is achieved in Ge0.9V0.02Bi0.08Te.
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•Facilely realizing the boost of interfacial carrier transports.•Effectively coating Bi0.5Sb1.5Te3 fillers with highly conductive CuTe layer.•Achieving highly crystallized PEDOT:PSS ...as the matrix.•Producing promising σ of ~2300 S cm−1 and peak S2σ of 312 µW m−1 K−2 at room temperature.•Generating promising open-circuit thermovoltage of ~7.7 mV with human wrist as the thermal source.
Incorporating inorganic thermoelectric fillers into conductive polymers is one promising strategy to develop high-performance flexible thermoelectric films. However, due to the relatively high interfacial contact resistance between fillers and polymers, carriers tend to be scattered at the interfaces during the interfacial transports, which deteriorates the electrical properties of the system, and in turn leads to low energy conversion efficiency. Here, a new strategy is developed to optimize interfacial carrier transports in Bi0.5Sb1.5Te3/PEDOT:PSS composite, by coating Bi0.5Sb1.5Te3 fillers with highly conductive CuTe layer. With highly crystallized PEDOT:PSS prepared as the matrix, high-performance Cu-Bi0.5Sb1.5Te3 /PEDOT:PSS film is fabricated with promising σ of ~2300 S cm−1 and peak S2σ of 312 µW m−1 K−2 at room temperature, which reaches to a record-high value in the reported Bi0.5Sb1.5Te3/PEDOT:PSS composites. Accordingly, a home-made flexible thermoelectric device is fabricated using our prepared composites, generating a promising open-circuit thermovoltage of ~7.7 mV with the human wrist as the thermal source. This study addresses the significance of interfacial carrier transport, hinting the bright prospects of cheap conductive polymers as the effective power source of wearable electronics.
Mn alloying in thermoelectrics is a long‐standing strategy for enhancing their figure‐of‐merit through optimizing electronic transport properties by band convergence, valley perturbation, or ...spin‐orbital coupling. By contrast, mechanisms by which Mn contributes to suppressing thermal transports, namely thermal conductivity, is still ambiguous. A few precedent studies indicate that Mn introduces a series of hierarchical defects from the nano‐ to meso‐scale, leading to effective phonon scattering scoping a wide frequency spectrum. Due to insufficient insights at the atomic level, the theory remains as phenomenological and cannot be used to quantitatively predict the thermal conductivity of Mn‐alloyed thermoelectrics. Herein, by choosing the SnTe as a case study, aberration‐corrected transmission electron microscopy (TEM)/scanning transmission electron microscopy (STEM) to characterize the lattice complexity of Sn1.02−xMnxTe is employed. Mn as a “dynamic” dopant that plays an important role in SnTe with respect to different alloying levels or post treatments is revealed. The results indicate that Mn precipitates at x = 0.08 prior to reaching solubility (≈10 mol%), and then splits into MnSn substitution and γ‐MnTe hetero‐phases via mechanical alloying. Understanding such unique crystallography evolution, combined with a modified Debye‐Callaway model, is critical in explaining the decreased thermal conductivity of Sn1.02−xMnxTe with rational phonon scattering pathways, which should be applicable for other thermoelectric systems.
Structural evolution induced by Mn alloying is comprehensively investigated in thermoelectric materials, selecting SnTe as a case study. Comprehensive electron microscopy investigations indicate that, through rational structural manipulation, multiscale crystal imperfections are introduced as phonon scattering sources and in turn renders a high thermoelectric performance.
Although they offer great potentials, the high reactivity and diverse pathways of radical chemistry pose difficult problems for applications in organic synthesis. In addition to the differentiation ...of multiple competing pathways, the control of various selectivities in radical reactions presents both formidable challenges and great opportunities. To regulate chemoselectivity and regioselectivity, as well as diastereoselectivity and enantioselectivity, calls for the formulation of conceptually new approaches and fundamentally different governing principles. Here we show that Co(II)-based metalloradical catalysis enables the radical chemoselective intermolecular amination of allylic C-H bonds through the employment of modularly designed D
-symmetric chiral amidoporphyrins with a tunable pocket-like environment as the supporting ligand. The reaction exhibits a remarkable convergence of regioselectivity, diastereoselectivity and enantioselectivity in a single catalytic operation. In addition to demonstrating the unique opportunities of metalloradical catalysis in controlling homolytic radical reactions, the Co(II)-catalysed convergent C-H amination offers a route to synthesize valuable chiral α-tertiary amines directly from an isomeric mixture of alkenes.
Cationic doping is mainly used to improve the performance of rocksalt‐structured GeTe thermoelectric materials. However, its counterpart anionic doping is scarcely facilitated. Here, a comprehensive ...discussion is provided on doping at the anion site of rocksalt‐structured thermoelectric materials, surrounding its influence on bonding mechanisms, carrier and phonon transport characteristics, and thermoelectric figure‐of‐merit. To verify the viewpoint, a modified flux‐assist method is adopted to synthesize anionic Iodine (I) doped GeTe samples, which show comparably optimized electrical and thermal properties with that of cationic Antimony (Sb) or Bismuth (Bi) doped GeTe samples. Further combining cationic Bi and anionic I co‐doping, an enhanced figure‐of‐merit from 0.8 in pristine GeTe to 2.5 at 675 K can be realized in 8% (Bi and I) co‐doped GeTe, which corresponds to a maximum heat‐to‐electricity conversion efficiency of 14.6% under a temperature difference of 430 K. This study rationalizes the influence of anionic doping on the electrical and thermal properties of the rocksalt‐structured materials, which serves as an effective yet previously neglected strategy toward high‐performance GeTe thermoelectrics.
This study rationalizes the anionic doping effect in rocksalt‐structured thermoelectric materials, which can be an effective yet large neglected strategy towards high‐performance GeTe thermoelectrics with a figure‐of‐merit of 2.5 and a promising conversion efficiency of 11.6%.
In this work, a LaB6‐alloying strategy is reported to effectively boost the figure‐of‐merit (ZT) of Ge0.92Bi0.08Te‐based alloys up to ≈2.2 at 723 K, attributed to a synergy of La‐dopant induced band ...structuring and structural manipulation. Density‐function‐theory calculations reveal that La dopant enlarges the bandgap and converges the energy offset between the sub‐valence bands in cubic‐structured GeTe, leading to a significantly increased effective mass, which gives rise to a high Seebeck coefficient of ≈263 µV K−1 and in turn a superior power factor of ≈43 µW cm−1 K−2 at 723 K. Besides, comprehensive electron microscopy characterizations reveal that the multi‐scale phonon scattering centers, including a high density of planar defects, Boron nanoparticles in tandem with enhanced boundaries, dispersive Ge nanoprecipitates in the matrix, and massive point defects, contribute to a low lattice thermal conductivity of ≈0.67 W m−1 K−1 at 723 K. Furthermore, a high microhardness of ≈194 Hv is witnessed in the as‐designed Ge0.92Bi0.08Te(LaB6)0.04 alloy, derived from the multi‐defect‐induced strengthening. This work provides a strategy for developing high‐performance and mechanical robust middle‐temperature thermoelectric materials for practical thermoelectric applications.
The LaB6‐alloying strategy is demonstrated to enhance ZT of GeTe‐based alloys up to ≈2.2 at 723 K owing to rational band structuring and structural manipulation. The dissolving of LaB6 leads to multiscale crystal imperfections, contributing to the low lattice conductivity and the high hardness.
Rock-salt structured GeTe has been reckoned as a promising medium temperature thermoelectric material due to its decent thermal conductivity and multiple electronic valence bands that can be easily ...modified. However, the applications of GeTe-based thermoelectric materials are strongly impeded by their excessive hole concentration and detrimental phase transition, which deteriorates both thermoelectric performance and mechanical robustness. In this study, we simultaneously solve these two issues by co-doping Ti and Sb in GeTe, achieving an ultrahigh figure-of-merit (ZT) of ~2.2 at 725 K with an average ZT over 2.0 plateauing from 625 to 755 K. Our X-ray spectroscopy analysis and electron microscopy investigation, coupled with first-principle calculation, attribute the extraordinary thermoelectric performance of Ge1-x-yTixSbyTe to the synergetic effects of: a) resonant bonding properties induced by symmetrized crystal lattice; b) high Seebeck coefficient and quality factor due to enhanced band degeneracy and effective mass; c) optimized hole concentration by the aliovalent TiGe and SbGe substitution; and d) minimized thermal conductivity due to the evident frequency-selective phonon scattering by diverse types of defects. Our study indicates that manipulating structure and bonding properties by crystal symmetry modification can explore new-type and high-performance thermoelectric candidates in GeTe and its derivatives, as well as other phase-transition materials.
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•Comprehensive synthesis, characterization and modelling for Ti and Sb co-doped GeTe.•Lattice symmetrisation optimizes charge and phonon transport properties in GeTe.•Significant thermoelectric figure-of-merit and efficiency in Ge1-x-yTixSbyTe.•The thermoelectric properties of Ge1-x-yTixSbyTe is rationalized by rigorous first-principle calculation.
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