| 1. |
- Kotmool, Komsilp, et al.
(författare)
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Revealing an unusual transparent phase of superhard iron tetraboride under high pressure
- 2014
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 111:48, s. 17050-17053
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Tidskriftsartikel (refereegranskat)abstract
- First principles-based electronic structure calculations of super-hard iron tetraboride (FeB4) under high pressure have been undertaken in this study. Starting with a "conventional" superconducting phase of this material under high pressure leads to an unexpected phase transition toward a semiconducting one. This transition occurred at 53.7 GPa, and this pressure acts as a demarcation between two distinct crystal symmetries, metallic orthorhombic and semiconducting tetragonal phases, with Pnnm and I4(1)/acd space groups, respectively. In this work, the electron-phonon coupling-derived superconducting T-c has been determined up to 60 GPa and along with optical band gap variation with increasing pressure up to 300 GPa. The dynamic stability has been confirmed by phonon dispersion calculations throughout this study.
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| 2. |
- Tang, Hu, et al.
(författare)
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Boron-Rich Molybdenum Boride with Unusual Short-Range Vacancy Ordering, Anisotropic Hardness, and Superconductivity
- 2020
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Ingår i: Chemistry of Materials. - : AMER CHEMICAL SOC. - 0897-4756 .- 1520-5002. ; 32:1, s. 459-467
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Tidskriftsartikel (refereegranskat)abstract
- Determination of the structures of materials involving more light elements such as boron-rich compounds is challenging and technically important in understanding their varied compositions and superior functionalities. Here we resolve the long-standing uncertainties in structure and composition about the highest boride (termed MoB4, Mo1-xB3, or MoB3) through the rapid formation of large sized boron-rich molybdenum boride under pressure. Using high-quality single-crystal X-ray diffraction analysis and aberration-corrected scanning transmission electron microscopy, we reveal that boron-rich molybdenum boride with a composition of Mo0.757B3 exhibits P6(3)/mmc symmetry with a partial occupancy of 0.514 in 211 Mo sites (Mol), and direct observations reveal the short-range ordering of cation vacancies in (010) crystal planes. Large anisotropic Young's moduli and Vickers hardness are seen for Mo0.757B3, which may be attributed by its two-dimensional boron distributions. Mo0.757B3 is also found to be superconducting with a transition temperature (T-c) of 2.4 K, which was confirmed by measurements of resistivity and magnetic susceptibility. Theoretical calculations suggest that the partial occupancy of Mo atoms plays a crucial role in the emergence of superconductivity.
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| 3. |
- Tian, Ruifeng, et al.
(författare)
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Pressure-promoted highly-ordered Fe-doped-Ni2B for effective oxygen evolution reaction and overall water splitting
- 2021
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 9:10, s. 6469-6475
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Tidskriftsartikel (refereegranskat)abstract
- Accurate doping at special atomic sites can achieve effective control of active centers for the oxygen evolution reaction (OER), leading to the synthesis of active intermediates with higher conversion efficiency. Here we report the successful doping of Ni2B with Fe/Co to form highly ordered FeNiB and CoNiB electrocatalysts with a tetragonal Ni2B structure. A highly crystalline FeNiB electrode is found to have a very low polarization overpotential of 257 mV for the OER and a water splitting potential of 1.54 V at a current density of 10 mA cm(-2). XRD refinement, XPS and XAFS characterization found that doping with iron leads to the weakening of the bond strength of TM-B, which facilitates the adsorption of oxygen. During the OER process, the increasing dissolution of boron oxides promotes the effective exposure of metal active centers and boosts the catalytic performance. Theoretical calculations reveal that the substitution of Fe atoms in Ni2B make its DOS near the Fermi level higher by 2.78 times compared to that of the original Ni2B, which helps to increase the electronic conductivity and the catalytic performance.
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| 4. |
- Zhao, Shijing, et al.
(författare)
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Elucidating the reaction pathway of crystalline multi-metal borides for highly efficient oxygen-evolving electrocatalysts
- 2022
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Ingår i: Journal of Materials Chemistry A. - : ROYAL SOC CHEMISTRY. - 2050-7488 .- 2050-7496. ; 10:3, s. 1569-1578
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the fundamental principle of catalytic performance and the mechanism of multimetal-based electrocatalysts is essential for the rational design of advanced renewable energy systems. Here, highly crystalline MMMoB4 (M = Fe, Co) compounds with controllable compositions of multiple active metal atoms and polyacene-type boron networks were synthesized delicately by a one-step high-pressure technique to explore electrocatalytic selectivity and activity. CoFeMoB4 and Co2MoB4 are revealed to be highly active and durable oxygen evolution reaction (OER) electrocatalysts under alkaline conditions. The mutually promotive activation of metals with amorphous clusters and ultra-small grains on the surface are responsible for the enhanced activity of CoFeMoB4. More specifically, Co and Fe coupling in CoFeMoB4 facilitates surface reconstruction into active Co hydroxide and Fe oxyhydroxide, in contrast to Co oxyhydroxide in Co2MoB4 and Fe oxides in Fe2MoB4. Dissolving Mo may provide potential space for adsorbing hydroxyl, and the optimized electronic structure with boron is mainly responsible for the long-term durability. In contrast, Mo atoms are responsible for hydrogen evolution reaction (HER) properties, and the optimized d-band center and density of states at the Fermi level make Co2MoB4 a superior HER catalyst. Our findings provide insight into distinguishing the catalytic pathway of multi-metal borides with improved OER activity and different roles of Mo and Co/Fe in the HER and OER.
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