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- 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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| 2. |
- 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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| 4. |
- Gao, Chuansi, et al.
(författare)
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Clothing Insulation Required for Energy Efficiency (IREQee) and Thermal Comfort
- 2016
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Ingår i: Proceedings of the 11th International Meeting on Thermal Manikin and Modeling(11i3m). - 9789887766209 ; , s. 28-29
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Konferensbidrag (refereegranskat)abstract
- Thermal comfort has direction implications for energy efficiency and sustainable development. From a global perspective, about 40% of total primary energy is used in buildings, contributing to more than 30% of CO2 emissions [1]. The fact that the common practices of clothing choices have impact on energy efficiency is ignored [2-3]. This paper analyzed and proposed clothing insulation required for energy efficiency (IREQee) in order to increase indoor temperature interval and energy efficiency. In many heated/air-conditioned indoor environments, it is not unusual that occupants wear T-shirts/suits. The basic clothing insulation of these clothing ensembles is estimated to be about 0.5/1.0 clo [4]. The benefit of adding/reducing clothing insulation in heated/cooled environments, e.g. change clothing between 1.2 and 0.4 clo, is that the temperature of the whole room or building can be changed by 5.1 °C (between 20.4 and 25.5 °C) while still maintaining thermal comfort (Fig. 1) calculated according to international standard [5] and related web based tool [6], given that other parameters are the same (metabolic rate M=70 W/m2, relative humidity=50%, mean radiant temperature=air temperature, mechanic work=0, relative air velocity (m/s)=0.0052*(M-58)). As a result, the energy for heating/cooling the indoor environment is saved. The saved energy is about 10% for each degree Celsius decrease or increase in heated or air-conditioned indoor air temperature [7]. Hence, informed occupant’s clothing behavior change based on IREQee can extend the interval of comfort temperature, e.g. from 18.6 to 26.1 °C (rather than a fixed set point at 22 or 23 °C) for office work in heated and air-conditioned environments. The analysis indicates that the proposed IREQee in relation to physical work intensity can function as a low cost measure to maintain thermal comfort, save energy, and enhance sustainable development. Figure 1. Required clothing insulation for energy efficiency (IREQee) and comfortable temperature in heated or air-conditioned indoor environments in relation to physical work intensity (metabolic rate: M=70 and 100 W/m2 corresponding to office work and low physical intensity work).
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| 7. |
- Gao, Chuansi, et al.
(författare)
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Personal cooling with phase change materials to improve thermal comfort from a heat wave perspective
- 2012
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Ingår i: Indoor Air. - : Hindawi Limited. - 0905-6947. ; 22:6, s. 523-530
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedAbstract The impact of heat waves arising from climate change on human health is predicted to be profound. It is important to be prepared with various preventive measures for such impacts on society. The objective of this study was to investigate whether personal cooling with phase change materials (PCM) could improve thermal comfort in simulated office work at 34°C. Cooling vests with PCM were measured on a thermal manikin before studies on human subjects. Eight male subjects participated in the study in a climatic chamber (T(a) = 34°C, RH = 60%, and ν(a) = 0.4 m/s). Results showed that the cooling effect on the manikin torso was 29.1 W/m(2) in the isothermal condition. The results on the manikin using a constant heating power mode reflect directly the local cooling effect on subjects. The results on the subjects showed that the torso skin temperature decreased by about 2-3°C and remained at 33.3°C. Both whole body and torso thermal sensations were improved. The findings indicate that the personal cooling with PCM can be used as an option to improve thermal comfort for office workers without air conditioning and may be used for vulnerable groups, such as elderly people, when confronted with heat waves. PRACTICAL IMPLICATIONS: Wearable personal cooling integrated with phase change materials has the advantage of cooling human body's micro-environment in contrast to stationary personalized cooling and entire room or building cooling, thus providing greater mobility and helping to save energy. In places where air conditioning is not usually used, this personal cooling method can be used as a preventive measure when confronted with heat waves for office workers, vulnerable populations such as the elderly and disabled people, people with chronic diseases, and for use at home.
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