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1. chinaXiv:201803.01543 [pdf]

Ultrafine nickel nanoparticles modified reduced graphene oxide as efficient non-platinum catalysts for methanol oxidation

Hongmei Sun; Jun Liu; Zhenfei Tian; Yixing Ye; Changhao Liang
分类: 物理学 >> 交叉学科物理及相关领域的科学与技术

Synthesis of low-cost, highly-active and durable non-platinum metal catalysts for methanol oxidation reaction (MOR) is always full of challenge. Here, Ni nanoparticles modified reduced graphene oxide (Ni/rGO) as an efficient non-platinum catalyst were synthesized by laser ablation of Ni target in graphene oxide (GO) solution and the following in situ reduction process. It found that GO played an important role to restrict the growth and aggregation of ultrafine nickel colloids (< 5 nm) in the process of laser ablation. The resulting Ni/rGO catalyst showed advantageous in active sites and charge transport resulting from the small particle size, uniform dispersion and electronic effect arising from the electron interactions between reduced graphene oxide (rGO) and Ni. The obtained Ni/rGO exhibited the ultrahigh catalytic mass activity of 1600 mA/mg, methanol saturation concentration (4 M), which was superior to that of the reported Ni-based catalysts. Remarkably the mass activities of Ni/rGO before and after 1000 cycles exceed that of the commercial Pt/C catalyst, indicating excellent catalytic activity and stability.

提交时间: 2018-03-30 点击量862下载量334 评论 0

2. chinaXiv:201803.01544 [pdf]

Ni3+ doped cobalt-¬¬nickel layered double hydroxides as high performance electrode material for supercapacitors

Hongmei Sun; Yixing Ye; Zhenfei Tian; Shouliang Wu; Jun Liu
分类: 物理学 >> 交叉学科物理及相关领域的科学与技术

Co-Ni layered double hydroxides (LDHs), as promising supercapacitor electrode materials with high specific capacity, have suffered poor rate property and cycle stability. By doping and topochemical oxidation of Ni ions is considered as efficivent rout to overcome these drawbacks. In this work, Ni3+ doped cobalt-nickel layered double hydroxides (Co-Ni-LDHs) were synthesized by pluse laser ablation of Ni taget in CoCl2 aqeous solution. The existence of Ni3+ ions doped in Co-Ni-LDHs decline the conductive resistance, and increase the mobility of surface charge and transfer rate of electrolyte. As a results, the Ni3+ doped Co-Ni-LDHs display a maximum specific capacitance of 2275 F/g and 1450 F/g at the current density of 1 A/g and 20 A/g, respectivly, indicating a high rate specific capacitance. Moreover, the capacitance retention is to be 80% after 1800 cycles at the current density of 6 A/g, manifesting good cycling stability of Ni3+ doped Co-Ni-LDHs.

提交时间: 2018-03-30 点击量818下载量343 评论 0

3. chinaXiv:201803.01545 [pdf]

Site-specifically Immobilize Pt Nanocrystals on NiFe Layered Double Hydroxide: Old Catalysts with Enhanced Stability Through strong Fe3+-O(H)-Pt Interfacial Contact

Yechuang Han; Pengfei Li; Jun Liu; Shouliang Wu ; Yixing Ye; Zhenfei Tian; Changhao Liang
分类: 物理学 >> 交叉学科物理及相关领域的科学与技术

Agglomeration-triggered deactivation of supported platinum electrocatalysts markedly hinders their application in methanol oxidation reaction (MOR). In this study, graphene-supported nickel–iron layered double hydroxide (NiFe–LDH/rGO), in which Fe3+ was introduced to replace Ni2+ partially in the Ni(OH)2 lattice to provide stronger metal–support bonding sites, was utilized to immobilize Pt nanoparticles (NPs). Given the optimized metal–support interfacial contact (Fe3+–O(H)–Pt) between Pt NPs and NiFe–LDH/rGO nanosheets for Pt/NiFe–LDH/rGO electrocatalysts, the Pt/NiFe–LDH/rGO electrocatalysts displayed dramatically enhanced durability than that of Pt/Ni(OH)2/rGO counterpart as well as commercial Pt/C, and 86.5% of its initial catalytic activity can be maintained even after 1200 cycles of cyclic voltammetry (CV) tests during MOR. First-principle calculations toward the resultant M–O(H)–Pt (M = Fe3+, Ni2+) interfacial structure further corroborates that the NiFe–LDH nanosheets can provide stronger bonding sites (via the Fe3+–O(H)–Pt bonds) to immobilize Pt NPs than those of Ni(OH)2 nanosheets (via the Ni2+–O(H)–Pt bonds).

提交时间: 2018-03-30 点击量846下载量316 评论 0

4. chinaXiv:201803.01547 [pdf]

Thermoelectric performance for SnSe hot-pressed at different temperature

D. Li; J. C. Li; X. Y. Qin; J. Zhang; C. J. Song; L. Wang; H. X. Xin
分类: 物理学 >> 交叉学科物理及相关领域的科学与技术

Herein, nanoparticles SnSe are prepared by fusion method together with ball-milling technique and the effect of hot-pressing temperatures on the thermoelectric properties of the dense materials is explored. Due to the optimization of carrier concentration, the peak figure of merit (ZT) value of the compacted material reaches 0.73 for SnSe sample hot-pressed at 400°C and 450°C. The present investigation indicates that the thermoelectric performance of the SnSe compound can be significantly improved by sintering with suitable temperature.

提交时间: 2018-03-30 点击量801下载量296 评论 0

5. chinaXiv:201803.01548 [pdf]

Optimized thermoelectric properties of AgSbTe2 through adjustment of fabrication parameters

Jian Zhang; Xiaoying Qin; Di Li; Chunjun Song; Yongfei Liu; Hongxing Xin; Tianhua Zou; Yuanyue Li
分类: 物理学 >> 交叉学科物理及相关领域的科学与技术

AgSbTe2 bulk sample is obtained by hot-pressing under different fabrication parameters, and their thermoelectric properties are investigated in the temperature range of 300-550K. The highest ZT=0.86 is achieved at 475K for the sample hot-pressed at 423K and 500MPa due to the lower thermal conductivity and higher power factor. The results indicate that the optimized thermoelectric properties can be obtained for AgSbTe2 compound at the sintering temperature of 423K under the pressure of 500MPa.

提交时间: 2018-03-30 点击量748下载量315 评论 0

6. chinaXiv:201803.01549 [pdf]

Enhanced thermoelectric performance of SnSe based composites with carbon black nanoinclusions

J. C. Li; D. Li; X. Y. Qin; Y. Y. Li; J. Zhang
分类: 物理学 >> 交叉学科物理及相关领域的科学与技术

Recently, single crystalline SnSe and its sodium doped compound were reported to have an ultralow thermal conductivity and high thermoelectric figure of merit. However, the highest high thermoelectric figure of merit for polycrystalline SnSe-based materials is not larger than unity. In this study, we report a high thermoelectric figure of merit 1.21 at 903K along the hot pressing direction for polycrystalline SnSe, realized by incorporating a proper proportion of carbon black as nano-inclusions. The exceptional performance arises from the ultra-high power factor, which comes from a high electrical conductivity and an enhanced Seebeck coefficient through energy-dependent scattering.

提交时间: 2018-03-30 点击量789下载量321 评论 0

7. chinaXiv:201803.01550 [pdf]

Enhanced thermoelectric performance of CuGaTe2 by Gd-doping and Te incorporation

Jian Zhang; Xiaoying Qin; Di Li; Chunjun Song; Xiaoguang Zhu; Yongfei Liu; Hongxing Xin; Li Chen; Tianhua Zou
分类: 物理学 >> 交叉学科物理及相关领域的科学与技术

Gd-doped compounds CuGa1-xGdxTe2 (0x0.02) incorporated with tellurium nanoparticles are synthesized by fusion method. Their thermoelectric properties are investigated in the temperature range of 300-800K. The results indicate that the synergistic effect of Gd-doping and Te incorporation remarkably enhances the thermoelectric performance of CuGaTe2. Specially, the thermal conductivity  of the specimen CuGa0.98Gd0.02Te2/0.7vol.%Te reduces to 0.45 Wm-1K-1 at 684K, which is ~74% smaller than that of pure CuGaTe2 (=1.76 Wm-1K-1 at 684K) due to the incorporation of nanostructure Te. The thermoelectric figure of merit value (ZT) reaches 0.75 at 737K for the specimen CuGa0.99Gd0.01Te2/0.7vol.%Te, which is ~115% larger than that of pure CuGaTe2.

提交时间: 2018-03-30 点击量714下载量317 评论 0

8. chinaXiv:201803.01551 [pdf]

Enhanced thermoelectric performance of CuGaTe2 based composites incorporated with graphite nanosheets

Jian Zhang; Xiaoying Qin; Di Li; Yongfei Liu; Yuanyue Li; Chunjun Song; Hongxing Xin; Xiaoguang Zhu
分类: 物理学 >> 交叉学科物理及相关领域的科学与技术

CuGaTe2 based composites incorporated with graphite nanosheets(GNs) CuGaTe2/x G (G=GNs, 0x3.04 vol.%) were prepared, and the thermoelectric properties of the composites were studied from 300 to 875 K. The results show that the incorporation of GNs into the CuGaTe2 matrix can enhance the Seebeck coefficient and power factor over the whole temperature range investigated due to energy filtering effects, and the reduction of thermal conductivity below 750K owing to interface scattering. Although the resistivity increases, energy filtering significantly raises the Seebeck component, and the overall effect on power factor is positive. The sample with 2.28 vol.% GNs had the largest ZT value, reaching 0.93 at 873K, which is a ~21% improvement on pure CuGaTe2.

提交时间: 2018-03-30 点击量661下载量266 评论 0

9. chinaXiv:201803.01552 [pdf]

Fe-N-doped mesoporous carbon loaded on reduced graphene oxides with dual active sites for efficient oxygen reduction catalysts

Chao Zhang; Jun Liu; Zabeada Aslam; Rik Drummond-Brydson; Changhao Liang
分类: 物理学 >> 交叉学科物理及相关领域的科学与技术

Transition metal/nitrogen/carbon (M-N/C) catalysts are considered as one of the most promising candidates to replace Pt/C catalysts for oxygen reduction reactions (ORR). Here, we have designed novel reduced graphene oxides (rGO) supported Fe-N-doped carbon (Fe-N-C/rGO) catalysts via simple pyrolysis of polypyrrole(Ppy)-FeO-GO composites. The as-prepared catalysts induced an onset potential of 0.94 V, a half-wave potential of 0.81 V in alkaline solutions, which is much better than that of the counterpart N-C and N-C/rGO catalysts, and comparable to that of Pt/C catalysts. Moreover, the Fe-N-C/rGO catalysts showed improved durability and higher tolerance against methanol crossover than Pt/C in alkaline solutions. This superior ORR perfomance can be ascribed to the combined catalytic effect of both Fe-based nanoparticles (Fe3O4, Fe4C) and Fe-Nx sites, as well as fast mass transfer and accessible active sites benefitting from the mesporous structure and high specific surface area. This work provides new insight for synthesis of a more promising non-platinum electrocatalyst for metal-air batteries and fuel-cell applications.

提交时间: 2018-03-30 点击量661下载量283 评论 0

10. chinaXiv:201702.00158 [pdf]

毫米波检波二极管特性与检波原理

徐伟业
分类: 物理学 >> 交叉学科物理及相关领域的科学与技术

毫米波检波二极管是用于回旋管功率实时监测的重要器件,本文对二极管特性进行了讨论。通过对二极管特性的分析,给出了二极管模型参数的简易获得方法,极大的方便了二极管测试,并可以通过测试的结果建立二极管等效电路模型,以便进行检波器的设计。本文利用泰勒展开分析了二极管小信号检波原理,利用二极管折线模型分析了二极管大信号检波原理;并从二极管电流电压特性方程出发,推导了小信号和大信号检波原理。本文系统地分析了二极管检波原理,提出了二极管模型参数提取方法,为检波电路的设计提供了依据。

提交时间: 2017-02-16 点击量1535下载量842 评论 0

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