氧电催化一般涉及到氧还原反应(ORR)和氧析出应(OER),是诸如燃料电池,金属空气电池和水电解池等能源转换与存储技术的关键步骤.其中,可充电的金属锌空气电池具有较高的能量密度,开发成本较低,运行安全且环境友好.然而,开发并采用高效,...氧电催化一般涉及到氧还原反应(ORR)和氧析出应(OER),是诸如燃料电池,金属空气电池和水电解池等能源转换与存储技术的关键步骤.其中,可充电的金属锌空气电池具有较高的能量密度,开发成本较低,运行安全且环境友好.然而,开发并采用高效,低成本且储量丰富的催化材料代替贵金属基电催化剂,仍旧是现阶段尚未完全解决的问题和挑战.最近,金属有机框架(MOFs)以及碳基的金属有机框架衍生物作为高效电催化剂,因其超乎寻常的形貌,结构,组分和功能性的可调节能力,已经逐渐引起了广泛的关注和研究兴趣.因此,本文报道了一种泡沫镍负载的二维金属有机框架及其衍生物耦合阵列作为无粘结剂型ORR/OER双效催化剂,能够实现高比表面积,高电导率和高双功能性,同时避免了使用有机粘结剂的复杂制备过程和不可避免的电池性能影响.与传统设计不同,本文主要通过集成各司其职的不同功能组分并充分暴露电化学活性面积来提高双效电极的整体活性.电化学测试结果表明,耦合阵列电极(R-NCM)相比于MOFs阵列(NCM)和MOFs衍生物阵列(A-NCM)等对比电极,具有显著提高的双效氧电极性能,氧还原反应的起峰电位约为0.90 V,而氧析出反应电流密度达到100 m Acm-2时的过电势为319 m V.由于其在生长–热裂解–再生长过程中所具有的稳定的站立多级二维纳米片结构,所制备的双效氧电极材料表现出显著增强的双官能团性,电化学活性面积,反应动力学和稳定性,并可进一步用于可充电的金属锌空气电池(ZABs).考虑到制备过程的可行性与简洁性,所提出的生长–热裂解–再生长策略不仅能够用于耦合型分级纳米片阵列结构的合成,还能为设计开发相关能源电化学装置的高活性电极结构提供借鉴.展开更多
In this research,a detailed multi-physics study has been carried out by numerically simulating a solid fractured gun barrel for 20 thermo-mechanical cycles.The numerical model is based on thermal effects,mechanical st...In this research,a detailed multi-physics study has been carried out by numerically simulating a solid fractured gun barrel for 20 thermo-mechanical cycles.The numerical model is based on thermal effects,mechanical stress fields and fatigue crack mechanics.Elastic-plastic material data of modified AISI 4340 at temperatures ranging from 25 to 1200℃and at strain rates of 4,16,32 and 48 s^(-1) was acquired from high-temperature compression tests.This was used as material property data in the simulation model.The boundary conditions applied are kept similar to the working gun barrel during continuous firing.A methodology has been provided to define thermo-mechanically active surface-to-surface type interface between the crack faces for a better approximation of stresses at the crack tip.Comparison of results from non-autofrettaged and autofrettaged simulation models provide useful information about the evolution of strains and stresses in the barrel at different points under combined thermo-mechanical loading cycles in both cases.The effect of thermal fatigue under already induced compressive yield due to autofrettage and the progressive degradation of the accumulated stresses due to thermo-mechanical cyclic loads on the internal surface of the gun barrel(mimicking the continuous firing scenario)has been analyzed.Comparison between energy release rate at tips of varying crack lengths due to cyclic thermo-mechanical loading in the non-autofrettaged and autofrettaged gun has been carried out.展开更多
Row spacing has a pivotal role in enhancing sugarcane yield and improving its quality. A study was undertaken to evaluate the influence of different planting techniques on performance of sugarcane at Agronomic Researc...Row spacing has a pivotal role in enhancing sugarcane yield and improving its quality. A study was undertaken to evaluate the influence of different planting techniques on performance of sugarcane at Agronomic Research Area, Department of Agronomy, University of Agriculture Faisalabad during Kharif 2014. Experimental treatments comprised of: 180 cm spaced trenches with tripple row strips, 180 cm spaced trenches with alternate row strips, 120 cm spaced trenches with double row strips and 60 cm spaced furrows with single rows. Sugarcane cultivar HSF-240 was used as experimental material. The experimental was conducted in RCBD with four replications. The expeimental results revealed that sugarcane number of tillers, plant height, cane length, stripped cane weight and stripped cane yield increased progressively with the increase in row spacing from 60 to 180 cm. While germination percentage and number of millable canes were not affected by different sowing techniques, maximum number of tillers (15.96 m-2), plant height (333.25 cm), stripped cane weight (0.94 kg) and stripped cane yield (107 t·ha-1) were recorded from 180 cm spaced trenches with tripple row strips.展开更多
Being a typical state of the art heterogeneous catalyst,supported noble metal catalyst often demonstrates enhanced catalytic properties.However,a facile synthetic method for realizing large-scale and low-cost supporte...Being a typical state of the art heterogeneous catalyst,supported noble metal catalyst often demonstrates enhanced catalytic properties.However,a facile synthetic method for realizing large-scale and low-cost supported noble metal catalyst is strictly indispensable.To this end,by making use of the strong metal-support interaction(SMSI)and mechanochemical reaction,we introduce an efficient synthetic route to obtain ultrafine Pt and Ir nanoclusters immobilized on diverse substrates by wet chemical milling.We further demonstrate the scaling-up effect of our approach by large-scale ball-milling production of Pt nanoclusters immobilized on TiO_(2)substrate.The synthesized Pt/Ir@Co_(3)O_(4)catalysts exhibit superior oxygen evolution reaction(OER)performance with only 230 and 290 mV overpotential to achieve current density of 10 and 100 mA·cm^(-2),beating the catalytic performance of Co_(3)O_(4)supported Pt or Ir clusters and commercial Ir/C.It is envisioned that the present work strategically directs facile ways for fabricating supported noble metal heterogeneous catalysts.展开更多
Large-area, pinhole-free, and ultrathin polymer membranes with thicknesses of only a few nanometers have attracted increasing attention for their applications in molecular separation, flexible optoelectronics, and sen...Large-area, pinhole-free, and ultrathin polymer membranes with thicknesses of only a few nanometers have attracted increasing attention for their applications in molecular separation, flexible optoelectronics, and sensors. They can potentially be developed for surface protection as well. In this study, we report an effective way to obtain large-scale polymer coatings with a thickness down to 10 nm, which effectively protects metals from corrosion. We develop a facile and scalable method to fabricate freestanding polymer membranes with thickness below 10 nm by dropping the precursor polymer solution on a water surface. By optimizing the surface tension of the polymer solution, the solution could spontaneously spread on the water surface to form a continuous and uniform solid membrane, collected as a freestanding thin membrane. The obtained polymer membranes could then easily be transferred on a metal substrate as highly flexible and stable anti-corrosion coatings. Electrochemical measurements performed in a 0.1 M Na2SO4 solution demonstrated the excellent anti-corrosion properties of the sub-10 nrn polymer membranes whose corrosion rate was less than 1% of the corrosion rate of the bare metal. We also demonstrate that the polymer membrane exhibits high performance as a protection layer for flexible circuits.展开更多
文摘氧电催化一般涉及到氧还原反应(ORR)和氧析出应(OER),是诸如燃料电池,金属空气电池和水电解池等能源转换与存储技术的关键步骤.其中,可充电的金属锌空气电池具有较高的能量密度,开发成本较低,运行安全且环境友好.然而,开发并采用高效,低成本且储量丰富的催化材料代替贵金属基电催化剂,仍旧是现阶段尚未完全解决的问题和挑战.最近,金属有机框架(MOFs)以及碳基的金属有机框架衍生物作为高效电催化剂,因其超乎寻常的形貌,结构,组分和功能性的可调节能力,已经逐渐引起了广泛的关注和研究兴趣.因此,本文报道了一种泡沫镍负载的二维金属有机框架及其衍生物耦合阵列作为无粘结剂型ORR/OER双效催化剂,能够实现高比表面积,高电导率和高双功能性,同时避免了使用有机粘结剂的复杂制备过程和不可避免的电池性能影响.与传统设计不同,本文主要通过集成各司其职的不同功能组分并充分暴露电化学活性面积来提高双效电极的整体活性.电化学测试结果表明,耦合阵列电极(R-NCM)相比于MOFs阵列(NCM)和MOFs衍生物阵列(A-NCM)等对比电极,具有显著提高的双效氧电极性能,氧还原反应的起峰电位约为0.90 V,而氧析出反应电流密度达到100 m Acm-2时的过电势为319 m V.由于其在生长–热裂解–再生长过程中所具有的稳定的站立多级二维纳米片结构,所制备的双效氧电极材料表现出显著增强的双官能团性,电化学活性面积,反应动力学和稳定性,并可进一步用于可充电的金属锌空气电池(ZABs).考虑到制备过程的可行性与简洁性,所提出的生长–热裂解–再生长策略不仅能够用于耦合型分级纳米片阵列结构的合成,还能为设计开发相关能源电化学装置的高活性电极结构提供借鉴.
基金the DAAD Faculty Development for Ph.D.Candidates(Balochistan)2016(57245990)-HRDI-UESTP’s/UET’s funding scheme in cooperation with the Higher Education Commission of Pakistan(HEC)for sponsoring the stay at IMF TU Freiberg,Germany.
文摘In this research,a detailed multi-physics study has been carried out by numerically simulating a solid fractured gun barrel for 20 thermo-mechanical cycles.The numerical model is based on thermal effects,mechanical stress fields and fatigue crack mechanics.Elastic-plastic material data of modified AISI 4340 at temperatures ranging from 25 to 1200℃and at strain rates of 4,16,32 and 48 s^(-1) was acquired from high-temperature compression tests.This was used as material property data in the simulation model.The boundary conditions applied are kept similar to the working gun barrel during continuous firing.A methodology has been provided to define thermo-mechanically active surface-to-surface type interface between the crack faces for a better approximation of stresses at the crack tip.Comparison of results from non-autofrettaged and autofrettaged simulation models provide useful information about the evolution of strains and stresses in the barrel at different points under combined thermo-mechanical loading cycles in both cases.The effect of thermal fatigue under already induced compressive yield due to autofrettage and the progressive degradation of the accumulated stresses due to thermo-mechanical cyclic loads on the internal surface of the gun barrel(mimicking the continuous firing scenario)has been analyzed.Comparison between energy release rate at tips of varying crack lengths due to cyclic thermo-mechanical loading in the non-autofrettaged and autofrettaged gun has been carried out.
文摘Row spacing has a pivotal role in enhancing sugarcane yield and improving its quality. A study was undertaken to evaluate the influence of different planting techniques on performance of sugarcane at Agronomic Research Area, Department of Agronomy, University of Agriculture Faisalabad during Kharif 2014. Experimental treatments comprised of: 180 cm spaced trenches with tripple row strips, 180 cm spaced trenches with alternate row strips, 120 cm spaced trenches with double row strips and 60 cm spaced furrows with single rows. Sugarcane cultivar HSF-240 was used as experimental material. The experimental was conducted in RCBD with four replications. The expeimental results revealed that sugarcane number of tillers, plant height, cane length, stripped cane weight and stripped cane yield increased progressively with the increase in row spacing from 60 to 180 cm. While germination percentage and number of millable canes were not affected by different sowing techniques, maximum number of tillers (15.96 m-2), plant height (333.25 cm), stripped cane weight (0.94 kg) and stripped cane yield (107 t·ha-1) were recorded from 180 cm spaced trenches with tripple row strips.
基金Acknowledgments This work is supported by the National Natural Science Foundation of China (Grand No. 21271114) Tsinghua University independent research and development fund (20111080982) and Program for Changjiang Scholars and Innovative Research Team in University (IRT13026).
基金This study was supported by the National Natural Science Foundations of China(Nos.51902027,61874014,61874013,51788104,61974011 and 61976025)the Basic Science Center Program of the National Natural Science Foundation of China(No.51788104)+2 种基金National Basic Research of China(Nos.2016YFE0102200 and 2018YFB0104404)Beijing Natural Science Foundation(No.JQ19005)Fund of State Key Laboratory of Information Photonics and Optical Communications(Beijing University of Posts and Telecommunications,China).
文摘Being a typical state of the art heterogeneous catalyst,supported noble metal catalyst often demonstrates enhanced catalytic properties.However,a facile synthetic method for realizing large-scale and low-cost supported noble metal catalyst is strictly indispensable.To this end,by making use of the strong metal-support interaction(SMSI)and mechanochemical reaction,we introduce an efficient synthetic route to obtain ultrafine Pt and Ir nanoclusters immobilized on diverse substrates by wet chemical milling.We further demonstrate the scaling-up effect of our approach by large-scale ball-milling production of Pt nanoclusters immobilized on TiO_(2)substrate.The synthesized Pt/Ir@Co_(3)O_(4)catalysts exhibit superior oxygen evolution reaction(OER)performance with only 230 and 290 mV overpotential to achieve current density of 10 and 100 mA·cm^(-2),beating the catalytic performance of Co_(3)O_(4)supported Pt or Ir clusters and commercial Ir/C.It is envisioned that the present work strategically directs facile ways for fabricating supported noble metal heterogeneous catalysts.
基金This study was supported by the National Basic Research Program of China (Nos. 2015CB932500 and 2013CB632702) and the National Natural Science Foundation of China (No. 51302141).
文摘Large-area, pinhole-free, and ultrathin polymer membranes with thicknesses of only a few nanometers have attracted increasing attention for their applications in molecular separation, flexible optoelectronics, and sensors. They can potentially be developed for surface protection as well. In this study, we report an effective way to obtain large-scale polymer coatings with a thickness down to 10 nm, which effectively protects metals from corrosion. We develop a facile and scalable method to fabricate freestanding polymer membranes with thickness below 10 nm by dropping the precursor polymer solution on a water surface. By optimizing the surface tension of the polymer solution, the solution could spontaneously spread on the water surface to form a continuous and uniform solid membrane, collected as a freestanding thin membrane. The obtained polymer membranes could then easily be transferred on a metal substrate as highly flexible and stable anti-corrosion coatings. Electrochemical measurements performed in a 0.1 M Na2SO4 solution demonstrated the excellent anti-corrosion properties of the sub-10 nrn polymer membranes whose corrosion rate was less than 1% of the corrosion rate of the bare metal. We also demonstrate that the polymer membrane exhibits high performance as a protection layer for flexible circuits.