The purpose of this study was to compare the ventilatory threshold (VT) between treadmill walking against a horizontal impeding force (horizontal load walking) and a cycle ergometer exercise. Seven adult men volunteer...The purpose of this study was to compare the ventilatory threshold (VT) between treadmill walking against a horizontal impeding force (horizontal load walking) and a cycle ergometer exercise. Seven adult men volunteered to participate in this study. They performed horizontal load walking (velocity: 1.11 m/s) and a cycle ergometer exercise (pedaling frequency: 60 rpm), with loads imposed using a ramp slope technique. Oxygen uptake at the VT during horizontal load walking was greater than that during a cycle ergometer exercise展开更多
Durability is one of the critical issues to restrict the commercialization of proton exchange membrane fuel cells(PEMFCs) for the vehicle application.The practical dynamic operation significantly affects the PEMFCs du...Durability is one of the critical issues to restrict the commercialization of proton exchange membrane fuel cells(PEMFCs) for the vehicle application.The practical dynamic operation significantly affects the PEMFCs durability by corroding its key components.In this work,the degradation behavior of a single PEMFC has been investigated under a simulated automotive load-cycling operation,with the aim of revealing the effect of load amplitude(0.8 and 0.2 A/cm2 amplitude for the current density range of0.1-0.9 and 0.1-0.3 A/cm^(2),respectively) on its performance degradation.A more severe degradation on the fuel cell performance is observed under a higher load amplitude of 0.8 A/cm^(2) cycling operation,with$10.5% decrease of cell voltage at a current density of 1.0 A/cm2.The larger loss of fuel cell performance under the higher load amplitude test is mainly due to the frequent fluctuation of a wider potential cycling.Physicochemical characterizations analyses indicate that the Pt nanoparticles in cathodic catalyst layer grow faster with a higher increase extent of particle size under this circumstance because of their repeated oxidation/reduction and subsequent dissolution/agglomeration process,resulting in the degradation of platinum catalyst and thus the cell performance.Additionally,the detected microstructure change of the cathodic catalyst layer also contributes to the performance failure that causes a distinct increase in mass transfer resistance.展开更多
Hetero-element doped lithium orthosilicates have been considered as advanced tritium breeders due to the superior performances.In this work,Li_(4)Si_(1-x)Ti_(x)O_(4) ceramics were prepared by proprietary hydrothermal ...Hetero-element doped lithium orthosilicates have been considered as advanced tritium breeders due to the superior performances.In this work,Li_(4)Si_(1-x)Ti_(x)O_(4) ceramics were prepared by proprietary hydrothermal process and multistage reactive sintering.The reaction mechanism of Li_(4)Si_(1-x)Ti_(x)O_(4) was put forward.XRD and SEM analyses indicate that insertion of Ti leads to lattice expansion,which promotes the grain growth and changes the fracture mode.The compressive tests show that the crush load increases almost four times by increasing x from 0 to 0.2.However,the thermal conductivity and ionic conductivity are the best when x=0.05 and x=0.1,respectively.Thermal cycling stability of Li_(4)Si_(1-x)Ti_(x)O_(4) pebbles was further appraised through investigating the changes of microstructure and crush load.After undergoing thermal cycling,the Li_(4)Si_(1-x)Ti_(x)O_(4) still show higher crush load compared with Li_(4)SiO_(4),despite Ti segregation in some samples.The x=0.05 sample exhibits excellent thermal cycling stability.In summary,proper amount of Ti doping can improve the crush load,thermal and ionic conductivity,and thermal cycling stability of Li_(4)SiO_(4).展开更多
In this paper, a novel accelerated test method was proposed to analyze the durability of MEA, considering the actual operation of the fuel cell vehicle. The proposed method includes 7 working conditions： open circuit...In this paper, a novel accelerated test method was proposed to analyze the durability of MEA, considering the actual operation of the fuel cell vehicle. The proposed method includes 7 working conditions： open circuit voltage （OCV）, idling, rated output, overload, idling-rated cycle, idling-overload cycle, and OCV-idling cycle. The experimental results indicate that the proposed method can effectively destroy the MEA in a short time （165 h）. Moreover, the degradation mechanism of MEA was analyzed by measuring the polarization curve, CV, SEM and TEM. This paper may provide a new research direction for improving the durability of fuel cell.展开更多
文摘The purpose of this study was to compare the ventilatory threshold (VT) between treadmill walking against a horizontal impeding force (horizontal load walking) and a cycle ergometer exercise. Seven adult men volunteered to participate in this study. They performed horizontal load walking (velocity: 1.11 m/s) and a cycle ergometer exercise (pedaling frequency: 60 rpm), with loads imposed using a ramp slope technique. Oxygen uptake at the VT during horizontal load walking was greater than that during a cycle ergometer exercise
基金supported by the National Key R&D Program of China (No.2018YFB0105503)。
文摘Durability is one of the critical issues to restrict the commercialization of proton exchange membrane fuel cells(PEMFCs) for the vehicle application.The practical dynamic operation significantly affects the PEMFCs durability by corroding its key components.In this work,the degradation behavior of a single PEMFC has been investigated under a simulated automotive load-cycling operation,with the aim of revealing the effect of load amplitude(0.8 and 0.2 A/cm2 amplitude for the current density range of0.1-0.9 and 0.1-0.3 A/cm^(2),respectively) on its performance degradation.A more severe degradation on the fuel cell performance is observed under a higher load amplitude of 0.8 A/cm^(2) cycling operation,with$10.5% decrease of cell voltage at a current density of 1.0 A/cm2.The larger loss of fuel cell performance under the higher load amplitude test is mainly due to the frequent fluctuation of a wider potential cycling.Physicochemical characterizations analyses indicate that the Pt nanoparticles in cathodic catalyst layer grow faster with a higher increase extent of particle size under this circumstance because of their repeated oxidation/reduction and subsequent dissolution/agglomeration process,resulting in the degradation of platinum catalyst and thus the cell performance.Additionally,the detected microstructure change of the cathodic catalyst layer also contributes to the performance failure that causes a distinct increase in mass transfer resistance.
基金supported by National Natural Science Foundation of China(No.51802257)Natural Science Foundation of Shaanxi Provincial Department of Education(18JK0570)China Postdoctoral Science Foundation(2019M663788).
文摘Hetero-element doped lithium orthosilicates have been considered as advanced tritium breeders due to the superior performances.In this work,Li_(4)Si_(1-x)Ti_(x)O_(4) ceramics were prepared by proprietary hydrothermal process and multistage reactive sintering.The reaction mechanism of Li_(4)Si_(1-x)Ti_(x)O_(4) was put forward.XRD and SEM analyses indicate that insertion of Ti leads to lattice expansion,which promotes the grain growth and changes the fracture mode.The compressive tests show that the crush load increases almost four times by increasing x from 0 to 0.2.However,the thermal conductivity and ionic conductivity are the best when x=0.05 and x=0.1,respectively.Thermal cycling stability of Li_(4)Si_(1-x)Ti_(x)O_(4) pebbles was further appraised through investigating the changes of microstructure and crush load.After undergoing thermal cycling,the Li_(4)Si_(1-x)Ti_(x)O_(4) still show higher crush load compared with Li_(4)SiO_(4),despite Ti segregation in some samples.The x=0.05 sample exhibits excellent thermal cycling stability.In summary,proper amount of Ti doping can improve the crush load,thermal and ionic conductivity,and thermal cycling stability of Li_(4)SiO_(4).
文摘In this paper, a novel accelerated test method was proposed to analyze the durability of MEA, considering the actual operation of the fuel cell vehicle. The proposed method includes 7 working conditions： open circuit voltage （OCV）, idling, rated output, overload, idling-rated cycle, idling-overload cycle, and OCV-idling cycle. The experimental results indicate that the proposed method can effectively destroy the MEA in a short time （165 h）. Moreover, the degradation mechanism of MEA was analyzed by measuring the polarization curve, CV, SEM and TEM. This paper may provide a new research direction for improving the durability of fuel cell.
