he bond lengths and bond orders of four kinds of chemical bonds in crownethers(15) were calculated based on the model molecules using MNDO method.With the calculation results, some predictions to the EI mass spectral ...he bond lengths and bond orders of four kinds of chemical bonds in crownethers(15) were calculated based on the model molecules using MNDO method.With the calculation results, some predictions to the EI mass spectral fragmenta-tion behaviour of crown ethers are suggested. The EI mass spectra of studied crownethers are in satisfactory agreenient with the predictions.展开更多
This paper deals with two basic issues of fuel cell research： modelling and experimental validation. In particular, the EIS （electrochemical impedance spectroscopy） technique is applied to a PEMFC （proton exchange...This paper deals with two basic issues of fuel cell research： modelling and experimental validation. In particular, the EIS （electrochemical impedance spectroscopy） technique is applied to a PEMFC （proton exchange membrane fuel cell）. Experiments have been performed using a low-cost test bench and instrumentation developed around a 1,200 W Ballard Nexa fuel cell system. An electrical and dynamic model in VHDL-AMS language for PEM fuel cell stack is described. The privileged approach in this paper is an electrical method. Few papers deal with the modelling of a fuel cell in VHDL-AMS language with an electric approach. The fuel cell is characterised cell wise in VHDL-AMS; AC and DC measurements show the good agreement between the simulation results of the model and those measured in experiments. The model is capable to predict accurate stack profiles. The model is validated using temporal and impedance spectroscopy method; the impedance spectroscopy is performed at low and high frequencies. The experimental and simulated Nyquist plots show that the frequency response of the fuel cell stack can be predicted by the proposed fuel cell stack model. At high frequencies, comparisons between experimental and model impedance results are performed and show some similarities between the two Nyquist. Error between the two approaches is below 1.5%.展开更多
Nano structured LiFexMn1-xPO4 （x=0, 0.2, 0.4） materials were successfully prepared by one-step reflux method in a water/PEG400 mixed solvent, and were coated by carbon using glucose as the precursor. The materials w...Nano structured LiFexMn1-xPO4 （x=0, 0.2, 0.4） materials were successfully prepared by one-step reflux method in a water/PEG400 mixed solvent, and were coated by carbon using glucose as the precursor. The materials were characterized by X-ray diffraction （XRD）, field emission scanning electron microscopy （FESEM） and transmission electron microscopy （TEM）. The electrochemical properties of the materials were investigated by galvanostatic cycling, cyclic voltammetry （CV） and electrochemical impedance spectroscopy （EIS）. It was found that the materials consisted of nanorods with a diameter of 50 nm and a length of 500 nm. Galvanostatic cycling showed that the capacity of LiMnPO4 could be largely increased by Fe2＋ substitution. At a current rate of C/20, the capacity of the three samples （x=0, 0.2, 0.4） were 47, 107 and 150 mA-h.g-1, respectively. CV result showed that the Fe2＋ substitution could decrease the polarization during charging/discharging, ac- celerating the electrochemical process. EIS result showed that the Fe2＋ substitution could decrease the charge transfer resistance between the electrode and electrolyte, as well as increase the Li-ion diffusion coefficient in the bulk material, resulting in an improved electrochemical performance.展开更多
文摘he bond lengths and bond orders of four kinds of chemical bonds in crownethers(15) were calculated based on the model molecules using MNDO method.With the calculation results, some predictions to the EI mass spectral fragmenta-tion behaviour of crown ethers are suggested. The EI mass spectra of studied crownethers are in satisfactory agreenient with the predictions.
文摘This paper deals with two basic issues of fuel cell research： modelling and experimental validation. In particular, the EIS （electrochemical impedance spectroscopy） technique is applied to a PEMFC （proton exchange membrane fuel cell）. Experiments have been performed using a low-cost test bench and instrumentation developed around a 1,200 W Ballard Nexa fuel cell system. An electrical and dynamic model in VHDL-AMS language for PEM fuel cell stack is described. The privileged approach in this paper is an electrical method. Few papers deal with the modelling of a fuel cell in VHDL-AMS language with an electric approach. The fuel cell is characterised cell wise in VHDL-AMS; AC and DC measurements show the good agreement between the simulation results of the model and those measured in experiments. The model is capable to predict accurate stack profiles. The model is validated using temporal and impedance spectroscopy method; the impedance spectroscopy is performed at low and high frequencies. The experimental and simulated Nyquist plots show that the frequency response of the fuel cell stack can be predicted by the proposed fuel cell stack model. At high frequencies, comparisons between experimental and model impedance results are performed and show some similarities between the two Nyquist. Error between the two approaches is below 1.5%.
基金supported by Zijin Program of Zhejiang University, Chinathe Fundamental Research Funds for the Central Universities (No. 2010QNA4003)+3 种基金the Ph.D.Programs Foundation of Ministry of Education of China(No. 20100101120024)the Foundation of Education Office of Zhejiang Province, China (No. Y201016484)the Qianjiang Talents Project of Science Technology Department of Zhejiang Province, China (No. 2011R10021)the National Natural Science Foundation of China (No.51101139)
文摘Nano structured LiFexMn1-xPO4 （x=0, 0.2, 0.4） materials were successfully prepared by one-step reflux method in a water/PEG400 mixed solvent, and were coated by carbon using glucose as the precursor. The materials were characterized by X-ray diffraction （XRD）, field emission scanning electron microscopy （FESEM） and transmission electron microscopy （TEM）. The electrochemical properties of the materials were investigated by galvanostatic cycling, cyclic voltammetry （CV） and electrochemical impedance spectroscopy （EIS）. It was found that the materials consisted of nanorods with a diameter of 50 nm and a length of 500 nm. Galvanostatic cycling showed that the capacity of LiMnPO4 could be largely increased by Fe2＋ substitution. At a current rate of C/20, the capacity of the three samples （x=0, 0.2, 0.4） were 47, 107 and 150 mA-h.g-1, respectively. CV result showed that the Fe2＋ substitution could decrease the polarization during charging/discharging, ac- celerating the electrochemical process. EIS result showed that the Fe2＋ substitution could decrease the charge transfer resistance between the electrode and electrolyte, as well as increase the Li-ion diffusion coefficient in the bulk material, resulting in an improved electrochemical performance.
