Papers by Keyword: PEM

Abstract: Polymer electrolyte membranes (PEM) have a potential to become power sources in automotive industry and other household applications. PEM such as sulfonated polyetheretherketone (SPEEK) have acceptable operating temperature range but proton conductivity is dependent on amount of sulfonic groups attached to the polymer backbone (degree of sulfonation). At the same time, the sulfonic groups cause sorption of water from surrounding vapour or liquid. This factor may lead to mechanical failure if membrane absorbs too much water. Modification of PEM by adding ionic liquids (IL) may provide good proton conductivity but presence of water could also be critical factor of membrane stability as in high humidity conditions IL are washed out of membrane and replaced by water molecules. PEM with IL inclusions could be potentially used at temperatures close to water boiling point and higher as IL used in this research are thermally stable in temperatures up to 200°C.

Abstract: To clarify the effect of relative humidity on molecular chain’s network structure, we at first employ Molecular Dynamics (MD) method to constitute the computational model for Nafion membrane, in which the water channel is artificially reproduced with an aggregation of water molecules. And then, relaxation calculation is performed and a relatively stable microstructure of Nafion membrane is derived. It is found that the regions of relatively low density of molecular chain’s network appear interchangeably together with those of relatively high density of water molecules.

Abstract: In proton exchange membrane (PEM) fuel cell cathode, oxygen reduction reaction (ORR) behavior have important effects on fuel cell performance. In this paper, the dynamic oxygen adsorption model and then the redox reaction model for hydrogen and oxygen system were established on the surface of the electricity catalyst Pt. The reaction process of hydrogen and oxygen on the surface of Pt was simulated by first-principles molecular dynamics method, and the influence of temperature on oxygen reduction reaction characteristics was analyzed. The simulation results show that the oxygen atom adsorption on the Pt (111) surface and reaction with the first hydrogen atom are the control step of the oxygen reduction reaction; and the oxygen reduction reaction accelerates with increasing temperature, but the temperature does not affect the geometric structure of the products in the oxygen reduction reaction steps. The results of the simulation agree well with our previous first-principles calclation, and this will be helpful for understanding the mechanism of oxygen reduction reaction in PEM fuel cell cathode.

Abstract: The proton exchange membrane (PEM) plays a key role on performance of PEM fuel cell. This paper reviewed recent developments of perfluorinated and partially fluorinated PEMs for PEM fuel cells.Comparative analysis of various PEM parameters was presented. Perfluorinated sulfonic PEMs with better technology have the issues of complicated preparation process and high cost.Partially fluorinated PEMs have lower price,but performance is not good enough.

Abstract: With the increasing integration and complexity of microelectronic devices, fault isolation has been challenged. Photon Emission Microscopy (PEM) and Optical Beam Induced Resistance Change (OBIRCH) are effective tools for defect localization and fault characterization in failure analysis. In this paper, the principles and different application condition of PEM and OBIRCH are discussed. PEM is very helpful for locating defects emitting photon, but can not detect the defects which have no photon emitting, such as shorted metal interconnects; OBIRCH as a complementary, has a high success rate for locating resistance defects. Two cases with failure mechanisms illuminated are presented to show the different application of PEM and OBIRCH.

Abstract: Sulfonated polymer membranes play an important role in PEMFC (proton exchange membrane fuel cell). Series of sulfonated polyamides were prepared by polycondensation of a CF₃-containing diamine with various ratios of terephthalic acid and 5-Sodiosulfoisophthalic acid. Sulfonated polyamides were characterized by ¹H-NMR, FTIR and intrinsic viscosity. The resulting polyamides exhibited outstanding thermal stability. Membranes were prepared by solution casting, then characterized by determining ion-exchange capacity (IEC), water uptake, swelling ratio, proton conductivity and mechanical properties. With the gradual growth of sulfonic acid groups from 70% to 100% (molar ratio), IEC increased to 1.0223meq/g, and proton conducticity reached up to 3.82×10^-2S/cm, while water uptake and swelling ratio remained in proper values. And the tensile strength of membranes was beyond 46.63MPa, which showed very good perspectives in PEMFC applications.

Abstract: Sulfonated poly (ethersulfone) s (S-PDHTPEs) were prepared from 4,4-(2,2-diphenylethenylidene) bisphenol (DHTPE), 4,4-sulfonyldiphenol, 4-fluorophenylsulfone using potassium carbonate, and followed sulfonation reaction with conc. sulfuric acid. DHTPE is a conjugated structure, which enables to form planar conformation between aromatic rings, and selectively sufonated on phenyl rings of polymer side chain. Composite membranes were prepared with copolymers and SiO₂ nanoparticles (20 nm, 4~10%wt). The composite membranes were cast from DMSO. A series of composite membranes structures and characteristic were evaluated by the ¹H-NMR spectroscopy, and thermal stabilities. The membranes were performed by ion exchange capacity (IEC), water uptake and proton conductivity as a function of degree of sulfonation.

Abstract: Quantitative efficacies of several methods for stacking fault (SF) reduction are evaluated using Monte Carlo (MC) simulation. SF density on a 3C–SiC {001} surface depends on interactions of adjoining SFs: annihilation between counter pairs of SFs and termination by orthogonal SF pairs. However, SFs are not entirely eliminated when growth occurs on undulant-Si and switch back epitaxy (SBE) due to spontaneous SF collimation that suppresses the annihilation probability of counter SFs. The MC simulation also reveals the efficacy of SF reduction method which includes the growth of 3C–SiC on finite area bounded by side walls. One can theoretically reduce the SF density below 100 cm^-1 on 3C–SiC {001} surface. A practical way for eliminating the SF by termination at side walls is demonstrated, and it clearly exhibits that the SF density can be reduced under 120 cm^-1.

Abstract: During the reactive sputtering process, due to the hysteresis effect, the sputtering state should be maintained in the transition region of the hysteresis curve which can used to obtain stoichiometric compound films at a high deposition rate. If sputtering state changes, it is impossible to make the sputtering state step back to the original point by manually control the process parameters, because the hysteresis is irreversible. Thus it requires a method of fast feedback to control the sputtering power and the reaction gas flow rate into the chamber. In this paper the PEM (plasma emission monitor) control system and the single neuron self-adaptive PID algorithm have been designed to maintain the sputtering state in proper condition, namely preventing the target from poisoned in the reactive sputtering. The signal acquisition and the controller design were the major parts of the PEM system. The signal acquisition was realized by the optical emission spectrometer. And the single neuron self-adaptive PID controller has been designed in the paper. Using the MATLAB software, the simulation experiments have been done. The output waveforms showed that using traditional non-adaptive PID control algorithm, the overshoot is over 6% and the regulation time is over 1.8s, but using single neuron self-adaptive PID algorithm the overshoot 0 and regulation time 0.5s. Monitoring the target spectral intensity at various reaction gas flow rate, several conclusions could be obtained. The overshoot 6% indicated that the reactive gas flow into the chamber was excessive, the target was poisoned and the sputtering state in chemical mode. And while the overshoot was zero which indicated that the target poisoned was avoided and the reaction ran in defined condition. The PEM using the single neuron self-adaptive PID algorithm responded faster than that using the traditional PID algorithm. The PEM system designed in the paper can effectively avoid the target poisoned and make the reactive sputtering maintain at an ideal state.

Abstract: Suspension aerial crossing structures are broadly applied for supporting petroleum pipelines across special terrain for their optimal structural style and constructional benefit. Due to the general flexibility of the structures, pipeline suspension bridges easily vibrate under the action of random wind forces. One of the typical vibration responses, known as buffeting, is considered to be an important factor for the serviceable safety of suspension bridges. In this paper, the dynamical model of a suspension pipeline bridge is presented and buffeting analysis under the action of wind loads is carried out through the Finite Element Method. It is shown that the frequency spectrum of the suspension pipeline bridge is composed of densely distributed modal frequencies. Low frequencies are mainly focused on horizontal and vertical bending motions of the bridge. Based on the standard harmonic response analysis, the Pseudo-Excitation Method (PEM) is introduced to obtain the buffeting vibration in response to the wind excitation. The correlative formulas of quasi-static buffeting force model are derived, and the buffeting analysis of the bridge using PEM is achieved on the solution platform Ansys.