Design of 1 kW high temperature PEM fuel cell system and performance analysis under different operating conditions

This paper demonstrates the mathematical and MATLAB simulation model of 1 KW (28.8V_dc) PEM fuel cell system with boost convertor and RL load to analyze the yield behavior in accordance to control the hydrogen fuel utilization. Two cases have been designed to evaluate the performance of this model. In the first case, fuel cell parameters are examined with and without a fuel regulator that controls the hydrogen fuel rate while in the second case, the operating temperature of a fuel cell stack is varied to observe the impact on the system. PEM fuel cell based power systems can become an alternate choice in the transportation sector to overcome contamination concerns, especially in South Asia where the environmental issues are at peak. The purpose of this work is to introduce such environmentally friendly system of transportation in South Asia, especially in Pakistan and this stack model can be used as a prototype for developing FC based motorbike as currently no practical models have been tested in this region. Therefore, this model has unique advantages over the existing in the literature.     

质子交换膜燃料电池及其发电系统模拟

本文通过质子交换膜燃料电池单电池子模型、布气管子模型、流场子模型相互耦合,对电池堆传热传质过程加以数值模拟,得到单电池及电池堆的流场、温场、当地电流密度分布、过电位分布;给定平均电流密度下单电池及电池堆输出电压等参数;并比较了平均电流密度、布气管尺寸对电池输出电压、堆内反应物分配的影响;在此基础上,对整个ＰＥＭＦＣ发电系统进行流程模拟和参数分析,得到平均电流密度、重整器Ｓ／Ｃ等主要参数对系统性能影响．     

Study on Electrical Conductivity and Mechanical Performance of Polymeric Composite Flow Field Plates for Fuel Cell Applications

Fuel cell technology has received a great deal of attention as a candidate for an alternative power source due to its environmental benefits compared to conventional sources. Flow-field plates are one of the most important components of the Proton Exchange Membrane (PEM) and Direct Methanol (DM) fuel cells technology, which is expected to possess high electrical and thermal conductivity, low hydrogen permeability, and good mechanical performance. In this study, a systematic investigation was carried out to formulate and fabricate electrically conductive polymer composites to be used in production of flow field plates using a simple low temperature, single step moulding process. It focused on the careful selection of both materials and processing methodology. ElectroPhen^? binders, various concentrations of graphite powder and enhanced dispersion agents were employed to make composite plates with high electrical conductivity and satisfactory mechanical performance. Electrical conductivity measurements were carried out using purpose-built in-plane and through-plane electrical conductivity test kits. Flexural tests were carried out to evaluate the mechanical performance of the composites. It has been found that polymer composite flow field plates can attain the electrical conductivity and mechanical performance requirements for commercial fuel cell applications without requiring a high temperature multi-step production process.     

质子交换膜中的传质分析

质子交换膜燃料电池是最有应用前景的汽车动力替代系统。质子交换膜中的传质是质子交换膜燃料电池性能的控制因素之一。论文从宏观和微观角度分析了质子交换膜中的质子和水分的传递机理,分析了操作参数对质子在质子交换膜中传递的影响。研究发现:外载荷对质子和水分在质子交换膜中的传递有很大影响;（H₅O₂）⁺是水合质子的主要结构形式;通过（H₅O₂）⁺中氢氧键不断形成与断裂,电荷在质子交换膜中得以传递。研究结果对理解质子交换膜中的传质机理及其推广应用具有积极意义。     

Polymer electrolyte membrane fuel cell as a hydrogen flow rate monitoring device

There is a substantial demand for hydrogen flow rate monitoring devices in applications where hydrogen is utilised or produced and which include oil refineries, ammonia production, food and chemical industries, coal gasification, methane steam reforming and water electrolysis. In this paper, a polymer electrolyte membrane (PEM) fuel cell has been demonstrated for measuring accurate flow rates of hydrogen or hydrogen-containing gases. The concept involves applying a constant voltage to a PEM fuel cell to oxidise the entire hydrogen supplied to the anode compartment of the fuel cell and observing limiting current values attained and relating these to the hydrogen flow rates. PEM fuel cells with an active area of 50 cm² were constructed and used to accurately measure the flow rates of hydrogen up to 170 mL/min. A device with a capability to monitor significantly higher hydrogen flow rates can be constructed by using several cells in a stacking arrangement or by using electrically isolated cells in a single device. The paper discusses advantages and limitations of the technique and the flow rate-measuring response for gases containing 5–100 % hydrogen. The response time for hydrogen gas was of the order of 1–2 min. However, the fuel cell flow field design can be optimised for faster response times.     

Fuel quality and operational issues for polymer electrolyte membrane (PEM) fuel cells

Polymer electrolyte membrane (PEM) fuel cells are susceptible to degradation due to the catalyst poisoning caused by CO present in the fuel above certain limits. Although the amount of CO in the fuel may be within the permissible limit, the fuel composition (% CO₂, CH₄, CO and H₂O) and the operating conditions of the cell (level of gas humidification, cell temperature and pressure) can be such that the equilibrium CO content inside the cell may exceed the permissible limit leading to a degradation of the fuel cell performance. In this study, 50 cm² active area PEM fuel cells were operated at 55–60 °C for periods up to 250 hours to study the effect of methane, carbon dioxide and water in the hydrogen fuel mix on the cell performance (stability of voltage and power output). Furthermore, the stability of fuel cells was also studied during operation of cells in a cyclic dead end / flow through configuration, both with and without the presence of carbon dioxide in the hydrogen stream. The presence of methane up to 10% in the hydrogen stream showed a negligible degradation in the cell performance. The presence of carbon dioxide in the hydrogen stream even at 1–2% level was found to degrade the cell performance. However, this degradation was found to disappear by bleeding only about 0.2% oxygen into the fuel stream.     

质子交换膜燃料电池电流分布的动态响应

动态特性是理解质子交换膜燃料电池性能的重要参数之一.运用燃料电池测试系统、恒电流/恒电压多通道测试仪和燃料电池电流密度分布测试装置,试验测量了质子交换膜燃料电池在不同加湿温度、电池温度和压力下的电流分布动态响应和动态特性.研究发现:不同区域的局部电流达到新的平衡所需的时间不同;加湿温度变化时,不同区域的局部电流的变化趋...     

Effect of gas diffusion layer and membrane properties in an annular proton exchange membrane fuel cell

A complete three-dimensional and single phase computational dynamics model for annular proton exchange membrane (PEM) fuel cell is used to investigate the effect of changing gas diffusion layer and membrane properties on the performances, current density and gas concentration. The proposed model is a full cell model, which includes all the parts of the PEM fuel cell, flow channels, gas diffusion electrodes, catalyst layers and the membrane. Coupled transport and electrochemical kinetics equations are solved in a single domain; therefore no interfacial boundary condition is required at the internal boundaries between cell components. This computational fluid dynamics code is used as the direct problem solver, which is used to simulate the two-dimensional mass, momentum and species transport phenomena as well as the electron- and proton-transfer process taking place in a PEMFC that cannot be investigated experimentally. The results show that by increasing the thickness and decreasing the porosity of GDL the performance of the cell enhances that it is different with planner PEM fuel cell. Also the results show that by decreasing the thickness of the membrane the performance of the cell increases.     

Focusing and waveguiding of Lamb waves in micro-fabricated piezoelectric phononic plates

This paper presents results on the numerical and experimental studies of focusing and waveguiding of the lowest anti-symmetric Lamb wave in micro-fabricated piezoelectric phononic plates. The phononic structure was based on an AT-cut quartz plate and consisted of a gradient-index phononic crystal (GRIN PC) lens and a linear phononic plate waveguide. The band structures of the square-latticed AT-cut quartz phononic crystal plates with different filling ratios were analyzed using the finite element method. The design of a GRIN PC plate lens which is attached with a linear phononic plate waveguide is proposed. In designing the waveguide, propagation modes in square-latticed PC plates with different waveguide widths were studied and the results were served for the experimental design. In the micro-fabrication, deep reactive ion etching (Deep-RIE) process with a laboratory-made etcher was utilized to fabricate both the GRIN PC plate lens and the linear phononic waveguide on an 80 μm thick AT-cut quartz plate. Interdigital transducers were fabricated directly on the quartz plate to generate the lowest anti-symmetric Lamb waves. A vibro-meter was used to detect the wave fields and the measured results on the focusing and waveguiding of the piezoelectric GRIN PC lens and waveguide are in good accordance with the numerical predictions. The results of this study may serve as a basis for developing an active micro plate lens and related devices.     

Temperature dependences of the ion-electron emission of glassy carbons under 30-keV argon ion irradiation

The temperature dependences (?200°C < T ≤ 350°C) of the ion-induced electron emission yield γ and the structures of modified surface layers have been studied experimentally for SU-850, SU-1000, SU-1300, SU-2000, and SU-2500 glassy carbons under high-dose 30-keV Ar⁺ and N ₂ ⁺ ion irradiation. Glassy carbons manufactured using a relatively high heat-treatment temperature T _ht exhibit a stepwise increase in the electron yield at certain annealing temperatures T _a. The same behavior is observed for graphitized carbon materials. For low-temperature glassy carbons, the electron yield exhibits a monotonic increase with increasing irradiation temperature. The observed differences are related to the occurrence of different structural types of fullerene-like nanoparticles in the low-and high-temperature glassy carbons.     

Development and application of chip calorimeter as an X-ray detector

Radiotherapy for cancer patients requires accurate measurement of the absorbed dose of radiation in a treatment planning step. Various types of radiation detectors are currently utilized for dose measurement. Among them, calorimeters are known to be the most precise detector for measuring absorbed dose, but their on-site application is limited by the large size of the equipment. We developed a miniaturized chip calorimeter for application as a radiation detector. The calorimetric radiation detector was built using micro/nano fabrication techniques, and consists of an SU-8 photoresist absorber and high-sensitivity vanadium oxide (VO_x) thermistors. The thermistors had a temperature resolution of 135 μK, and the calorimeter showed a thermal conductance of 11 μW/K. The detector was irradiated with various X-ray dose rates from a linear accelerator, and the absorbed dose to SU-8 was measured. The detector responses showed high linearity with dose rates, demonstrating the feasibility of the radiation detector for practical uses.     

基于NOA73微球与SU-8微柱的微探针制作

集成紫外固化胶NOA73微球与SU-8微柱制造的亚毫米探针,可以作为关键部件应用于三坐标测量机。NOA73微球通过NOA73对其他溶液的界面张力形成,柱子由深紫外光穿过微球曝光SU-8形成。这种新技术利用甘油补偿NOA73与空气折射率差,使得紫外光透过NOA73微球后保持接近平行。最终得到高深宽比的探针结构,高度超过1 200 m,微柱侧壁与基底呈89。     

Influence of methanol impurity in hydrogen on PEMFC performance

Proton exchange membrane fuel cells [PEMFC] have become highly attractive for stationary as well as mobile energy applications due to their good efficiency compact cell design and zero emissions. PEM fuel cells mainly consist of anode and cathode containing platinum/platinum alloy electrocatalysts and Nafion membrane as the electrolyte. They operate on hydrogen fuel, which is generally produced by reforming of hydrocarbons, alcohols such as methanol and may contain large amounts of impurities such as methanol, carbon dioxide, trace amounts of carbon monoxide, etc. The studies on the effect of methanol impurity in hydrogen on fuel cell performance and methods of mitigation of poisoning are very important for the commercialization of fuel cells and are described in a limited number of papers only. In this paper, we present the studies on the influence of methanol impurity in hydrogen for the PEM fuel cells. The effect of various parameters such as methanol concentration, cell voltage, current density, exposure time, reversibility, operating temperature, etc. on the cell performances was investigated using pure hydrogen. Various methods of methanol poisoning mitigation were also investigated.     

SU-8光栅结构中的液晶激光特性

设计制作了SU-8光栅结构的染料掺杂手性向列相液晶激光器件,在器件正面和侧面均实现了随机激光辐射。将激光染料PM597、手性剂S-811、向列性液晶TEB30A按一定比例均匀混合,注入反平行摩擦处理的液晶盒中,器件的下基板通过光掩模法刻蚀出周期为15μm的光栅。利用532 nm的Nd∶YAG固体脉冲激光器作为泵浦源,器件的侧面既在580~590 nm范围内出现了多个离散分立的随机激光辐射峰,FWHM约0.19 nm,又在579~585 nm范围内出现独立的两个激光辐射峰,FWHM约0.19 nm;在器件正面获得了584~590 nm范围的随机激光辐射谱,FWHM约0.17 nm。加热器件至61℃,液晶相变为各向同性态,器件侧面仍出现了波长约590.60 nm、FWHM约0.24 nm的激光辐射峰。分析得出,液晶盒中引入SU-8光栅结构后,光子同时在液晶分子间多重散射和SU-8光栅中布拉格反射获得反馈放大,两种机制相辅相成。器件侧面出现的独立激光辐射峰主要由SU-8光栅布拉格反射提供反馈放大形成,而器件侧面和正面的随机激光辐射峰主要由液晶分子间多重散射提供反馈放大形成。     

Effect of nitrogen and carbon dioxide as fuel impurities on PEM fuel cell performances

Polymer electrolyte membrane (PEM) fuel cells are considered to have the highest power density of all the fuel cells. They operate on hydrogen fuel, which is generally produced by reforming of hydrocarbons, and may contain large amounts of impurities such as carbon dioxide, nitrogen, and trace amounts of carbon monoxide. We studied the effect of dilution of hydrogen gas with carbon dioxide on PEM fuel cells by polarization studies. The polarization curves were different when hydrogen gas was diluted with same quantities of carbon dioxide and with nitrogen. It may be due to carbon monoxide formation by reverse shift reaction and poisoning of anode platinum catalyst. Use of Pt–Ru alloy catalyst was found to suppress the poisoning. The effects of hydrogen gas composition, temperature, current density, and anode catalyst on fuel cell performances were examined in this study.     

PEMFC插指型流道阴极中气体扩散特性的数值分析

本文对PEMFC插指型流道阴极扩散层建立了二维单相的多组分物理数学模型,对PEMFC插指型流道的阴极扩散层中气体的扩散特性及反应行为进行了数值研究,采用有限容积法对模型控制方程进行求解,比较了插指型和平直型流道两类电池的性能曲线,以及两种流道中氧气的组分摩尔浓度和局部电流密度的分布,分析了插指型流道结构参数对电池性能的影响。     

操作参数对PEM燃料电池中水迁移的影响

质子膜内水分和阴极多孔电极中液态水含量是PEM燃料电池正常运行的控制因素。本文给出了一个用于研究PEM燃料电池内水迁移的稳态、等温、两相流模型。模型耦合了连续方程、动量守恒方程和物质守恒方程,以及水在质子膜中传递方程。运用试验结果验证了模型的有效性。分析模拟结果表明,增大系统操作压力、升高电池操作温度和降低加湿温度将会使质子膜中水的净迁移通量增大;增大操作压力、降低操作温度和升高加湿温度会增加阴极CTL与GDL界面上液态水含量。     

SU-8 based planar metamaterials with fourfold symmetry as selective terahertz absorbers

We report on the absorption properties of polarization-insensitive transmissive and reflective metamaterial absorbers based on two planar aluminium periodic structures and SU-8 epoxy resist. These absorbers were investigated using numerical simulation and experimental methods in the terahertz range (below 2 THz). SU-8 is a very promising organic material for dielectric layers in planar metamaterials, because its application simplifies the process of fabricating these structures and significantly reduces the fabrication time. The experimental absorption of the metamaterial absorbers has narrowband characteristics that were consistent with the numerical simulations. Power flow analysis in the transmissive metamaterial unit cell shows that the absorption in the terahertz range occurs primarily in the SU-8 layer of the absorber.     

Silanization and antibody immobilization on SU-8

SU-8, an epoxy based negative photoresist, has emerged as a structural material for microfabricated sensors due to its attractive mechanical properties like low Young's modulus and chemical properties like inertness to various chemicals used in microfabrication. It can be used to fabricate MEMS structures of high aspect ratio. However, the use of SU-8 in BioMEMS application has been limited by the fact that immobilization of biomolecules on SU-8 surfaces has not been reported. In this study, the epoxy groups on the SU-8 surface were hydrolyzed in the presence of sulphochromic solution. Following this, the surface was treated with [3-(2-aminoethyl) aminopropyl]-trimethoxysilane (AEAPS). The silanized SU-8 surface was used to incubate human immunoglobulin (HIgG). The immobilization of HIgG was proved by allowing FITC tagged goat anti-human IgG to react with HIgG. This process of antibody immobilization was used to immobilize HIgG on microfabricated SU-8 cantilevers.     

Fabrication of a graphene field effect transistor array on microchannels for ethanol sensing

A new approach to the fabrication of back-gated graphene FET (field effect transistor) arrays on microchannels was investigated. Narrow walls fabricated on a substrate with SU-8 (a negative photoresist), with top metal electrodes were pressed onto another silicon/SiO₂ substrate with predeposited graphene pieces such that the electrodes came into contact with graphene pieces and formed the source and drain contact. The SU-8 narrow walls with the top metal layer were fabricated by the conventional lift-off process. The graphene pieces were reduced chemically from graphite oxide. The I_DS changed immediately by more than 17% when the device was exposed to an ethanol atmosphere. The current recovered very well after the ethanol gas was pumped out. The SU-8 microchannels served as gas flow passages that helped the ethanol vapor reach the sensitive region of the device: the graphene channel. This work provides a convenient way of constructing back-gated graphene FETs for sensing applications. This method could potentially be scaled up for mass production.