钠水玻璃/石墨复合双极板的性能

在室温下,用模压法制备了钠水玻璃/石墨亲水性导电复合材料;讨论了石墨含量、石墨粒径、模压压力以及模压时间对复合材料电导率的影响,并对不同石墨含量的复合材料的含水量进行了分析.结果表明:含有40%石墨的钠水玻璃/石墨导电复合材料的电导率能满足PEMFC双极板的要求;通过优化模压工艺,可进一步提高该复合材料的电导率;复合材料含有凝胶毛细孔,拥有约9%的含水量,在PEMFC运行时能够对质子交换膜进行增湿.     

质子交换膜燃料电池动态特性的建模与仿真

详细分析了质子交换膜燃料电池（PEMFC）的电化学模型。在此基础上，运用Matlab的Simulink仿真工具建立仿真模型，通过此模型，分析当电池电流出现阶跃变化时，电池电压、输出功率、消耗功率、电池效率以及电池等效内阻的动态响应。此模型也可用于电堆的仿真与设计，此研究对燃料电池的优化与控制可提供帮助。     

Design of a fuel cell generation system using a PEMFC simulator

In this paper, a PCS (power conditioner system) design for a fuel cell generation system has been proposed. In order to analyze the dynamic performance of the PCS, a fuel cell stack simulator is also designed, which can consider the dynamic V–I characteristics of the PEMFC (proton exchange membrane fuel cell). First, we explain the PCS design for a fuel cell generation system in detail along with the system configuration and operational principle of the developed PEMFC simulator that has been investigated. In addition, we cover the validity of the proposed system that has been verified by informative simulation and experimental results.     

Investigations on the variation of corrosion and contact resistance characteristics of metallic bipolar plates manufactured under long-run conditions

Tribological variations, surface conditions (roughness, hardness, coating) and surface interactions between micro-stamping dies and bipolar plate blanks play a critical role in determining the surface quality, channel formation and precision of bipolar plates. This study is aimed to understand the cause, mechanism and consequences of interactions between micro-stamping process conditions and bipolar plate quality. A total of 2000 repeated micro-stamping of 51 μm-thick uncoated and 1 μm-thick ZrN coated SS316L sheet blanks into an array of 750 μm micro-channels were performed using 175-220 kN force levels with constant stamping speed of 1 mm/s. Microscopic examinations were conducted periodically on both die and coated & uncoated plate surfaces to observe topographic variations. In addition, corrosion and contact resistance tests were carried out in the same intervals. Analysis of variance (ANOVA) technique was used to determine the significance of the process parameters on channel height, roughness, corrosion and contact resistance differences. The results revealed similar roughness trends for die and plate surfaces during 2000 micro-stampings. ZrN coating with 1 μm thickness dramatically improved corrosion and contact resistance behavior of plates.     

Effect of manufacturing processes on formability and surface topography of proton exchange membrane fuel cell metallic bipolar plates

Metallic bipolar plates in PEM fuel cells offer low-volume, low-mass and low-cost stack fabrication in addition to superior durability when compared to composite bipolar plates, which suffer due to their much higher thickness and less durability. This study aims to address the formability and surface topography issues of metallic bipolar plates fabricated by stamping and hydroforming technologies. Particular emphasis was given to process repeatability, surface topology, and dimensional quality of bipolar plates that would greatly affect the corrosion and contact resistance characteristics. Thin metal sheets of several alloys (i.e., SS304, SS316L, SS430, Ni270, Ti grades 1 and 2) were used in the fabrication experiments. SS304 and SS316L were shown to possess better formability when compared to other alloys that were used in this study, while SS430 and Ti grade 2 demonstrated the worst among all. Channel formability was observed to be greatly affected by the hydroforming pressure, while it does not differ much above certain level of stamping force. The confocal microscopy analyses showed that surface roughness values of the formed samples were altered significantly when compared to the initial flat blanks. In general, increasing hydroforming pressure and stamping force yielded higher surface roughness values at channel peaks. In addition, the surface topography was shown to be influenced mainly by the pressure level rather than the pressure rate in hydroforming process.     

A study on the integration of micro‐reformer and high‐ temperature PEM fuel cell

This study presented an integration platform for a methanol reformer and high‐temperature proton exchange membrane fuel cell (PEMFC). The methanol micro‐reformer was combined with the catalytic reaction section and reforming section, whereas the catalytic reaction section with Pt catalysis maintained the constant temperature environment for a reforming process. SRM reforming results showed that 74 to 74.9% hydrogen and 23.5 to 25.7% of carbon dioxide in the mixture product, and less than 2% of carbon monoxide, was produced. Using the reforming product of low carbon monoxide concentration and the highest methanol conversion rate, a micro reformer link with a fuel cell integration experiment was performed. Results showed a high temperature PEMFC with 3 to 4 W power output under methanol flow rates of 15 ml/hr. Due to the lower hydrogen pressure supplied from the micro reformer, the fuel cell power output may become unstable. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/htj.20322     

Rotating disk electrode analysis of oxygen reduction at platinum particles under limiting diffusion conditions

An analysis is carried out of oxygen reduction under limiting diffusion conditions on a rotating disk electrode partially covered with platinum particles (‘particulate electrode’). First a model is developed for the current response at a rotating particulate electrode, because Levich equation, used for the classical continuous disk electrodes, is not applicable in this case. The model allows for the calculation of the limiting diffusion current by an iterative algorithm, as a function of the density and size of the particles, and the constants for the adsorption/desorption and diffusion of reactants over non-covered areas of the substrate. The model is valid when there is no overlapping of surface diffusion areas around the particles. In a second part, the oxygen reduction on platinum particles electrodeposited on a glassy carbon disk is studied. Platinum particulate electrodes with a variable density and size of particles are prepared by single pulse electrodeposition technique. Limiting diffusion currents for oxygen reduction are analysed on the light of the proposed model. Values for the oxygen surface diffusivity and the equilibrium adsorption/desorption constant on the glassy carbon substrate are obtained from the analysis.     

Influence of ammonia on the conductivity of Nafion membranes

The effect of NH₃ and NH₄⁺ poisoning on the conductivity of Nafion membranes was investigated via electrochemical impedance spectroscopy. The conductivities of membranes prepared with different NH₄⁺ compositions were measured in deionized water at room temperature and compared to those at 80 °C in a gas phase for various relative humidities. The liquid-phase conductivity decreased linearly with an increase in the NH₄⁺ composition in the membrane (y_NH4⁺), with that of the NH₄⁺-form having a conductivity 25% that of the H⁺-form. The gas-phase conductivity of the NH₄⁺-form, on the other hand, declined by 66–98% relative to the H⁺-form depending on humidity. The conductivities of fresh membranes in the presence of gas-phase NH₃ at different humidities were also studied. The conductivity decreased with time-on-stream and reached the same conductivity at a given humidity regardless of the NH₃ concentration, but the time to reach steady-state varied with NH₃ concentration. The y_NH4⁺ at steady-state conductivity was equivalent for all the NH₃ concentrations studied. The kinetics of conductivity decrease was slower at higher humidities. The humidity and y_NH4⁺ appear to have a concerted effect on the conductivity. The quantitative conductivity data under practical fuel cell conditions should be useful for future fuel cell modeling.     

Experiment and simulation investigations for effects of flow channel patterns on the PEMFC performance

Experiments and simulations are presented in this paper to investigate the effects of flow channel patterns on the performance of proton exchange membrane fuel cell (PEMFC). The experiments are conducted in the Fuel Cell Center of Yuan Ze University and the simulations are performed by way of a three‐dimensional full‐cell computational fluid dynamics model. The flow channel patterns adopted in this study include the parallel and serpentine flow channels with the single path of uniform depth and four paths of step‐wise depth, respectively. Experimental measurements show that the performance (i.e. cell voltage) of PEMFC with the serpentine flow channel is superior to that with the parallel flow channel, which is precisely captured by the present simulation model. For the parallel flow channel, different depth patterns of flow channel have a strong influence on the PEMFC performance. However, this effect is insignificant for the serpentine flow channel. In addition, the calculated results obtained by the present model show satisfactory agreement with the experimental data for the PEMFC performance under different flow channel patterns. These validations reveal that this simulation model can supplement the useful and localized information for the PEMFC with confidence, which cannot be obtained from the experimental data. Copyright © 2007 John Wiley & Sons, Ltd.     

Water removal characteristics of proton exchange membrane fuel cells using a dry gas purging method

Water removal from proton exchange membrane fuel cells (PEMFC) is of great importance to improve start-up ability and mitigate cell degradation when the fuel cell operates at subfreezing temperatures. In this study, we report water removal characteristics under various shut down conditions including a dry gas-purging step. In order to estimate the dehydration level of the electrolyte membrane, the high frequency resistance of the fuel cell stack was observed. Also, a novel method for measuring the amount of residual water in the fuel cell was developed to determine the amount of water removal. The method used the phase change of liquid water and was successfully applied to examine the water removal characteristics. Based on these works, the effects of several parameters such as purging time, flow rate of purging gas, operation current, and stack temperature on the amount of residual water were investigated.