聚苯并咪唑(PBI)渗透汽化膜的研究进展

聚苯并咪唑(PBI,polybenzimidazole)是一种高性能芳香族聚合物材料.由于具有突出的耐化学性、热稳定性和机械性能,以及良好的亲水性和可纺性,PBI成为一种很有前途的渗透汽化分离膜材料.本文综述用于渗透汽化的PBI分离膜的研究进展,扼要介绍PBI渗透汽化膜几种不同的形态,包括致密平板膜、单层中空纤维膜、双层中空纤维膜以及混合基质膜,并对不同形态的PBI膜进行对比;同时也阐述分析了交联、表面改性、共混、填充等多种改性方法以及其对膜分离性能的影响.基于上述讨论,本文最后对PBI渗透汽化膜的发展方向和研究前景进行了总结.     

A novel H3PO4/Nafion–PBI composite membrane for enhanced durability of high temperature PEM fuel cells

A novel phosphoric acid doped Nafion–polybenzimidazole (H₃PO₄/Nafion–PBI) composite membrane was prepared and the H₂/O₂ single cell durability was tested at 150 °C without humidification. The durability was improved 55% compared with that of phosphoric acid doped polybenzimidazole (H₃PO₄/PBI). During the durability test, the hydrogen permeability of the membrane and the internal resistance of the single cell were detected using linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS), respectively. Before and after the durability test, the mechanical strength of the membranes was measured by stress–strain tests. The results of characterization indicated that the enhanced durability of the membrane attributed to the improved mechanical strength, which benefited from the presence of Nafion in the Nafion and PBI matrix. The preliminary results suggested that the novel H₃PO₄/Nafion–PBI composite membrane is a good candidate in high temperature PEMFC for achieving longer cell lifetime.     

机器视觉在焊点检测中的应用

阐述了利用图像处理的一些算法对半导体封装过程中的焊点进行检测,主要包括图像预处理、自动阈值图像分割、图像膨胀、空洞填充、图像连通、区域开圆运算、形状检测、计算区域特征等算法,并通过大量实验确定了参数,得到一种确实可行的应用方法完成焊点的检测。     

Durability of ABPBI‐based MEAs for High Temperature PEMFCs at Different Operating Conditions

High temperature PEMFCs based on phosphoric acid‐doped ABPBI membranes have been prepared and characterised. At 160 °C and ambient pressure fuel cell power densities of 300 mW cm^–2 (with hydrogen and air as reactants) and 180 mW cm^–2 (with simulated diesel reformate/air) have been achieved. The durability of these membrane electrode assemblies (MEAs) in the hydrogen/air mode of operation at different working conditions has been measured electrochemically and has been correlated to the cell resistivity, the phosphoric acid loss rate and the catalyst particle size. Under stationary conditions, a voltage loss of only –25 μV h^–1 at a current density of 200 mA cm^–2 has been deduced from a 1,000 h test. Under dynamic load changes or during start–stop cycling the degradation rate was significantly higher. Leaching of phosphoric acid from the cell was found to be very small and is not the main reason for the performance loss. Instead an important increase in the catalyst particle size was observed to occur during two long‐term experiments. At high gas flows of hydrogen and air ABPBI‐based MEAs can be operated at temperatures below 100 °C for several hours without a significant irreversible loss of cell performance and with only very little acid leaching.     

Iron(III) tetramethoxyphenylporphyrin(FeTMPP) as methanol tolerant electrocatalyst for oxygen reduction in direct methanol fuel cells

Carbon supported iron (III) tetramethoxyphenylporphyrin (FeTMPP) heat treated at 800°C under argon atmosphere was used as catalysts for the electroreduction of oxygen in direct methanol polybenzimidazole (PBI) polymer electrolyte fuel cells that were operated at 150°C. The electrode structure was optimized in terms of the composition of PTFE, polymer electrolyte and carbon-supported FeTMPP catalyst loading. The effect of methanol permeation from anode to cathode on performance of the FeTMPP electrodes was examined using spectroscopic techniques, such as on line mass spectroscopy (MS), on line Fourier transform infrared (FTIR) spectroscopy and conventional polarization curve measurements under fuel cell operating condition. The results show that carbon supported FeTMPP heat treated at 800°C is methanol tolerant and active catalyst for the oxygen reduction in a direct methanol PBI fuel cell. The best cathode performance under optimal condition corresponded to a potent ial reached of 0.6V vs RHE at a current density of 900 mAcm–2.     

Effects of anodic gas conditions on performance and resistance of a PBI/H3PO4 proton exchange membrane fuel cell with metallic bipolar plates

In this study, polybenzimidazole (PBI) is used as membrane material of the high-temperature membrane electrode assembly which has the features of high-performance stability and high CO tolerance. Moreover, compared to graphite bipolar plates, metallic bipolar plates have better mechanical properties and seismic capacity, as well as lighter weight. We thus use metallic bipolar plates and a PBI-based membrane electrode assembly to setup a single cell and examine its performance. The experimental results show that the cell temperature has a significant effect on the cell performance. When the temperature increases from 120 °C to 180 °C, the performance is significantly enhanced. Moreover, the CO tolerance of the fuel cell increases along with the temperature. At the same time, methane is fed in the anode stream to assess the performance of the cell under different simulated methane reformate gases. The test of various CH₄/H₂ mixtures reveals the residual methane in the reformate gases only decreases fuel cell performance slightly due to the dilution effect. We also examined H₂/CO/N₂/CH₄ mixtures in this study, and these had only a small effect on the fuel cell performance at cell temperatures higher than 160 °C. As such, it is recommended that the cell temperature should be kept higher than 160 °C.     

A PBI‐Sb0.2Sn0.8P2O7‐H3PO4 Composite Membrane for Intermediate Temperature Fuel Cells

Fine particles of a solid proton conductor Sb_0.2Sn_0.8P₂O₇ were incorporated in PBI‐H₃PO₄ membranes with 20 wt.%. In SEM figures, the Sb_0.2Sn_0.8P₂O₇ particles exhibited even and uniform distribution in the PBI‐Sb_0.2Sn_0.8P₂O₇ membrane. Influences of the immersing time and the concentration of H₃PO₄ solution for immersion on H₃PO₄ loading level were investigated. H₃PO₄ loading level was found an important factor on membrane conductivity. Incorporation of Sb_0.2Sn_0.8P₂O₇ in the PBI‐H₃PO₄ membrane resulted in greater membrane conductivities. In the single cell tests, the peak power density of the membrane electrode assembly (MEA) with the PBI‐Sb_0.2Sn_0.8P₂O₇‐H₃PO₄ membrane was also greater than that of a MEA with PBI‐H₃PO₄ membrane. One MEA using PBI‐Sb_0.2Sn_0.8P₂O₇‐H₃PO₄ membrane achieved a peak power density of 0.67 W cm^–2 at 175 °C with H₂/O₂ and exhibited satisfactory stability.     

CO electrooxidation study on Pt and Pt-Ru in H3PO4 using MEA with PBI-H3PO4 membrane

CO electrooxidation on Pt and Pt-Ru in H₃PO₄ was studied in the temperature range 120-180 °C using CO-N₂-H₂O gas mixtures of controlled composition. On Pt and Pt-Ru the voltammetry curves exhibited Tafel behavior in a wide potential range with a slope of 80-100 mV per decade. Replacement of Pt with Pt-Ru on the anode resulted mainly in a shift of CO electrooxidation voltammetry curves by approx. −0.3 V. Reaction order in respect to water vapor pressure was found close to unity with both electrocatalysts. Reaction order in respect to CO partial pressure was found negative, close to zero. Values of apparent activation energy of CO electrooxidation on these electrocatalysts were nearly equal, E_a app = 110 ± 15 kJ mol⁻¹. The results were interpreted within the framework of Langmuir-Hinshelwood mechanism. An equation, which describes the observed features of CO electrooxidation on Pt and Pt-Ru, was suggested. Comparing results of the present study with results of earlier studies of CO tolerance of Pt and Pt-Ru electrocatalysts, it was concluded that CO electrooxidation can hardly play a significant role in CO tolerance of PEM FC with PBI-PA membranes.     

Effects of temperature and humidity on the cell performance and resistance of a phosphoric acid doped polybenzimidazole fuel cell

Performance and electrochemical impedance spectroscopy (EIS) tests were performed at different temperatures and humidity levels to understand the effects of temperature and humidity on the performance and resistance of a PBI/H₃PO₄ fuel cell.The results of the performance tests indicated that increasing the temperature significantly improved the cell performance. In contrast, no improvement was observed when the gas humidity was increased. On the other hand, the EIS results showed that the membrane resistance was reduced for elevated temperatures. This development can be interpreted by the increase in membrane conductivity, as reflected by the Arrhenius equation. As the formation of H₄P₂O₇ and the self-dehydration of H₃PO₄ start around 130-140 °C, in PBI, they increase the membrane resistance at temperatures that are higher than 130 °C. In addition, the membrane resistance was reduced for elevated gas humidity levels. This is because an increase in humidity leads to an increase of the membrane hydration level.The resistance of the catalyst kinetics mainly contributes to the charge transfer resistance. However, under certain conditions, the interfacial charge transfer resistance is also important. It was concluded that the gas diffusion is the main contributor to the mass transfer resistance under dry conditions while it is the gas concentration under humid conditions.