Improvement of fuel cell performances through the enhanced dispersion of the PTFE binder in electrodes for use in high temperature polymer electrolyte membrane fuel cells

In high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), it is important that the structure of the electrode catalyst layer is formed uniformly. To achieve this, the binder must be well dispersed; however, polytetrafluoroethylene (PTFE), which is commonly employed in the preparation of HT-PEMFCs, is difficult to disperse during electrode manufacture due to its high hydrophobicity. In this study, we fabricate electrodes containing a surfactant to improve the dispersion of the PTFE binder and to enhance reproducibility during electrode manufacture. The electrodes are commonly prepared via a bar coating method, which is known to exhibit poor dispersion due to the small amounts of solvent employed compared to the spraying method. We then compare the properties of the obtained electrodes prepared in the presence and absence of the surfactant through physical and electrochemical characterization. It is found that the electrode containing the surfactant is structurally superior, and its single cell performance is significantly higher (i.e., 0.65 V at 0.2 Am cm⁻²). The single cells are suitable for operation at 150 °C using H₂/air at atmospheric pressure and a total platinum loading of 2.0 mg cm⁻².     

光固化3D打印离型膜在树脂作用下的变形分析

在光固化光敏树脂成型过程中,聚四氟乙烯离型膜会在树脂液位的波动影响下发生变形,进而影响光固化制件的精度,因此需要减小离型膜在制件过程的变形量,确保其相对稳定。首先分析树脂液位变化,通过液位变化量,等效出树脂液波动带给离型膜的载荷,建立离型膜受力模型。然后基于离型薄膜的挠度变形理论,应用Ansys软件进行模拟研究,对不施加预应力和施加不同预应力作用下的离型膜变形结果分析,结果表明施加预应力有利于提高离型膜稳定性,且施加预应力为2. 645M Pa时离型膜受到树脂波动影响最小,位置精度变化在0. 01 mm。     

载荷对PTFE/AlSi10Mg复合材料摩擦磨损行为的影响

采用选区激光熔化(SLM)、浸渗和真空烧结工艺制备了以AlSi10Mg为基体的多孔骨架填充聚四氟乙烯(PTFE)的自润滑复合材料。采用往复式Bruker UMT-3摩擦试验机研究了速度为5mm/s、不同载荷下复合材料的摩擦磨损性能,并采用SEM、EDS等对其成分、结构以及摩擦学行为进行了研究。结果表明,复合材料的平均摩擦因数和磨损率随着载荷的增加呈现先增大后减小的趋势;复合材料的摩擦稳定性主要由存储在骨架中的PTFE决定。其摩擦机制主要是在载荷的作用下,当磨擦表面发生磨损时,骨架中的PTFE将磨屑捕获,形成完整的PTFE润滑层,并且发生膜的转移,从而增加了复合材料的摩擦学稳定性。     

耐磨增韧改性聚甲醛的制备及性能研究

用双螺杆共混挤出法制备了不同比例的聚四氟乙烯(PTFE)纤维改性聚甲醛(POM),考察了PTFE纤维含量对POM摩擦磨损性能、力学性能和热稳定性的影响。在POM/PTFE耐磨体系中,创新性地引入聚氧化乙烯(PEO)作为相容剂,制备出耐磨性能和韧性俱佳的POM改性材料。对POM改性材料进行了耐磨性和力学性能分析,利用偏光显微镜进一步证实了PEO能促进PTFE纤维和POM的相容性。结果表明,随着PTFE纤维含量的增加,POM的摩擦磨损性能有所提高,但力学性能不理想。在8%PTFE+92%POM体系中引入PEO,改性材料的摩擦因数低至0.169,缺口冲击强度比POM提高了173%,得到了耐磨和增韧效果显著的POM改性材料。     

Variations in surface and electrical properties of polytetrafluoroethylene film after plasma-induced grafting of acrylic acid

Polytetrafluoroethylene(PTFE) film was graftpolymerized with acrylic acid(AAc) via a low-temperature plasma technique.The effect of plasma treatment parameters(radio-frequency power and treatment time) on the spin number of free radicals in PTFE film was examined.Attenuated total reflection Fourier transform infrared(ATR-FTIR)spectroscopy,X-ray photoelectron spectroscopy,scanning electron microscopy,and atomic force microscopy were employed to characterize the chemical structure,surface composition,and microstructure of the original PTFE and PTFE-g-PAAc films,respectively,in order to verify the successful graft polymerization of AAc onto a PTFE film surface.Thermogravimetric analysis illustrated that the thermal stability of bulk PTFE film remains unchanged after graft modification.Water contact angle measurements confirmed that the hydrophilicity of PTFE-g-PAAc film was effectively improved as compared to the original PTFE film.The dielectric constant(ε_r) of PTFE-g-PAAc(GD =218 μg/cm~2) film remained invariable,compared to that of the unmodified PTFE film.Nevertheless,the dielectric loss(tanδ) of PTFE film increased considerably,from 0.0002(GD = 0μg/cm~2) to 0.0073(GD = 218 μg/cm~2),which might be due to the increase in surface polarity and moisture resulting from AAc graft modification.In addition,the surface electrical resistance(R_s) of PTFE film decreased slightly,from 131.89(GD = 0 μg/cm~2) to 110.28 Ω cm~2(GD = 218μg/cm~2) after surface modification,but still retained its inherent high impedance.     

Optimization of polytetrafluoroethylene content in cathode gas diffusion layer by the evaluation of compression effect on the performance of a proton exchange membrane fuel cell

This research investigates the optimal polytetrafluoroethylene (PTFE) content in the cathode gas diffusion layer (GDL) by evaluating the effect of compression on the performance of a proton exchange membrane (PEM) fuel cell. A special test fixture is designed to control the compression ratio, and thus the effect of compression on cell performance can be measured in situ. GDLs with and without a microporous layer (MPL) coating are considered. Electrochemical impedance spectroscopy (EIS) is used to diagnose the variations in ohmic resistance, charge transfer resistance and mass transport resistance with compression ratio. The results show that the optimal PTFE content, at which the maximum peak power density occurs, is about 5 wt% with a compression ratio of 30% for a GDL without an MPL coating. For a GDL with an MPL coating, the optimal PTFE content in the MPL is found to be 30% at a compression ratio of 30%.     

PTFE的辐射裂解、交联及其应用

聚四氟乙烯（PTFE）是一种性能优异的工程塑料，通常被认为是典型的辐射裂解材料。PTFE可以在不同条件下实现裂解并生成PTFE微粉。在高于PTFE的熔点即温度为330～340℃，真空或惰性气氛下进行辐照，可实现PTFE的交联。本工作综述了PTFE辐射裂解和交联研究的历史和最新进展，并对交联PTFE在润滑材料、燃料电池、光刻等领域的应用进行了介绍。     

Power generation using carbon mesh cathodes with different diffusion layers in microbial fuel cells

An inexpensive carbon material, carbon mesh, was examined to replace the more expensive carbon cloth usually used to make cathodes in air-cathode microbial fuel cells (MFCs). Three different diffusion layers were tested using carbon mesh: poly(dimethylsiloxane) (PDMS), polytetrafluoroethylene (PTFE), and Goretex cloth. Carbon mesh with a mixture of PDMS and carbon black as a diffusion layer produced a maximum power density of 1355 ± 62 mW m⁻² (normalized to the projected cathode area), which was similar to that obtained with a carbon cloth cathode (1390 ± 72 mW m⁻²). Carbon mesh with a PTFE diffusion layer produced only a slightly lower (6.6%) maximum power density (1303 ± 48 mW m⁻²). The Coulombic efficiencies were a function of current density, with the highest value for the carbon mesh and PDMS (79%) larger than that for carbon cloth (63%). The cost of the carbon mesh cathode with PDMS/Carbon or PTFE (excluding catalyst and binder costs) is only 2.5% of the cost of the carbon cloth cathode. These results show that low cost carbon materials such as carbon mesh can be used as the cathode in an MFC without reducing the performance compared to more expensive carbon cloth.     

Effect of the Anodic Diffusion Layer on the Performance of Liquid Fuel Cells

Novel diffusion layers for liquid direct methanol fuel cells (DMFCs) are designed and fabricated. The factors affecting the performance of DMFCs are determined. The results demonstrate that the diffusion layers made by micrometer scale particles and a hydrophilic binder can reduce the liquid sealing effect and increase the mass transfer property. The performance of DMFCs made using novel diffusion layers is greatly improved. The porous structure of such diffusion layers may improve the channels therein, which allows liquid methanol to diffuse in and gaseous CO₂ to diffuse out easily. Higher methanol concentrations can be used due to the formation of a larger three‐phase interfacial area.