共查询到20条相似文献，搜索用时 15 毫秒
1.
A. Mohseninia D. Kartouzian M. Eppler P. Langner H. Marktter F. Wilhelm J. Scholta I. Manke 《Fuel Cells》2020,20(4):469-476
The influence of hydrophobicity and porosity of the catalyst layer (CL) and cathode microporous layer (MPLC) on water distribution and performance of polymer electrolyte membrane fuel cell (PEMFC) is investigated. Hydrophobicity of the layers is altered with the addition of PTFE (polytetrafluoroethylene) and mono‐dispersed polymer particles are utilized to introduce the macro‐pores with a diameter of 0.5 µm and 30 µm within the CL and MPLC, respectively. The treated materials are implemented in a specially designed fuel cell with an active area of 8 cm2 to perform operando high‐resolution neutron tomography measurements. At high current density and humid operating conditions, MPLs with higher PTFE content increase the overall water content of the cell. The more hydrophobic MPL (40 wt.% PTFE) performs below the corresponding reference MPL (20 wt.% PTFE), whereas the performance result of double layer MPLC gives hint for further potential improvements of such design. The local water saturation beneath the land regions with the presence of perforated CL and MPLC is increased which is explained by lower capillary pressure barriers of bigger pores. Despite a higher water content, the perforated layers enhance the performance of the cell at both dry (RH 70%) and humid conditions (RH 120%), indicating that the parallel two‐phase flow is facilitated where the oxygen is transported through small pores and the water is preferentially transported through the bigger pores. 相似文献
2.
To alleviate membrane dehydration in polymer electrolyte fuel cells (PEFCs) during low‐humidity operations, it is essential to deeply understand two water crossover phenomena through electrolyte membranes. This study presented the quantitative method for separately evaluating the electro‐osmotic and back‐diffusion water transports in the electrolyte of an operating PEFC based on the measurements of water vapor and current distributions. Firstly, the water vapor distribution in the anode flow field was investigated by the visualization technique using humidity test paper (HTP). Subsequently, the detailed transport processes of water through the electrolyte membrane can be numerically estimated from the measurement results of water and current profiles by using a simple fuel cell model. In this work, the effects of inlet gas humidification, microporous layer (MPL) addition and flow configuration on the two water transports in the membrane were demonstrated under low‐humidity conditions to verify the validity of the proposed methodology. Results revealed that the introduction of MPL on the cathode side increases the water concentration in the anode channel due to the back‐diffusion effect. The counter‐flow configuration effectively improves the membrane hydration at the anode inlet because of the strong back‐diffusion from the wetted cathode outlet. 相似文献
3.
We demonstrate an enhanced new architecture for fuel cell membrane electrode assemblies (MEAs), by deposition of the microporous layer (MPL) directly on the catalyst coated membrane (CCM), in order to reduce any gaps at the cathode catalyst layer (CCL) surface. A low bonding temperature Teflon was used to allow low temperature sintering of the CCM with the MPL. This modified structure enhances PEMFC performance by improving the electronic contact and minimizing water pooling at the CCL|MPL interface. The improvement in water management at the CCL|MPL is beneficial especially for thinner CCLs to fulfill the performance demand with low cathode catalyst loading MEAs (≤0.125 mgPt cm−2 as targeted by the US Department of Energy). 相似文献
4.
The achievement of durability targets is an important challenge for the commercialization of fuel cell electric vehicles (FCEV). In order to meet the requirements, knowledge about the most severe degradation mechanisms of fuel cell stacks under automotive conditions is crucial. In the present work, degradation analysis of an automotive full size stack is performed. Herein, we focus on defects at the cathode catalyst layer and their interrelation including inhomogeneous adhesion of the microporous layer on the catalyst layer, crack formation, cathode catalyst layer thinning and wrinkling of the catalyst coated membrane. In addition, we report linear and circular Pt depositions on top of the cathode catalyst layer, which have to the best of our knowledge not been described in literature yet. For the latter, a degradation mechanism based on liquid water formation, local fuel starvation and current density distribution at the interface between microporous layer and cathode catalyst layer is postulated. Finally, a fast indication for stack degradation is suggested by correlating different degradation phenomena. This improved stack analysis approach allowed us to detect local differences in degradation on both cell and stack level. 相似文献
5.
A proper water management is important for an efficient operation of a polymer electrolyte membrane (PEM) fuel cell system. The humidity distribution in the anode gas channels is highly dependent on the cathode humidity and the resulting transmembrane water transport. Therefore, it can be assumed that the cell humidification is optimal when the relative anode humidity is nearly 100% and homogeneously distributed. In contrast to state‐of‐the‐art approaches, this study focuses on the humidity distribution on anode side in consideration of the anode recirculation loop. Therefore, a macroscopic 1D+1D simulation model was developed, which simulates humidity profiles along the gas channels with consideration of the transmembrane water transport and the anode gas recirculation. This study shows the impact of relevant input parameters, such as pressure, stoichiometry and cathode inlet humidity. Furthermore, the results show that it is possible to reach a nearly homogeneous humidity distribution along the anode gas channels for automotive fuel cell systems. This can be achieved through appropriate operation conditions, e.g., suitable combination of pressure and stoichiometry, and supportive flow directions of the gases and the coolant. The analysis was made for fuel cells operating at full load at system relevant conditions with and without external humidification. 相似文献
6.
7.
A. Kulikovsky 《Fuel Cells》2016,16(6):754-759
A recently pubilshed experimental polarization curve of a PEM fuel cell with the non–Pt cathode catalyst layer (CCL) exhibits unusual feature: in the region of small current densities, the curve is close to linear. We report a model for the CCL performance which explains this effect. The model includes finite rate of the oxygen adsorption on the catalyst surface. Qualitatively, due to a very high exchange current density of the non–Pt catalyst, the ORR rate close to the membrane is determined by the potential–independent oxygen adsorption rate. This leads to a specific regime of the CCL operation, when only part of the CCL thickness contributes to current production, while the rest part is completely inactive. With the growth of the cell current, the active part increases in width, while the inactive part shrinks. The resulting polarization curve appears to be close to linear. 相似文献
8.
Oxygen transport in the porous gas diffusion layer (GDL), which is generally characterised by the oxygen effective diffusivity, is of great importance for the performance of proton exchange membrane fuel cells (PEMFCs). The determination of the oxygen effective diffusivity is challenging due to the complex structure of the porous GDL samples. In the present study, a two‐dimensional network consisting of arms and nodes is adopted to illustrate how oxygen effective diffusivity is affected by the GDL structure under the condition with/without water invasion. Water permeation in the network is simulated using the invasion percolation algorithm and oxygen transport in the arms is described by Fick's law. The simulation results reveal that oxygen effective diffusivity under dry condition decreases with increase in the network heterogeneity. With water permeation, the oxygen effective diffusivity goes to zero even though water saturation is rather less than unity. The critical water saturation, above which the oxygen effective diffusivity becomes zero, is found to decrease with increasing heterogeneity. To enhance oxygen transport, four different modified networks are introduced in the present study. It is found that the network with large arms in oxygen transport direction has the best oxygen and water transport properties. 相似文献
9.
《Fuel Cells》2018,18(4):413-421
Effect of freeze/thaw cycles on the performance of polymer electrolyte membrane fuel cell (PEMFC) is investigated. Freeze/thaw cycle is repeated 40 times. The performance is degraded, as the number of freeze/thaw cycles increases. The maximum degradation is about 35% at high current density. The performance degradation is analyzed based on the change of water distribution. X‐ray visualization is conducted 3 times; before, after 10th and 40th freeze/thaw cycle, respectivly. The water saturation in PEMFC is getting reduced, as the number of freeze/thaw cycles increases. Over‐potential analysis is conducted using visualization result by calculating the proton conductivity. The proton conductivity is decreased about 30% at high current density after 40th freeze/thaw cycle. The change of water distribution is analyzed based on the structural change of the GDL. The water volume change upon freeze/thaw cycle leads to cracks in the micro porous layer. It facilitates water removal from the GDL and leads to low water saturation in PEMFC. 相似文献
10.
M. Ahadi J. Jankovic M. Tam B. Zahiri M. S. Saha J. Stumper M. Bahrami 《Fuel Cells》2019,19(5):550-560
This work proposes new and accurate systematic methodologies for ex situ measurements of through‐plane thermal and in‐plane electronic conductivities of catalyst layers (CLs) of polymer electrolyte membrane fuel cells (PEMFC). The developed methods are based on measurements of different thicknesses/lengths of a CL on different substrates. Suitability of the proposed methods is confirmed through a set of microstructural properties measurements on a typical CL design to ensure the measured CLs would be representative of CLs in a real fuel cell product. Conductivity measurements of two CL designs with different compositions and microstructures confirm capability of the developed procedures to track structural changes in CLs. The present characterization platform is not limited to CLs and may be used for other composite porous materials with similar structures. 相似文献
11.
A sulfophenylated polysulfone (PSU‐sph), carrying 0.8 sulfonic acid units per repeating unit of the polymer, is evaluated as a membrane electrolyte for DMFC applications. The liquid uptake, methanol transport characteristics, electrolyte conductivity, and fuel cell performance are investigated. The methanol transport and DMFC performance results are compared to those of Nafion® 117. The PSU‐sph membrane investigated shows superior qualities with regard to methanol crossover, with a methanol permeability of approximately 25% compared to that of Nafion®. The conductivity was measured to be 15% compared to that of Nafion®. However, this could not fully account for the internal resistance of the cell, implying that the contact resistance between the electrodes and electrolyte is higher when PSU‐sph is used, probably because the electrodes are developed for use with Nafion® membranes. The stability of the PSU‐sph membrane seems promising, with very low degradation observed over a period of 72 hours. It was concluded that although the mass transport properties of the PSU‐sph membrane sample investigated were superior, it could not match the performance of Nafion® 117 in a DMFC application. However, a higher degree of sulfonation may have a significant positive effect on cell performance. The results also showed that a fully intergrated MEA is needed to fully assess new menbrane materials. 相似文献
12.
We report a three‐dimensional (3D), pore‐scale analysis of morphological and transport properties for a polymer electrolyte fuel cell (PEFC) catalyst layer. The 3D structure of the platinum/carbon/Nafion electrode was obtained using nano‐scale resolution X‐ray computed tomography (nano‐CT). The 3D nano‐CT data was analyzed according to several morphological characteristics, with particular focus on various effective pore diameters used in modeling gas diffusion in the Knudsen transition regime, which is prevalent in PEFC catalyst layers. The pore diameter metrics include those based on chord length distributions, inscribed spheres, and surface area. Those pore diameter statistics are evaluated against computational pore‐scale diffusion simulations with local gas diffusion coefficients determined from the local pore size according to the Bosanquet formulation. According to our comparison, simulations that use local pore diameters defined by inscribed spheres provide effective diffusion coefficients that are consistent with chord‐length based estimations for an effective Knudsen length scale. By evaluating transport rates in regions of varying porosity within the nano‐CT data, we identified a Bruggeman correction scaling factor for the effective diffusivity. 相似文献
13.
《Fuel Cells》2018,18(2):129-136
Membrane‐electrode assemblies (MEAs) are fabricated using different catalysts and ionomers, in order to investigate the effects of these factors on the performance and stability of the polymer electrolyte membrane fuel cell (PEMFC). Platinum catalysts with different degrees of graphitization in the carbon support (less graphitized: Tanaka, more graphitized: RTX) are used. Perfluorosulfonic acid polymer‐based ionomers with water‐based or organic solvent‐based solvents are also prepared as binders for the electrode. The optimum composition of catalyst and ionomer is identified based on the results of cyclic voltammetry, electrochemical impedance spectroscopy, single cell performance, and long‐term durability tests. Tanaka catalyst and water‐based ionomer show the best performance and durability. In addition, the ionomer to carbon (I/C) weight ratio affects the fuel cell performance, and the optimum value is I/C = 1 for both water‐based and organic solvent‐based ionomers. 相似文献
14.
Water management in polymer electrolyte membrane fuel cells (PEMFCs) is extremely important for the high performance and durable operation of fuel cells. Therefore, fundamental understanding of water transport involved in operating PEMFCs is necessary. This article presents a review of in situ magnetic resonance imaging (MRI) visualisation of water in operating PEMFCs, which is recognised as a powerful diagnostic tool for probing water behaviours, both in flow fields and in the membrane electrode assembly (MEA). The basic principles and hardware related to MRI visualisation are described with emphasis on the design, construction and material selection of a PEMFC for MRI experiments. The MRI results reported by several groups are outlined to illustrate the versatility and potential usefulness of in situ visualisation of water in operating PEMFCs using MRI. 相似文献
15.
A three‐dimensional numerical model of the polymer electrolyte fuel cell (PEFC) is applied to study current distribution and cell performance under a current density boundary condition. Since the electronic resistance in the along‐channel direction in the current collector plate is much larger than in the other two directions, i.e., 50 mΩ cm2 vs. 0.5 mΩ cm2, it significantly affects current flow, and current and cell voltage distributions in a PEFC. An identical polarization curve results with two different boundary conditions, constant cell voltage and constant current density, however, the current density profiles in the along‐channel direction differ significantly; it is much flatter for the constant current boundary condition. Increasing the electronic conductivity of the bipolar plate diminishes the difference in the current density distribution under the two boundary conditions. The results also point out that an experimental validation of a PEFC model based on the polarization curve alone is insufficient, and that detailed current density distribution data in the along‐channel direction is essential. 相似文献
16.
Impact of graphite on the physicochemical properties of high density polyethylene (HDPE)/copper composites has been investigated at various volume percentages of copper. The two sets of composites are prepared by simple melt blending and injection molding approach. Thermal conductivity increases from 0.5 W m−1 K−1 for pure HDPE to 6.5 and 8 Wm−1 K−1 for 30 and 40 vol.% of copper loading with and without graphite, respectively. A huge increment in synergistic efficiency has been evidenced for the mixed filled polymer composites. Incorporation of graphite has also improved the percolation threshold from 19 to 13 vol.% of copper loading to the HDPE matrix, which indicates the synergistic effect of mixed filler system. Development of leafy morphology of copper promotes large number of inter‐particle contacts and hence improves the percolation threshold of the composites. The corrosion resistive, mechanically robust, electrically and thermally conductive composites with good flexural properties and light in weight than conventional metallic bipolar plates suggest it a material of choice for fuel cell devices. 相似文献
17.
Two materials, polyaniline (PANI) and titanium nitride (TiN), used for bipolar plate (BPP) coatings have each shown promise in improving the corrosion resistance and contact resistance, respectively, of metallic bipolar plates. Polyaniline was shown to provide a barrier for the bipolar plate and to effectively lower the corrosion currents observed in ex situ corrosion tests. However, the interfacial contact resistance (ICR) between polyaniline coatings and gas diffusion layer (GDL) is high and results in high electrical losses. On the other hand, TiN is reported to achieve good conductivity and in some cases improved corrosion resistance. The two materials have also been investigated together in a composite coating and showed promising results, but the contact resistance of the coating was still too high for use in a commercial fuel cell. In this study, the application of an additional layer of TiN over the TiN‐polyaniline composite coating (a bilayer coating) is investigated. Composite bilayered PANI TiN coatings were deposited upon SS316L substrates. The optimized coating achieved U.S. Department of Energy (DoE) targets with potentiostatic corrosion currents of ∼0.024 μA cm−2 and ICR values of 11.2 mΩ cm2. PANI polymerization was confirmed, using Fourier‐transform infrared (FTIR) spectroscopy and TiN loadings were investigated with energy dispersive X‐ray (EDX) spectroscopy . 相似文献
18.
It is well known that the electrode structure of a PEMFC has a huge influence on the water management and thereby on the cell performance. In this work, two MEAs – one prepared by an airbrushing technique and the other by a novel fast spray coating technique (multilayered MEA) – were analysed with respect to porosity, pore size distribution, tortuosity and their electrochemical performance. FIB nanotomography with following 3D reconstruction, SEM investigation on ultramicrotomic thin‐sections, and single cell tests were performed on these MEAs. The results show a higher porosity and lower pore size for the multilayered MEA. The multilayered MEA reaches a Pt utilisation of 1,962 mW mg–1 and a peak power density of 210 mW cm–2, whereas the airbrushed MEA only provides a Pt utilisation of 879 mW mg–1 and a peak power density of 218 mW cm–2. The Pt utilisation calculations showed in combination with the structural characterisations that a homogeneous pore structure and Pt distribution provide an advantage with regard to performance and efficiency of the PEMFC. Furthermore, the multilayered MEA may offer an advantage over the airbrushed MEA in its long term stability, which was observed in preliminary tests. 相似文献
19.
The catalytic activity of Pt1–xPdx nanoparticles supported on carbon nanotubes (CNTs) was evaluated for both the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) of polymer electrolyte membrane fuel cells (PEMFCs). Using a colloidal method, Pt1–xPdx/CNTs catalysts (x = 0, 0.46, 0.76, and 0.9) were prepared, and their physical and electrochemical characteristics were analyzed using a variety of characterization techniques, including XRD, TEM, energy dispersive spectrometer, cyclic voltammetry, and electrochemical impedance spectroscopy. Both Pt and Pd atoms formed a continuous solid solution and thus were randomly mixed in Pt1–xPdx nanoparticles. Due to the high hydrogen absorption of Pd, the use of Pd in the catalyst provided an advantage for HOR but a disadvantage for ORR. The Pt0.53Pd0.47/CNTs catalyst in the anode and cathode showed the best cell performance of PEMFCs. 相似文献
20.
This work demonstrates that the operation of a subsaturated polymer electrolyte fuel cell in counterflow mode results in a significantly elongated relaxation time after a load change, if compared to coflow mode. This effect is investigated here by using combined dynamic locally resolved measurements of the current density, the high frequency resistance, and the relative humidity. It is shown that the elongated relaxation time is a consequence of slow membrane hydration in the region of the cell, downstream the anode flow field, where the diffusive flux of water across the membrane occurs from the anode to the cathode. Here, the anode gas stream, which is humidified upstream the anode flow field via back diffusion of water from the cathode to the anode, is the only source of water for both membrane hydration and the internal humidification of the cathode gas stream, which passes the cell in opposite direction. 相似文献