Abstract:The focus of the current study is on a state-of-the-art twin-layer gas diffusion layer (GDL) which consists of carbon tissues with a fibre diameter of 5~20 µm, and contains a microporous layer (MPL) coating which has sub-micron porous features. In the current study, real-world digital threedimensional images of the GDL-MPL assembly are created through X-ray nano-tomography with a 680 nm pixel resolution for the GDL and focused ion beam/scanning electron microscopy (FIB/SEM) nano-tomography with a 14 nm pixel resolution for the MPL. The critical nano-structural features including porosity, characteristics lengths and 3D pore size distribution are determined directly from the 3D digital representation. In addition to morphological parameters, the FIB/SEM nanotomography technique has been combined with lattice Boltzmann (LB) numerical modelling in order to calculate the tortuosity and permeability of the MPL.
The high frequency electrochemical impedance measurements with positive imaginary components in the impedance complex plot of a polymer electrolyte fuel cell (PEFC) are attributable to the inductance of the electrical cables of the measurement system. This study demonstrates that the inductive effect of the electrical cables deforms the high frequency region of the cathode impedance spectrum and as such leads to an erroneous interpretation of the electrochemical mechanisms in the cathode catalyst layer (CCL). This study is divided into a theoretical analysis and an experimental analysis. In the theoretical analysis a validated model that accounts for the impedance spectrum of the CCL as reported in the authors’ previous study is applied with experimental impedance data reported in the literature. The results show that the ionic resistance of the CCL electrolyte which skews the oxygen reduction reaction (ORR) current distribution toward the membrane interface is masked in the cathode impedance spectrum by the inductive component. In the experimental analysis cathode experimental impedance spectra were obtained through a three-electrode configuration in the measurement system and with two different electrical cables connected between the electronic load and the PEFC. The results agree with the theoretical analysis and also show that the property of causality in the Kramers-Kronig mathematical relations for electrochemical impedance spectroscopy (EIS) measurements is violated by the external inductance of the measurement cables. Therefore the experimental data presenting inductance at high frequencies do not represent the physics and chemistry of the PEFC. The study demonstrates that a realistic understanding of factors governing EIS measurements can only be gained by applying fundamental modeling which accounts for underlying electrochemical phenomena and experimental observations in a complementary manner.
This work reports a feasibility study into the combined full morphological reconstruction of fuel cell structures using X-ray computed micro- and nanotomography and lattice Boltzmann modeling to simulate fluid flow at pore scale in porous materials. This work provides a description of how the two techniques have been adapted to simulate gas movement through a carbon paper gas diffusion layer (GDL). The validation work demonstrates that the difference between the simulated and measured absolute permeability of air is 3%. The current study elucidates the potential to enable improvements in GDL design, material composition, and cell design to be realized through a greater understanding of the nano- and microscale transport processes occurring within the polymer electrolyte fuel cell.
DOI: 10.1243/09576509JPE603Abstract: A qualitative account of the causes and effects of performance degradation and failure in hydrogen-fuelled polymer electrolyte fuel cells (PEFCs) is given in the present review. The purpose of the review is to establish a backbone understanding of the phenomenological processes that occur within the PEFC, how they interact, how they are influenced through elements of design, manufacturing and operation, and ultimately how they result in performance degradation and cell failure. In the current work, 22 common faults are identified which are induced by 48 frequent causes. The major PEFC components considered here that are susceptible to faults are the polymer electrolyte-based membrane, the anode and cathode catalyst layers, gas diffusion and microporous layers, seals and the bipolar plate. Faults pertaining to these components can cause irreversible increases in activation, mass transportation, ohmic and fuel efficiency losses, or indeed cause catastrophic cell failure.
Morphological parameters of a 3D binary image of a porous carbon gas diffusion layer (GDL) for polymer electrolyte fuel cells (PEFC) reconstructed using X-ray nano-tomography scanning have been obtained, and influence of small alterations in the threshold value on the simulated flow properties of the reconstructed GDL has been determined. A range of threshold values with 0.4% increments on the greyscale map have been applied and the gas permeability of the binary images have been calculated using a single-phase lattice Botlzmann model (LBM), which is based on the treatment of nineteen velocities in the three dimensional domain (D3Q19). The porosity, degrees of anisotropy and the mean pore radius have been calculated directly from segmented voxel representation. A strong relationship between these parameters and threshold variation has been established. These findings suggest that threshold selection can significantly affect some of the flow properties and may strongly influence the computational simulation of micro and nano-scale flows in a porous structure.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.