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Chaoyang Wang - One of the best experts on this subject based on the ideXlab platform.

  • liquid water transport in a mixed wet gas Diffusion Layer of a polymer electrolyte fuel cell
    Chemical Engineering Science, 2008
    Co-Authors: Puneet K Sinha, Chaoyang Wang
    Abstract:

    After PTFE treatment, a gas Diffusion Layer (GDL) of a polymer electrolyte fuel cell (PEFC) features mixed wettability, which substantially impacts liquid water transport and associated mass transport losses. A pore-network model is developed in this work to delineate the effect of GDL wettability distribution on pore-scale liquid water transport in a GDL under fuel cell operating conditions. It is found that in a mixed-wet GDL liquid water preferentially flows through connected GDL hydrophilic network, and thereby suppresses the finger-like morphology observed in a wholly hydrophobic GDL. The effect of GDL hydrophilic fraction distribution is investigated, and the existence of an optimum hydrophilic fraction that leads to the least mass transport losses is established. The need for controlled PTFE treatment is stressed, and a wettability-tailored GDL is proposed.

  • pore network modeling of liquid water transport in gas Diffusion Layer of a polymer electrolyte fuel cell
    Electrochimica Acta, 2007
    Co-Authors: Puneet K Sinha, Chaoyang Wang
    Abstract:

    A pore-network model is developed to study the liquid water movement and flooding in a gas Diffusion Layer (GDL), with the GDL morphology taken into account. The dynamics of liquid water transport at the pore-scale and evolution of saturation profile in a GDL under realistic fuel cell operating conditions is examined for the first time. It is found that capillary forces control liquid water transport in the GDL and that liquid water moves in connected clusters with finger-like liquid waterfronts, rendering concave-shaped saturation profiles characteristic of fractal capillary fingering. The effect of liquid coverage at the GDL–channel interface on the liquid water transport inside GDL is also studied, and it is found that liquid coverage at the GDL–channel interface results in pressure buildup inside the GDL causing the liquid water to break out from preferential locations.

  • liquid water transport in gas Diffusion Layer of polymer electrolyte fuel cells
    Journal of The Electrochemical Society, 2004
    Co-Authors: Ugur Pasaogullari, Chaoyang Wang
    Abstract:

    High-current-density performance of polymer electrolyte fuel cells ~PEFCs! is known to be limited by transport of reactants and products. In addition, at high current densities, excessive amount of water is generated and condenses, filling the pores of electrodes with liquid water, and hence limiting the reactant transport to active catalyst. This phenomenon known as ‘‘flooding’’ is an important limiting factor of PEFC performance. In this work, the governing physics of water transport in both hydrophilic and hydrophobic Diffusion media is described along with one-dimensional analytical solutions of related transport processes. It is found that liquid water transport across the gas Diffusion Layer ~GDL! is controlled by capillary forces resulting from the gradient in phase saturation. A one-dimensional analytical solution of liquid water transport across the GDL is derived, and liquid saturation in excess of 10% is predicted for a local current density of 1.4 A/cm 2

Aimy Bazylak - One of the best experts on this subject based on the ideXlab platform.

  • heterogeneous porosity distributions of polymer electrolyte membrane fuel cell gas Diffusion Layer materials with rib channel compression
    International Journal of Hydrogen Energy, 2016
    Co-Authors: Rupak K Banerjee, James Hinebaugh, Hang Liu, Ronnie Yip, Aimy Bazylak
    Abstract:

    Abstract In this study, X-ray Computed Tomography (X-CT) is used to study the structure of the bi-Layered gas Diffusion Layer (GDL) of polymer electrolyte membrane (PEM) fuel cells. This work presents a unique, calibrated segmentation procedure developed in-house to identify the distinct components of the bi-Layer GDL, isolating the carbon fibre, the microporous Layer and the void regions as individual phases. The novel use of the areal mass and areal volume of the GDL facilitates calibrated, reliable and repeatable multi-component segmentation and removes the high degree of subjectivity that might otherwise be encountered in typical thresholding procedures. Samples with and without MPLs are studied for the impact of rib – channel compression on porosity profiles. Under the channel, the porosity profile is nearly identical to the uncompressed profile. Under the land region, there is a significant decrease in the GDL thickness. It is also observed that the majority of the compression is exhibited by the substrate region while the MPL undergoes significantly reduced compression.

  • the impact of fibre surface morphology on the effective thermal conductivity of a polymer electrolyte membrane fuel cell gas Diffusion Layer
    Journal of Power Sources, 2014
    Co-Authors: S J Botelho, Aimy Bazylak
    Abstract:

    Abstract In this work, the effect of fibre surface morphology on the effective thermal conductivity of the gas Diffusion Layer of a polymer electrolyte membrane fuel cell is presented. Atomic force microscopy was used to measure the fibre surface roughness and asperity height distributions for various fibres for Toray carbon paper. Hertzian contact mechanics was used to determine individual micro-contact areas and thermal resistances, and results were compared with the smooth cylinder approximation. The effective thermal contact resistance between rough fibres was determined using resistance network theory. The thermal contact resistance and total contact area were determined for various angles of fibre orientation and contact forces; results are presented as empirical formulations. It was found that the effective thermal contact resistance is significantly affected by fibre roughness features when compared to the smooth fibre case, which is often used in the literature. The analysis conducted provides an alternative to computationally expensive surface feature analyses by providing a tool which can be used to implement the nano-scale features of gas Diffusion Layer fibres into existing effective thermal conductivity models.

  • the impact of fibre surface morphology on the effective thermal conductivity of a pem fuel cell gas Diffusion Layer
    224th ECS Meeting (October 27 – November 1 2013), 2013
    Co-Authors: S J Botelho, Aimy Bazylak
    Abstract:

    In this work, the preliminary findings for determining the effect of fibre surface morphology on the effective thermal conductivity of the gas Diffusion Layer of a polymer electrolyte membrane fuel cell is presented. Atomic force microscopy was used to measure the fibre surface roughness and asperity height distribution for various fibres and locations along each fibre for Toray carbon paper TGP-H-120. The thermal contact resistance was measured using preliminary methods, which will be further advanced in the near future. Hertzian contact mechanics was used to validate the results obtained, and to compare with smooth fibre thermal contact resistance for rough and smooth fibres. The thermal contact resistance was determined for various angles of fibre orientation and contact forces; it was determined that values for rough fibre contact are on average twice that of the contact of smooth fibres.

  • modeling the effective thermal conductivity of an anisotropic gas Diffusion Layer in a polymer electrolyte membrane fuel cell
    Journal of The Electrochemical Society, 2012
    Co-Authors: J Yablecki, Aydin Nabovati, Aimy Bazylak
    Abstract:

    The anisotropic and heterogeneous effective thermal conductivity of the gas Diffusion Layer (GDL) of the polymer electrolyte membrane fuel cell was determined in the throughplane direction using an analytical thermal resistance model. The geometry of the GDL was reconstructed using porosity profiles obtained through microscale computed tomography imaging of four commercially available GDL materials. The effective thermal conductivity increases almost linearly with increasing bipolar plate compaction pressure. The effective thermal conductivity was also seen to increase with increasing GDL thickness as bulk porosity remained almost constant. The effect of the heterogeneous through-plane porosity distribution on the effective thermal conductivity is discussed. The outcomes of this work will provide insight into the effect of heterogeneity and anisotropy of the GDL on the thermal management required for improved PEMFC performance. NOMENCLATURE A Area (m 2 ) a,b major and minor semi axes of elliptical contact area (m)

  • pem fuel cell gas Diffusion Layer modelling of pore structure and predicted liquid water saturation
    International Conference on Fuel Cell Science Engineering and Technology FUELCELL Collocated with ASME International Conference on Energy Sustainabili, 2011
    Co-Authors: James Hinebaugh, Aimy Bazylak
    Abstract:

    An unstructured, three-dimensional pore network model is employed to describe the effect of through-plane porosity profiles on liquid water saturation within the gas Diffusion Layer (GDL) of the polymer electrolyte membrane fuel cell. Random fibre placements are based on the porosity profiles of six commercially available GDL materials recently obtained through x-ray computed tomography experiments. The pore space is characterized with a maximal ball algorithm, and invasion percolation-based simulations are performed. It is shown that water tends to accumulate in regions of relatively high porosity due to the lower associated capillary pressures. It is predicted that GDLs tailored to have smooth porosity profiles will have fewer pockets of high saturation levels within the bulk of the material. The results provide a more detailed picture of the possible water distributions in GDLs during operation.Copyright © 2011 by ASME

Trung Van Nguyen - One of the best experts on this subject based on the ideXlab platform.

  • an experimental study of the liquid water saturation level in the cathode gas Diffusion Layer of a pem fuel cell
    Journal of Power Sources, 2012
    Co-Authors: Xuhai Wang, Trung Van Nguyen
    Abstract:

    Abstract A proton exchange membrane (PEM) fuel cell with a flow field that can be switched between the serpentine and the interdigitated flow modes was used to measure the liquid water saturation level in the gas Diffusion Layer (GDL) of the cathode and the effect of the liquid water saturation level on the fuel cell performance. Using correlations between the liquid water saturation level and gas relative permeability obtained by neutron imaging, the liquid water saturation level in the GDL under serpentine flow mode was determined by the gas pressure drop across the GDL right after the flow field was switched from the serpentine mode to interdigitated mode. The results showed that the saturation levels in the cathode GDL during the interdigitated mode was much lower than that during the serpentine mode leading to better oxygen gas access to the cathode catalyst Layer and consequently better fuel cell performance, especially at high current densities and low oxygen stoichiometric flow rate. In most cases, the fuel cell became unstable when the average liquid water saturation level exceeded 20%.

  • effect of thickness and hydrophobic polymer content of the gas Diffusion Layer on electrode flooding level in a pemfc
    Journal of The Electrochemical Society, 2005
    Co-Authors: Trung Van Nguyen
    Abstract:

    The effect of thickness and wetproof level of the gas Diffusion Layer on electrode flooding and cell performance was investigated. Three types of gas Diffusion media were tested: SGL SIGRACET carbon papers, with and without a microporous Layer, and Toray TGPH carbon paper without a microporous Layer. Overall, it was found that SGL carbon paper with the microporous Layer gave the best fuel cell performance even at low air stoichiometries. It was also found that adding poly(tetralluoroethylene) (PTFE) to the gas Diffusion Layer could enhance gas transport and water transport when a cell operates under flooding condition, but excessive PTFE loading could lead to a high flooding level in the catalyst Layer. It is our opinion that a combination of hydrophobic pores for gas transport and hydrophilic pores for liquid water transport within the macroporous Layer is needed. It is also our opinion that the optimal ratio of hydrophobic and hydrophilic pores depends on the pore size and its distribution. Finally, it was observed that without the microporous Layer, thinner gas Diffusion materials were more sensitive to liquid water accumulation than the thicker ones.

Sreenivas Jayanti - One of the best experts on this subject based on the ideXlab platform.

  • peclet number analysis of cross flow in porous gas Diffusion Layer of polymer electrolyte membrane fuel cell pemfc
    Environmental Science and Pollution Research, 2016
    Co-Authors: P.v. Suresh, Sreenivas Jayanti
    Abstract:

    Adoption of hydrogen economy by means of using hydrogen fuel cells is one possible solution for energy crisis and climate change issues. Polymer electrolyte membrane (PEM) fuel cell, which is an important type of fuel cells, suffers from the problem of water management. Cross-flow is induced in some flow field designs to enhance the water removal. The presence of cross-flow in the serpentine and interdigitated flow fields makes them more effective in proper distribution of the reactants on the reaction Layer and evacuation of water from the reaction Layer than Diffusion-based conventional parallel flow fields. However, too much of cross-flow leads to flow maldistribution in the channels, higher pressure drop, and membrane dehydration. In this study, an attempt has been made to quantify the amount of cross-flow required for effective distribution of reactants and removal of water in the gas Diffusion Layer. Unit cells containing two adjacent channels with gas Diffusion Layer (GDL) and catalyst Layer at the bottom have been considered for the parallel, interdigitated, and serpentine flow patterns. Computational fluid dynamics-based simulations are carried out to study the reactant transport in under-the-rib area with cross-flow in the GDL. A new criterion based on the Peclet number is presented as a quantitative measure of cross-flow in the GDL. The study shows that a cross-flow Peclet number of the order of 2 is required for effective removal of water from the GDL. Estimates show that this much of cross-flow is not usually produced in the U-bends of Serpentine flow fields, making these areas prone to flooding.

  • effect of air flow on liquid water transport through a hydrophobic gas Diffusion Layer of a polymer electrolyte membrane fuel cell
    International Journal of Hydrogen Energy, 2010
    Co-Authors: P.v. Suresh, Sreenivas Jayanti
    Abstract:

    Abstract The transport of liquid water through an idealized 2-D reconstructed gas Diffusion Layer (GDL) of a polymer electrolyte membrane (PEM) fuel cell is computed subject to hydrophobic boundary condition at the fibre–fluid interface. The effect of air flow, as would occur in parallel/serpentine/interdigitated type of flow fields, on the liquid water transport through the GDL, ejection into the channel in the form of water droplets and subsequent removal of the droplets has been simulated. Results show that typically water flow through the fibrous GDL occurs through a fingering and channelling type of mechanism. The presence of cross-flow of air has an effect both on the path created within the GDL and on the ejection of water into the channel in the form of droplets. A faster rate of liquid water evacuation through the GDL (i.e., more frequent ejection of water droplets) as well as less flooding of the void space results from the presence of cross-flow. These results agree qualitatively with experimental observations reported in the literature.

Branko N Popov - One of the best experts on this subject based on the ideXlab platform.

  • a review of gas Diffusion Layer in pem fuel cells materials and designs
    International Journal of Hydrogen Energy, 2012
    Co-Authors: Sehkyu Park, Branko N Popov
    Abstract:

    Abstract The gas Diffusion Layer (GDL) plays a key role on reactant gas Diffusion and water management in proton exchange membrane (PEM) fuel cells. This paper reviews recent developments of single- and dual-Layer GDLs for PEM fuel cells and various materials and approaches used for development of novel GDL. A variety of carbon- and metal-based macroporous substrates are presented. Hydrophobic treatments using different fluorinated polymers are addressed. Engineering parameters which control the performance of microporous Layer such as carbon treatment, wettability, thickness, and microstructure are also reviewed. In addition, future prospects for development of new GDL development are discussed.

  • development of supported bifunctional oxygen electrocatalysts and corrosion resistant gas Diffusion Layer for unitized regenerative fuel cell applications
    Journal of Power Sources, 2012
    Co-Authors: Shengyang Huang, Prabhu Ganesan, Hoyoung Jung, Branko N Popov
    Abstract:

    Abstract A novel bifunctional oxygen electrode (BOE) consisting of titania supported electrocatalysts (Pt/TiO 2 and Ir/TiO 2 ) and a corrosion-resistant gas Diffusion Layer (GDL) were developed for application in unitized regenerative fuel cells (URFCs). The corrosion-resistant GDL comprised of a conventional carbon substrate and a protective micro-porous Layer (MPL) of iridium–titanium nitride (Ir–TiN). Transmission electron microscopy (TEM) images revealed uniform distribution of Pt and Ir nanoparticles on the TiO 2 support with particle sizes of 4.5 and 2.0 nm, respectively, which was also confirmed by the XRD analysis. Among the various Pt–Ir compositions prepared, Pt 85 Ir 15 (with a Pt/Ir weight ratio of 85/15) showed the highest catalyst efficiency towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The URFC testing results showed that the round-trip energy conversion efficiency ( ɛ RT ) of supported Pt–Ir/TiO 2 (42%) was significantly higher than that of unsupported Pt–Ir black (30%). The TiO 2 support provided high surface area for the uniform dispersion of the catalyst particles. The URFC performance increase was ascribed to the uniform dispersion and better utilization of noble metal catalysts. Furthermore, the stability of URFC cycle performance was significantly improved by using Ir–TiN as an additional protective MPL mainly due to reduced carbon corrosion of the GDL especially during water electrolysis.