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Chaoyang Wang - One of the best experts on this subject based on the ideXlab platform.
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liquid water transport in a mixed wet Gas Diffusion Layer of a polymer electrolyte fuel cell
Chemical Engineering Science, 2008Co-Authors: Puneet K Sinha, Chaoyang WangAbstract: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.
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pore network modeling of liquid water transport in Gas Diffusion Layer of a polymer electrolyte fuel cell
Electrochimica Acta, 2007Co-Authors: Puneet K Sinha, Chaoyang WangAbstract: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.
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anisotropic heat and water transport in a pefc cathode Gas Diffusion Layer
Journal of The Electrochemical Society, 2007Co-Authors: Ugur Pasaogullari, Chaoyang Wang, Partha P Mukherjee, Ken S ChenAbstract:A nonisothermal, two-phase model was developed to investigate simultaneous heat and mass transfer in the cathode Gas Diffusion Layer GDL of a polymer electrolyte fuel cell PEFC. The model was applied in two-dimensions with the in-plane i.e., channel-to-land and through-plane i.e., catalyst Layer-to-channel directions to investigate the effects of anisotropy of GDL. For the first time, the anisotropy in the GDL properties was taken into account and found to be an important factor controlling the temperature distribution in the GDL. The maximum temperature difference in the GDL was found to be a strong function of GDL anisotropy. A temperature difference of up to 5°C at a cell voltage of 0.4 V was predicted for an isotropic GDL while it reduced to 3°C for an anisotropic GDL. Significant effect of temperature distribution on liquid water transport and distribution was also observed. In addition, the latent heat effects due to condensation/evaporation of water on the temperature and water distributions were analyzed and found to strongly affect the two-phase transport.
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liquid water transport in Gas Diffusion Layer of polymer electrolyte fuel cells
Journal of The Electrochemical Society, 2004Co-Authors: Ugur Pasaogullari, Chaoyang WangAbstract: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
Trung Van Nguyen - One of the best experts on this subject based on the ideXlab platform.
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an experimental study of the liquid water saturation level in the cathode Gas Diffusion Layer of a pem fuel cell
Journal of Power Sources, 2012Co-Authors: Xuhai Wang, Trung Van NguyenAbstract: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%.
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effect of thickness and hydrophobic polymer content of the Gas Diffusion Layer on electrode flooding level in a pemfc
Journal of The Electrochemical Society, 2005Co-Authors: Trung Van NguyenAbstract: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.
Adam Z Weber - One of the best experts on this subject based on the ideXlab platform.
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non isothermal melting of ice in the Gas Diffusion Layer of a proton exchange membrane fuel cell
International Journal of Heat and Mass Transfer, 2013Co-Authors: Thomas J Dursch, Gregory J Trigub, Jianfeng F Liu, C J Radke, Adam Z WeberAbstract:Abstract Non-isothermal ice melting in the fibrous Gas-Diffusion Layer (GDL) of a proton-exchange-membrane fuel cell (PEMFC) is investigated using differential scanning calorimetry (DSC). Non-isothermal ice-melting rates and ice-melting times are obtained from heat-flow measurements in water-saturated Toray GDLs at heating rates of 1, 2.5, 5, 10, and 25 K/min. In all cases, ice-melting times decrease nonlinearly with increasing heating rate. Nevertheless, melting temperatures remain at 272.9 ± 0.5 and 272.7 ± 0.4 K for bulk ice and ice within the GDL, respectively, reiterating that melting is thermodynamic-based at a rate limited by heat transfer. The slight GDL ice melting-point depression is consistent with the Gibbs–Thomson equation for equilibrium melting using an average pore diameter of 30 μm. Ice-melting endotherms are predicted from overall DSC energy balances coupled with a moving-boundary Stefan problem, where an ice-melting front within a GDL propagates with volume-averaged properties through an effective medium. Agreement between DSC experiment and theory is excellent. The proposed model accurately predicts ice-melting endotherms for Toray GDLs with two ice saturations and for bulk ice. Further, a pseudo-steady-state analysis obtains an analytical expression for ice-melting time, which is controlled by the time for heat addition to the propagating solid/liquid interface. Significantly, the new expression elucidates parameters controlling ice melting and allows for better design of both GDL materials and heating strategies to enhance the success of PEMFC cold-start.
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pseudo isothermal ice crystallization kinetics in the Gas Diffusion Layer of a fuel cell from differential scanning calorimetry
International Journal of Heat and Mass Transfer, 2013Co-Authors: Thomas J Dursch, Gregory J Trigub, C J Radke, Monica A Ciontea, Adam Z WeberAbstract:Abstract Non-isothermal ice-crystallization kinetics in the fibrous Gas-Diffusion Layer (GDL) of a proton-exchange-membrane fuel cell is investigated using differential scanning calorimetry (DSC). Non-isothermal ice-crystallization rates and ice-crystallization temperatures are obtained from heat-flow measurements in a water-saturated commercial GDL at cooling rates of 2.5, 5, 10, and 25 K/min. Our previously developed isothermal ice-crystallization rate expression is extended to non-isothermal crystallization to predict ice-crystallization kinetics in a GDL at various cooling rates. Agreement between DSC experimental results and theory is good. Both show that as the cooling rate increases, ice-crystallization rates increase and crystallization temperatures decrease monotonically. Importantly, we find that the cooling rate during crystallization has a negligible effect on the crystallization rate when crystallization times are much faster than the time to decrease the sample temperature by the subcooling. Based on this finding, we propose a pseudo-isothermal method for obtaining non-isothermal crystallization kinetics using isothermal crystallization kinetics evaluated at the non-isothermal crystallization temperature.
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isothermal ice crystallization kinetics in the Gas Diffusion Layer of a proton exchange membrane fuel cell
Langmuir, 2012Co-Authors: Thomas J Dursch, C J Radke, Monica A Ciontea, Adam Z WeberAbstract:Nucleation and growth of ice in the fibrous Gas-Diffusion Layer (GDL) of a proton-exchange membrane fuel cell (PEMFC) are investigated using isothermal differential scanning calorimetry (DSC). Isothermal crystallization rates and pseudo-steady-state nucleation rates are obtained as a function of subcooling from heat-flow and induction-time measurements. Kinetics of ice nucleation and growth are studied at two polytetrafluoroethylene (PTFE) loadings (0 and 10 wt %) in a commercial GDL for temperatures between 240 and 273 K. A nonlinear ice-crystallization rate expression is developed using Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory, in which the heat-transfer-limited growth rate is determined from the moving-boundary Stefan problem. Induction times follow a Poisson distribution and increase upon addition of PTFE, indicating that nucleation occurs more slowly on a hydrophobic fiber than on a hydrophilic fiber. The determined nucleation rates and induction times follow expected trends from classical nuclea...
Huamin Zhang - One of the best experts on this subject based on the ideXlab platform.
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electrochemical durability of Gas Diffusion Layer under simulated proton exchange membrane fuel cell conditions
International Journal of Hydrogen Energy, 2009Co-Authors: Huamin Zhang, Guobao Chen, Hexiang ZhongAbstract:An effective ex-situ method for characterizing electrochemical durability of a Gas Diffusion Layer (GDL) under simulated polymer electrolyte membrane fuel cell (PEMFC) conditions is reported in this article. Electrochemical oxidation of the GDLs are studied following potentiostatic treatments up to 96 h holding at potentials from 1.0 to 1.4 V (vs.SCE) in 0.5 mol L � 1 H2SO4. From the analysis of morphology, resistance, Gas permeability and contact angle, the characteristics of the fresh GDL and the oxidized GDLs are compared. It is found that the maximum power densities of the fuel cells with the oxidized GDLs hold at 1.2 and 1.4 V (vs.SCE) for 96 h decreased 178 and 486 mW cm � 2 , respectively. The electrochemical impedance spectra measured at 1500 mA cm � 2 are also presented and they reveal that the ohmic resistance, charge-transfer and mass-transfer resistances of the fuel cell changed significantly due to corrosion at high potential.
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facilitating mass transport in Gas Diffusion Layer of pemfc by fabricating micro porous Layer with dry Layer preparation
Journal of Power Sources, 2008Co-Authors: Jian Chen, Huamin ZhangAbstract:Abstract For a proton exchange membrane fuel cell (PEMFC), dry Layer preparation was optimized and applied to fabricate a micro-porous Layer (MPL) for a Gas Diffusion Layer (GDL). The MPLs fabricated by dry Layer preparation and the conventional wet Layer preparation were compared by physical and electrochemical methods. The PEMFC using dry Layer MPLs showed better performance than that using wet Layer MPLs, especially when the cells were operated under conditions of high oxygen utilization rate and high humidification temperature of air. The mass transport properties of the GDLs with the dry Layer MPLs were also better than with the wet Layer MPLs, and were found to be related to the pore size distribution in GDLs. The differences in surface morphology and pore size distribution for the GDLs with the dry Layer and wet Layer MPLs were investigated and analyzed. The dry Layer preparation for MPLs was found to be more beneficial for forming meso-pores (pore size in the range of 0.5–15 μm), which are important and advantageous for facilitating Gas transport in the GDLs. Moreover, the GDLs with the dry Layer MPLs exhibited better electronic conductivity and more stable hydrophobicity than those with the wet Layer MPLs. The reproducibility of the dry Layer preparation for MPLs was also satisfying.
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bifunctional oxygen electrode with corrosion resistive Gas Diffusion Layer for unitized regenerative fuel cell
Electrochemistry Communications, 2006Co-Authors: Shidong Song, Huamin Zhang, Zhigang Shao, Yining Zhang, Baolian YiAbstract:To develop the unitized regenerative fuel cell (URFC) with low cost and high performance, a novel bifunctional oxygen electrode with a thin-film electrocatalyst Layer and a corrosion-resistive Gas Diffusion Layer (GDL) prepared by the carbon paper backing and a protective micro-porous Layer (MPL) was developed. The protective MPL was made of the IrO2 deposited fine Ti powders. The cycle performance and polarization curves for both fuel cell and water electrolysis modes of URFC operation were investigated. The cycle performance of the URFC was stable during 20 cycles. It exhibits a high fuel cell performance as good as the URFC using the conventional GDL and a much higher water electrolysis performance. � 2006 Elsevier B.V. All rights reserved.
Branko N Popov - One of the best experts on this subject based on the ideXlab platform.
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a review of Gas Diffusion Layer in pem fuel cells materials and designs
International Journal of Hydrogen Energy, 2012Co-Authors: Sehkyu Park, Branko N PopovAbstract: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.
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development of supported bifunctional oxygen electrocatalysts and corrosion resistant Gas Diffusion Layer for unitized regenerative fuel cell applications
Journal of Power Sources, 2012Co-Authors: Shengyang Huang, Prabhu Ganesan, Hoyoung Jung, Branko N PopovAbstract: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.
