The aim of this paper is obtaining a 3D model for designing bipolar plates by simulating fuel cell behavior with different flow field configuration and thus improving the performance of a direct ethanol fuel cell by modeling different flow fields using a 3D representation. Experimental results presented here were obtaining with hydrogen fuel cells as a first approach of modeling. Results show that activation zone is not well simulated. Flow fields better performance is obtaining with a width ratio of .Current and flow distribution shows that deeper channels had better performance in serpentine flow field.
Fuel cells represents one of the most promising ways to obtain sustainable energy because they provide power and heat cleanly and efficiently, using diverse domestic fuels like hydrogen produced from renewable resources, biomass-based fuels, and natural gas. Fuel cells open the way to integrated “open energy systems” and they have the potential to reduce greenhouse gas emissions in many applications. For instance, applications have been demonstrated in combined heat and power (CHP) systems, light-duty highway vehicles, fuel cell electric vehicles (FCEVs) and Auxiliary power units (APUs) [1]. Transportation is one of the wider areas of application for fuel cells. While Internal Combustion Engines (ICEs) generate power without any catalysts, needing precious metals only for catalytic converters in order to eliminate noxious gases, the catalysts found in electrodes are key to electric power generation by Polymer Electrolyte Membrane Fuel Cells (PEMFCs). Moreover, efforts in the catalysis of the PEMFC reactions (1) and (2) are the key to enhance sustainable power generation. The cathode is the most studied electrode as the major source of losses in efficiency and power density due to the five-orders-of-magnitude slower kinetics of the oxygen reduction reaction (ORR) on Pt, Reaction 2 [2]. 2H2 →4H+ Anode Reaction (1) O2+4H++ 4e-→2H2O Cathode Reaction (2) Pt is expensive and of limited availability. This greatly impacts the cost of PEMFCs, and consequently limits their potential for mass commercialization. In order to reduce the Pt loading in cathodes without decreasing their performance there are three options: (1) enhancing Pt mass activity for ORR via alloying or core-shell nanostructuring, (2) improving mass-transport properties of Pt-based cathodes, and (3) developing well-performing non-precious metal catalysts (NPMCs) for ORR [2, 3]. The aim of this study is to estimate the voltage drop due to transport processes inside a non-precious metal loaded cathode catalyst layer, namely, electron, proton and oxygen transport. There are many problems with obtaining accurate fits to polarization data, both in the kinetic region of the polarization curve as Figure 1 shows, and in mass-transport-controlled regions. In an NPM catalyst layer, we need to identify and classify the main parameters to describe catalyst layers such as catalyst loading and thickness, diffusion coefficients, active catalyst surface area, volume fraction of polymer in the agglomerate. For this we will use the Jaouen model [4] as a starting point and then validate the result with our catalyst characterization and structure measurements. It is also critical to use adequately complex experimental data sets to be analyzed and to include as many independently and experimentally determined parameters as are available to reduce the degrees of freedom for fitting. Only then will a modeling study serve to reveal the physical basis of the important performance differences resulting from the use of given catalyst layer structures, on one hand, and different non-precious reaction pathways on the other. Figure 1.Kinetic model vs. experimental results for NPMC. Acknowledgement We gratefully acknowledge the support of the NSF EPSCoR program and Colciencias for support of this work. References 1. Program, U.S.D.o.E.-F.C.T., The Department of Energy Hydrogen and Fuel Cells Program Plan, U.S.D.o. Energy, Editor. 2011. p. 92. 2. Jaouen, F., et al., Recent advances in non-precious metal catalysis for oxygen-reduction reaction in polymer electrolyte fuel cells. Energy & Environmental Science, 2011. 4(1): p. 114-130. 3. Goenaga, G.A., et al., Synthesis and Electrochemical Characterization of Co, Cu, Fe, Ni and Mn-Based Catalysts for ORR in PEM Fuel Cells. ECS Transactions, 2013. 50(2): p. 1749-1757. 4. Jaouen, F., Electrochemical Characterization of Porous Cathodes in the Polymer Electrolyte Fuel Cell, in Department of Chemical Engineering and Technology. 2003, Kungl Tekniska Hogskolan. p. 68.
Proton Exchange Membrane Fuel Cells (PEMFC) are considered one of the most promising alternative energy technologies due to the low operation temperature, compact structure and wide range of applications, among other advantages 1. The demand for low platinum loading in PEMFC electrodes has driven recent research on electrode structure-function correlations. The structure and morphology of the electrode layer play important roles in controlling many aspects of fuel cell performance. Within the catalyst layers (CLs), the hydrogen oxidation and the oxygen reduction reactions take place, involving complex mass and charge transport processes (diffusion of reactants and products, migration and diffusion of protons, migration of electrons, permeation, electroosmotic drag, as well as vaporization/condensation of water) 2. Previous studies performed on the influence of the ionomer loading on the catalyst layers has shown that this parameter has an effect on the dispersion of the carbon aggregates, the thickness of Nafion® films covering the catalyst/carbon surface and therefore the porosity of the CLs. Typical loadings for Nafion® ionomer have been reported to be within the range of 30-40% 3. In this study, the microstructure of PEMFC electrodes with different variations in terms of ionomer to carbon (IC) ratios, ionomer equivalent weights and electrode thickness (by means of variations in Pt loading) were evaluated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) nitrogen adsorption, including materials dispersion and porosity in CLs for freestanding electrodes (Figure 1). Some images of a typical catalyst layer are shown in Figure 1. Several typical features are shown here, providing indications of the large-scale porosity of the layer as well as images showing expanses of ionomer with and without embedded Pt particles. In previous studies4, measurements of water transport in similar CLs suggested that sub-saturated catalyst layers have a less connected ionomer network than that expected from uniform coverage of particles in the layer. Microscopy and other measurements noted above on a series of systematically modified catalyst layers will be summarized in an attempt to assess this finding. Single cell performance with these catalyst layers was evaluated in order to analyze the relationship with the structure properties. Acknowledgements NMC gratefully acknowledges the support from a Fulbright Fellowship. Additional support was provided by the NSF EPSCoR program. Research supported at ORNL by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy. References 1. A. L. W. Vielstich, H. A. G., Handbook of fuel cells, fundamentals, technology and applications 2003. 2. Zhang, J., PEM Fuel Cell Electrocatalysts and Catalyst Layers. Fundamentals and Applications. Springer London: 2008. 3. (a) Antolini, E.; Giorgi, L.; Pozio, A.; Passalacqua, E., Influence of Nafion loading in the catalyst layer of gas-diffusion electrodes for PEFC. Journal of Power Sources 1999, 77 (2), 136-142; (b) Sasikumar, G.; Ihm, J. W.; Ryu, H., Optimum Nafion content in PEM fuel cell electrodes. Electrochimica Acta 2004, 50 (2–3), 601-605. 4. Sun, C.-N. and Zawodzinski, T. A. ECS Electrochem Lett., 2012, 1 (5) F36-39.
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