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Advanced Models for Predicting Performance of Polymer Electrolyte Membrane Fuel Cells

Kamarajugadda, Sai K.
http://rave.ohiolink.edu/etdc/view?acc_num=osu1323758118

Abstract Details

2012, Doctor of Philosophy, Ohio State University, Mechanical Engineering.
The primary objective of this study is to develop a multi-scale computational fluid dynamics (CFD) model to predict the performance of a polymer electrolyte membrane fuel cell (PEMFC). In particular, two critical factors affecting PEMFC performance, namely water and current transport through the polymer electrolyte membrane, and the effect of the cathode catalyst layer structure and composition are examined in detail. The implementation of phenomenological membrane models within CFD codes requires coupling of the conservation equation for the so-called water content within the membrane to the conservation equations for species mass outside the membrane. The first part of this dissertation investigates the accuracy and efficiency of various strategies for implementing phenomenological membrane models within the framework of a CFD code for prediction of the overall PEMFC performance. First, three popular phenomenological membrane models are investigated, and the accuracy of each model is assessed by comparing predicted results against experimental data. Results indicate that the Springer model and the Nguyen and White model over-predict the drying of the membrane, while the Fuller and Newman model provides the best match with experimental data. Following these studies, three strategies for implementation of the membrane model are investigated: (1) two-dimensional (2D) transport of water and current in membrane, (2) one-dimensional (1D) transport and (3) 1D transport with approximate transport properties. Fuller and Newman’s membrane model is used for these studies. The results obtained using the three approaches are found to be within 4% of each other, while there is no significant difference in the computational time required by the three strategies, indicating that an analytical 1D transport model for the membrane that uses approximate properties is adequate for describing transport through it. In the second part of the dissertation, the effect of the cathode catalyst layer’s structure and composition on the overall performance of a PEMFC is investigated. The starting point of this investigation is the well-known flooded agglomerate model, which is generalized to address the effects of ionomer (Nafion) loading, catalyst (platinum) loading, platinum/carbon ratio, cathode layer thickness, and agglomerate size and shape. Initially, spherical agglomerates are considered. This allows for an analytical solution of the governing equations. Following this, the model is generalized in order to account for arbitrary agglomerate shapes. The generalized flooded agglomerate model is first validated against previously published results, and then used to study the effect of the agglomerate shape (single sphere vs. intersecting spheres) and size on the oxidation reduction reaction (ORR) rate at the agglomerate scale. Results from the agglomerate scale studies indicate that the current per unit volume generated by the agglomerates is proportional to the surface-area-to-volume ratio of the agglomerates. It shows that, for a given agglomerate volume, the ORR is more efficient for non-spherical agglomerates than for spherical agglomerates. The generalized flooded agglomerate model provides the current generated per unit volume at the agglomerate scale, which is much smaller than a typical control volume used in CFD calculations of the overall PEMFC, i.e., it is a sub-grid scale model. This sub-grid scale agglomerate model is then embedded within a 2D CFD code for the prediction of the overall performance of the fuel cell. In order to do so, lookup tables are first generated and logarithmic interpolation is used. The integrated model is used to explore a wide range of the compositional and structural parameter space, mentioned earlier. In each case, the model is able to correctly predict the trends observed by past experimental studies. It is found that the performance trends are often different at intermediate versus high current densities – the former being governed by agglomerate-scale (or local) losses, while the latter is governed by catalyst layer thickness-scale (or global) losses. The presence of an optimal performance with varying Nafion content in the cathode is more due to the local agglomerate-scale mass transport and conductivity losses in the polymer coating around the agglomerates than due to the amount of Nafion within the agglomerate. It is also found that platinum mass loading needs to be at a moderate level in order to optimize fuel cell performance, even if cost is to be disregarded. For agglomerates of small size, the shape of the agglomerate is found to have a smaller effect on overall PEMFC performance than for agglomerates of larger size. The results from this dissertation provide, for the first time, a quantitative confirmation of the assumption of 1D transport of water and current within the membrane. Second, the generalized flooded agglomerate model developed as part of this dissertation presents a new framework for incorporating cathode structure and composition into full-scale CFD models for predicting PEMFC performance.
Sandip Mazumder (Advisor)
A Terrence Conlisk, Jr (Committee Member)
Yann Guezennec (Committee Member)
Vishwanath Subramaniam (Committee Member)
185 p.
Chemical Engineering; Energy; Engineering; Mechanical Engineering
Polymer Electrolyte Membrane; Fuel Cell; Computational Fluid Dynamics; Cathode Catalyst Layer; Flooded Agglomerate; Membrane Transport; oxygen reduction reaction; ORR; modeling

Recommended Citations

Citations

  • Kamarajugadda, S. K. (2012). Advanced Models for Predicting Performance of Polymer Electrolyte Membrane Fuel Cells [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1323758118

    APA Style (7th edition)

  • Kamarajugadda, Sai. Advanced Models for Predicting Performance of Polymer Electrolyte Membrane Fuel Cells. 2012. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1323758118.

    MLA Style (8th edition)

  • Kamarajugadda, Sai. "Advanced Models for Predicting Performance of Polymer Electrolyte Membrane Fuel Cells." Doctoral dissertation, Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1323758118

    Chicago Manual of Style (17th edition)

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This open access ETD is published by The Ohio State University and OhioLINK.