Simplified mathematical model of proton exchange membrane fuel cell based on horizon fuel cell stack

This paper presents a simplified zero-dimensional mathematical model for a self-humidifying proton exchange membrane (PEM) fuel cell stack of 1 kW. The model incorporates major electric and thermodynamic variables and parameters involved in the operation of the PEM fuel cell under different operational conditions. Influence of each of these parameters and variables upon the operation and the performance of the PEM fuel cell are investigated. The mathematical equations are modeled by using Matlab–Simulink tools in order to simulate the operation of the developed model with a commercial available 1 kW horizon PEM fuel cell stack (H-1000), which is used for the purposes of model validation and tuning of the developed model. The model can be extrapolated to higher wattage fuel cells of similar arrangements. New equation is presented to determine the impact of using air to supply the PEM fuel cell instead of pure oxygen upon the concentration losses and the output voltage when useful current is drawn from it

Thermal Stresses in an Operating Micro-Tubular Solid Oxide Fuel Cell

A multi-physics model is developed to investigate the thermal stresses in a micro-tubular SOFC, based on a previously developed thermal-fluids model predicting cell operation. Mechanical properties of the anode and cathode are determined theoretically through composite structure approximation. Residual stresses arisen during the fabrication of the cell due to the mismatch in thermal expansion coefficients are calculated by accounting for each fabrication process separately. The interactions between the cell, the sealant and the alumina tube are accounted for a better representation of the actual fuel cell test setup. The effect of sealant and alumina tube on the stress distribution in the cell is investigated and it is found out that near the fuel cell-sealant interface stress distribution changes significantly. The effect of spatial temperature gradient on the stress distribution is also analyzed and found to have a minimal impact for a typical fuel cell operation at mid-range current densities. The effects of oxygen vacancies caused by the reduction of the GDC electrolyte on the overall stress distribution are also shown. Oxygen vacancies of the electrolyte result in relaxation of the stresses due to the alleviation of mismatch in Young's modulus between different layers of the cell. (C) 2010 Published by Elsevier B.V.X1126sciescopu

A transient analysis of a micro-tubular solid oxide fuel cell (SOFC)

A two-dimensional, axisymmetric transient computational fluid dynamics model is developed for an intermediate temperature micro-tubular solid oxide fuel cell (SOFC). which incorporates mass, species, momentum, energy, ionic and electronic charge conservation. In our model we also take into account internal current leak which is a common problem with ceria based electrolytes. The current density response of the SOFC as a result of step changes in voltage is investigated. Time scales associated with mass transfer and heat transfer are distinguished in our analysis while discussing the effect of each phenomenon on the overall dynamic response. It is found that the dynamic response is controlled by the heat transfer. Dynamic behavior of the SOFC as a result of failure in fuel supply is also investigated, and it is found that the external current drops to zero in less than 1s. (C) 2009 Elsevier B.V. All rights reserved.X1130sciescopu

Effects of operating conditions on the performance of a micro-tubular solid oxide fuel cell (SOFC)

A parametric analysis is carried out to study the effects of the operating conditions on the performance and operation of a micro-tubular solid oxide fuel cell. The computational fluid dynamics model incorporates mass, momentum, species and energy balances along with ionic and electronic charge transfers. Effects of temperature, fuel flow rate, fuel composition, anode pressure and cathode pressure on fuel cell performance are investigated. Polarization curves are compared to allow an understanding of the effects of different operating conditions on the performance of the fuel cell. Effects of anode flow rate on fuel cell efficiency and fuel utilization are also investigated. Moreover, influence of operating temperature on the internal electronic current leaks is outlined. Temperature distributions, current density profiles and hydrogen mole fraction profiles are also utilized to have a better understanding of the spatial effects of operating parameters. It is predicted that at 550 degrees C, for an output current demand of 0.53 A cm(-2), fuel cell needs to generate 0.65 A cm(-2) ionic current density where the difference in these values is attributed to internal current leaks. On the other hand for temperatures lower than 500 degrees C, the effect of electronic leakage currents are not significant. (C) 2009 Elsevier B.V. All rights reserved.X1130sciescopu

Computational thermal-fluid analysis of a microtubular solid oxide fuel cell

A computational fluid dynamics model is developed to study the steady-state behavior of a microtubular solid oxide fuel cell (SOFC). The model incorporates mass, momentum, species, and heat balances along with ionic and electronic charge transfers. The anode-supported SOFC studied in this work consists of a ceria-based electrolyte which is known as an electronic conductor in reducing atmospheres, letting electrons leak through the electrolyte. Related internal leakage currents are calculated implicitly in the model to incorporate the performance losses. Moreover, to have a more realistic approach while cutting down the computational effort, in this study a fuel cell test furnace is also modeled separately to evaluate the distribution of the oxygen concentration and temperature field inside the furnace. Results from the furnace model are used as boundary conditions for the fuel cell model. Fuel cell model results are compared with the experimental data which shows good agreement. (c) 2008 The Electrochemical Society.X112330sciescopu

Evaluation of water transport and oxygen presence in single chamber microbial fuel cells with carbon-based cathodes

Water transport through the cathode and oxygen presence/absence in the anodic solution, are important for operation and performance of single chamber microbial fuel cells (SCMFCs). This study focused on water transport and biofilm formation on carbon papers with different characteristics: hydrophobicity, thickness, and presence of a micro porous layer (MPL). The results showed that higher hydrophobicity, thicker structures and the presence of the MPL decreased the water transport over time. The carbon papers with low hydrophobicity had complete penetration of biofilms and higher water transport, while those with high hydrophobicity and MPL had no biofilm penetration and lower water transport, indicating a clear correlation of biofilm penetration and water transport across carbon papers. Salt precipitation on carbon papers clogged the pores and resulted in lower water transport. Cyclic voltammograms using Au/Hg microelectrode inserted near the cathode indicated the absence of oxygen in the anodic solution due to the oxygen consumption by aerobic/anaerobic biofilms on cathodes. The results of water transport and oxygen presence illustrated that the biofilms can be used as a cost-effective membrane/separator for SCMFCs

Two-phase flow in a proton exchange membrane electrolyzer visualized in situ by simultaneous neutron radiography and optical imaging

WOS: 000319232500036In proton exchange membrane (PEM) electrolyzers, oxygen evolution in the anode and flooding due to water cross-over in the cathode yields two distinct two-phase transport conditions which strongly affect the performance. Two-phase transport in an electrolyzer cell is visualized by simultaneous neutron radiography and optical imaging. Optical and neutron data are used in a complementary manner to aid in understanding the two-phase flow behavior. Two different patterns of gas-bubble evolution and departure are identified: periodic growth/removal of small bubbles vs. prolonged blockage by stagnant large bubbles. In addition, the bubble distribution across the active area is not uniform due to combined effects of buoyancy and proximity to the inlet. The effects of operating parameters such as current density, temperature and water flow rate on the two-phase distribution are investigated. Higher water accumulation is detected in the cathode chamber at higher current density, even though the cathode is purged with a high flow rate of N-2. The temperature is found to affect the volume of water; higher temperature yields less water and more gas volume in the anode chamber. Higher temperature also enhanced the water transport in the cathode chamber. Finally, water transported through the membrane to the cathode reduced the cell performance by limiting the hydrogen mass transport. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.Scientific and Research Council of Turkey (TUBITAK); National Science Foundation [CBET-0748063]; U.S. Department of Commerce; NIST Radiation and Biomolecular Physics Division; Director's Office of NIST; NIST Center for Neutron Research; Department of Energy [DEAI01-01EE50660]Omer F. Selamet would like to thank the Scientific and Research Council of Turkey (TUBITAK) for financial support for this research. Financial support for this work from the National Science Foundation (CBET-0748063) is gratefully acknowledged. This work was supported by the U.S. Department of Commerce, the NIST Radiation and Biomolecular Physics Division, the Director's Office of NIST, the NIST Center for Neutron Research, and the Department of Energy through Interagency Agreement No. DEAI01-01EE50660. We thank professors Ajay K. Prasad and Suresh G. Advani of the University of Delaware for their assistance with the experimental setup and equipment loan, Eli Baltic of the NIST for his help during the experiments in the NIST, and Richard S. Fu for his help with data analysis

In-situ two-phase flow investigation of Proton Exchange Membrane (PEM) electrolyzer by simultaneous optical and neutron imaging

11th Polymer Electrolyte Fuel Cell Symposium (PEFC) Under the Auspices of the 220th Meeting of the ECS -- OCT, 2011 -- Boston, MAWOS: 000309598800030In proton exchange membrane (PEM) electrolyzers, oxygen evolution in the anode and flooding due to water cross-over results in two distinct two-phase transport conditions, and these two phenomena were found to strongly affect the performance. A comprehensive understanding of two-phase flow in PEM electrolyzer is required to increase efficiency and aid in material selection and flow field design. In this study, two-phase transport in an electrolyzer cell is visualized by simultaneous neutron radiography and optical imaging. Optical and neutron data were used in a complementary manner to aid in understanding the two-phase flow behavior. The behavior of the gas bubbles was investigated and two different gas bubble evolution and departure mechanisms are found. It was also found that there is a strong non-uniformity in the gas bubble distribution across the active area, due to buoyancy and proximity to the water and purge gas inlet.ECS, Energy Technol (ETD), Phys & Analyt Electrochem (PAED), Battery (BATT), Ind Electrochem & Electrochem Engn (IEEE), Corros (CORR)Scientific and Research Council of Turkey (TUBITAK); National Science Foundation [CBET-0748063]; U.S. Department of Commerce; NIST Ionizing Radiation Division; Director's Office of NIST; NIST Center for Neutron Research; Department of Energy [DEAI01-01EE50660]Omer F. Selamet would like to thank the Scientific and Research Council of Turkey (TUBITAK) for financial support for this research. Financial support for this work from the National Science Foundation (CBET-0748063) is gratefully acknowledged. We thank professors Ajay K. Prasad and Suresh G. Advani of the University of Delaware for their assistance with the experimental setup. The authors thank Elias Baltic of the NIST for his technical help during the experiments in the NIST. This work was supported by the U.S. Department of Commerce, the NIST Ionizing Radiation Division, the Director's Office of NIST, the NIST Center for Neutron Research, and the Department of Energy through Interagency Agreement No. DEAI01-01EE50660. We also thank to Richard S. Fu for his help during the data analysis