bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling and Numerical Simulation of PEM Fuel Cell Transient
Authors: Wang Yun , Sun Pengtao
Published: December 2010

This paper develops a 3D dynamic model for polymer electrolyte fuel cells (PEFCs also called PEM fuel cells) and investigates the internal physicochemical processes that occur during PEFC transients as well as fuel cell dynamic responses. This model couples various dynamic mechanisms in the key components of PEFC, such as electrochemical double-layer discharging/charging, species transport, heat transfer, and membrane water uptake. The model is further discretized for 3D numerical simulations with focus on transient operation upon the step change in power density. The numerical results show that over/undershoot dynamic responses may take place during transient. A detailed picture of internal operating conditions, such as water and current density distributions, is presented to develop a comprehensive understanding of fuel cell transient during power/load variation.
Optimal Design and Control Strategies for Novel Combined Heat and Power (CHP) Fuel Cell Systems: Part I of II—Datum Design Conditions and Approach
Authors: Colella Whitney G.
Published: December 2010

Energy network optimization (ENO) models identify new strategies for designing, installing, and controlling stationary combined heat and power (CHP) fuel cell systems (FCSs) with the goals of 1) minimizing electricity and heating costs for building owners and 2) reducing emissions of the primary greenhouse gas (GHG) — carbon dioxide (CO2). A goal of this work is to employ relatively inexpensive simulation studies to discover more financially and environmentally effective approaches for installing CHP FCSs. ENO models quantify the impact of different choices made by power generation operators, FCS manufacturers, building owners, and governments with respect to two primary goals — energy cost savings for building owners and CO2 emission reductions. These types of models are crucial for identifying cost and CO2 optima for particular installations. Optimal strategies change with varying economic and environmental conditions, FCS performance, the characteristics of building demand for electricity and heat, and many other factors. ENO models evaluate both “business-as-usual” and novel FCS operating strategies. For the scenarios examined here, relative to a base case of no FCSs installed, model results indicate that novel strategies could reduce building energy costs by 25% and CO2 emissions by 80%. Part I of II articles discusses model assumptions and methodology. Part II of II articles illustrates model results for a university campus town and generalizes these results for diverse communities.
Hydrocarbon Fueled Operation of Metal-Supported Solid Oxide Fuel Cell
Authors: Jeong Jihoon , Baek Seung-Wook , Bae Joongmyeon
Published: December 2010

The metal-supported solid oxide fuel cell (SOFC) was studied. Hydrocarbon fueled operation was used to make SOFC system. Different operating characteristics for metal-supported SOFC are used than for conventional ones. Metal-supported SOFC was successfully fabricated by a high temperature sinter-joining method and the cathode was in-situ sintered. Synthetic gas, which is compounded as the diesel reformate gas composition and low hydrocarbons was completely removed by the diesel reformer. Metal-supported SOFC with synthetic gas was operated and evaluated and its characteristics analyzed. The performance of hydrogen operation shows 0.4 W·cm−2 of maximum power density. The maximum power density of the synthetic gas operation decreased to 0.22 W·cm−2 and to 0.11 W·cm−2 after 10 hours operation, respectively. Degradation occurred because a large steam quantity made an oxidation atmosphere at high temperature, causing the metallic part damage.
Evaluation of Mechanical Properties of SOFC Components by Nano-Indentation Tests
Authors: Ito Hideaki , Sato Kazuhisa , Unemoto Atsushi , Amezawa Koji , Kawada Tatsuya
Published: December 2010

The Young’s modulus and the hardness of single crystals and polycrystalline sintered compacts of yttria-stabilized zirconia (YSZ), (Y2O3)x(ZrO2)1−x (x = 0.08, 0.10) was investigated by using the nano-indentation method. Together with results obtained by the secondary electron microscope observation and the electron backscattering diffraction analysis, the effect of the crystal orientation on the mechanical properties was discussed. It was empirically demonstrated that the Young’s modulus of YSZ depends on the crystal orientation. The Young’s modulus of YSZ showed the highest value on the (001) surface while the lowest value on the (111) surface. However, the observed anisotropy of the Young’s modulus was rather small compared with predicted one from the single crystal elastic constants in literature. Compared with the Young’s modulus, the anisotropy of the hardness of YSZ was less significant.
Analysis of the Membrane Humidifier Fault Modes and Its Effects on the Performance of PEMFC
Authors: Kim Sung Il , Kim Beom Jun , Choi Jong Won , Kim Min Soo
Published: December 2010

Polymer electrolyte membrane fuel cell is one of the most promising energy sources in the future because of its high efficiency and eco friendly property. However, there are several problems to solve in order to commercialize the PEM fuel cell such as heat management, cold start and humidification. Many researchers and companies try to improve the performance of the fuel cell, so the performance of PEMFC is getting better. Another important problem to improve in PEMFC is durability. Durability can be one of the most important factors to commercialize the PEMFC. Usually products produced by companies using fuel cell consist of several parts such as humidifier, heating source, air blower and so on. Usually it is called balance of plant and in order to operate it proper, each part of BOP should operate in a right way. When one part of BOP is fault, the performance of PEMFC can be decreased and the amount of decreased power sometimes can not be large because it is very small amounts. However, the effects of the fault can destroy another part of BOP, so detecting the fault of BOP is very important work. In this study, numerical analysis about the membrane humidifier performed by assuming several fault modes and the performances were recorded. Membrane humidifier using in automobile and vibration, shock from the outer condition can make humidifier malfunction. Various fault modes of membrane humidifier were considered and its effect on performance was portrayed by power curve and I-V curve. The results of this simulation showed that the good performance of membrane humidifier is important factor to get more power from PEMFC and some experimental studies are need to evaluate this simulation result.
Effect of MEAs Preparation Procedure on Their Performance in Room Temperature DMFC
Authors: Gribov Evgeniy N. , Krivobokov Ivan M. , Okunev Aleksey G.
Published: December 2010

In this work the effect of the MEA preparation techniques on the performance of DMFC was evaluated using three different methods of electrocatalyst deposition: i) catalyst coated membrane; ii) catalyst coated carbon paper; and iii) decal deposition. Optimization of the nafion content (5–15 wt. %) at anode and cathode sides of the MEA and the pressure (150–500 atm) were also performed. Activities of both supported and unsupported Pt and PtRu catalysts (Johnson Matthew) were compared in room temperature DMFC (RT-DMFC) using polarization curves. All MEAs prepared were also characterized by electrochemical (cyclic voltammetry, impedance spectroscopy) methods. It was shown that optimal nafion content is 5–10 wt. % at both anode and cathode sides, while the optimal pressure is in the 300–500 atm. range. The unsupported catalysts showed slightly higher power density at RT-DMFC (∼ 14 mW/cm2) as compared to the supported ones (∼10 mW/cm2) at the same Pt load. Variation of the wetness of MEAs upon mounting in DMFC allowed us to increase of the power density of RT-DMFC up to 32 mW/cm2.
Investigation of Electroactive Polymers for the PEMFC GDL
Authors: Wang Jingwen , Naguib Hani E. , Bazylak Aimy
Published: December 2010

In this work, electroactive polymers (EAPs) are introduced as novel materials for the polymer electrolyte membrane fuel cell (PEMFC). Polypyrrole (PPy) is selected as a promising EAP for the PEMFC. The fabrication procedures including the polymer solution preparation and the electro-chemical deposition process for producing a thin and porous PPy film are presented. The activation behavior of PPy thin film is observed, and the surface properties are analyzed.
Oxygen Starvation Effects on PEMFC Durability
Authors: Gerard Mathias , Poirot-Crouvezier Jean-Philippe , Hissel Daniel , Pe´ra Marie-Cecile
Published: December 2010

The problem of oxygen starvation on PEMFC is often observed (partially or totally in a cell). It is caused by water management problems (water droplet in the channels) or air management faults (delay during peak power). In our previous work, the current distribution has been measured along the cell during air starvation and calculated by modeling; the effects of the local temperature and the hygrometry in the MEA have been identified. However the mechanisms of degradation are still not completely understood. Several points have to be investigated like the short and long dated changes in performances and the degradation mechanisms in such a condition. In this paper, the study is completed by two sets of experiments. The first one is carried out with a bi-cell stack developed with specific design to compute the local current density by measuring the local induced magnetic field. Secondly, a long time ageing test is run with a 6 cells stack (220 cm2) during oxygen starvation cycling conditions. Both tests (with characterizations) coupled with the 2D serpentine meshing stack model (taking into account transport phenomena, heat transfer and semi-empirical electrochemical reactions) provide information on the MEA local conditions effects during oxygen starvation. Especially the different reaction mechanisms at the cathode side are explained likewise the consequences on ageing.
Ripple Current Effects on PEMFC Ageing Test by Experimental and Modeling
Authors: Gerard Mathias , Poirot-Crouvezier Jean-Philippe , Hissel Daniel , Pe´ra Marie-Cecile
Published: December 2010

PEMFCs’ systems usually require power conditioning by a DC/DC boost converter to increase the output fuel cell voltage, especially for automotive applications and stationary applications. The output fuel cell current is then submitted to the high frequency switching leading to a current ripple. The ripple current effects on fuel cell are studied by experimental ripple current ageing test on a 5 cell stack (MEA surface of 220 cm2) and compare to a reference ageing test. The stack is run in nominal conditions but an AC component is added to the DC current load. The AC component is a 5 kHz triangle which amplitude is ±20% of the DC component in order to simulate a boost waveform. Fuel cell characterizations (polarization curves, impedance spectra and voltammetry) provide information on the PEMFC ageing and the performance evolution. Local conditions are computed through a dynamic stack model. The model takes into account transport phenomena, heat transfer, and semi-empirical electrochemical reactions and includes a meshing to calculate local conditions on the MEA surface (gas reactant pressures, local temperature, gas molar fractions, water activity, and local electronic current density). The consequences about performance and ageing during high frequency ripple current are explained.
Experimental Performance Comparison of a Single Cell and Multi-Cell Stack of High Temperature PEM Fuel Cell Prototype
Authors: Das Susanta K. , Ubong Etim U. , Reis Antonio , Berry K. Joel
Published: December 2010

In this study, we experimentally studied our newly designed and built single cell and multi-cell high temperature (140°C∼180°C) polymer electrolyte membrane (HTPEM) fuel cell stack prototype at different operating conditions to investigate the effects of operating temperature, pressure and CO concentration on the cell performance. In particular, the effects of these parameters on the current-voltage characteristics of the fuel cell stack are investigated extensively. Experimental results obtained from both the single cell and multi-cell stack with high temperature PBI-based membrane show that the high CO tolerance at high operating temperature of HTPEM fuel cell stack makes it possible to feed the reformate gas directly from the reformer without further CO removal. In order to develop design parameters for fuel reformer, experimental data of this type would be very useful. The experimental results revealed the fact that a fuel reformer is a consumer of heat and water, and the HTPEM fuel cell stacks are a producer of heat and water. Therefore, the integration of the fuel cell stack and the reformer is expected to improve the entire system’s performance and efficiency. The results obtained from this study showed significant variations in current-voltage characteristics of HTPEM fuel cell stack at different temperatures with different CO poisoning rates. The results are promising to understand the overall system performance development strategy of HTPEM fuel cell in terms of current-voltage characteristics while fed with on-site reformate with different CO ratios in the anode fuel stream.
Fuel Cell Frequency Response Function Modeling for Control Applications
Authors: Roberts Thomas C. H. , Cunningham Patrick J.
Published: December 2010

This paper provides the framework for first-order transfer function modeling of a fuel cell for controls use. It is shown that under specific conditions a fuel cell can be modeled as a first-order system. With a first order model, it is possible to determine how the fuel cell responds dynamically on a systems level before incorporating it into a larger more complex system. Current data sheets for fuel cells provide limited information of the output of the fuel cell, and a polarization curve based on static operation. This is vital information, but gives no insight into how the fuel cell responds under dynamic conditions. Dynamic responses are important when incorporating fuel cells as a power source in larger systems, such as automobiles, as loads and conditions are constantly changing. The modeling technique used in this research is the frequency response function. In this approach an experimental frequency response, or Bode plot, is computed from a frequency rich input signal and corresponding output signal. Here the controlled input is the Hydrogen flow and the output is the fuel cell voltage. During these tests, the fuel cell was connected to a constant resistance load. Using the frequency response function approach, a family of first-order transfer function models was created for a fuel cell at different operating temperatures and reactant relative humidity. These models are validated through comparison to experimental step responses. From this family of models the variations in the first-order model parameters of static gain and time constant are quantified. Static gain varied from 0.675 to 0.961 and the time constant ranged between 4.5 seconds and 10.5 seconds.
An Experimental Investigation of Air-Water Flow Through the Serpentine Flow Field of a Bipolar Plate in Presence of Powdered Wax
Authors: Talwar Sudhanshu , Syed Iltesham Z. , Utturkar Aditya , Mukherjee Abhijit
Published: December 2010

Water management in Proton Exchange Membrane Fuel Cell (PEMFC) is an important issue that needs to be addressed appropriately at all loads. Water is formed as a product of reaction, which is removed by airflow at the cathode. However, at part load operations, when the required airflow is less, water can build up inside the cell resulting in reduction of fuel cell output. A bio-mimetic solution to this problem is proposed where a minute amount of powdered wax is introduced along with the incoming air into the gas distribution channel of a bipolar plate. The bi-polar plate is covered with a transparent plexi-glass and water is introduced using a syringe pump through a minute hole on the cover at a location downstream of the air inlet. The air and water flow rates are varied simulating the different load conditions observed in a typical PEMFC. The movement of water inside the serpentine channel is recorded using a high-speed camera. Presence of micronized wax resulted in significant increase in water movement inside the channels.
Flow-Field Study in a Microjet PEM Fuel Cell
Authors: Badaru Akintunde , Greska Brenton , Krothapalli Anjaneyulu
Published: December 2010

Microjets have been implemented into a PEM fuel cell in an attempt to achieve even distribution of reactants and passive cooling of the fuel cell unit and a preliminary investigation of this application has yielded positive results. Unlike conventional reactant supply, the reactant microjets impinge on the back side of the flow field plate before wrapping around and traversing the flow field channels where they are involved in electrochemical activity. However, it was observed that the fuel cell was subject to significant flooding, which limited its continuous operation. This paper discusses the results from an experimental study that has been carried out in an attempt to reduce or eliminate the occurrence of flooding through the use of two different flow-field configurations. Measurements of these flow field configurations, identified as MJFC I and MJFC II, are presented here. MJFC I, the first generation prototype, uses a variant of parallel flow field while MJFC II, the second generation prototype, uses multiple independent serpentine flow field channels. For similar operating conditions, characteristic curves obtained showed that MJFC I is susceptible to flooding while MJFC II has superior water management capability. Secondary tests using Electrode Impedance Spectroscopy confirm these findings.
Phosphine Effects on Ni-Based Anode Material and Related SOFC Button Cell Performance Investigation
Authors: Guo Huang , Iqbal Gulfam , Kang Bruce S.
Published: December 2010

Phosphine (PH3) is one of the trace contaminants found in coal-derived syngas that degrade the solid oxide fuel cells (SOFCs) anode structural properties and electrochemical performances. In this research, the SOFC button cells are exposed to ppm level of PH3 in dry and moist hydrogen under OCV and loading conditions to study PH3 poisoning effect on SOFC performance. A modified Sagnac optical system is utilized for in-situ SOFC anode surface IR emission measurements as a function of current density, along with the cell electrochemical performance investigation. The experimental results indicate that the Ni-based SOFC anode is more susceptible to degradation due to PH3 in moist hydrogen than in dry hydrogen condition. The degradation effects of PH3 on the SOFCs anode are also analyzed by post experiment characterization using SEM, EDX, and XRD.
Plasticity of Nanoporous Ni/YSZ Anode: A Numerical Analysis
Authors: Gan Yong X. , Pothula Surya V. , Franchetti Matthew J.
Published: December 2010

Thin electrolytes (YSZ) and anode-supported (nanoporous Ni-YSZ ) cells operating in the temperature range of 650–850°C are considered as promising solid oxide fuel cell systems. Understanding the thermal-mechanical deformation behavior of the Ni/YSZ interface is critical for the design and durability assessment of the YSZ high temperature fuel cells. One of the problems still remains to be solved is the microstructure instability of the nanoporous Ni at the elevated temperatures. In this work, modeling the thermal-mechanical deformation in the nanoporous Ni/YSZ interface region was performed. Nanoporous Ni thin film bounded to YSZ was considered to establish a simplified 2-D model. On the Ni/YSZ interface, the nanopores are modeled as spherical or cylindrical pores. Crystal lattice rotation due to dislocation motion was simulated and the numerical solutions to the in-plane lattice rotation for the nanoporous Ni was used to predict the microstructure evolution in the interface area of the Ni/YSZ anode.
Catalytic Material Development for a SOFC Reforming System: Application of an Oxidative Steam Reforming Catalyst to a Monolithic Reactor
Authors: Smith Mark W. , Berry David A. , Shekhawat Dushyant , Haynes Daniel J.
Published: December 2010

The main objective of this work was to develop fuel reforming technologies to produce a H2-rich synthesis gas to power a solid oxide fuel cell being developed by US DOE for applications like diesel auxiliary power units. In order to accomplish this objective the following efforts were required: 1) examination of the effect of oxygen-conducting supports on reforming catalyst performance, 2) demonstration of the long-term stability under reforming conditions of an oxide powder catalyst deposited onto an oxygen-conducting support, 3) fabrication of a catalyst system by depositing the active catalyst and oxygen-conducting material onto a monolithic support structure for scaled-up reforming tests, 4) demonstration of the scaled-up reforming tests using the monolithic reactor. A successful 1,000-hr diesel reforming test was completed on a powder pyrochlore catalyst developed by NETL deposited onto an oxygen-conducting support. This test demonstrated that the catalyst and support compositions developed have significant potential in a commercial reforming application for the production of synthesis gas. Transforming this powder catalyst into a commercially viable form was the next major step to the development of a usable product. An alumina monolith structure coated with both the oxygen-conducting support and the active pyrochlore phase was fabricated and its performance was validated by short term partial oxidation (POX) tests on pump diesel, and in an integrated reformer-fuel cell test for 100 hrs on a biodiesel fuel under oxidative steam reforming (OSR) conditions.
Integrating Catalytic Coal Gasifiers With Solid Oxide Fuel Cells
Authors: Siefert Nicholas , Shekhawat Dushyant , Kalapos Thomas
Published: December 2010

A review was conducted for coal gasification technologies that integrate with solid oxide fuel cells (SOFC) to achieve system efficiencies near 60% while capturing and sequestering >90% of the carbon dioxide [1–2]. The overall system efficiency can reach 60% when a) the coal gasifier produces a syngas with a methane composition of roughly 25% on a dry volume basis, b) the carbon dioxide is separated from the methane-rich synthesis gas, c) the methane-rich syngas is sent to a SOFC, and d) the off-gases from the SOFC are recycled back to coal gasifier. The thermodynamics of this process will be reviewed and compared to conventional processes in order to highlight where available work (i.e. exergy) is lost in entrained-flow, high-temperature gasification, and where exergy is lost in hydrogen oxidation within the SOFC. The main advantage of steam gasification of coal to methane and carbon dioxide is that the amount of exergy consumed in the gasifier is small compared to conventional, high-temperature, oxygen-blown gasifiers. However, the goal of limiting the amount of exergy destruction in the gasifier has the effect of limiting the rates of chemical reactions. Thus, one of the main advantages of steam gasification leads to one of its main problems: slow reaction kinetics. While conventional entrained-flow, high-temperature gasifiers consume a sizable portion of the available work in the coal oxidation, the consumed exergy speeds up the rates of reactions. And while the rates of steam gasification reactions can be increased through the use of catalysts, only a few catalysts can meet cost requirements because there is often significant deactivation due to chemical reactions between the inorganic species in the coal and the catalyst. Previous research into increasing the kinetics of steam gasification will be reviewed. The goal of this paper is to highlight both the challenges and advantages of integrating catalytic coal gasifiers with SOFCs.
Component Failure Analysis From a Fleet of PEM Fuel Cells
Authors: Lux Scott , Nelson Arif , Josefik Nicholas , Holcomb Franklin
Published: December 2010

The U.S. Army Engineer Research and Development Center, Construction Engineering Research Laboratory (ERDC-CERL) managed the Residential Proton Exchange Membrane (PEM) Fuel Cell Demonstration. The U.S. Congress funded this project for fiscal years 2001–2004. A fleet of 91 residential-scale PEM fuel cells, ranging in size from 1–5 kW, was demonstrated at various U.S. Department of Defense (DoD) facilities worldwide. This detailed analysis looks into the most prevalent means of failure in the PEM fuel cell systems as categorized from the stack, reformer, and power-conditioning systems as well as the subsequent subsystems. Also evaluated are the lifespan and failure modes of selected fuel cell components, based on component type, age, and usage. The analysis shows while the fuel cell stack components had the single highest number of outages, the balance of plant made for 60.6% of the total outages. The hydrogen cartridges were the most prevalent component replaced during the entire program. The natural gas fuel cell stacks had the highest average operational lifetime; one stack reached a total of 10,250 hours.
Study of Influence of Electrode Geometry on Impedance Spectroscopy
Authors: Ahmed Riaz , Reifsnider Kenneth
Published: December 2010

Electrochemical Impedance Spectroscopy (EIS) is a powerful and proven tool for analyzing AC impedance response. A conventional three electrode EIS method was used to perform the investigation in the present study. Saturated potassium chloride solution was used as the electrolyte and three different material rods were used as working electrodes. Different configurations of electrode area were exposed to the electrolyte as an active area to investigate electrode geometry effects. Counter to working electrode distance was also altered while keeping the working electrode effective area constant to explore the AC response dependence on the variation of ion travel distance. Some controlled experiments were done to validate the experimental setup and to provide a control condition for comparison with experimental results. A frequency range of 100 mHz to 1 MHz was used for all experiments. In our analysis, we have found a noteworthy influence of electrode geometry on AC impedance response. For all electrodes, impedance decreases with the increase of effective area of the electrolyte. High frequency impedance is not as dependent on geometry as low frequency response. The observed phase shift angle drops in the high frequency region with increased working electrode area, whereas at low frequency the reverse is true. Resistance and capacitive reactance both decrease with an increase of area, but resistance response is more pronounce than reactance. For lower frequencies, small changes in working area produce very distinctive EIS variations. Electrode material as well as geometry was systematically varied in the present study. From these and other studies, we hope to develop a fundamental foundation for understanding specific changes in local geometry in fuel cell (and other) electrodes as a method of designing local morphology for specific performance.
Radiative Heat Transfer Effects on Transient Operation of a Planar Solid Oxide Fuel Cell
Authors: Ford J. Chris , Haynes Comas L.
Published: December 2010

A considerable design and operational challenge for solid oxide fuel cells (SOFCs) is the material degradation caused by high temperature (600–1000°C) operation. At such high temperatures, it is reasonable to assume that radiative heat transfer effects may be significant; however, few studies have rigorously investigated the impact of radiative heat transfer on the operation of SOFCs. Accordingly, modeling efforts have been made to characterize the temperature profile evolutions that occur within planar SOFCs during transient operation. Therefore, initial results are presented to elucidate the impact of radiation upon SOFCs during start up, load changes, and shut down.
Evaluating Methods for Infiltration of LSCF Cathodes With Mixed Electric/Ionic Conductors for Improved Oxygen Exchange
Authors: Tucker David , Manivannan Ayyakkannu , Haynes Dan , Abernathy Harry , Miller Nick , Wynne Karon , Matos Angine´s
Published: December 2010

Infiltration methods for improving lanthanum strontium cobalt ferrite (LSCF) cathode performance through catalyst surface modification were evaluated at the U.S. Department of Energy, National Energy Technology Laboratory. Infiltration of mixed conductors into LSCF cathodes of solid oxide fuel cells promises a low cost method of improving oxygen exchange and performance in these materials at lower temperatures. LSCF cathodes on Nickel-Yttria Stabilized Zirconia (Ni-YSZ) anode supported cells were infiltrated with strontium-doped lanthanum zirconate (LSZ) pyrochlores using two methods. An aqueous solution of nitrate salts was vacuum infiltrated into the cathodes of anode supported button cells, and the cells were heated to form the pyrochlore phase in-situ. This was compared to the efficacy of infiltrating a suspension of pyrochlore nanoparticles. Different dispersants were used to prepare the nanoparticle suspensions at varying concentrations and pH levels, and the results are compared.
Deposition of Porous Anode Electrode of a Solid Oxide Fuel Cell by Ultrasonic Spray Pyrolysis
Authors: Liu Lin , Kim Gap-Yong , Chandra Abhijit
Published: December 2010

A modified spray pyrolysis approach has been utilized to fabricate anode electrode of a Solid Oxide Fuel Cell (SOFC). It was designed to control the anode microstructure to achieve large triple phase boundaries (TPBs) and high gas diffusion capability, which are critical in enhancing the performance of a SOFC. Deposition of porous anode film of Nickel and Ce0.9Gd0.1O1.95 on dense 8 mol.% yttria stabilized zirconia (YSZ) substrate was carried out using the modified spray pyrolysis. Effects of precursor solution feed rates, precursor solution concentrations and deposition temperatures on the TPB formation and porosity were investigated. The composition of the deposited anode film was evaluated by energy dispersive X-ray spectroscopy (EDS). Scanning electron microscope (SEM) examinations revealed that the deposition temperature and precursor solution concentration were the most critical parameters that influenced the morphology, porosity and the particle size of the anode film.
A Thermal Management System for a PEM Fuel Cell System in Commercial Vehicles
Authors: Ahn Jong-Woo , Choe Song-Yul
Published: December 2010

Polymer electrolyte membrane (PEM) fuel cell operating in commercial vehicles produces a relatively high amount of heat. In order for securing durable operations, the produced heat should be rejected to keep the temperature in the cell under the limit. High temperature increases the rate of electrochemical reactions and mobility of water vapor. However, a thermal stress imposing on the thin layers of catalysts and membranes can accelerate degradation processes. Therefore, proper design of a thermal management system (TMS) and the associated control is required for ensuring highly reliable and efficient operations of the system. A typical thermal circuit consisting of a radiator, a fan, a reservoir and a coolant pump has been used to reject the excessive heat from the fuel cell. However, the capability of heat rejection is limited by sizes of the components that cannot be employed in heavy duty vehicles. In this study, we used two coolant loops, where the inner circuit consists of a bypass valve, a heat exchanger, a reservoir and a water pump and the outer circuit includes a radiator, a fan, a reservoir and a coolant pump. A state feedback control for the two loops was designed. Objectives for the controls were to maintain the temperature at the set value and to reduce the parasitic loss of the system. The controllers were tested on a dynamic model of a stack developed in the laboratory. Included is analysis of dynamic performance of the designed controllers at multiple step currents and FUDS. As a result of the proposed thermal management system, the size of radiator and the capacity of the pumps for proposed design become 10% smaller than those for the typical one. In addition, the overall net power of the fuel cell system increases to 5%.
Dynamic Modeling of a 110-Cell PEM Fuel Stack Considering Temperature and Two-Phase Effects
Authors: Ahn Jong-Woo , Choe Song-Yul
Published: December 2010

Dynamic models currently proposed in published papers are either based on Computational Fluid Dynamics or lumped parameters. The model based on the CFD needs high number of parameters and variables that cannot be easily measured and characterized, while the lumped model does not well represent the real behavior. We developed a stack model that considers two-phase effects in gas flow channels and gas diffusion layers, and temperature effects in the cell. Firstly, we construct a 20 cell model and analyze the cell performance dependent upon locations of the cells. The results of distribution of the physical quantities are used to extend the cells to a 100 cell. Included are analyses of the dynamic performances of the 20-cell stack and the proposed 110-cell stack models.
Effect of Liquid Water Saturation on Oxygen Transport in Gas Diffusion Layers of Polymer Electrolyte Fuel Cells
Authors: Shiomi Takeshi , Fu Richard S. , Pasaogullari Ugur , Tabuchi Yuichiro , Miyazaki Shinichi , Kubo Norio , Shinohara Kazuhiko , Hussey Daniel S. , Jacobson David L.
Published: December 2010

Improved oxygen diffusivity is essential for reducing mass transport losses in polymer electrolyte fuel cells (PEFCs). In this work, effective oxygen diffusivity in the presence of liquid water inside a gas diffusion layer (GDL) was investigated by means of coupled experimental and numerical analyses. In order to control the liquid water content inside the GDL, a temperature gradient method was developed. In a separate experiment liquid water content inside the GDL was measured by neutron radiography (NR) and analyzed by using a two-phase, non-isothermal numerical model. The model accurately reproduced the total liquid water content and was in qualitative agreement with the liquid saturation trend as obtained from the NR experiments, which was utilized to estimate the liquid saturation in the limiting current experiment. Based on the predicted liquid water profile, the dependence of effective oxygen diffusivity on the liquid water saturation is deduced. It is found that the Bruggeman exponent factor is much larger than the predictions from network models and this suggests that the understanding of the relationship between liquid water transport and the GDL local structure is important.
Adaptive Process Control and In-Situ Diagnostics for High Temperature PEM MEA Manufacturing
Authors: Gullotta Justin , Krishnan Lakshmi , Share Dylan , Walczyk Daniel , Puffer Raymond
Published: December 2010

The most critical step in high temperature proton exchange membrane (PEM) MEA manufacturing is sealing of the membrane between the two electrodes. This sealing process is typically conducted using a precision hydraulic thermal press. In order to achieve cost-effective high-volume MEA manufacturing, it is important to reduce the variability in MEA performance due to variations in incoming material properties and dimensions, and to reduce the unit process cycle time. This paper explains the application of real time adaptive process controls (APC) combined with effective in-situ diagnostics during the MEA sealing process to achieve greater uniformity and performance of high temperature PEM MEAs. The in-situ impedance measurement is carried out in a precision thermal press using a milliohmmeter by reading the complex impedance of the MEA at 1 kHz as the components of the MEA are sealed. This signal is then used to adjust the pressing process parameters in real time to achieve more uniform MEA performance. An experiment was carried out in an attempt to identify the impedance parameter which correlated most closely with the MEA’s future performance. Using these impedance parameters during pressing, we are able to reliably produce MEAs using the real time APC technique that perform consistently in a single cell test fixture with more than a 50% reduction in pressing time.
Changed Heat and Mass Transfer Evaluation of a Gas-to-Gas Type Membrane Humidifier by Mass Collection
Authors: Kim ByungJun , Yu SangSeok , Lee YoungDuk , Ahn KookYoung
Published: December 2010

In this paper, a technique of the humidity measurement is developed to identify the performance of membrane humidifier. The technique is designed to measure the performance of membrane humidifier during steady state and transient state. In particular, the measurement technique is very useful to understand dynamic behavior of humidifier because the response of commercial humidity sensor is too slow to capture the transient response of mass and heat transfer through the membrane. Accordingly, the heat and mass transfer characteristics of membrane humidifier are figured out with the experimental analysis. The parameters used in experiment are dry air pressure, humid air temperature and dry air flow rate.
Development of a Proof-of-Concept Series-Hybrid Vehicle Utilizing Multiple Power Sources
Authors: Strahs Peter , Breziner Luis , Weaver Jordan , Garant Christophe , Diloyan Georgiy , Shaffer Keith , Hutapea Parsaoran
Published: December 2010

The demand for fuel efficient vehicles is on the rise with higher costs of gasoline and increasing environmental concerns. To address these issues, a hybrid vehicle with the capability of running on multiple power sources has been developed. A 2000 Audi TT was converted to an AC electric vehicle with range extended capabilities provided by a small internal combustion engine and a hydrogen PEM fuel cell stack. This allows the vehicle to bridge the gap between the current gasoline based economy and a possible hydrogen based economy in the future. Using the Environmental Protection Agency’s (EPA) standard city and highway driving tests, the vehicle has a theoretical increase in fuel economy from 20/29 miles per gallon (MPG) respectively to 230/173 miles per gallon gasoline equivalent (MPGGE).
Effect of Internal and Interface Structure of GDL on Liquid Water and Oxygen Transport in PEFC
Authors: Inoue Gen , Matsukuma Yosuke , Minemoto Masaki
Published: December 2010

In order to improve the output performance of PEFC, it is important to increase the oxygen concentration at Pt catalyst surface, so the mass transfer performance of gas diffusion layer (GDL) and micro porous layer (MPL) have to be increased. In this study, the real GDL structure was reconstructed by X-ray CT image of carbon paper GDL with MPL. Two-phase flow analysis in GDL with MPL was carried out. In addition, the oxygen transfer calculation was combined with this model. So the effect of MPL on the liquid water distribution in GDL and the gas diffusion performance in wet condition were examined. Furthermore, considering the overlap layer of GDL and MPL, the overall oxygen transfer from channel to catalyst layer was evaluated, and the optimum condition was examined.
Coating of SOFC Metallic Interconnects and Their Oxygen Diffusivity
Authors: Horita Teruhisa
Published: December 2010

La0.8Sr0.2Co0.2Fe0.8O3 (LSCF) coating on Fe-Cr alloy was examined for use as interconnects in SOFC. Thermal cyclic oxidation was conducted on the LSCF coated Fe-Cr alloy to evaluate the interface evolution at LSCF/oxide scale/Fe-Cr alloy. The thickness of oxide scales increased at the LSCF coating/Fe-Cr alloy interfaces with increasing the number of thermal cycles. SIMS depth profiles were obtained after thermal cycling for the LSCF/alloy interfaces region: the oxide scale consisted of (Fe)-Mn-Cr spinel, Cr2O3, and SiO2. Elemental distribution of oxide scales is very similar to the non-coated Fe-Cr alloy. A relatively high diffusivity of oxygen (oxide ions) was observed within the LSCF coating. However, the diffusion of oxygen was blocked by the oxide scales, especially at the Cr2O3 region. The oxide scale growth rates were effectively reduced by the LSCF coating on the Fe-Cr alloy. The effects of the LSCF coating on the oxide scale growth are discussed.
Dynamic Analysis of a Planar SOFC Stack Fuelled by Biogas
Authors: Salogni A. , Alberti D.
Published: December 2010

This paper analyzes the dynamic behaviour of a 50 kW stack using planar co-flow solid oxide fuel cells with direct internal reforming fuelled by a biologically derived gaseous mixture of methane and carbon dioxide. The system modelled is composed by the SOFC stack, a catalytic burner, the heat recovery system and the control device aimed to keep the air temperature at the stack exit and the fuel utilization near to the set values. The model has been implemented using standard and user-defined components of an a-causal software based on the open-source Modelica modelling language. After a brief introduction to the production of the gaseous fuel derived from the anaerobic digestion of pig manure, data obtained from a case study on a pig farm situated in Lombardia (Italy) are presented, focusing on the yield of methane which can be exploited. The steady-state performance of the SOFC system fuelled by pure methane are compared with those obtained for the biogas working conditions, showing that the stack voltage is affected by greater concentration losses. Then, starting from a steady-state delivered current of 750 mA cm−2, the dynamic behaviour of the system when a load change of −150 mA cm−2 occurs is investigated for both pure methane and biogas fuelling hypothesis. The results of the simulations show that the transient phase is only marginally affected by the composition of the fuel, which causes a delay of about 50 s in the voltage transient. Finally, the effect obtained by imposing a linear variation in the fuel composition, which can be representative of a modification in the biological degradation of the organic substrate within the anaerobic digester, is discussed. After an initial transient, which is comparable with that obtained for a variation in the load current, the SOFC system is capable to restore the initial delivered power, provided that the required amount of fuel can be supplied to the anode.
A Dry-Borohydride/Injected-Hydrogen-Peroxide Fuel Cell
Authors: Miley George H. , Luo Nie , Kim Kyu-Jung
Published: December 2010

The design and testing of a 20-W (average power with short pulses to 45W) prototype fuel cell is presented. This cell is intended as an auxiliary power supply for a small robotic vehicle. The energy density exceeds 300 Watt-hour/kg. This cell is essentially a dry-borohydride/injected-hydrogen-peroxide fuel cell. This enables extremely long shelf life prior to use. The anode utilizes dry NaBH4 for storage while the cathode chamber is empty during storage. The initiation of cell operation is done by injection of the oxidizer, an aqueous H2O2 solution (stored in a separate container) to the cathode side of the fuel cell. The ionic conduction required for membrane operation is initially helped by the H2O content from the H2O2 solution. Once the electrochemical reaction starts, more water is generated as the reaction product and this continues to maintain a good ionic conductance over the run time of the cell. Continued operation is done with auxiliary fuel tanks to maintain very long run time when required. Once a run is over, the cell can be drain, flushed clean and returned to storage waiting for the next mission. The experimental details of such a cell stack are described in this paper.
Modeling, Design and Fabrication of Non-Uniform Catalyst Layers for PEM Fuel Cells
Authors: Roshandel R.
Published: December 2010

Catalyst layers are one of the most important parts of the PEM fuel cells and the cell performance is highly related to its structure. Catalyst layers are generally made by uniform distribution of catalyst on carbon cloth or carbon papers to form electrodes. In this paper, the idea of using non-uniform catalyst layer instead of common uniform catalyst layers is presented and simulated by a two-dimensional steady-state computational model. The model accounts for species transport, electrochemical kinetics, charge transport and current density distribution. A fuel cell test stand is designed and built to facilitate experimental validation of the model. Modeling results show that electrical current in catalyst layer is non-uniform, influenced by the channel-land patterns in bipolar plate geometry. Our simulations results also suggest that some non-uniform catalyst distribution patterns regarding to bipolar plate configuration will improve the performance of the whole catalyst layer by increasing catalyst utilization factor. Therefore, it is necessary to design non-uniform catalyst layers regarding to specific procedure. Plasma sputtering method is used to fabricate non-uniform catalyst layers. In this method, the platinum is deposited on the carbon cloth in the plasma-processing chamber. Indeed, an experimental procedure is presented to facilitate the fabrication of non-uniform catalyst layers by plasma sputtering.
Investigation of Aerosol Jet Deposition Parameters for Printing SOFC Layers
Authors: Sukeshini A. M. , Jenkins T. , Gardner P. , Miller R. M. , Reitz T. L.
Published: December 2010

This work entails an investigation of the Aerosol Jet® Printing (AJP) method for depositing dense and porous layers necessary for the fabrication of solid oxide fuel cells (SOFCs). Ink preparation, method of printing, and the impact of various printing and processing parameters on the microstructure of layers will be presented. In addition, the electrochemical performance of anode supported button cells produced via the AJP process will be discussed. Thin electrolyte and cathode layers were deposited onto a standard anode-supported substrate and consisted of a yttria stabilized zirconia (YSZ) electrolyte, a strontium doped lanthanum manganate (LSM)/YSZ cathode functional interlayer, and a neat LSM cathode current collection layer. Optimal printing parameters for depositing dense electrolyte layers with thickness ranging from a few microns to a few tens of microns (8–33 μm) were identified. Porous composite cathode interlayers were printed from mixtures of individually aerosolized components of YSZ and LSM. Button cells incorporating the electrolyte and cathode layers on a NiO/YSZ support substrate exhibited stable voltage of 1.16–1.20 V at open circuit at 700–850 °C for hydrogen and air as fuel and oxidant, respectively. The results demonstrate the capability and potential of AJP method for deposition of layers necessary for SOFC fabrication and suggest that the method is very viable for obtaining highly reproducible microstructures with potential for mass manufacturing.