bluuebunny/crossref_metadata_2025 huggingface dataset:
Ni-Co-Zn-Al Catalysts From Hydrotalcite-Like Precursors for Hydrogen Production by Ethanol Steam Reforming
Authors: Ramis Gianguido , Busca Guido , Montanari Tania , Sisani Michele , Costantino Umberto
Published: December 2010

A series of well crystallized Ni-Co-Zn-Al LDHs materials has been prepared by the urea hydrolysis method as precursors of mixed oxide catalysts for the Ethanol Steam Reforming (ESR) reaction. The calcination of the layered precursors gives rise to high surface area mixed oxides, mainly a mixture of rock-salt phase (NiO), wurtzite phase (ZnO) and spinel phase. Both precursors and mixed oxides have been throughtfully characterized and the steam reforming of ethanol has been investigated over the calcined catalysts in flow reactor and in-situ FT-IR experiments. The data here reported provide evidence of the good catalytic activity of Co-Zn-Al and Co-Ni-Zn-Al catalysts prepared from hydrotalcite-like LHD precursors for ethanol steam reforming. At 823 K the most active Co/Ni catalyst containains a predominant spinel phase with composition near Zn0.58Ni0.42[Al0.44Co0.56]2O4 and small amounts of NiO and ZnO. On the other side, at 873 K the selectivity to hydrogen increases with cobalt content. In particular, the presence of cobalt increases selectivity to H2 and CO2 and decreases selectivity to methane in the low temperature range 720–870 K. The most selective catalyst is the Ni-free Co-Zn-Al mixed oxide essentially constituted by a single spinel type phase Zn0.55Co0.45[Al0.45Co0.55]2O4. Cobalt catalysts appear consequently to behave better than nickel based catalysts in this temperature range. The key feature for high selectivity to hydrogen is proposed to be associated to a stability of a relatively high oxidation state at the catalyst surface, the most relevant selectivity determining step being constituted by the evolution of surface acetate species. In fact, over oxidized catalyst surface the acetate species evolve producing carbon dioxide and hydrogen while over a more reduced surface they evolve giving rise to methane and COx. Water is supposed to have the main role of allowing surface sites to stay in an unreduced state at least in the temperature range 720–870 K.
Systematic Parameter Estimation and Sensitivity Analysis Using a Multidimensional PEMFC Model Coupled With DAKOTA
Authors: Carnes Brian , Chen Ken S. , Jiang Fangming , Luo Gang , Wang Chao-Yang
Published: December 2010

Current computational models for proton exchange membrane fuel cells (PEMFCs) include a large number of parameters such as boundary conditions, material properties, and numerous parameters used in sub-models for membrane transport, two-phase flow and electrochemistry. In order to successfully use a computational PEMFC model in design and optimization, it is important to identify critical parameters under a wide variety of operating conditions, such as relative humidity, current load, temperature, etc. Moreover, when experimental data is available in the form of polarization curves or local distribution of current and reactant/product species (e.g., O2, H2O concentrations), critical parameters can be estimated in order to enable the model to better fit the data. Sensitivity analysis and parameter estimation are typically performed using manual adjustment of parameters, which is also common in parameter studies. We present work to demonstrate a systematic approach based on using a widely available toolkit developed at Sandia called DAKOTA that supports many kinds of design studies, such as sensitivity analysis as well as optimization and uncertainty quantification. In the present work, we couple a multidimensional PEMFC model (which is being developed, tested and later validated in a joint effort by a team from Penn State Univ. and Sandia National Laboratories) with DAKOTA through the mapping of model parameters to system responses. Using this interface, we demonstrate the efficiency of performing simple parameter studies as well as identifying critical parameters using sensitivity analysis. Finally, we show examples of optimization and parameter estimation using the automated capability in DAKOTA.
Investigation of Failure Mechanisms in Ti Containing Brazing Alloys Used in SOFC/SOEC Environments
Authors: Kiebach Wolff-Ragnar , Knibbe Ruth , Frederiksen Kristian B. , Chen Ming , Mikkelsen Lars , Hendriksen Peter V.
Published: December 2010

The two braze alloys TiCuNi® and Silver-ABA® were tested as possible candidates for seals in SOFC or SOEC stacks. The different Ti amount in the samples allowed an evaluation of Ti as a matrix filler and as an active metal/wetting agent in brazing alloys. The sealing ability towards ferritic steel and yttria-stabilized-zirconia (YSZ) was investigated. After the sealing process steel/braze/YSZ joints were further annealed in oxidizing (Air) or reducing (9% H2 in Ar) atmospheres at 750 °C for 150 h. The boundaries of the braze and the joining partners for as-sealed and annealed samples were examined with SEM/EDS. XRD and EXAFS were used to characterize reaction products after the annealing process. Based on these results and taking before reported data into consideration, the advantages and disadvantages of Ti containing seals and the role of Ti in failure mechanism are discussed. Even if the use of Ti in active brazing alloys has its benefits, the disadvantages caused by Ti and its reaction products strongly suggest the use of Ti free brazes in SOFC/SOEC applications.
RIB/Channel Effect on Cell Performance Under High Current Density Operation
Authors: Tabuchi Yuichiro , Shiomi Takeshi , Aoki Osamu , Kubo Norio , Shinohara Kazuhiko
Published: December 2010

Heat and water transport in polymer electrolyte membrane fuel cell (PEMFC) has considerable impacts on cell performance under high current density which is desired in PEMFC for automobiles. In this study, the impact of rib/channel, heat and water transport on cell performance under high current density was investigated by experimental evaluation of liquid water distribution and numerical validation. Liquid water distribution between rib and channel is evaluated by Neutron Radiography. In order to neglect the effect of liquid water in channel and the distribution of oxygen and hydrogen concentration distribution along with channel length, the differential cell was used in this study. Experimental results show that liquid water under channel was dramatically changed with Rib/Channel width. From numerical study, it is found that the change of liquid water distribution was strongly affected by temperature distribution between rib and channel. In addition, not only heat transport but also water transport through membrane also significantly affected cell performance under high current density operation. From numerical validation, it is concluded that this effect on cell performance under high current density could be due to the enhancement of back-diffusion of water through membrane.
Integrated 5 kWe + 5 kWt PEM-FC Generator From Bioethanol: A Demonstrative Project
Authors: Rossetti Ilenia , Biffi Cesare , Forni Lucio , Tantardini Gian Franco , Faita Giuseppe , Raimondi Mario , Vitto Edoardo , Alberti Davide
Published: December 2010

A power unit constituted by a reformer, a H2 purification section and a fuel cell is being installed c/o the Dept. of Physical Chemistry and Electrochemistry of Universita` degli Studi di Milano, on the basis of a collaboration with Helbio S.A. (Hydrogen and Energy Production Systems, supplier) and the support of some sponsors (Linea Energia S.p.A., Parco Tecnologico Padano and Provincia di Lodi). The system is suitable to obtain 5 kWelectric (a.c.) + 5 kWthermal (hot water at 70°C) as peak output. H2 is produced by steam reforming (SR) of second generation bioethanol, obtainable by different non-food competitive biomass. The assessment of the effect of biomass nature and of the consequent different impurities left in the produced bioethanol is part of the experimentation, together with the evaluation of the impact of bioethanol production cost on the final energy cost. Furthermore, the effect of different ethanol/steam ratios will be taken into account to lighten as much as possible the energy demanding ethanol dehydration process. The former point focuses on catalyst life, imposing careful ethanol characterisation and proper catalyst formulation, whereas the latter is connected with the overall energetic efficiency and economic sustainability. Indeed, the reforming process requires co-feeding of water, opening the way to the research of different, cheaper, ethanol purification strategies, leading to lower ethanol concentration with respect to the azeotrope. The reformate is purified from CO down to a concentration below 20 ppm, suitable to feed the proton exchange membrane fuel cells (PEMFC) stack integrated in the fuel processor. This result is achieved by feeding it to two water gas shift reactors, connected in series and operating at high and low temperature, respectively. The expected CO concentration in the outcoming gas is ca. 1 vol% and the final CO removal to meet the specifications is accomplished by selective methanation. The purified H2 is fed to a 5 kWe PEMFC stack, which should have an expected overall efficiency around 80% (including thermal output). The main goal of the present project is to check system performance under widely different operating conditions and load, to verify the effectiveness of the proposed technology and to suggest adequate improvements. Different operating conditions are under evaluation as for ethanol origin, purity, concentration, temperature and space velocity of every reaction step, so to obtain the best compromise between H2 yield, power output and operating costs.
Design and Development of Thermoplastic Polyurethane Based Composite Membranes
Authors: Vasanthakumari R.
Published: December 2010

Polymer electrolyte membranes used in fuel cells are proton selective and hence allows only protons to pass through it. The electrolyte composition, morphology and water absorption properties of the membrane greatly influence the performance of the fuel cell. For example the membranes used in fuel cells should meet following requirements. • Good thermal stability above 250°C. • Proton conductivity greater than 10^-2 S/cm. • Good water absorption and water retaining capacity. • mechanical strength and flexibility. The present paper is focused on design and development of a membrane suitable for fuel cell application. The base polymer chosen in this present work has been thermoplastic polyurethane because of its high flexibility, temperature resistance and solubility in organic solvent such as DMF. Fabrication of the coating machine was done and thermoplastic polyurethane (TPU) based Composite membranes with an average thickness of 40 microns were cast. Sulphonation of polystyrene was carried out to get SPS with assay 98%. TPU based composite membranes with conducting resins of 25% SPEEK, 4%SPS and 10% PANI were cast and characterized by FTIR, DSC, four probe conductivity and SEM. The composite membranes were studied for fuel cell suitability. The studies show that a current in the range of 0.5×10−4 A to 0.8344×10−4 A and about 0.5V can be drawn out of these membranes. The results were compared with that of NAFION membrane.
EIS Characterization of the Poisoning Effects of CO and CO2 on a PBI Based HT-PEM Fuel Cell
Authors: Andreasen So̸ren Juhl , Mosbæk Rasmus , Vang Jakob Rabjerg , Kær So̸ren Knudsen , Araya Samuel Simon
Published: December 2010

This paper presents test results regarding the poisoning effects of CO and CO2 on H3PO4/Polybenzimidazole (PBI) membrane based high temperature proton exchange membrane fuel cell (HT-PEMFC). Electrochemical impedance spectroscopy (EIS), which is a non intrusive diagnostic tool for electrochemical systems, has been used to investigate these effects. A single cell test setup consisting of an electrically heated single cell assembly with a PEMEAS CELTEC P membrane electrode assembly (MEA) of an active area of 45cm2 and mass flow controllers for Air, H2, CO and CO2 was constructed in the laboratory. All operational parameters as well as data acquisition are controlled by two LabView programs, running on two separate computers. The impedance spectrum of the fuel cell is recorded at different operating points and then an Equivalent Circuit (EC), proposed for modelling the cell impedance, is fitted to the spectrum in order to analyze and quantify the impact of the individual factors on HT-PEMFC performance. Results showed that CO poisoning has an effect on all the losses monitored. Intermediate frequency resistances showed higher increase with increasing contamination and decreasing temperature than high frequency resistances, which is attributable to the adsorption of CO on Pt catalyst.
Analysis of Nonuniform Cell Voltage Distribution in a PEMFC Stack
Authors: Zhai Shuang , Sun Pengtao , Chen Fengxiang , Zhang Chuansheng , Zhou Su
Published: December 2010

The nonuniform cell voltage distribution greatly influences design complexity, heat management and system performance, such as life time, reliability and output power, etc., in a real PEMFC system. To get insight into the corresponding influence factors, a fully coupled non-isothermal, electrochemical and transport 3D model for a 10-cell PEMFC stack with coolant channels is set up in this paper and the nonuniform characteristics are reconstructed under the defined operating conditions by simulations. It is found that the temperature profile in the stack has an important impact on the cell voltage distribution through influencing the distribution of activation potential and ohmic overpotential.
Gasified Biomass Fueled Hybrid SOFC Based Power Cycle: Impacts of Carbon Monoxide Fraction in Inlet Fuel
Authors: Zabihian Farshid , Fung Alan S. , Koksal Murat
Published: December 2010

One of the main challenges to use biogas as fuel in hybrid solid oxide fuel cell (SOFC) cycles is variable nature of biogas composition which may cause significant changes in plant performance. On the other hand, carbon monoxide is one of the main components in gasified biomass. Therefore, it is vital to investigate the influences of CO fraction in inlet fuel on the cycle performance. This paper presents the analysis of impacts of carbon monoxide concentration in inlet fuel on the performance of hybrid tubular SOFC and gas turbine (GT) cycle with two configurations, system with and without anode exhaust recirculation. The simulation results are considered when system is fueled by pure methane as a reference case. Then, the performance of the hybrid SOFC-GT system when methane is partially replaced by CO from concentration of 0% to 90% with an increment of 5% at each step is investigated. The proposed model is intended for steady state simulation of hybrid SOFC-GT cycle and is developed in Aspen Plus®. The system performance was monitored by investigating parameters like SOFC and system thermal efficiency; SOFC, GT, and cycle net and specific work; air to fuel ratio; as well as air and fuel mass flow rate. The results of the sensitivity analysis demonstrate that CO concentration has significant effects on the system operational parameters, such as efficiency and specific work.
Improvement of Mechanical Properties of Elastomer-Plastic Conductive Composites for Bipolar Plates in Proton Exchange Membrane Fuel Cells
Authors: Petrach Elaine , Abu-Isa Ismat , Wang Xia
Published: December 2010

Bipolar plates account for about 80% of the fuel cell stack weight. The use of low density and high strength conductive composites for making bipolar plates will result in a lighter and more compact fuel cell stack assembly. Light weight composites were developed based on a two component elastomeric silicone RTV matrix. However, two shortcomings of this composite material are low mechanical strength and relatively high permeability to gases. The purpose of this paper is to develop a new composite material which will overcome high permeability and low strength issues through the use of elastomer-plastic blends as the composite matrix. The elastomer-plastic blends consist of vinyl ester with either urethane elastomer or ethylene-propylene-diene (EPDM) rubber. The chosen elastomers have higher tensile strength and lower gas permeability than silicone rubber. The elastomers will be blended with vinyl ester thermoset plastic to further enhance these characteristics. Synergistic conductive filler system developed in previous work will be used for the new composites to make them conductive. Compatibility of blends ranging in concentration from pure plastic to pure elastomeric composition will be presented along with in-plane electrical resistivity and mechanical properties.
Effect of Flow Channel Design on Planar SOFC Performance
Authors: Yang Choongmo , Kim Dohyung , Jun Junghwang , Choi Samdeuk , Lee Jung-Eui
Published: December 2010

For a planar SOFC interconnect, channel design parameters such as channel width, depth, numbers, wall conditions, etc. are strongly related to the overall cell performance in the way of fuel utilization. Heat and mass transfer rate can be improved by flow mixing enhancement in the properly designed flow channel. In this paper, the influence of flow channel parameters on cell performance in SOFC is discussed. The flow aerodynamic characteristics and friction loss from the bottom surface geometry considered using a three-dimensional computational modeling method. Specially the effect of channel depth and channel mixing on performance and fuel utilization is investigated with an in-depth analysis. As well as a simplified single channel to see the detailed phenomena, an interconnect including whole channels and manifold hole are simulated. The results including a comparison between experimental data and simulation show that to reduce side loss enhanced cell performance with flow and temperature distribution. Based on the result of channel modeling, single cell test with modified design is conducted to achieve performance improvement. This work can be helpful in understanding the channel flow and provide a valuable guideline to channel design for a planar SOFC.
Analysis of Water Agglomeration Inside the GDL Using a Pore-Network Model
Authors: Shahraeeni Mehdi , Hoorfar Mina
Published: December 2010

This article investigates the transient response of water motion inside the GDLs having different pore size distributions. A pore-network model is developed and applied to the problem. The results of the simulation are in agreement with the analytical model available in the literature.
An Optimization Study of an Evaporator in a Fuel Cell System Adopting Oxygen as a Fuel
Authors: Song C. H. , Yu S. S. , Ahn K. Y.
Published: December 2010

This study aims to analyze the effect of an evaporator in a fuel cell system which uses oxygen as a fuel. The oxygen from a liquid storage tank flows to the evaporator in order to supply gaseous oxygen fuel to the fuel cell stack. The design of the evaporator has an effect on the temperature and mass flow rate of the gaseous oxygen being supplied to the stack, which results in a change in the performance of the fuel cell system. In order to evaluate the characteristics, several components such as an oxygen storage tank, evaporator, stack, etc. were modeled and the parameters of the evaporator simulated. Increasing the heat exchange area in an evaporator enhances the effect of heat transfer, but its cost and overheated supplying oxygen gas may have a negative effect on the performance of the system. It is important to evaluate the optimization of the evaporator in a fuel cell system to ensure the better performance of the system.
The Role of Remote Monitoring in Promoting Increased Adoption of Mission Critical Fuel Cells
Authors: Redler Adam , Paul Shawn , Berry Charles
Published: December 2010

Fuel cells are seen by the general public as a new and potentially risky energy source, despite their long history of reliable operation. Fuel cells have been applied in critical applications since their deployment in NASA’s Gemini missions in the mid-1960’s. They are still being used in today’s space shuttles to provide electrical power and drinking water. Over the past decade hundreds of stationary systems have been installed in commercial applications for primary, backup and supplemental power. To promote a better understanding of the benefits of fuel cells, a wider dissemination of real world performance data is needed to show the efficiency, reliability and economic reality of fuel cells. Fuel cell performance is of special interest to the mission critical data center industry, which is slowly considering blending conventional and alternative power sources. Fuel cells are a cleaner and more efficient alternative to grid-supplied electricity in addition to being a viable alternative to batteries and diesel generators for backup power. In areas with poor grid reliability or other power quality issues, fuel cells can be used as the primary power source to provide high quality prime power while the grid provides backup and supplemental power. Waste heat from the fuel cells may be captured and used for space heating or hot water production, or used in absorption chillers to provide air-conditioning for server rooms. With a well-designed heat recovery system, the overall combined heat and power efficiency of a fuel cell installation can approach 90%. This paper will discuss the implementation and applications of the web-based fuel cell monitoring system currently being deployed across Connecticut to promote fuel cell technology awareness and highlight their economic benefits. This monitoring system is being used as a proof-of-concept demonstration that is expected to drive technology adoption in the very competitive and critical private sector data center industry. The monitoring system is already providing publicly accessible data on fuel cell performance via the Internet, and can be used to analyze real-world fuel cell performance data from a wide variety of applications as the system is expanded across the state.
Numerical Analysis of Heat and Mass Transfer in Metal-Supported Solid Oxide Fuel Cells
Authors: Park Joonguen , Kim Sunyoung , Bae Joongmyeon , Bae Gyujong
Published: December 2010

For solid oxide fuel cells (SOFCs) to be commercialized, their strength needs to be improved, as ceramic materials result in reduced strength. Thus, the concept of metal-supported SOFCs has been developed. However, the mass transfer rate in this type of SOFC may be decreased due to the contact layer and the support layer, which can result in low performance. In this paper, the mass transfer characteristics of a metal-supported SOFC were investigated using numerical simulation. The physical property models, the electrochemical reaction models and the governing equations (mass, momentum, energy and species balance) were simulated simultaneously for a multi-physics analysis. Numerical results are compared with experimental data for a code validation. And then, Current density, temperature and mole fraction in single cell were predicted as numerical results.
Experimental Investigation and Modeling of Direct Internal Reforming of Biogases in Tubular SOFC
Authors: Lanzini Andrea , Leone Pierluigi , Pieroni Marco , Santarelli Massimo , Beretta Davide , Ginocchio Stefano
Published: December 2010

Biogas-fed SOFC systems can be considered as interesting power systems in the framework of distributed generation plants. In particular, bio-methane (CH4/CO2 60/40 vol.) and bio-hydrogen (H2/CO2 50/50 vol.), produced from anaerobic digestion of wastes, represent renewable fuels for high efficiency electrochemical generators. This study investigates the behavior of an anode-supported (Ni-YSZ) tubular cell fed by the two fuels. The tubular geometry has been considered since it causes a complete separation of the electrodes reactants, allowing the analysis of the evolution of the fuel gas inside the tube, in terms of composition (consequence of electrochemical and heterogeneous chemical reactions) and temperature field. The experiments have been designed in order to analyse the behavior under different load and fuel utilization conditions. In particular, the fuel mixtures have been conditioned to avoid carbon build-up on the anode electrode. The experimental results have been then used to validate a 2D model (taking into account the cell axial symmetry) of the multi-physics phenomena occurring along the tubular cell. The model shows a good accordance with the experimental data, and has therefore been used to analyse the effects linked to the modification of some geometrical parameters of the tube in terms of performance of the cell.
Development of Direct Carbonate Fuel Cell Systems for Achieving Ultra High Efficiency
Authors: Ghezel-Ayagh Hossein , McInerney Joseph , Venkataraman Ramki , Farooque Mohammad , Sanderson Robert
Published: December 2010

FuelCell Energy, Inc (FCE) has developed products based on its Direct FuelCell® (DFC®) technology with efficiencies near 50 percent based on lower heating value of (LHV) of natural gas. DFC is an internally reformed molten carbonate fuel cell (MCFC) which operates in the 550–700 C range. The combination of the internal reforming of methane and atmospheric pressure and moderately high temperature of operation has resulted in very simple power plant system configurations. Recently, FCE has developed system concepts to further increase the net electric efficiency to beyond 60% efficiency in subMW and MW class power plants. One of these system concepts is the arrangement of the fuel cell stacks in series for very high utilization of fuel in the stacks. Although, in principle, the concept of fuel cell stacks in series is very simple, the implementation of the concept in the actual hardware poses challenges requiring innovative solutions. These challenges include concerns with thermo-mechanical issues, flow and utilization patterns within the fuel cell stacks, and management of the pressure balance between the anode-and-cathode. To address, these issues, various analytical tools including system-level modeling and simulation and Computational Fluid Dynamics (CFD) were utilized. FCE has developed a comprehensive fuel cell stack operation simulation model including hydrodynamics, kinetics, electro-chemical, and heat transfer mechanisms to investigate and optimize the design for performance as well as endurance. Various system configurations were developed which included methods for fueling the second tier stacks in the series. System simulation studies using first principle mass and energy conversation laws were performed. Parametric studies were completed. Subsequent to the system modeling results, the fuel cell stacks operations were analyzed using the Comprehensive Stack Simulation model. The CFD modeling of the fuel cell stacks were performed in support of the system simulation parametric studies. The results of the CFD modeling provided insight to the thermal and flow profiles of both first and second tier stacks in series. The net outcome of the investigation was the design of the system which met the goals of ultra high efficiency and yet complied with the thermo-mechanical requirements of the fuel cell stack components. In this paper, FCE will describe various system options for the very high efficiency systems, the issues related to the design, and the practical solutions to overcome the issues.
Utilisation of Biogas From an Urban Sewage Treatment Plant in a Solid Oxide Fuel Cell
Authors: Lanzini Andrea , Leone Pierluigi , Santarelli Massimo
Published: December 2010

A biogas coming from anaerobic digestion of urban sewage has been used to feed a SOFC planar anode-supported cell. The sewage is produced from the urban area of Torino (IT), and eventually collected and treated by SMAT (the municipal company managing the potable and waste water of the city). The biogas is produced by the thermophilic fermentation of the sludge which remains after the several treatments the sewage goes through in the above-mentioned plant. The biogas is of a high quality: it has on average a a methane content around 65% (the balance being essentially CO2), and the only significant impurity measured is H2S in a range of 70–80 ppm. The as-produced biogas has been used for feeding a planar Ni-YSZ anode-supported SOFC with a LSCF cathode. The biogas desulphurization was accomplished flowing the gas in a fixed-bed reactor, filled with activated. The fuel processing with POX has been assessed to avoid carbon deposition into the Ni-YSZ anode and convert the CH4 into H2 and CO. Short tests to check for eventual anode degradation were performed under typical operating conditions. The cell voltage was always stable under load with the tested mixtures. A cell electrical efficiency around 45% has been measured at 800°C and 80% FU. System simulations have performed as well to assess the whole system configuration under a biogas feeding. Optimization routines have been implemented to predict the best net AC efficiency achievable by a SOFC system running on biogas. Additional considerations on the management of poor LHV biogas mixture have been also assessed, showing how dry-reforming of CH4 with the CO2 already available in the biogas stream would be an excellent option needed to be investigated with further detail in the next future.
Power Management of a Portable Proton Exchange Membrane Fuel Cell-Battery Power System
Authors: Zhang Yan , Zhou Biao
Published: December 2010

A portable Proton Exchange Membrane (PEM) fuel cell-battery power system with hydrogen as fuel has higher power density than conventional batteries and is one of the promising environment-friendly small-scale alternative energy sources. Power management system, as the major control system in the portable PEM fuel cell-battery power system, directly controls the fuel cell stack sub-system, battery charging sub-system and power distribution control sub-system. How to design the power management system is one of the critical issues in optimizing the power system performance, efficiency and components life time. In this study, a set of portable PEM fuel cell-battery system model is introduced. A power management approach with an emergency shutdown function is presented, which not only balances the power distribution between fuel cell and battery at prescribed load condition, but also controls the battery charging cycles to extend the battery life. The simulation results shows the proposed power management approach can effectively control the system performance as expected.
Performance and Stability of Carbonate Fuel Cell Electrodes
Authors: Hilmi Abdelkader , Yuh Chao-Yi , Farooque Mohammad
Published: December 2010

Polarization studies and post analysis have been carried out for characterizing the electrochemical performance and processes affecting life and stability of carbonate fuel cell electrodes. Based on this understanding optimized electrodes design and new electrolyte composition were developed to improve cell performance and achieve the useful life of >5 years. The anode performance and stability were improved by developing an optimized microstructure with better electrolyte retention capabilities. Tests with an advanced electrolyte composition showed 25 mV improvement at 650°C and more than 45 mV at low temperatures compared to baseline. The NiO dissolution in advanced electrolyte is reduced by >60% compared to baseline electrolyte. Anode and cathode electrodes showed stable mechanical strength and stable electrochemical performance.
Anisotropic Porosity Profiles of PEMFC GDLs
Authors: Fishman Z. , Hinebaugh J. , Bazylak A.
Published: December 2010

A first comparison is made of the anisotropic porosity profiles for various polymer electrolyte membrane fuel cell (PEMFC) gas diffusion layer (GDL) materials. Microscale computed tomography (μCT) imaging is performed for two main categories of commercially available GDL materials (carbon fibre paper and felt). The methodology to analyze the through-plane porosities for various materials is presented, and conclusions are drawn about the material pore structures. This work provides insight into both the internal GDL material properties for liquid water transport and the external GDL properties for droplet transport in a PEMFC gas channel.
Optimizing Operation of Stationary Fuel Cell Systems (FCS) Within District Cooling and Heating Networks
Authors: Colella Whitney G.
Published: December 2010

We evaluate innovative design, installation, and control strategies for generating combined cooling, heating, and electric power (CCHP) with fuel cell systems (FCS). The addition of an absorptive cooling cycle allows unrecovered FCS heat to be converted into cooling power, such as for air-conditioning. For example, unrecovered low temperature (80–160°C) heat can be used to drive absorption chillers to create a chilled water stream to cool building spaces. Compared with separate devices that individually generate electricity, heat, and cooling power, such CCHP FCS can reduce feedstock fuel consumption and the resulting greenhouse gas emissions (GHG) by at least 30%. We develop economic and environmental models that optimize the installed capacity of CCHP FCS to minimize either global carbon dioxide (CO2) emissions or global energy costs. Our models evaluate innovative engineering design, installation, and control strategies not commonly pursued by industry, and identify strategies most beneficial for reducing CO2 emissions or costs. Our models minimize costs for building owners consuming cooling power, electricity, and heat by changing the installed capacity of the FCS and by changing FCS operating strategies. Our models optimize for a particular location, climatic region, building load curve set, FCS type, and competitive environment. Our models evaluate the benefits and drawbacks of pursuing more innovative FCS operating strategies; these include 1) connecting FCS to distribution networks for cooling power, heat, and electricity; 2) implementing a variable heat-to-power ratio, to intentionally produce additional heat to meet higher heat demands; 3) designing in the ability to tune the quantity of cooling power from the absorption chiller compared with the amount of recoverable heat from the FCS; and 4) employing the ability to load-follow demand for cooling, heat, or electricity. We base our datum design conditions on measured data describing generator performance in-use, and on measured data describing real-time electricity, heating, and cooling demand over time. A unique feature of our data sets is that the space cooling demand is directly measured and distinguishable from electricity demand (unlike as with standard air conditioning systems). We report results for optimal installed capacities and optimal FCS operating strategies. We generalize these results so that they are applicable to a wide-range of environments throughout the world.
Optimizal Design and Control Strategies for Novel Combined Heat and Power (CHP) Fuel Cell Systems: Part II of II—Case Study Results
Authors: Colella Whitney G.
Published: December 2010

Innovative energy system optimization models are deployed to evaluate novel fuel cell system (FCS) operating strategies, not typically pursued by commercial industry. Most FCS today are installed according to a “business-as-usual” approach: 1) stand-alone (unconnected to district heating networks and low-voltage electricity distribution lines), 2) not load following (not producing output equivalent to the instantaneous electrical or thermal demand of surrounding buildings), 3) employing a fairly fixed heat-to-power ratio (producing heat and electricity in a relatively constant ratio to each other), and 4) producing only electricity and no recoverable heat. By contrast, models discussed here consider novel approaches as well. Novel approaches include 1) networking (connecting FCSs to electrical and/or thermal networks), 2) load following (having FCSs produce only the instantaneous electricity or heat demanded by surrounding buildings), 3) employing a variable heat-to-power ratio (such that FCS can vary the ratio of heat and electricity they produce), 4) co-generation (combining the production of electricity and recoverable heat), 5) permutations of these together, and 6) permutations of these combined with more “business-as-usual” approaches. (The detailed assumptions and methods behind these models are described in Part I of this article pair. Reprinted from Part 1, TABLE 1 below summarizes twelve novel operating strategies investigated by the models.
Experimental Investigation Focusing on Heat and Mass Transfer in a Passive Planer PEMFC Module
Authors: Ejiri Eiji , Kohara Sho , Iijima Takuya
Published: December 2010

Most of the polymer electrolyte fuel cells now under research and development are referred to as stacks because of their stacked structure consisting of many cells and are aimed at automotive or domestic cogeneration system applications. However, a fuel cell with a much simpler structure and capable of operating at nearly ambient temperature and pressure is suitable for small-sized generator sets for home and outdoor use. In this study, detailed experimental analyses were conducted with a newly designed banded structure membrane fuel cell module consisting of 20 cells laid out in a plane in order to investigate the cause of a sudden power breakdown during long-term operation. The airflow near the cathode of a single cell was visualized with a particle image velocimetry system, as the cause of the sudden power breakdown was closely related to heat and mass transfer near the cathode.
A New Formulation and an Efficient Numerical Technique for a Nonisothermal, Anisotropic, Two-Phase Transport Model of PEMFC
Authors: Sun Pengtao , Wang Yun
Published: December 2010

In this paper, a new formulation and an efficient numerical technique are preliminarily studied for a nonisothermal, anisotropic, two-phase transport model of PEMFC, where flow, species, charge and energy equations are all addressed. The importance of water and temperature management are investigated in the anisotropic and nonisothermal point of view. Due to the employment of multi-phase mixture (M2) model, the diffusivity of water transport presents the significant discontinuity and degeneracy across the interface of single gas phase region and two-phase region. In addition, the distinct discontinuity of water diffusivity also emerges through the membrane. Such discontinuities and degeneracy of water diffusivity challenge the fast convergence of nonlinear iteration in numerical simulation, showing oscillating and even divergent iteration process. Based on an intensive new formulation of M2 model for PEMFC, an efficient numerical technique, Kirchhoff transformation, is specifically employed in order to overcome such numerical difficulties and achieve fast and convergent simulation. Numerical experiment is implemented accordingly to indicate the efficiency of the presented numerical technique, in contrast to the oscillating iterations without new numerical technique.
Service Life Prediction of Liquid Silicone Rubber Seal in PEM Fuel Cells
Authors: Cui Tong , Lin C.-W. , Chien C.-H. , Chao Y. J. , Van Zee J.
Published: December 2010

Proton exchange membrane fuel cell (PEMFC) is a promising power source for automobiles in the near future. During operation, there are gases and liquids inside the fuel cell. Sealing around the perimeter of the cell is therefore required to prevent the gases/liquids inside the cell from leaking. Polymers are usually used as the sealing or gasket materials. They in general possess the property of viscoelasticity. The stress relaxation behavior of a polymer, liquid silicone rubber, is studied in this article. Applying the time-temperature superposition, master curve is generated for the prediction of service life of this material used as seals in PEMFC.
Review of High-Temperature Fuel Cell Hardware Materials
Authors: Yuh Chao-Yi , Chen Ling , Franco Adam , Farooque Mohammad
Published: December 2010

The high-temperature carbonate fuel cell is an ultra-clean and high-efficiency power generator. Its intermediate operating temperature, ∼600–650°C, is considered optimum to facilitate fast fuel cell reaction kinetics, utilize waste heat efficiently in a combined heat and power or bottoming power cycle, and at the same time allow use of commercial commodity materials for cell hardware and balance-of-plant (BOP) piping/equipment construction. MW size power plants manufactured by FCE are being operated at customer sites throughout the world. The cell hardware and BOP materials selections are founded on many years of focused research. Microstructure and mechanical property evolution, oxidation, hot corrosion and carburization have been extensively investigated. Long-term subscale stack endurance as well as power plant field operation results to date show that the baseline hardware construction materials meet the endurance goals. Material durability is well understood and solutions are available to further extend life. This paper will review durability experience of hardware materials (cell, stack and BOP).
In Situ Measurements of Through-Plane, Ionic Potential Distributions in Porous Electrodes
Authors: Hess Katherine C. , Epting William K. , Litster Shawn
Published: December 2010

We present a novel apparatus for gathering in situ measurements of through-plane, ionic potential distributions in the porous electrodes of a polymer electrolyte membrane (PEM) fuel cell. Our diagnostic method uses a micro-structured electrode scaffold (MES) that is comprised of alternating layers of insulating and sensing materials into which a 100 μm diameter hole is micro-milled and then filled with catalyst ink. Using the MES, we performed a polarization curve experiment where the ionic potential was measured within a 50 μm thick catalyst layer at 8 and 24 μm from membrane. Our results show that there are significant ionic potential variations within the electrode. Such data is valuable in the electrochemical characterization of electrodes and catalysts. The MES potential measurements also provide insight into reaction distributions across the thickness of the electrode, which is valuable in the validation of porous electrode models.
A Lumped Model of Single Droplet Deformation, Oscillation and Detachment on the GDL Surface of a PEM Fuel Cell
Authors: Esposito Angelo , Polverino Pierpaolo , Pianese Cesare , Guezennec Yann G.
Published: December 2010

Proton Exchange Membrane Fuel Cell performance significantly depends on electrode water content. Indeed, an excess of liquid water in the pores of the gas diffusion layer (GDL) and in the gas flow channel (GFC) can drastically bring down the output power. Depending on the operating conditions, liquid water emerging from the GDL micro-channels can form droplets, films or slugs in the GFC. In the regime of droplets formation, the interaction with the gas crossing-flow leads to an oscillating mechanisms that is fundamental to studying the detachment from the GDL surface, as the authors have shown in a previous publication. In this work, a numerical model of a droplet growing on the GDL surface is developed to describe the interaction between droplet cross-flowing gas stream. The droplet shape and its deformation are reconstructed assuming a known geometry. Therefore, a lumped force balance is enforced to determine the center of mass motion law. Oscillation frequencies during growth and at detachment are found as a function of droplet size. The model is also exploited to find the relationship between droplet critical detachment size and gas velocity. The numerical results are compared with the droplet frequency-size and detachment size-gas velocity experimental results previously presented by the authors. The matching between the numerical and experimental data is very good and is a mean of validation for the model. The low computational burden and the conciseness of the results make the model suitable for applications such as control and optimization strategies development to enhance PEMFC performance. Additionally, the model can be exploited to implement monitoring and diagnostic algorithm.
CFD Modeling of a Catalytic Flat Plate Fuel Reformer for Hydrogen Generation
Authors: Gadde Kranthi K. , Kolavennu Panini K. , Das Susanta K. , Berry K. J.
Published: December 2010

In this study, steam reforming of methane coupled with methane catalytic combustion in a catalytic plate reactor is studied using a two-dimensional mathematical model for co-current flow arrangement. A two-dimensional approach makes the model more realistic by increasing its capability to capture the effect of parameters such as catalyst thickness, reaction rates, inlet temperature and velocity, and channel height, and eliminates the uncertainties introduced by heat and mass transfer coefficients used in one-dimensional models. In our work, we simulate the entire flat plate reformer (both reforming side and combustion side) and carry out parametric studies related to channel height, inlet velocities, and catalyst layer thickness that can provide guidance for the practical implementation of such design. The operating conditions chosen make possible a comparison of the catalytic plate reactor and catalytic combustion analysis with the conventional steam reformer. The CFD results obtained in this study will be very helpful to understand the optimization of design parameters to build a first generation prototype.
Anode Structure Degradation Model for Planar-SOFC Configuration Under Fuel Gas Contaminants
Authors: Iqbal Gulfam , Pakalapati Suryanarayana R. , Elizalde-Blancas Francisco , Guo Huang , Celik Ismail , Kang Bruce
Published: December 2010

Solid Oxide Fuel Cells (SOFCs) is one of the enabling technologies that are being extensively researched for clean power generation from coal-derived syngas. Anode structural degradation is one of the problems that limit the SOFCs operation lifetime and it is further aggravated by some common contaminants found in coal syngas such as phosphine. An accurate model for predicting the degradation patterns inside an SOFC anode operating under different conditions will be an effective tool for advancement of this technology. In this study, a structural durability model developed earlier for button SOFC anodes is extended to simulate the planar-SOFC anodes. The model accounts for thermo-mechanical and fuel gas contaminants effects on the anode material properties to predict evolution, in space and time, of degradation patterns inside the anode and consequently its lifetime. The temperature field and contaminant concentration distribution inside the SOFC anode are the required inputs for the degradation model which are obtained from DREAM-SOFC: a multi-physics code for SOFC modeling. Due to larger active areas compared to button cell, planar-SOFCs bear greater spatial and temporal temperature gradients which lead to higher thermo-mechanical degradation. Moreover, fuel contaminants are distributed on the anode surface which leads to non-uniform microstructure degradation along the fuel flow. For the case of co-flow configuration, anode thermo-mechanical degradation is severe at the anode-electrolyte interface at the fuel outlet. Whereas the fuel gas contaminants effects on the anode microstructure begin at the fuel inlet and propagate through the anode thickness and along the fuel flow. This research will be useful to establish control parameters to achieve desired service life of SOFC stacks working under coal syngas.