Journal of Fuel Cell Science and Technology 

About: Journal of Fuel Cell Science and Technology is an academic journal. The journal publishes majorly in the area(s): Proton exchange membrane fuel cell & Solid oxide fuel cell. It has an ISSN identifier of 1550-624X. Over the lifetime, 761 publications have been published receiving 9443 citations.

Syngas Production via High-Temperature Coelectrolysis of Steam and Carbon Dioxide

Abstract: This paper presents results of recent experiments on simultaneous high-temperature electrolysis (coelectrolysis) of steam and carbon dioxide using solid-oxide electrolysis cells. Coelectrolysis is complicated by the fact that the reverse shift reaction occurs concurrently with the electrolytic reduction reactions. All reactions must be properly accounted for when evaluating results. Electrochemical performance of the button cells and stacks were evaluated over a range of temperatures, compositions, and flow rates. The apparatus used for these tests is heavily instrumented, with precision mass-flow controllers, on-line dewpoint and CO2 sensors, and numerous pressure and temperature measurement stations. It also includes a gas chromatograph for analyzing outlet gas compositions. Comparisons of measured compositions to predictions obtained from a chemical equilibrium coelectrolysis model are presented, along with corresponding polarization curves. Results indicate excellent agreement between predicted and measured outlet compositions. Cell area-specific resistance values were found to be similar for steam electrolysis and coelectrolysis. Coelectrolysis significantly increases the yield of syngas over the reverse water gas shift reaction equilibrium composition. The process appears to be a promising technique for large-scale syngas production.

Stresses in Proton Exchange Membranes Due to Hygro-Thermal Loading

Abstract: Durability of the proton exchange membrane (PEM) is a major technical barrier to the commercial viability of polymer electrolyte membrane fuel cells (PEMFC) for stationary and transportation applications. In order to reach Department of Energy objectives for automotive PEMFCs, an operating design lifetime of at least 5000 h over a broad temperature range is required. Reaching these lifetimes is an extremely difficult technical challenge. Though good progress has been made in recent years, there are still issues that need to be addressed to assure successful, economically viable, long-term operation of PEM fuel cells. Fuel cell lifetime is currently limited by gradual degradation of both the chemical and hygro-thermomechanical properties of the membranes. Eventually the system fails due to a critical reduction of the voltage or mechanical damage. However, the hygro-thermomechanical loading of the membranes and how this effects the lifetime of the fuel cell is not understood. The long-term objective of the research is to establish a fundamental understanding of the mechanical processes in degradation and how they influence the lifetime of PEMFCs based on perfluorosulfuric acid membrane. In this paper, we discuss the finite element models developed to investigate the in situ stresses in polymer membranes.

Viscoelastic Stress Analysis of Constrained Proton Exchange Membranes Under Humidity Cycling

Abstract: Many premature failures in proton exchange membrane (PEM)fuel cells are attributed to crossover of the reactant gas from microcracks in the membranes. The formation of these microcracks is believed to result from chemical and/or mechanical degradation of the constrained membrane during fuel cell operation. By characterizing the through-membrane leakage, we report failures resulting from crack formation in several PEMs mounted in 50 cm 2 fuel cell fixtures and mechanically stressed as the environment was cycled between wet and dry conditions in the absence of chemical potential. The humidity cycling tests also show that the failure from crossover leaks is delayed if membranes are subjected to smaller humidity swings. To understand the mechanical response of PEMs constrained by bipolar plates and subjected to changing humidity levels, we use Nafion® NR-111 as a model membrane and conduct numerical stress analyses to simulate the humidity cycling test. We also report the measurement of material properties required for the stress analysis-water content, coefficient of hygral expansion, and creep compliance. From the creep test results, we have found that the principle of time-temperature-humidity superposition can be applied to Nafion® NR-111 to construct a creep compliance master curve by shifting individual compliance curves with respect to temperature and water content. The stress prediction obtained using the commercial finite element program ABAQVS® agrees well with the stress measurement of Nafion® NR-111 from both tensile and relaxation tests for strains up to 8%. The stress analysis used to model the humidity cycling test shows that the membrane can develop significant residual tensile stress after humidity cycling. The result shows that the larger the humidity swing and/or the faster the hydration/dehydration rate, the higher the residual tensile stress. This result is confirmed experimentally as PEM failure is significantly delayed by decreasing the magnitude of the relative humidity cycle. Based on the current study, we also discuss potential improvements for material characterization, material state diagnostics, and a stress model for PEMs.

Dynamic Simulation of a Pressurized 220kW Solid Oxide Fuel-Cell–Gas-Turbine Hybrid System: Modeled Performance Compared to Measured Results

Abstract: R. A. Roberts J. Brouwer e-mail: jb@nfcrc.uci.edu National Fuel Cell Research Center, University California, Irvine, Irvine, CA 92697-3550 Dynamic Simulation of a Pressurized 220 kW Solid Oxide Fuel-Cell–Gas-Turbine Hybrid System: Modeled Performance Compared to Measured Results Hybrid fuel-cell–gas-turbine (FC/GT) systems are technologically advanced systems that are promising for electric power generation with ultralow emissions and high efficiency for a large range of power plant sizes. A good understanding of the steady-state and dynamic performance of a FC/GT system is needed in order to develop and advance this hybrid technology. In this work, a detailed dynamic model of a solid oxide fuel cell/gas turbine (SOFC/GT) system has been developed. The system that is simulated represents the 220 kW SOFC/GT hybrid system developed by Siemens Westinghouse. Results of the dynamic model and experimental data gathered during the operation and testing of the 220 kW SOFC/GT at the National Fuel Cell Research Center are compared and presented. 关DOI: 10.1115/1.2133802兴 Introduction and Background Fuel cell/gas turbine 共FC/GT兲 hybrids integrate high- temperature fuel cells with gas turbine engines in a manner that converts fuel cell thermal energy through turbo machinery to power compressors and/or electric generators. In both thermody- namic simulation and experiment, these hybrid systems have dem- onstrated lower environmental impact compared to conventional combustion-driven power plants. Lower carbon dioxide emissions can be achieved through higher fuel-to-electrical efficiencies, while NO x and other criteria pollutant emissions are greatly re- duced by primary electrochemical conversion of the fuel versus the combustion process of conventional plants 关1兴. In this work, a dynamic model of a hybrid system is developed and applied to analyze a specific hybrid cycle that is applicable to distributed generation. More complex cycles have been considered for larger scale power plants that may utilize a combined cycle to drive the efficiency up and the environmental impact down 关2兴. Today much work is being done to reduce the cost and increase the reliability of solid oxide fuel cell 共SOFC兲 systems. Several cell geometries are being advanced by fuel cell manufacturers includ- ing tubular and planer SOFC designs, and even cell geometries that combine planer and tubular features. Each geometry has its advantages and disadvantages with regard to thermal expansion compliance, power density, potential cost, manufacturability, and internal resistivity 关3兴. Many companies are advancing these dif- ferent types of SOFCs, but no commercial products exist today. Only demonstration and prototype systems have been built and tested to date. Mathematical models provide a cost-effective and efficient tool in aiding the development of SOFCs and SOFC/GT systems. Sev- eral entities around the world have developed steady-state simu- lation capabilities for FC/GT systems. These research groups in- clude efforts at the Georgia Institute of Technology, University of Genova, NFCRC, Nanyang Technical University, and others Manuscript received February 8, 2005; final manuscript received August 19, 2005. Review conducted by Subhash C. Singhal. 18 / Vol. 3, FEBRUARY 2006 关2–8兴. Dynamic FC/GT simulation capabilities are less common, but increasingly being developed as the demand for dynamic un- derstanding and controls development grows. Examples of previ- ous dynamic simulation efforts include work at the National En- ergy Technology Laboratory and FuelCell Energy among others 关9–13兴. Model validation is very important, and there remains a great need to produce experimental hybrid system data. To date there have been two hybrid systems built and success- fully demonstrated. The first uses an atmospheric fuel cell located after the turbine exhaust has been built and demonstrated by Fu- elCell Energy that integrated a molten carbonate fuel cell and a Capstone C30 gas turbine. This system successfully ran for 2900 h in grid-connected mode at 51.7% fuel-to-electrical effi- ciency. See Ghezel-Ayagh et al. 关14兴 for more information on this system. The second system uses a pressurized fuel cell located between the compressor and turbine, which is the system of direct interest to the current work. Experiment Description Siemens Westinghouse developed the very first pressurized SOFC/GT hybrid system using their tubular SOFC stack design. This system, presented in Fig. 1, was tested at the NFCRC with support from Southern California Edison, the U.S. Department of Energy, and others. The system was designed, constructed, and tested to demonstrate and prove the hybrid concept. The system operated for over 2900 h and produced up to 220 kW at fuel-to- electricity conversion efficiencies of up to 53%. In parallel, NFCRC developed dynamic simulation capabilities for each of the system components together with a simulation framework for modeling and developing control strategies for integrated SOFC/GT systems. A diagram of the integrated SOFC/GT system is presented in Fig. 2. This system is comprised of a tubular SOFC with inte- grated internal reformer and anode off-gas oxidizer as illustrated in Fig. 3. These components 共stack, reformer兲 are placed between the compressor and turbine so that they operate under pressurized conditions. The gas turbine is a dual shaft Ingersoll-Rand 75 kW Copyright © 2006 by ASME Transactions of the ASME Downloaded From: http://fuelcellscience.asmedigitalcollection.asme.org/ on 12/02/2015 Terms of Use: http://www.asme.org/about-asme/terms-of-use