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In this paper we perform a model-based analysis of a solid oxide fuel cell (SOFC) system with an integrated steam reformer and with methane as a fuel. The objective of this study is to analyze the steady-state and transient characteristics of this system. For the analysis, we develop a detailed control-oriented model of the system that captures the heat and mass transfer, chemical kinetics, and electrochemical phenomena. We express the dynamics of the reformer and the fuel cell in state-space form. By applying coordinate transformations to the state-space model, we derive analytical expressions of steady-state conditions and transient behaviors of two critical performance variables, namely, fuel utilization and steam-to-carbon balance. Using these results, we solve a constrained steady-state fuel optimization problem using linear programming. Our analysis is supported by simulations. The results presented in this paper can be applied in predicting steady-state conditions and certain transient behaviors and will be useful in control development for SOFC systems.

Solid oxide fuel cells (SOFCs) offer many potential benefits as an energy conversion device. This paper addresses experimental validation of a numerical SOFC model that has been developed. Results are compared at steady state operation for temperatures ranging from 1073 K to 1173 K and for H2 gas concentrations fuel supplies of 10–90% with a balance of N2. The results agree well with a maximum of 13.3% difference seen between the numerical and experimental results, which is within the limit of the experimental uncertainties and the material constants that are measured, with most comparisons well below this level. It is concluded that since the model is very sensitive to material properties and temperature that for the best results they should be as specific as possible to the experiment. These specific properties were demonstrated in this paper and a validation of a full fuel cell model, with a concentration on the anode, was presented.

A new high temperature fuel cell-micro gas turbine physical emulator has been designed and installed in the framework of the European Integrated Project “FELICITAS” at the Thermochemical Power Group (TPG) laboratory located at Savona. The test rig is based on a commercial 100 kWe recuperated micro gas turbine (mGT) (Turbec T100) modified to be connected to a modular volume designed for physical emulation of fuel cell stack influence. The test rig has been developed starting with a complete theoretical analysis of the micro gas turbine design and off-design performance and with the definition of the more flexible layout to be used for different hybrid system (molten carbonate fuel cell or solid oxide fuel cell) emulation. The layout of the system (connecting pipes, valves, and instrumentation, in particular mass flow meter locations) has been carefully designed, and is presented in detail in this paper. Particular attention has been focused on the viscous pressure loss minimization: (i) to reduce the unbalance between compressor and expander, (ii) to maintain a high measurement precision, and (iii) to have an effective plant flexibility. Moreover, the volume used to emulate the cell stack has been designed to be strongly modular (different from a similar system developed by U.S. Department Of Energy-National Energy Technology Laboratory) to allow different volume size influence on the mGT rig to be easily tested. The modular high temperature volume has been designed using a computational fluid dynamics (CFD) commercial tool (FLUENT). The CFD analysis was used (i) to reach a high level of uniformity in the flow distribution inside the volume, (ii) to have a velocity field (m/s) similar to the one existing inside the emulated cell stack, and (iii) to minimize (as possible) the pressure losses. The volume insulation will also allow to consider a strong thermal capacity effect during the tests. This paper reports the experimental results of several tests carried out on the rig (using the mGT at electrical stand-alone conditions with the machine control system operating at constant rotational speed) at different load values and at both steady-state and transient conditions.

Solid oxide fuel cells (SOFC) are a promising technology for distributed electricity generation and cogeneration. Numerous papers have been published in the past several years proposing mathematical/computational fluid dynamics (CFD) models for predicting the transient and steady-state performance of such cells. In this paper, a detailed steady-state CFD model of a planar anode supported SOFC is proposed, which accounts for mass, thermal, and charge transport as well as electrochemistry and the chemistry of internal fuel reforming. Its main characteristics include the use of a continuous model for the electrochemistry, allowing one to examine different three-phase boundary geometries. This is an improvement over the typical model reported in literature, which utilizes an equivalent resistive circuit approach or a homogeneous distribution of three-phase boundaries. The model proposed here is used to simulate the degradation of anode, cathode, and electrolyte due to instabilities (e.g., anode oxidation due to fuel depletion) or to the delamination of the electrodes from the electrolyte. Such degradations result in a drop in cell performance but are difficult to predict without the use of models that can be helpful for diagnosis. The model is applied to experimental data available in literature both for the nondegraded and degraded cases.

Power demand patterns, such as for houses, fluctuate sharply. Therefore, if fuel cell cogeneration is installed in a house, partial-load operations with low efficiency frequently occur. On the other hand, if the hydrogen rate of hydrogenation gas-engine generation is increased at the time of low load, emission cleanup and brake thermal efficiency improve. So, in this paper, a hybrid cogeneration system that combines a hydrogenation gas engine and a solid polymer membrane-type fuel cell is proposed. So, operation of a fuel cell or a gas engine with the threshold value of load is investigated. In this paper, four systems were investigated by numerical analysis: independent hydrogenation gas-engine operation, solid polymer membrane-type fuel cell independent operation, that operates a fuel cell or a gas engine with the threshold value of load, and operation using a fuel cell to a base load. As a result, the operating method corresponding to a base load in polymer membrane-type fuel cell had the highest total efficiency. In this case, gas-engine generator (NEG) is operated corresponding to load fluctuation. Moreover, in the comparison results of carbon dioxide emissions, the hydrogenation operation of NEG achieved the best result.

Within the framework of the Greening of Gas project, in which the feasibility of mixing hydrogen into the natural gas network in the Netherlands is studied, we are exploring alternative hydrogen production methods. Fuel cells are usually seen as the devices that convert hydrogen into power and heat. It is less well known that these electrochemical energy converters can produce hydrogen, or form an essential component in the systems for coproduction of hydrogen and power. In this paper, the coproduction of hydrogen-rich syngas (that can be converted into hydrogen) and power from natural gas in an internal reforming fuel cell is worked out by flow sheet calculations on an internal reforming solid oxide fuel cell system. The goal of this paper is to study the technical feasibility of such a system and explore its possibilities and limitations for a flexible coproduction. It is shown that the system can operate in a wide range of fuel utilization values at least down to 60&percent; representing highest hydrogen production mode up to 95&percent; corresponding to standard FC operation mode.

Fuel cell technology continues to advance and offers to be a potentially promising solution to many energy needs. Of particular interest are manufacturing techniques to improve performance and decrease overall cost. For catalyst deposition on the membrane electrode assembly (MEA), there are a number of techniques that have been used in the past decades. This paper aims to review many of these main techniques that have been published to show the wide variety of catalyst deposition methods.

Most single-phase inverters, being sourced by fuel cell stacks (FCSs), subject the stacks to reflected low-frequency (120 Hz) current ripples that ride on average dc currents. The ripple current impacts the sizing and efficiency of the FCS. As such and typically, a passive or active filter is required at the input of the inverter (or output of the FCS) to mitigate the ripple current. Toward that end, this paper outlines a guideline to choose the optimum size of a passive input-filter capacitor for a fuel-cell-based power system from the standpoints of the overall system energy density and cost. Detailed case-specific simulation results, based on an analytical approach, are provided to illustrate key issues for both unity power factor as well as harmonic loads.

Proper water management is required for the operation of polymer electrolyte fuel cells (PEFCs), in order to maintain the critical balance between adequate membrane hydration and prevention of water flooding in the catalyst layer. In PEFCs, the membrane electrode assembly (MEA) is sandwiched between two gas diffusion layers (GDLs). In addition, a microporous layer (MPL) is generally applied to the GDL substrates for better water removal from the cathode catalyst layer. This paper is the first to report on an ex situ characterization method for water flooding in GDLs. As the humidity of O2 gas on the substrate side of the GDL was increased in incremental steps, O2 gas began to diffuse into the MPL side of the GDL. When the O2 relative humidity exceeded the dew point, water flooding was observed on the surface of the MPL and the O2 concentration dropped sharply because the O2 diffusion was suppressed by the produced liquid water. When comparing to the estimated mass transfer loss based on the actual polarization curves of an MEA using the GDL, it was found that the decrease in the O2 concentration on the MPL side of the GDL can be used as an index of water flooding in the PEFC.

Fuel cell systems represent a promising alternative energy converter. In the past years, researches have been conducted for their modeling, control, and diagnosis. The model should accurately reproduce the behavior without being too complex. Due to the highly multiphysical interactions and coupling within the fuel cell, using a graphical representation for developing this model seems well suited. This paper presents a review of recent literature on graphical representation of proton exchange membrane fuel cell (PEMFC). Three main graphical representations are discussed: bond graph (BG), EMR, and equivalent electrical circuit. Their fields of application will be shown as well.

Chemical compatibility of sealing glass with metal interconnects is a critical issue for planar solid oxide fuel cell (SOFC). In this paper, interface reactions between a sealing glass and a ferritic metal interconnect (SS410) are tested under three different heat treatment conditions: sealing (static), aging (static), and thermal cycling (dynamic). The results show that the BaCrO4 crystals with two different morphology (round-shaped and needle-shaped) form both at the three-phase boundary (where air, glass, and SS410 meet) and on the surface of the sealing glass under the three conditions. Round-shaped BaCrO4 crystals form with low O2 concentration and short reaction time. Needle-shaped BaCrO4 crystals form with high O2 concentration and long reaction time. For the thermal cycling condition, the BaCrO4 formed at early stages causes the delamination of the sealing interface. Then, O2 diffuses into the interior interface along the delamination path, which results in the formation of BaCrO4 at the interior interface. The delamination-enhanced BaCrO4 formation during thermal cycling will lead to crack along the sealing interface, causing the striking increase of leak rates.

In a proton exchange membrane fuel cell (PEMFC), gas diffusion layers (GDLs) play a major role in the overall system performances. This is the reason why many research investigations try to model and optimize the GDL physical properties. Currently, the major drawback of these models is to obtain representative GDL mechanical and physical input parameters under different excitations and, particularly, under dynamic excitations. In this paper, an experimental method using a dynamic mechanical analysis (DMA) is detailed to properly obtain the GDL Young's modulus in compression (or compression modulus) for high compressive loads under dynamic excitation. As an example, a very stiff GDL is characterized and analyzed. Only the first mechanical compression is considered. The GDL compression modulus is clearly nonlinear versus the compressive loads. The dynamic load amplitude has a strong effect on the GDL hysteretic behavior. However, the frequency value of the dynamic excitation seems to have no effect on the GDL compression modulus.

This paper presents a reliability approach to analyze the degradation of proton exchange membrane fuel cell. This approach is based on the dependability analysis tools such as the causal and fault trees to establish an analysis of the internal state of the fuel cell energy conversion performance and evaluate its lifetime. The elaboration of causal tree offers powerful tools to a deductive analysis, which consists on seeking the various combinations of events leading to the fuel cell degradation. The parameters of fuel cell model are identified in order to found the degree of degradation. The experimental determination of the variation interval of the parameters is done according to each of degradation modes. A diagnostic method is proposed in order to identify the depth of each aging process of the fuel cell. The diagnosis is done by comparing the experimental output characteristic at beginning of life of the fuel cell with the used fuel cell to qualify and quantify the depth of degradation.

Solid materials forming the boundaries of a lubrication interface may be elastoplastic, heat treated, coated with multilayers, or functionally graded. They may also be composites reinforced by particles or have impurities and defects. Presented in this paper is a model for elastohydrodynamic lubrication interfaces formed with these realistic materials. This model considers the surface deformation and subsurface stresses influenced by material inhomogeneities, where the inhomogeneities are replaced by inclusions with properly determined eigenstrains by means of the equivalent inclusion method. The surface displacement or deformation caused by inhomogeneities is introduced to the film thickness equation. The stresses are the sum of those caused by the fluid pressure and the eigenstrains. The lubrication of a material with a single inhomogeneity, multiple inhomogeneities, and functionally graded coatings are analyzed to reveal the influence of inhomogeneities on film thickness, pressure distribution, and subsurface stresses.

In this research, the impact of structural parameters of bipolar plates on the proton exchange membrane (PEM) fuel cell performance has been investigated using numerical method, and this model incorporates all the essential fundamental physical and electrochemical processes occurring in the membrane electrolyte, cathode catalyst layer, electrode backing, and flow channel, with some assumptions in each part. In formulation of this model, the cell is assumed to work under steady state conditions. Also, since the thickness of the cell is negligible compared to other dimensions, one-dimensional and isothermal approximations are used. The structural parameters considered in this paper are: the width of channels (Wc), the width of support (Ws), the number of gas channels (ng), the height of channels (hc), and the height of supports (hp). The results show that structural parameters of bipolar plates have a great impact on outlet voltage in high current densities. Also, the number of gas channels, their surface area, the contacting area of bipolar plates, and electrodes have a great effect on the rate of reaction and consequently on outlet voltage. The model predictions have been compared with the existing experimental results available in the literature, and excellent agreement has been demonstrated between the model results and the experimental data for the cell polarization curve.

In this paper, a Polymer Electrolyte Membrane (PEM) fuel cell power system including burner, steam reformer, heat exchanger, and water heater has been considered. A PEM fuel cell system is designed to meet the electrical, domestic hot water, heating, and cooling loads of a residential building located in Tehran. Operating conditions of the system with consideration of the electricity cost has been studied. The cost includes social cost of the environmental pollutants (e.g. CO2, CO and NO). The results show that the maximum energy needs of the building can be met by 12 fuel cell stacks with nominal capacity of 8.5 kW. Annual average electricity cost of thissystem is equal to 0.39 US$/kWh and entropy generation of this system through a year is equal to 1004.54 GJ/K1. It is also concluded that increase in ambient temperature from 1 °C to 40 °C increases the entropy generation by 5.73%, carbon monoxide by 14.56%, and nitrogen monoxide by 8.9%, but decreases carbon dioxide by 0.47%.

This paper reports a series of new electrochemical impedance measurements that were performed on an anode supported planar solid oxide fuel cell (SOFC) tested at different anode gas conditions and at different applied voltages. This study indicates that impedance spectroscopy can resolve four different processes, as long as one of those processes does not become too large. At open circuit voltage the four processes can be resolved best; however, as a voltage is applied the processes are convoluted and cannot be resolved properly. Two of the processes seem to remain almost unchanged as the fuel conditions are changed and can be attributed to the cathode. The two anode processes change with the fuel conditions and both indicate a dependence on charge transfer and diffusion. This methodology can be applied to determine the mode or modes of SOFC degradation for long term testing where one or both electrodes are deteriorating over time.

As fuel cells continue to improve in performance and power densities levels rise, potential applications ensue. System-level performance modeling tools are needed to further the investigation of future applications. One such application is small-scale aircraft propulsion. Both piloted and unmanned fuel cell aircrafts have been successfully demonstrated suggesting the near-term viability of revolutionizing small-scale aviation. Nearly all of the flight demonstrations and modeling efforts are conducted with low temperature fuel cells; however, the solid oxide fuel cell (SOFC) should not be overlooked. Attributing to their durability and popularity in stationary applications, which require continuous operation, SOFCs are attractive options for long endurance flights. This study presents the optimization of an integrated solid oxide fuel cell-fuel processing system model for performance evaluation in aircraft propulsion. System parameters corresponding to maximum steady state thermal efficiencies for various flight phase power levels were obtained through implementation of the particle swarm optimization (PSO) algorithm. Optimal values for fuel utilization, air stoichiometric ratio, air bypass ratio, and burner ratio, a four-dimensional optimization problem, were obtained while constraining the SOFC operating temperature to 650–1000 °C. The PSO swarm size was set to 35 particles, and the number of iterations performed for each case flight power level was set at 40. Results indicate the maximum thermal efficiency of the integrated fuel cell-fuel processing system remains in the range of 44–46% throughout descend, loitering, and cruise conditions. This paper discusses a system-level model of an integrated fuel cell-fuel processing system, and presents a methodology for system optimization through the particle swarm algorithm.

Fuel cells generally become promising candidates for the electrical power supply in automotive and stationary applications. The power control of the fuel cell is one of the essential problems. In this paper, a power control concept with a master-slave structure for fuel cell systems is suggested. Within that concept, a DC/DC converter, several slave controllers, and a master controller are combined to achieve the control objectives. The DC/DC converter conditions the power and transfers it from the fuel cell to the load. The task of the slave controller is to maintain the controlled variables at their set points. The master controller has to select the set points for the slave controllers and limits the fuel cell output power, if the requested power exceeds the maximum power, which can be instantaneously produced by the controlled fuel cell system. The proposed control concept is demonstrated by simulations of a proton exchange membrane (PEM) fuel cell system taken from the literature. For that purpose, different controllers are designed based on model-free methods. For the master controller design, two alternative options are discussed: high efficiency tracking and fast power tracking. As shown in the simulation results, high efficiency tracking leads to higher system efficiency, however, an additional energy buffer is required. In contrast, no energy buffer is needed for the option of fast power tracking. However, the system efficiency is lower. The presented control concept is meaningful for systems with dynamic load requirements and can be easily applied to different fuel cell systems due to the model-free design approach.

Lateral impedance and local characteristics of anode-supported solid oxide fuel cells (SOFCs) are studied in this paper. The testing device, which combines the original cell housing with a four-point probe equipment, is set for measuring SOFC single cell. The current collectors on anode and cathode in the original cell housing are, respectively, replaced by four independent probe units. They are not only to collect current, but also become measuring probes. Therefore, the lateral impedance of anode and cathode can be measured. Furthermore, the local characteristics are examined by open circuit voltage (OCV), I-V curve, and electrochemical impedance spectroscopy (EIS) measurements. The results show that the lateral impedance is substantially varied with temperature, the OCV at the center of the cell are higher than the edge, the central location on cell have better performance and lower impedance than the marginal location.

The gas diffusion layers (GDLs) in polymer proton exchange membrane fuel cells are under compression in operation. Understanding and then being able to quantify the reduced ability of GDLs to conduct gases due to the compression is hence important in fuel cell design. In this paper, we investigated the change of anisotropic permeability of GDLs under different compressions using the improved multiple-relaxation time (MRT) lattice Boltzmann model and X-ray computed micro-tomography. The binary 3D X-ray images of GDLs under different compressions were obtained using the technologies we developed previously, and the permeability of the GDLs in both through-plane and in-plane directions was calculated by simulating gas flow at micron scale through the 3D images. The results indicated that, in comparison with the single-relaxation time (SRT) lattice Boltzmann model commonly used in the literature, the MRT model is robust and flexible in choosing model parameters. The SRT model can give accurate results only when using a specific relaxation parameter whose value varies with porosity. The simulated results using the MRT model reveal that compression could lead to a significant decrease in permeability in both through-plane and in-plane directions, and that the relationship between the decreased permeability and porosity can be well described by both Kozeny-Carman relation and the equation derived by Tomadakis and Sotirchos (1993, “Ordinary and Transition Rdgime Diffusion in Random Fiber Structure,” AIChE J., 39, pp. 397–412) for porosity in the range from 50% to 85%. Since GDLs compression takes place mainly in the through-plane direction, the results presented in this work could provide an easy way to estimate permeability reduction in both through-plane and in-plane directions when the compressive pressure is known.

Perfluorosulfonic acid polymer membranes, such as Nafion®, Aciplex®, and Flemion®, are attracting great attention as electrolyte membranes for fuel cells because they have high proton conductivity. In this paper, the effect of γ rays on the electrical properties of perfluorosulfonic acid membranes by applying a variable voltage and measuring the current and dimension of the sample have been investigated. In order to understand the irradiation effects on conductivity changes, we have used optical absorption measurement in the wavelength of 190 ∼ 500 nm. The results show that the electrical conductivity has been increased by increasing the absorption dose, and intensity of the absorption bands have increased by increasing the absorption dose. The electrical conductivities of the irradiated membranes at room temperature are enhanced about one order of magnitude higher than the conductivities of an unirradiated membrane. Moreover, an optical absorption measurement shows that the structures of the membranes are modified by γ radiation. Intensity absorption bands associated to fluorocarbon and peroxy radicals and C=O groups increased with increasing the dose. The change in electrical conductivity seems to be related to the high production of peroxy radicals in the irradiated membrane.

A one-dimensional, dynamic proton exchange membrane fuel cells stack model is developed in this paper, where the transports of reactant and water (in both liquid and vapor phase) are described by partial differential equations (PDEs) in gas diffusion layers (GDLs) of both anode and cathode, and the lumped model is applied to channels and MEA. The boundary conditions needed for PDEs in GDLs are provided by the lumped model. In addition, the convection term is considered in PDEs for GDLs to describe the convection effect on hydrogen gas purge process on the anode side. As a result, the purge effect under medium current density (corresponding to ohmic polarization dominated region) can be simulated in an efficient manner by improving the mass transfer and reducing the effect of water back diffusion from cathode to anode. The presented gas purge model is validated by the experimental data obtained from our laboratory as well as other research group. The influence factors to the gas purge schedule on the anode side, such as the purge interval and purge time, are investigated as well.

In this paper we analyze the three-dimensional flow field in anode and cathode gas channels of polymer electrolyte membrane (PEM) fuel cells operating at high temperature (T >100 °C). Different gas flow channel designs (pin-type, parallel channels, comb-tipe and multiple serpentine), as well as different channel sections (squared, trapezoidal and rounded with different curvature radii) are evaluated in function of some relevant parameters. The analysis is performed accounting for overall pressure losses, gas distribution over the electrode area and residence time with focus on channel hydraulic diameter, active surface ratio, gas path. Differences with low temperature (LT) PEM fuel cell design are also adressed. The investigation is conducted by means of 3D-CFD softwares and the results of our simulations are compared to experimental data in literature.

This paper presents one-dimensional transient thermal model for the membrane electrode assembly (MEA) of a proton exchange membrane fuel cell (PEMFC). This model accounts for various heat generating mechanisms, including irreversible heat due to electrochemical reactions, entropic heat, and Joule heating arising from the electrolyte ionic resistance. Numerical results show the effects of many important factors on the transient phenomena in the PEMFC system.

The paper describes a mathematical analysis of multi-component diffusion with chemical reaction in the porous materials of high-temperature solid oxide fuel cells. The objectives are to clarify the underlying physics, to investigate different modeling approaches and to establish expressions for the cell voltage loss. The description proceeds from the simplest non-reactive binary diffusion process, through a multi-component analysis with non-reactive diluent gases present, to diffusion in the presence of the water-gas shift chemical reaction. Using a single average diffusion coefficient, an analytical solution can be found, not only for the limiting cases of frozen and equilibrium water-gas shift chemistry but also for the general non-equilibrium situation. A Damköhler number is identified and it is shown that shift equilibrium is not necessarily preserved in the anode flow. The non-equilibrium analysis also reveals unusual behavior whereby the molar fluxes become discontinuous in the equilibrium limit while the mole fractions and cell voltage loss approach the limit continuously. A physically more realistic model based on two diffusion coefficients provides a more detailed description for frozen and equilibrium chemistry but does not yield an explicit non-equilibrium solution. In all, the analysis provides fundamental insight and quantitative predictions for many of the flow phenomena occurring in the porous materials of SOFCs.

This paper presents a spatially resolved transient fuel cell model applied to the simulation of high temperature PEM fuel cell impedance spectra. The model is developed using a 2D finite volume method approach. The model is resolved along the channel and across the membrane. The model considers diffusion of cathode gas species in gas diffusion layers and catalyst layer, transport of protons in the membrane and the catalyst layers, and double layer capacitive effects in the catalyst layers. The model has been fitted simultaneously to a polarization curve and to an impedance spectrum recorded in the laboratory. A simultaneous fit to both curves is not achieved. In order to investigate the effects of the fitting parameters on the simulation results, a parameter variation study is carried out. It is concluded that some of the fitting parameters assume values which are not realistic. In order to remedy this, phenomena neglected in this version of the model must be incorporated in future versions.

Heterogeneous functional materials, e.g., “HeteroFoaMs” are at the heart of countless energy systems, including heat storage materials, batteries, solid oxide fuel cells, and polymer electrolyte fuel cells. HeteroFoaMs are generally nanostructured and porous to accommodate transport of gasses or fluids, and must be multifunctional (i.e., active operators on mass, momentum, energy, or charge, in combinations). This paper will discuss several aspects of modeling the relationships between the constituents and microstructure of these material systems and their device functionalities. Technical advances based on these relationships will also be identified and discussed. Three major elements of the general problem of how to model HeteroFoaM electrodes will be addressed. Modeling approaches for ionic charge transfer with electrochemistry in the nanostructured porosity of the electrode will be discussed. Second, the effect of morphology and space charge on conduction through porous doped ceria particle assemblies, and their role in electrode processes will be modeled and described. And third, the effect of local heterogeneity and morphology on charge distributions and polarization in porous dielectric electrode materials will be analyzed using multiphysics field equations set on the details of local morphology. Several new analysis methods and results, as well as experimental data relating to these approaches will be presented. The value, capabilities, and limitations of the approaches will be evaluated.

This paper presents an analysis of advanced cycles with limited CO2 emissions based onthe integration of molten carbonate fuel cells (MCFCs) in natural gas fired combined cycles (NGCC) in order to efficiently capture CO2 from the exhaust of the gas turbine. In the proposed cycles, the gas turbine flue gases are used as cathode feeding for a MCFC, where CO2 is transferred from the cathode to anode side, concentrating the CO2 in the anode exhaust. At the anode side, the MCFCs are fed with natural gas, processed by an external reformer which is thermally integrated within the FC module; the corresponding CO2 production is completely concentrated at the anode. The resulting anode exhaust stream is then sent to a CO2 removal section which is based on a cryogenic CO2 removal process, based on internal or external refrigeration cycles, cooling the exhaust stream in the heat recovery steam generator and recycling residual fuel compounds to the power cycle. In all cases, a high purity CO2 stream is obtained after condensation of water and pumped in liquid form for subsequent storage. The possibility to arrange the MCFC section with different configurations and operating parameters of the fuel cell modules is investigated, and the option to include two fuel cell modules in series connection, with intermediate cooling of the cathode stream, in order to enhance the plant CO2 separation effectiveness, is also examined. The MCFC section behavior is simulated taking into account Ansaldo Fuel Cells experience and reference data based on a dedicated simulation tool. Detailed energy and material balances of the most promising cycle configurations are presented; fuel cell and conventional components’ working parameters are described and discussed, carrying out a sensitivity analysis on the fuel cell CO2 utilization factor. The plant shows the potential to achieve a CO2 avoided fraction approaching 70–80%, depending on the CO2 concentration limit at cathode outlet, with overall electric efficiency only 1–2% points lower than the reference combined cycle. The plant power output increases by over 40%, thanks to the contributions of the MCFC section which acts as an active CO2 concentrator, giving a potentially relevant advantage with respect to competitive carbon capture technologies.

Idaho National Laboratory (INL) is performing high-temperature electrolysis research to generate hydrogen using solid oxide electrolysis cells (SOECs). The project goals are to address the technical and degradation issues associated with the SOECs. This paper provides a summary of various ongoing INL and INL sponsored activities aimed at addressing SOEC degradation. These activities include stack testing, post-test examination, degradation modeling, and a list of issues that need to be addressed in future. Major degradation issues relating to solid oxide fuel cells (SOFC) are relatively better understood than those for SOECs. Some of the degradation mechanisms in SOFCs include contact problems between adjacent cell components, microstructural deterioration (coarsening) of the porous electrodes, and blocking of the reaction sites within the electrodes. Contact problems include delamination of an electrode from the electrolyte, growth of a poorly (electronically) conducting oxide layer between the metallic interconnect plates and the electrodes, and lack of contact between the interconnect and the electrode. INL’s test results on high temperature electrolysis (HTE) using solid oxide cells do not provide clear evidence of whether different events lead to similar or drastically different electrochemical degradation mechanisms. Post-test examination of the solid oxide electrolysis cells showed that the hydrogen electrode and interconnect get partially oxidized and become nonconductive. This is most likely caused by the hydrogen stream composition and flow rate during cool down. The oxygen electrode side of the stacks seemed to be responsible for the observed degradation due to large areas of electrode delamination. Based on the oxygen electrode appearance, the degradation of these stacks was largely controlled by the oxygen electrode delamination rate. Virkar and co-workers have developed a SOEC model based on concepts in local thermodynamic equilibrium in systems otherwise in global thermodynamic nonequilibrium. This model is under continued development. It shows that electronic conduction through the electrolyte, however small, must be taken into account for determining local oxygen chemical potential, within the electrolyte. The chemical potential within the electrolyte may lie out of bounds in relation to values at the electrodes in the electrolyzer mode. Under certain conditions, high pressures can develop in the electrolyte just under the oxygen electrode (anode)/electrolyte interface, leading to electrode delamination. This theory is being further refined and tested by introducing some electronic conduction in the electrolyte.

This paper reports a new electrochemical performance study performed on a planar SOFC cell. This study consists of a 2D model developed using a commercial software, namely Comsol Multiphysics. The model includes fluid dynamics, electrochemistry, electrical conduction, and diffusion physics. This model was built using the actual button cell testing geometry and using experimental data for validation purposes. The objective of this study is to understand the effects of the testing setup used on the cell performance and to recommend an improved design or geometry where the cell performance is independent of any flow maldistribution in both the air and fuel side of the SOFC cell. The air and fuel flow rates are studied to determine the effects on the cell performance. The effects of electrode porosities are studied together with the fuel and air flow rates. The distance from the SOFC cell to the discharge fuel feed tube and air chamber geometry are studied as well. The modeling results indicate that the SOFC electrochemical performance becomes independent of any flow maldistribution at relatively high flow rates for both fuel and air. Reduced electrode porosities play a role in the cell performance, and larger flow rates are required in order to achieve a cell performance independent of flow rates. The cell performance is also affected by the distance from the SOFC cell to the fuel discharge tube and the air chamber geometry. The behavior seen in the cell performance can be explained by a non-uniform mole fraction of reactants near the electrode surface.