Integrated-planar Solid Oxide Fuel Cell Research Articles

Analysing carbon deposition on Ni/YSZ anode tested in an Solid Oxide Fuel Cell (SOFC)

Integrated Planar Solid Oxide Fuel Cells (IP-SOFC), which utilise a Ni/YSZ based anode, have been operated under direct hydrogen-methane mixture fuel injection at 900 oC. This process has shown some disadvantages in fuelling to the IP-SOFC; producing carbon deposition from the methane in the fuel mixture, causing direct structural damage to the IP-SOFC surface and blocking the area of activation for reaction processes and reducing the performances. These factors were shown to adversely affect the performance of the IP-SOFC over time. The aim of this paper is to calculate the amount of carbon deposited through the use of temperature programmed oxidation (TPO). In addition, the distribution of carbon is studied and analysed on all parts of the IP-SOFC cells. The results show that both amorphous and graphitic carbon were formed causing microstructural damage thereby reducing the cell performance. Furthermore, the reaction temperature was demonstrated to increase the total amount of carbon deposition.

Integrated Planar Solid Oxide Fuel Cell: Steady-State Model of a Bundle and Validation through Single Tube Experimental Data

This work focuses on a steady-state model developed for an integrated planar solid oxide fuel cell (IP-SOFC) bundle. In this geometry, several single IP-SOFCs are deposited on a tube and electrically connected in series through interconnections. Then, several tubes are coupled to one another to form a full-sized bundle. A previously-developed and validated electrochemical model is the basis for the development of the tube model, taking into account in detail the presence of active cells, interconnections and dead areas. Mass and energy balance equations are written for the IP-SOFC tube, in the classical form adopted for chemical reactors. Based on the single tube model, a bundle model is developed. Model validation is presented based on single tube current-voltage (I-V) experimental data obtained in a wide range of experimental conditions, i.e., at different temperatures and for different H2/CO/CO2/CH4/H2O/N2 mixtures as the fuel feedstock. The error of the simulation results versus I-V experimental data is less than 1% in most cases, and it grows to a value of 8% only in one case, which is discussed in detail. Finally, we report model predictions of the current density distribution and temperature distribution in a bundle, the latter being a key aspect in view of the mechanical integrity of the IP-SOFC structure.

Direct Operation of IP‐Solid Oxide Fuel Cell with Hydrogen and Methane Fuel Mixtures under Current Load Cycle Operating Condition

AbstractThe effects of methane concentration and current load cycle on the performance and durability of integrated planar solid oxide fuel cell (IP‐SOFC) obtained from Rolls Royce Fuel Cell Systems Ltd (RRFCS) has been investigated. The IP‐SOFC was operated with hydrogen–methane fuel mixture with up to 20% methane concentration at 900 °C for short term operation of the cells with high methane concentration increased the voltage of the IP‐SOFC due to increase in Gibbs free energy. However, it degraded the performance of the IP‐SOFC in long term operation due to carbon deposition on the anode surface. The current load cycle tests were carried out with 95% H2–5% CH4 and 80% H2–20% CH4 fuel mixtures at 900 °C with a constant current of 1 A. At low methane concentration, the decrease in the IP‐SOFC voltage was observed after operating nine current load cycles (384 h). At higher methane concentration, the voltage of IP‐SOFC decreased by almost 30% just after one current load cycle (48 h) due to faster carbon deposition. So future work is therefore required to identify viable alternative materials and optimum operating conditions.

Thermal stress and probability of survival investigation in a multi-bundle integrated-planar solid oxide fuel cells IP-SOFC (integrated-planar solid oxide fuel cell)

A multi-cell model based on a prototypical, IP-SOFC (integrated-planar solid oxide fuel cell) stack design was constructed in this study to perform comprehensive thermal stress analyses and to calculate the probability of survival. The temperature profiles generated by a thermo-electrochemical model were applied to calculate the thermal stress distributions in a multiple-cell module. The effect of coefficient of thermal expansion and Young's modulus variation of the materials used in the IP-SOFC are investigated in a parameter study.The results indicate that the IP-SOFC cells are submitted to the moderate thermal stress at the inlet fuel-flow and it undergoes a high thermal stress at the outlet of the module. The mechanical and the thermal proprieties mismatch between the layers had a greater influence on the strain and on the probability of survival of the cell components. The probability of survival of the electrolyte is lower than the other components. The global durability of the cell components has been increased by decreasing the operating temperature.The results obtained from the comparison between the bundles performances indicate that the bundle to bundle power increased continuously, however the probability of survival decreases. The optimum performances have been obtained for the fourth bundle.

Air flow modeling and performance prediction of the integrated-planar solid oxide fuel cell IP-SOFC

Modeling the air flow through an array of the integrated-planar solid oxide fuel cell (IP-SOFC) is very important for the optimization of the cell performance. The finites differences and the lattices Boltzmann methods are used to predict the evolution of the IP-SOFC fuel cell parameters. The effects of the inlet air velocity, the temperature and the pressure on the cell performance are investigated. The results indicate that the oxygen mole fraction decreases and the polarization concentration increases in the x-direction. The voltage losses became more and more important for the module of the next bundle, caused by the oxygen depleting. An increase in the inlet air velocity can reduce the oxygen mole fraction decrease and decrease polarization losses, however the concentration polarizations decrease imperceptibly with increasing temperature.

Cycling durability studies of IP-SOFC

The function of a cycling test is the investigation of fuel cell stability and degradation behaviour under non-steady operating conditions. Cell quality becomes increasingly likely to degenerate at greater numbers of cycles. This work seeks to comprehensively test the durability of three tubes (tubes 1–3) of the integrated-planar solid oxide fuel cell (IP-SOFC) (Rolls Royce Fuel Cell Systems Ltd). The three IP-SOFC tubes were tested at a constant current of 1 A at 900°C for more than 1200h for tubes 1 and 3, and more than 4940h for tube 2. The fuel utilization was 13.94%, and the average voltage degradation rate measured was 1.3 and 1.5% per 1000h for tubes 2 and 3, respectively. After 1200h work, tube 1 failed because the air supply was cut off from the test station due to compressor overheating. Subsequently, the station closed all gas supply for safety, but the furnace continued to work at a temperature of 900°C for 16h. The tube showed clear signs of damage leading to complete failure. Copyright , Oxford University Press.

Influence of reduced substrate shunting current on cell performance in integrated planar solid oxide fuel cells

Two-cell arrayed integrated planar solid oxide fuel cells (IP-SOFCs) were fabricated using a robo-dispensing method. Special emphasis was placed on the influence of reduced shunting current on cell performance. The resistivity of the substrate increased according to a mixture rule of composites by adding Al 2O 3 into the substrate of partially stabilized zirconia (PSZ). This strategy, which reduces shunting current through the substrate, enhances the power output. When the amount of Al 2O 3 added was more than 26 vol%, however, the Ni anode migrated into the PSZ substrate to react with Al 2O 3, which led to performance degradation. In the case of the two-cell arrayed IP-SOFC with a 20 vol%-Al 2O 3 added to the PSZ substrate, a reduced shunting current loss improved the power density by 30% compared to that of the Al 2O 3-free substrate.

Non-isothermal and electrochemical modelling of the multi-cell module performance in the integrated-planar solid oxide fuel cell

This article presents a performance analysis of a multi-cell integrated-planar solid oxide fuel cell (IP-SOFC) fuelled by pure hydrogen. A non-isothermal electrochemical model, taking into account the temperature variation produced by electrochemical reactions, air, and fuel flow, is used to predict the characteristics of the multi-cell module. The model results show good agreement with the experimental data obtained from a full-size IP-SOFC module prototype for both a first- and a second-generation hybrid application. In this study, a simulation model of individual cell voltage loss indicates that ohmic and activation losses dominate the performance. Sensitivity analyses of the multi-cell show that decreasing the electrolyte thickness can improve cell performance. An increase in operating temperature causes a decrease in ohmic loss and ameliorates the voltage and power cell. Further, increasing the operating pressure produces a weak increase in cell performance.

Investigation of methane steam reforming in planar porous support of solid oxide fuel cell

Adopting the porous support in integrated-planar solid oxide fuel cell (IP-SOFC) can reduce the operating temperature by reducing thickness of electrolyte layer, and also, provide internal reforming environment for hydrogen-rich fuel gas. The distributions of reactant and product components, and temperature of methane steam reforming for IP-SOFC were investigated by the developed physical and mathematical model with thermodynamic analysis, in which eleven possible reaction mechanisms were considered by the source terms and Arrhenius relationship. Numerical simulation of the model revealed that the progress of reforming reaction and the distribution of the product, H 2, were influenced by the operating conditions, included that of temperature, ratio of H 2O and CH 4, as well as by the porosity of the supporting material. The simulating results indicate that the methane conversion rate can reach its maximum value under the operating temperature of 800 °C and porosity of ε = 0.4, which rather approximate to the practical operating conditions of IP-SOFC. In addition, characteristics of carbon deposition on surface of catalyst were discussed under various operating conditions and configuration parameters of the porous support. The present works provided some theoretical explanations to the numerous experimental observations and engineered practices.

A Detailed Three-Dimensional Simulation of an IP-SOFC Stack

A typical integrated-planar solid oxide fuel cell (IP-SOFC) consists of modules with series connected electrochemical cells printed on their outer surfaces. Oxygen is supplied to the cathodes from air flowing over the outside of the module and hydrogen diffuses from the internal fuel channels to the anodes through the porous module support structure. The IP-SOFC is intended for use in medium scale stationary power applications, and such a system will use a fuel cell stack containing many thousands of modules housed inside a pressure vessel. For certain purposes, the geometry of this stack can be adequately described using a computational domain that considers just two modules. A computer code has been developed to simulate the many physical and chemical processes occurring within the stack, including fluid flow, heat transfer, water gas shift, and electrochemical reactions. The simulation results show how the performance of the IP-SOFC stack is strongly affected by these physical processes, the geometry of the stack, and the operating conditions. The temperature distribution, which is difficult to predict using a less realistic geometric model, is almost uniform within each fuel channel and rises steadily in the air flow direction. The shift reaction, which is catalyzed by the anodes, is of great importance, and as the fuel flow becomes depleted of hydrogen it enables the electrochemical cells to make increasing use of carbon monoxide. Overall it was found that the operating voltage produced by the fuel cells is typically 0.74V and the component efficiency, the ratio of the actual power output to the maximum available from the fuels consumed, is around 59%.

Design and Off-Design Analysis of a MW Hybrid System Based on Rolls-Royce Integrated Planar Solid Oxide Fuel Cells

In this paper the design point definition of a pressurised hybrid system based on the Rolls-Royce Integrated Planar-Solid Oxide Fuel Cells (IP-SOFCs) is presented and discussed. The hybrid system size is about 2 MWe and the design point analysis has been carried out using two different IP-SOFC models developed by Thermochemical Power Group (TPG) at the University of Genoa: (i) a generic one, where the transport and balance equations of the mass, energy and electrical charges are solved in a lumped volume at constant temperature; (ii) a detailed model where all the equations are solved in a finite difference approach inside the single cell. The first model has been used to define the hybrid system lay out and the characteristics of the main devices of the plant such as the recuperator, the compressor, the expander, etc. The second model has been used to verify the design point defined in the previous step, taking into account that the stack internal temperature behavior are now available and must be carefully considered. Apt modifications of the preliminary design point have been suggested using the detailed IP-SOFC system to obtain a feasible solution. In the second part of the paper some off-design performance of the Hybrid System carried out using detailed SOFC model are presented and discussed. In particular the influence of ambient conditions is shown, together with the possible part load operations at fixed and variable gas turbine speed. Some considerations on the compressor surge margin modification are reported.

Direct-write fabrication of integrated planar solid oxide fuel cells

Integrated planar solid oxide fuel cell (IP-SOFC) with multilayered structure has been fabricated via direct-writing process named robo-dispensing. Partially stabilized zirconia (PSZ) substrate with sufficient mechanical strength and gas permeability was utilized as a support for SOFC. The 2-cells serially integrated planar SOFC in which each cell is composed of the line-shaped electrode and electrolyte was produced The SOFC component paste materials were dispensed through cylindrical nozzle of 0.21 mm in diameter onto a moving plate that was controlled by robo-dispensing machine. The thicknesses of anode, electrolyte and cathode were 30 μm, 15 μm and 20 μm, respectively. The fabricated IP-SOFC exhibited OCV of 1.82 V and maximum power density of 35 mW.

Cycling studies of solid oxide fuel cells

The purpose of this work was to study the transient performance of solid oxide fuel cells (SOFCs) under several cycling conditions, in order to understand the degradation mechanisms. Initially, the Rolls Royce Fuel Cell IP-SOFC (Integrated Planar SOFC) single tube was investigated. The objective was to cycle up to 100 times to check if degradation was occurring and to assess its extent. In this paper the results of loading cycles at nominally constant operating temperature are reported. Work on two other kinds of cycles, i.e. thermal and redox, for this type of tube has commenced and the results will be reported in the follow-up paper.

Diffusion and Chemical Reaction in the Porous Structures of Solid Oxide Fuel Cells

The Rolls-Royce integrated-planar solid oxide fuel cell (IP-SOFC) consists of ceramic modules with electrochemical cells printed on the outer surfaces. The cathodes are supplied with oxygen from air flowing over the outside of the module and the anodes are supplied with fuel diffusing from the internal gas channels. Natural gas is reformed into hydrogen in a separate reformer module of similar design except that the fuel cells are replaced by a reforming catalyst layer. The performance of the modules is intrinsically linked to the behavior of the gas flows within their porous structures. The multi-component convective-diffusive flows are simulated using a new theory of flow in porous material, the cylindrical pore interpolation model. The effects of the catalyzed methane reforming and water-gas shift chemical reactions are also considered using appropriate kinetic models. It is found that the shift reaction, which is catalyzed by the anode material, has certain beneficial effects on the fuel cell module performance. The shift reaction enables the fuel cells to make effective use of carbon monoxide as a fuel when the supplied fuel has become depleted of hydrogen. In the reformer module the kinetics of the reaction make it difficult to sustain a high methane conversion rate. Although the analysis is based on IP-SOFC geometry, the modeling approach and general conclusions are applicable to other types of SOFCs.

Numerical investigation of the air flow through a bundle of IP-SOFC modules

The integrated-planar solid oxide fuel cell (IP-SOFC) consists of ceramic modules which have electrochemical cells printed on the outer surfaces. The cathodes are the outermost layer of each cell and are supplied with oxygen from air flowing over the outside of each module. The anodes are in direct contact with the ceramic structure and are supplied with fuel from internal gas channels. An IP-SOFC power plant will contain many modules closely packed together in an array inside a pressure vessel. The air flow is also used to cool the modules. This paper describes a three-dimensional numerical method for simulating the air flow. It uses an explicit time-marching scheme that incorporates a preconditioning method to increase the rate of numerical convergence at low flow velocities. The numerical method is used to simulate the air flow through an array of IP-SOFC modules. The scheme is straightforward to implement and can predict the recirculating flows existing between the modules within an array. The calculation procedure is used to investigate the effect of different sized gaps between modules on the local heat and mass transfer coefficients. The results show the effect of the module arrangement on the flow field and how increasing the gap between modules improves the heat and mass transfer at the module surfaces.

Modelling of Pressurised Hybrid Systems Based on Integrated Planar Solid Oxide Fuel Cell (IP‐SOFC) Technology

AbstractThis work describes different models, developed by the Thermochemical Power Group at the University of Genoa (Italy), for the simulation of solid oxide fuel cell and gas turbine hybrid systems. The paper focuses on both “cores” of the system: the fuel cell stack on the one hand and the turbomachinery and the auxiliaries on the other hand. Therefore, in the first part of the paper the models developed for the analysis of the Rolls‐Royce Integrated Planar SOFC cells are presented; the results are compared to experimental data, and carefully analysed and discussed. In the second part of the paper, design and off design models of IP‐SOFC pressurised hybrid systems in the range 250 kW–20 MW are presented; the hybrid performance results are presented and discussed, also taking ambient condition effects and a possible control strategy into account. Finally, using an in‐house general purpose transient system analysis code (TRANSEO code), where chemical composition, heat transfer, and fluid dynamic influences vs. time are considered in detail, a preliminary time dependent investigation of a pressurised hybrid system behaviour is presented.

Three-dimensional simulation of chemically reacting gas flows in the porous support structure of an integrated-planar solid oxide fuel cell

The behaviour of an integrated-planar solid oxide fuel cell (IP-SOFC) strongly depends on the reactive diffusive flows within its porous support structure. Fuel is transported through the porous structure to the anodes of the electrochemical cells and the structure may be impregnated with the required catalysts for the steam reforming of methane. It is important to be able to calculate the distribution of gas properties within the porous structure in order to predict the performance of each cell and to determine the amount of internal reforming that takes place. This paper describes a three-dimensional numerical calculation method which has been developed to solve the governing equations in the porous structure. The calculation method includes the interaction between the flow in the porous medium and that in the adjacent fuel supply channel. The results highlight the importance of the kinetics of the reforming reaction and the thermal boundary conditions, both of which have a significant effect on the flow field within the porous structure.

Electrochemical model of the integrated planar solid oxide fuel cell (IP-SOFC)

The Integrated Planar Solid Oxide Fuel Cell (IP-SOFC) is an innovative fuel cell concept which is substantially a cross between tubular and planar geometries, seeking to borrow thermal compliance properties from the former and low cost component fabrication and short current paths from the latter. In this study, a simulation model for the IP-SOFC is presented, with particular highlight on the simulation of the local reaction, taking into account the chemical and electrochemical processes occurring at the electrodes, together with mass transport issues. Some aspects of the overall reactor simulation are discussed as well. The model results have been compared to the experimental data obtained from both a small scale IP-SOFC module and a full-size prototype; in both cases the agreement is good. This electrochemical model is the basis of a detailed model of the full-scale IP-SOFC reactor to be included into a plant simulation tool designed to support thermodynamic analysis of hybrid IP-SOFC/GT (Gas Turbine) systems.

SOFC technology development at Rolls-Royce

Fuel cells have the prospect for exploiting fossil fuels more benignly and more efficiently than alternatives. The various types represent quite different technologies, with no clear winner, yet. Nevertheless, the high temperature MCFC and solid oxide fuel cell (SOFC) types seem better suited to power generation in a hydrocarbon fuel economy. Presently, the costs of MCFCs and SOFCs are too high to compete directly with contemporary power generation plant. Seeking to overcome the drawbacks of first generation fuel cells, over the past 7 years an innovative second generation SOFC concept has been evolved in the Rolls-Royce Strategic Research Centre, with encouraging results. It is distinguished from other types by the name: Integrated Planar Solid Oxide Fuel Cell (IP-SOFC). It is a family of integrated system concepts supporting product flexibility with evolutionary stretch potential from a common SOFC module. Fabrication of the key component of the IP-SOFC, the “multi-cell membrane electrode assembly (multi-cell MEA) module” carrying many series connected cells with supported electrolyte membranes only 10 to 20 μm thick, has been proved. Development of the internal reforming subsystem, the next big hurdle, is now in hand. Following an outline of its salient features and test results, the methodology and results of recent IP-SOFC stack costing studies are presented, and the continuing research and development programme indicated.