Single SOFC Research Articles

Double Conductive Ni-pads for a kW-class micro-tubular solid oxide fuel cell stack

Double Conductive Ni-pads (DCNPs) are prepared for the anode collector of micro-tubular solid oxide fuel cells (MTSOFCs) to fabricate a kW-class MTSOFC stack. The dimensions of the pad, in terms of width and length, are approximately 3.1 mm and 11.3 mm respectively. COMSOL Multiphysics software is utilized to simulate the multi-physical field of a single cell and SOFC stack to study anodic DCNPs current distribution and mass transfer operated at various voltages. A 160-cell stack consists of eight 20-cell sub-stacks exhibits a maximum power output exceeding 1 kW at an operating temperature of 700 °C. Furthermore, long-term operation tests under constant current or constant voltage conditions are conducted on both the 20-cell sub-stack and the 80-cell stack, demonstrating excellent performance and stability when utilizing DCNPs as anode collectors. The application potential for DCNPs as anode collectors in micro-tubular solid oxide fuel cells extends to various fields including auxiliary power units or high-power stacks, thereby introducing new possibilities for MTSOFC technology.

(Digital Presentation) Au-Mo-Fe-Ni/CeO2(Gd2O3) As Potential Fuel Electrodes for Internal CO2 Reforming of CH4 in Single SOFCs

In this study the catalytic and electro-catalytic performance, as well as the coking resistance of un-modified and modified Ni/CeO2(Gd2O3) with 3 wt.% Au−0.4 wt.% Mo and 3 wt.% Au−0.5 wt.% Fe electrocatalysts were studied as half and full electrolyte supported cells under internal CO2 reforming of CH4 in single SOFCs, at 750-900 oC. The aim was to elucidate their activity towards the consumption of CH4, CO2, the production of H2, H2O, CO and the production of carbon, as a function of temperature and the applied current density under a biogas fuel mixture of CH4/CO2=1. Additionally, the cells comprising the electrocatalysts as fuel electrodes, 8 mol% Y2O3 stabilized ZrO2 (8YSZ) as electrolyte and La0.6Sr0.4Co0.8Fe0.2O3- δ (LSCoF) as oxygen electrode were characterized using I-V measurements and Electrochemical Impedance Spectra (EIS) analysis in order to investigate the evolution of the ohmic and polarization resistance values as a reflection of current.

Characterizing the Performance of kW-Scale Multi-Stack Solid Oxide Fuel Cell Modules through Modeling

The development of commercial SOFC systems often utilizes models of a single representative SOFC stack to simulate the system’s prime mover. In practice, however, these representative single-stack SOFC models fail to consider effects due to the reality of multi-stack power modules needed to construct commercial-scale systems. Effects such as flow maldistribution, inter-stack heat transfer, and area-specific resistance (ASR) variation between stack units within a single module will create deviations in performance from a single stack-based system simulation. The following outlines efforts to consider these thermofluidic effects and the associated performance deviations of a novel 30kWe SOFC multi-stack module using models in the gPROMS Modelbuilder® environment. Specifically, the impacts of gas manifolding, heat loss, and stack placement are investigated, and their potential impacts are discussed.

Numerical and experimental analysis of the effects of tar components on single planar SOFC under high fuel utilization

One of the main challenges and obstacles for the application of SOFCs with wood gas is the degradation of Nickel anode caused by heavier hydrocarbons from the gasification process. The unclear conversion process on the anode and the fluctuant content of tars in wood gas will cause problems like the excess of critical fuel cell utilization and thus the oxidation of Nickel anode. This work focuses on the experimental and numerical analysis of tar conversion on the single SOFC under different conditions. A three-dimensional Computational Fluid Dynamics (CFD) model for an electrolyte-supported single cell was developed using the commercial CFD code FLUENT. The conversion kinetics of tar is validated by experimental results and implemented into the model. With this model, local distributions of Nernst voltage across the anode area are demonstrated. Areas, where an oxidation of Nickel is to be feared, are identified. Both experimental and simulative results have proved the positive effect of toluene reforming on preventing Ni from re-oxidation.

Performance study of solid oxide fuel cell with Ni-foam indirect internal reformer: Intrinsic reforming kinetics and temperature uniformity

For solid oxide fuel cells, non-uniform temperature distribution has a large effect on the cell’s efficiency over the long-term operation. A methane steam reformer with 10 %Ni/10 %MgO/Ni foam as a catalyst was designed, and the intrinsic kinetic model of the catalyst is developed based on the Langmuir-Hinshelwood theory. An indirect internal reforming (IIR)-SOFC stack is constructed by combing the reformer and the single SOFC stack to improve the uniform temperature distribution and reduce the cell temperature gradient under various operating conditions. The electrical performance and temperature distribution of the IIR-SOFC stack and direct internal reforming (DIR)-SOFC stack are comparatively studied by experiments and numerical simulations. The results show that the two SOFC stacks have almost identical polarization curves under different temperatures, fuel–air flow rates, or steam/methane (S/C). It indicates that the IIR-SOFC stack just changes the position of methane reforming, and the amount of hydrogen and carbon monoxide produced by methane reforming is almost the same. As compared to the DIR-SOFC stack, the IIR-SOFC stack observably lowers the cell temperature uniform index, and the cell global and local temperature gradient, making the cell temperature distribution more uniform. The maximum temperature difference and the maximum temperature gradient on the IIR-SOFC anode are 35.1 % and 307 % less than on the DIR-SOFC anode under the operating condition of 800 °C, S/C = 2.5 and 0.6 V. Overall, the Ni-foam-based IIR-SOFC stack can homogenize the cell temperature distribution, and reduce the cell carbon deposition and mechanical failure.

(Digital Presentation) Reactive Magnetron Sputtering Deposition of La1.6Nd0.4NiO4 Coating As Cathode for Solid Oxide Fuel Cell

Ln2NiO4 (Ln=La, Pr, Nd, etc.) materials with K2NiF4 structures are interesting materials for intermediate temperature solid oxide fuel cell (IT-SOFC) due to Mixed Ionic and Electronic Conductivity (MIEC) [1-2]. The present work is focused on the elaboration of La1.6Nd0.4NiO4 coating obtained by Reaction Magnetron Sputtering (RMS). This compound is a promising oxygen electrode able to decrease the operating temperature of SOFC. After a presentation of the deposition operating conditions for obtaining the films, the structural and microstructural characterizations of the coatings were, respectively, determined by XRD and SEM. The electrical properties were studied as a function of temperature by the 4-probe method. Electrochemical properties were investigated in a symmetrical cell electrode / YSZ / electrode by complex impedance spectroscopy. Finally, a complete cell composed of a commercial anode, and YSZ electrolyte made by RMS and the cathode of this study was tested under hydrogen and air in single SOFC cell configuration.It appeared that the films are amorphous when processed and that they crystallize after an annealing treatment under air. According to this study, a correlation between crystalline structure, morphology and electrical properties will be presented and its last ones are completed by a thermogravimetry analysis.

Performance and DRT analysis of infiltrated functional cathode based on the anode supported SOFCs with long-term stability

Designing cathode functional layer (CFL) to accelerate oxygen reduction reaction (ORR) is widely studied. However, the relationship between morphology and ORR kinetic of CFL need to be in-depth studied. Here, a highly efficient and robust La0·6Sr0·4CoO3 (LSC) CFL is prepared into Ce0.9Gd0.1O1.95 (GDC) scaffold in a commercial anode supported half-cell by infiltrating method, which exhibits remarkably enhanced ORR activity, compared with the traditional LSC CFL fabricated by mechanical mixing LSC-GDC. As a proof, the infiltrated LSC CFL based single SOFC delivers a maximum power density of 1.2 W cm−2 at 750 °C and an excellent long-term stability with a voltage attention rate of 0.058%/100 h at 0.5 A cm−2 for 550 h. The distribution of relaxation times (DRT) method is introduced to understand improved electrochemical performances. Optimized porosity, extend three phase boundary and shorted charge transfer path change the rate-determining step in the infiltrated CFL cell.

Proposing Strategies for Efficiency Improvement by Using a Residential Solid Oxide Fuel Cell Co-Generation System in a Small-Scale Apartment Building

The high levels of energy consumption commonly seen today have severe consequences. For example, energy consumption in buildings traditionally takes the form of electricity generated from fossil fuels, which causes serious air pollution. Hence, the efficient application of clean energy systems in buildings is crucial. An increasing number of small-scale apartment buildings, such as single-room apartments and dormitories, have emerged as modern culture, and societal trends have led to a greater number of people living on their own. In this study, two strategies were proposed to improve the efficiency of solid oxide fuel cell co-generation systems (SOFC–CGSs) in small-scale apartments. A small-scale apartment building in Busan, Korea, was selected as the research object to verify the effect of the proposed strategies. One strategy was sharing a single SOFC–CGS among multiple households, and the other was integrating an SOFC–CGS with a photovoltaic (PV) system. The efficiency of the SOFC–CGS is expected to improve under these two operational strategies. In addition, the two proposed operational strategies were combined to improve the efficiency of the SOFC–CGS. To verify the proposed strategies, various simulations were conducted in this study. The simulation results indicate that each of the proposed strategies can improve the efficiency of the SOFC–CGS and save energy to varying degrees.

Double-doped YFeO3 as new electrodes for protonic ceramic fuel cells

Mixed ionic-electronic conductors (MIECs) based on YFeO3 are positioned as one of the promising cathode materials for intermediate-temperature solid oxide fuel cells (so-called protonic ceramic fuel cells or PCFCs) based on proton-conducting electrolytes. Simultaneous modification of both basic cationic sublattices of YFeO3 by calcium and iron was used to tailor the functionality of the obtained Y0.9Ca0.1Fe1–хСoхO3–δ (x = 0.2, 0.3, 0.4 and 0.5) compounds. Following the successful synthesis of these oxides, such functional characteristics as structural, thermal, transport properties and electrochemical activity were extensively studied taking the composition (i.e. cobalt concentration, x) into account. The complex analysis carried out on the obtained data shows that Co-doping results in improved electrical conductivity and electrochemical polarisation resistance with no adverse effects on their thermal expansion, even at the highest cobalt content (x = 0.5). The performance of a single SOFC with the selected Y0.9Ca0.1Fe0.5Сo0.5O3–δ electrode confirms the prospects of Y0.9Ca0.1Fe1–хСoхO3–δ phases as modernized MIECs having good thermal properties and acceptable electrochemical activity.

Numerical Model of Sulfur Poisoning on LSCF Cathode and Its Application to a 2-D Single Cell Simulation

The progress of LSCF cathode degradation by sulfur poisoning is numerically investigated. A few degradation models are developed on the bases of different assumptions and available material properties and applied to 1D simulations. The results of 1D simulations are compared with the experimental data to see if the model can phenomenologically reproduce them. The model which gives a reasonable prediction is applied to 2D CFD simulations of a single planar-type anode-supported SOFC. The 2D simulation model consists of the conservation equations of mass, momentum, energy, species and charge carriers, which are coupled by the electrochemical reaction models. A volume-averaging method is applied to the porous electrodes. The simulation results show that the developed model fairly predicts the formation of SrSO4 near the cathode–electrolyte interface particularly in the upstream region of the air channel.

Individual impact of several impurities on the performance of direct internal reforming biogas solid oxide fuel cell using W-Ni-CeO2 as anode

Direct feeding of biogas to SOFC is theoretically feasible. However, several contaminants such as ammonia, siloxanes and chlorine compounds included in biogas can cause severely damage in the SOFC components. In this paper, the individual impact of 500 ppm NH3, 1 ppm D4 siloxanes and 250 ppm HCl on the performance of a single SOFC with W-Ni-Ce as anode directly fed by biogas has been investigated. Two singles cells (W-Ni-Ce/SDC/LSCF) were fabricated and tested at 750 °C. The first one was exposed to biogas with NH3 or siloxanes, and the second one to biogas with HCl. The electrochemical behaviour of cells was studied by I-V curves, impedance spectra, and under load demand in biogas with and without impurities. Post-test analyses of the anode/electrolyte interface were performed by SEM-EDS. The results showed that ammonia did not impact on the cell performance, whereas the presence of D4 siloxane caused the cell degradation by the formation of silica in the anode but the degradation rate is slower than SOFC with Ni-YSZ anode. The presence of HCl in biogas gave rise to important oscillations in the potential, and a performance loss under load demand that is probably due to adsorption-desorption processes of Cl on Ni and Ce surfaces. In addition, the presence of CO2 and H2O could improve the oxidation of Ni and CeO2-x reducing their catalytic activity; a severe corrosion in the stainless steel tubing and valves was also detected. Post-tests analysis suggested the formation of SiO2 deposits and Cl adsorbed on Ni and Ce particles.

Numerical research on carbon activity, fuel utilization, chemical reaction, and temperature distribution for IT single planar SOFC

ABSTRACTA steady-state and three-dimensional (3-D) model has been established for an intermediate temperature planar anode-supported solid oxide fuel cell. The model couples charge transfer, mass transfer, momentum transfer, and energy transfer equations. Chemical reactions (methane cracking reaction (MCR), Boudouard reaction, methane steam reforming reaction (MSR), and water gas shift reaction (WGSR)) and electrochemical oxidation of H2 and CO are considered. The variations of carbon activity, fuel utilization, and temperature distribution have been discussed with polarization and concentration separately. The thermal stress distribution in the positive electrode-electrolyte-negative electrode (P-E-N) structure is also discussed. The simulation results agree well with the literature.

Single SOFC with Supporting Ni-YSZ Anode, Bilayer YSZ/GDC Film Electrolyte, and La2NiO4 + δ Cathode

Characteristics of fuel cells with supporting Ni-YSZ anode, bilayer YSZ/GDC electrolyte with the thickness of 10 μm, and La2NiO4 + δ cathode are studied. It is shown that when humid (3% water) hydrogen is supplied to the anode and air is supplied to the cathode, the maximum values of cell’s power density are 1.05 and 0.75 W/cm2 at 900 and 800°С, respectively. After the introduction of praseodymium oxide and ceria into the cathode and the anode, respectively, the power density is ca. 1 W/cm2 at 700°С. It is found that the power density of a cell with impregnated electrodes weakly increases with the increase in temperature to ca. 1.4 W/cm2 at 900°С. The analysis of impedance spectra by the distribution of relaxation times shows that such behavior is associated with the gas-diffusion resistance of the SOFC anode. The latter is explained by the low porosity of the anode and the high rate of fuel consumption.

Thermo-environmental and economic comparison of three different arrangements of solid oxide fuel cell-gas turbine (SOFC-GT) hybrid systems

A comparative analysis is performed for three different layouts of SOFC-GT hybrid systems with internal reformer from the viewpoints of energy, exergy, environmental and economic. The three considered designs are distinguished by number of SOFC stack, as single SOFC stack is employed in one system, while two SOFC stacks (cell numbers halved) are used for the other designs. For the second system, two stacks are fed by fuel and air in parallel way; however, in the third case, two stacks are fed by fuel in parallel and air serially. A mathematical model is developed in EES software to simulate the performance of the cycles through a parametric study. In addition, exergy destruction rate of components of the plants are achieved to recognize the main sources of ireversibilities. The analyses demonstrated that two-stack SOFC-GT series type is more efficient, leading energy and exergy efficiencies to reach 63.22% and 60.81% correspondingly, which are about 20.3% and 8.89% higher than conventional SOFC-GT and parallel type, respectively. The highest source of exergy destruction amongst all system components belongs to after burner. Furthermore, it is observed that the highest total cost, 24.95 $/h, is attributed to conventional SOFC-GT hybrid system while the least amount corresponds to SOFC-GT series type, 18.5 $/h. The CO2 gas emission obtained for two-stack SOFC-GT hybrid system series type, 313.3 kg/MWh, obtained to be the lowest.

Development of a Segmented Single SOFC Test Equipment to Simulate Stack-Like Operating Conditions

A common problem when it comes to stack CFD modelling is the lack of detailed local information about temperatures and gas compositions. For the calibration and validation of the CFD models local measurements of these parameters are required. However, it is fairly difficult implementing such measurements in commercial stacks without changing the stack design to allow for additional thermocouples or gas extraction channels. Furthermore, such implementations would automatically change the stack behavior compared to a stack without additional instrumentation due to heat and gas losses caused by the measurement itself. On the other hand standardized single cell tests do not represent stack like conditions due to typically very homogenous temperature distributions. Therefore, a new single cell test equipment based on a segmented single SOFC which enables an operation of the cell under stack like conditions was developed. The aim of this development is to provide a single cell test equipment which provides comprehensive data about temperature distribution, cell voltage distribution and local gas compositions to be used for the calibration of a commercial CFD code [1]. The complete test equipment was simulated by means of CFD and the results were compared with experimental data. The single cell consists of a commercial anode supported SOFC with 4 segmented cathodes (40.5x44 mm2 each) and 1 anode (120x120 mm2). The segmented cathode allows the measurement of local cell voltages. Furthermore, several gas extraction channels along the anode flow channels were implemented to measure the gas conversion with respect to the electrochemical and steam reforming reactions taking place. As the steam reforming reaction has a significant impact on the temperature profile, in real stacks it is important to consider the conversion rate properly along the anode to allow for a correct simulation of the temperature distribution. The temperature profile was measured with 34 thermocouples which were distributed along the anode flow field below the anode surface. Several test cases to calibrate the CFD model regarding the thermal behavior were carried out by placing the test equipment in an electric oven and heating it up to 600 °C. The cell test equipment was additionally equipped with 4 electrical heaters placed below the anode channels to produce temperature profiles similar to real stack operating conditions. Therefore, also inhomogeneous temperature profiles can be produced. The 4 electrical heaters can be controlled individually to heat each of the 4 segments differently. The electrical heaters provide enough heat to increase the temperature of the cell up to 800 °C. Therefore, temperature profiles along the cell with gradients of 150 K between the hottest and coldest spot along the active cell area were achieved. By changing the set oven temperature this gradient can be further modified. Existing stack temperature profiles were used to calibrate the test equipment which enables similar temperature distributions as they occur for a stack under real operation. The CFD simulation meets the measured temperature profile within 10 K which is seen to be a very accurate result. Furthermore, this work will show the comparison of experimental and CFD simulation results for the operation of the cell at 700, 750 and 800 °C in H2 and CH4/H2O operation. The comparison covers local cell voltages, the temperature distribution and the gas compositions. For both gas feed mixtures a fitting of the CV curve within the CFD software was carried out. It can be seen that the electrochemical behavior can be simulated fairly accurately by the software. The software allows also for the consideration of steam reforming and shift reactions along the complete anode flow path. By adjusting the activation energy as well as the rate-constant for both reactions, the same behavior as it was measured in the experiment could be achieved. As expected it can be seen that the conversion of methane by steam reforming is higher at the inlet of the single cell. This effect correlates very well with the observed temperature decrease in this region caused by endothermic steam reforming which is in the range of 10 K. It has been proven that this kind of test equipment is a very powerful tool to calibrate the CFD simulation models as basis for further full scale stack simulations. A further potential utilization of this approach is the possibility to transfer the validated temperature profiles into a FE simulation to enable an experimentally supported investigation of thermo-mechanical stresses within the cell or sealing. [1] FIRETM v2017, User Manual, AVL List GmbH, 2017.

Effect of Oxygen Depletion to the Cathode on the Working of Solid Oxide Fuel Cells

During the recent years, SOFC research has mainly been aimed at reducing the capital cost to effectively compete with other power generation technologies. CMR Prototech, Norway is a provider of technical solutions, product designs and tools for various application areas. Currently, CMR Prototech is planning to develop 2 MW modular fuel cell systems for subsea operation. Each module consists of 200 stacks, each stack producing 10kW. In order to address the technical challenges faced during this development and to make SOFC technology feasible for offshore applications more research on fuel cells in marine environment is necessary. This research was aimed at determining the effects of a) reducing partial pressure of oxygen and b) NaCl contamination on the performance of the SOFC cathode of a single SOFC cell. This present paper focuses on the effect of oxygen partial pressure. Single cell tests were performed in a versatile test station, fully automated and controlled using LabVIEW programming. The fluid handling system with mass flow controllers and four-points measurement probes along with field-point connections were installed in the test station. A set of experiments were conducted, reducing the partial pressure of oxygen supplied to the cathode stopwise (at thre relevant temperatures, namely 800, 850 and 900oC). All the cells were characterized and analyzed by I-V curves. The grain structures of the cells were characterized by scanning electron microscopy (SEM) before and after the experiments.

CFD modelling of hydrogen starvation conditions in a planar Solid Oxide Fuel Cell

Abstract The aim of this study was to highlight the interest of using CFD technique as a diagnostic tool of a malfunctioning Solid Oxide Fuel Cells. Hydrogen starvation of a SOFC due to nitrogen dilution is one of the cell dysfunctions and can lead to its degradation. Identification of the starvation point allows to improve cell performance and establish the best conditions for degradation tests. To illustrate a potential of the CFD tool, several simulations of a single planar SOFC and its behaviour under hydrogen starvation were performed and analysed. The results showed that at lower cell voltage values of 0.3 and 0.5 V significant gradients in the electric current were noticed due to a local reduction in hydrogen concentration. The CFD analysis allowed defining desirable mass flow rate of hydrogen to SOFCs to avoid fuel starvation. The model constitutes a helpful tool for optimizing cell design and operational conditions.

Development of a Segmented Single SOFC Test Equipment to Simulate Stack-Like Operating Conditions

This work presents a new single cell test equipment based on a segmented single SOFC to perform cell tests under stack like conditions. The setup provides comprehensive data about temperature distribution, cell voltage distribution and local gas compositions to be used for the calibration of a commercial CFD code (1). Results from experiments will be compared with CFD simulations for operating temperatures at 700, 750 and 800 °C using H2/N2 or CH4/H2O as fuel, respectively. The CFD simulation meets the measured temperature profiles within 10 K. The simulation also includes steam reforming and shift reactions along the complete anode flow path. For both gas feeds, a fitting of the CV curve within the CFD model was carried out. It has been proven that this kind of test equipment is a very powerful tool to calibrate the CFD simulation models as a basis for further full scale stack simulations.

Nanoparticles Infiltration into SOFC Cathode Backbones

Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs) with yttrium stabilized zirconia (YSZ) electrolyte were fabricated by the impregnation of Sm0.2Ce0.8O2-δ (SDC), Sm0.5Sr0.5CoO3-δ (SSC), CeO2, Nd1.95NiO4+δ (NdN), Pr1.97NiO4+δ (PrN), and La0.8Sr0.2MnO3 (LSM) into specific backbone cathodes: electronic conductor LSM, ionic conductor SDC and mixed ionic and electronic conductor NdN. The electrochemical performances of the symmetrical half-cells and single cells were improved using impregnated cathodes. The loading amount of the promoters have been optimized to decrease the Area Specific Resistance of the electrode (ASRelec) and improve performance of IT-SOFCs with NdN composite cathode. The electrochemical measurements showed that a MIEC backbone is more efficient than a pure electronic or a pure ionic one. The highest ASRelec was given by LSM-impregnated sample (ASRelec = 1.15 Ω.cm2) at 700 °C. At the same temperature, the lowest ASRelec was measured on a PrN impregnated into a NdN backbone (ASRelec = 0.26 Ω.cm2). Complete single SOFC with and without infiltrated air electrodes have been then manufactured and the infiltration improved clearly the efficiency of the cell, more than 6% in the temperature range 650-750°C without specific optimization.

Study of Operating Parameters for Accelerated Anode Degradation in SOFCs

AbstractSolid oxide fuel cell (SOFC) applications require lifetimes of several years on the system level. A big challenge is to demonstrate such exceptionally long lifetimes in ongoing R&D projects. Accelerated or compressed testing are alternative methods to obtain this. Activities in this area have been carried out without arriving at a generally accepted methodology. This is mainly due to the complexity of degradation mechanisms on the single SOFC components as function of operating parameters. In this study, we present a detailed analysis of approx. 180 durability tests regarding degradation of single SOFC components as function of operating conditions. Electrochemical impedance data were collected on the fresh and long‐term tested SOFCs and used to de‐convolute the individual losses of single SOFC cell components – electrolyte, cathode and anode. The main findings include a time‐dependent effect on degradation rates and the domination of anode degradation for the evaluated cell types and operating conditions. Specifically, the steam content as determined by fuel inlet composition, current density and fuel utilization was identified as major parameter, more important than for example operating temperature. The obtained knowledge is adopted to identify optimal operation profiles in order to acquire accelerated testing for lifetime investigation of SOFCs.