Commercial Solid Oxide Fuel Cell Research Articles

An experimentally derived calibration model for hydrogen-fueled solid oxide fuel cells at intermediate temperature

The characteristic polarization curve (e.g. I–V curve) of a solid oxide fuel cell (SOFC) is a valuable outcome of experimental tests because it conveys crucial information about the SOFC's current-potential operational range and optimum performance point. Numerical analysis of the experimentally achieved I–V curve can yield information that is not readily available from it, such as parameters of operation, kinetics of electrochemical reactions, and mechanisms of mass and current transfer. Such details can be used to choose optimal operating conditions and improve the cell manufacturing process. Using experimental polarization curves of a commercial SOFC fed with hydrogen and air, this paper develops a calibration algorithm and extends the analysis to evaluate further operational parameters of the cell. The calibrated model was developed for a commercial SOFC operating at 700 °C and 800 °C. As target parameters, the calibrated model defined the anode and cathode exchange current densities as well as the effective diffusion coefficients of gas species within both electrodes and their respective pore radii. A comprehensive SOFC analysis model requires a detailed understanding of the morphology of the porous material inside the cell, and these parameters provided that insight. Using experimental and analytically optimized polarization curves, target parameters are defined with an accuracy of more than 98%. Based on the developed model, it was also possible to predict the maximum current density the cell could reach at temperatures of 800 °C and 700 °C, which was about 2 Acm−2 and 1.7 Acm−2, respectively. Compared with SOFC parameters reported in literature, the obtained values were fully consistent. In spite of this, the algorithm outcomes are considered “equivalent” parameters since they are solutions to a multivariable problem, and only their combination with other known parameters can result in fitting a benchmark curve. Additionally, their uniqueness criterion is not yet investigated as a means of describing actual cell parameters.

Crossflow flat solid oxide fuel cell (SOFC) semi-empirical modeling and the multi-fuel property based on a commercial 700 W stack

Solid Oxide Fuel Cell (SOFC) technology has attracted vast attention for combined heat and power (CHP) application on low or zero carbon emissions because of its high efficiency and multi-fuel selectivity. Due to the high operation temperature, a commercial SOFC system requires a complex system thermal balance and stack self-heating ability which are dramatically influenced by the inlet temperature, reaction heat and thermal radiation of the stack. Multi-fuel selectivity is a further distinct advantage when considering the future variety of renewable fuel sources, such as ammonia (from animal farming), bio-methane (from agriculture), and the other hydrocarbons using carbon capture as an effective H2 carrier. However, the alternating between different fuel types may result in reduced power and the internal heat balance to change, which may further lead to the stack cooling down or over heated. An appropriate model with fast calculation processing capability is necessary to assess the internal changes before switching the fuel source and to inform further decision making to enable the control system to adapt to the change. In this paper, a cross-channel, flat SOFC semi-empirical model is proposed and validated by a commercial 700 W stack using real testing data to assess the accuracy of the simulation results. The SOFC model has multi-fuel ability which presents different properties and internal understanding for H2, NH3, and reformed CH4 through relevant charts (for feed, velocity, temperature, reaction rate, current, power, heat, efficiency). The power outputs for the different fuel sources, H2, NH3, and reformed CH4, are 721.0 W, 628.9 W and 679.7 W respectively when calculated at an air inlet temperature of 893 K. The modeling work was completed using Aspen Plus for SOFC system thermal balance simulations which determined the power output property for 813.3 W (H2), 744.5 W (direct NH3) and 740.7 W (reformed CH4) at the 2.0 times stoichiometric ratio of air feed, and CHP rate of 0.903 (H2), 0.787 (direct NH3) and 0.311 (reformed CH4). This work has the potential to contribute to the United Nation Sustainable Development Goal for Affordable and Clean Energy, Goal 7.

Performance Assessment of the Heat Recovery System of a 12 MW SOFC-Based Generator on Board a Cruise Ship through a 0D Model

The present work considers a 12 MW Solid Oxide Fuel Cell (SOFC) power plant integrated with a heat recovery system installed on board an LNG-fuelled cruise ship of about 175,000 gross tonnes and 345 m in length. The SOFC plant is fed by LNG and generates electrical power within an integrated power system configuration; additionally, it provides part of the thermal energy demand. A zero-dimensional (0D) Aspen Plus model has been built-up to simulate the SOFC power plant and to assess the performances of the proposed heat recovery system. The model has been validated by comparing the results obtained with data from the literature and commercial SOFC modules. The integrated system has been optimized in order to maximize steam production since it is the most requested thermal source on board. The main design outcome is that the steam produced is made by the recovered water from the SOFC exhaust by about 50–60%, thus reducing the onboard water storage or production. Additionally, results indicate that such an integrated system could save up to about 14.4% of LNG.

Proposal and assessment of a solid oxide fuel cell cogeneration system in order to produce high-temperature steam aiming at industrial applications

The feature of operating at high temperature enables solid oxide fuel cell (SOFC) generating power at impressive efficiency while providing useful heat. Commercial SOFC cogeneration products for domestic hot water supply are already available, however, the potential of supplying high-temperature heat (especially in the form of steam) for industrial applications has not been well exploited yet. Here, a new SOFC cogeneration system layout is proposed and studied to address the problem. The core idea is to utilize the residual heat in parallel by the method of splitting the high-temperature streams, rather than in cascade as in traditional layouts. Therefore, the application of SOFC cogeneration can be expanded from providing low-temperature heat to high-temperature heat, from homes to industries. The simulation result shows that the layout with anode gas recycle (AGR) has the best performance in both net and cogeneration efficiency. The best predicted net efficiency is 56.9% and cogeneration efficiency 86.8% for the AGR layout. For the AGR layout with a net capacity of 10MW, the steam production ability of medium, low and super low pressures are 5903kg/h, 6436kg/h and 6748kg/h, respectively. The investigated gas split locations only have negligible effect on the steam production ability.

Investigation of La0.6Sr0.4Co1-xNixO3-δ (x=0, 0.2, 0.4, 0.6, 0.8) catalysts on solid oxide fuel cells anode for biogas dry reforming

The introduction of catalyst on anode of solid oxide fuel cell (SOFC) has been an effective way to alleviate the carbon deposition when utilizing biogas as the fuel. A series of La0.6Sr0.4Co1-xNixO3-δ (x = 0, 0.2, 0.4, 0.6, 0.8) oxides are synthesized by sol-gel method and used as catalysts precursors for biogas dry reforming. The phase structure of La0.6Sr0.4Co1-xNixO3-δ oxides before and after reduction are characterized by X-ray diffraction (XRD). The texture properties, carbon deposition, CH4 and CO2 conversion rate of La0.6Sr0.4Co1-xNixO3-δ catalysts are evaluated and compared. The peak power density of 739 mW cm−2 is obtained by a commercial SOFC with La0.6Sr0.4Co0.4Ni0.6O3-δ catalyst at 850 °C when using a mixture of CH4: CO2 = 2:1 as fuel. This shows a great improvement from the cell without catalyst for internal dry reforming, which is attributed to the formation of NiCo alloy active species after reduction in H2 atmosphere. The results indicate the benefits of inhibiting the carbon deposition on Ni-based anode through introducing the La0.6Sr0.4Co0.4Ni0.6O3-δ catalyst precursor. Additionally, the dry reforming technology will also help to convert part of the exhaust heat into chemical energy and improve the efficiency of SOFC system with biogas fuel.

Unconventional Highly Active and Stable Oxygen Reduction Catalysts Informed by Computational Design Strategies

AbstractDiscovering and engineering new materials with fast oxygen surface exchange kinetics and robust long‐term stability is essential for the large‐scale, economically viable commercialization of solid oxide fuel cell (SOFC) technology. The perovskite catalyst material BaFe0.125Co0.125Zr0.75O3 (BFCZ75), predicted to be promising from recent density functional theory (DFT) calculations and unconventional due to its extremely high Zr content and low electronic conductivity, exhibits oxygen reduction reaction surface exchange rates on par with Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF) and excellent stability at typical operating temperatures. New composite electrodes are engineered by integrating BFCZ75 with commercial electrode materials La1–xSrxMnO3 (LSM) and La1–xSrxCoyFe1–yO3 (LSCF) and achieve high performance as measured by low area specific resistance (ASR) values, with the LSCF/BFCZ75 ASR values comparable to top performing noncomposite electrode materials such as SrCo0.8Sc0.2O3–δ, BaNb0.05Fe0.95O3–δ and BaCo0.7Fe0.22Y0.08O3–δ. The use of BFCZ75 as a composite with LSCF achieving low ASR values shows that BFCZ75 is highly active and can easily integrate into existing SOFC material supply chains, lowering the barrier for potential commercial application of new electrode materials. Finally, these findings point to a broader unexplored class of perovskite materials with high fractions of redox inactive species (e.g., Zr, Nb, and Ta) that may unlock new pathways to realizing improved commercial SOFCs.

Insights on a Ruddlesden-Popper phase as an active layer for a solid oxide fuel cell fed with dry biogas

Solid oxide fuel cell (SOFC) is a mature opportunity for producing power energy in remote areas like islands, where access to the electrical grid is not favoured, and gas distribution is the only viable approach. In this context, generally, biogas represents the most convenient fuel resources in these areas. However, the direct use of biogas in SOFCs is still an issue to be solved due to its negative effect on the conventional Ni-YSZ anode. In this study, to overcome this issue, we suggested using a protective layer coated on the anode of a commercial SOFC. A nickel manganite showing mixed ionic and electronic conductivity tailored specifically for this approach was investigated. The preliminary characterisations showed that the formation of a Ruddlesden-Popper (RP) n = 1 structure supporting fine encapsulated particles based on Ni was formed around 800 °C in consequence of the reducing environment. The electrochemical experiments carried out for 270 h demonstrated for the coated cell significant stability in the presence of dry biogas, albeit an ageing effect was noticed in the electrical percolation of both cell electrodes. The post mortem analyses revealed an attractive redox property for the nickel manganite, which partially returned to the RP n = 2 phase. Moreover, the absence of carbon deposits on the anode suggests possible applications for this approach.

Degradation Analysis of a Commercial SOFC System

Solid Oxide Fuel Cell (SOFC) technology offers several advantages such as fuel flexibility, high efficiency, and zero criteria pollutant emissions. SOFC systems have the potential to be cheaper and provide more reliable and cleaner electrical load-following characteristics compared with other technologies by dynamic operation and control. Cost and durability are major challenges associated with current SOFC technology. Durability of Solid Oxide Fuel Cell (SOFC) technology is a key aspect for its commercialization and long-lasting deployment in different applications. Dynamic operating conditions have considerable effects on the long-term performance and durability of SOFC systems.In this study, we evaluate the performance and degradation of a 1.5 kW (AC) commercial system under steady state and dynamic load cycling conditions for over 6000 hours. We monitored and evaluated the initial and degraded performance characteristics of the SOFC stack, while testing under constant 1.6 kW load, 85% fuel utilization, and at 760°C stack temperature for 4000 hours and under dynamic cycling load for more than 2000 hours. We conducted degradation tests based upon two load cycling profiles: i) accelerated daily cycles with load changing from 0.5 kW to 1.6 kW, with stack temperatures ranging between 720°C and 760°C, and fuel utilization between 55% and 85% for 42 cycles (~1000 hours), and ii) weekly cycling test with load changing from 0.5 kW to 1.6 kW with lower slope for 10 cycles (1600 hours). A machine learning model based upon experimental data is developed to correlate the degradation rate of the system to different features of dynamic profiles to be used in the prediction of degradation rate for a wide range of dynamic load profiles.Test results show that the degradation rate is 0.025% (2mV) per 1000 hours of operation under steady state operating conditions. As the system degrades under steady state conditions, fuel consumption increases 0.3% while the efficiency drops 0.3% per 1000 hours of operation. We observe that at beginning of life and during the first 1000 hours of operation, the degradation rate is roughly twice as high as that achieved under steady state operation (i.e., 4.8mV). Results show that the system also degrades twice as fast when forced to meet daily dynamic cycling loads. The degradation rate observed under highly dynamic daily load cycling conditions is 0.58% (4.7mV) per 1000 hours of operation over 42 daily cycles.

Numerical analysis of afterburner chamber design for solid oxide fuel cell system

This article applies computational fluid dynamics (CFD) to investigate the thermal and flow fields in the afterburner of solid oxide fuel cell (SOFC) systems. The objective is to estimate the performance of the burner to serve as a reference for performance improvement through structure design. The elliptical baffled burner, which enhances the effect of convective heat transfer and temperature uniformity effectively and suppresses the NOx formation as well, is proposed in this work. Additionally, low residual fuel exhaust and pressure drop are achieved. These advantages make it highly capable of being adopted in the industrial and commercial SOFC systems. The fuel of lower caloric value causes decreases in temperature and generation of NOx in the burner as the stack fuel utilization increases. For a 25 kW SOFC system, the stack fuel utilization of 80% reduces exhaust temperature by 65 K and NO emission by 38% than that of 70%.

Digital twin model and dynamic operation for a plant-scale solid oxide fuel cell system

Large-scale solid oxide fuel cell (SOFC) systems create operational challenges owing to their size and scale. An SOFC dynamic digital twin model can help users understand the system status and determine the operating action. In this study, a dynamic digital twin of a 25 kW SOFC plant was presented as a simulator to help operators safely and stably determine the operating conditions for a real commercial SOFC plant. In the scale-up process, the data from the 1 kW SOFC pilot plant were used to analyze the reliability and electrode parameters and develop a digital twin model that matches actual conditions at the plant. The scale-up digital twin model is applied to a 25 kW SOFC system, in which the SOFC is connected with upstream reformers, downstream burners, and multiple heat exchangers. The 25 kW SOFC digital twin model was validated by steady-state data and applied to on-site operation prediction with very high accuracy. The digital twin was used as an operating reference in the field, and the results showed that it could effectively help operators determine operation strategies using simulations to safely and stably execute the process.

Efficient and controlled nano-catalyst solid-oxide fuel cell electrode infiltration with poly-norepinephrine surface modification

There is a growing attention to enhance the performance of solid oxide fuel cell (SOFC) electrodes through the incorporation of nano-catalyst materials within the electrodes’ active sites. In this study, we report a technique for increased efficiency and microstructural control of the nano-catalyst infiltration process through polymerized norepinephrine (pNE) treatment. Nano-CeO2 catalysts were incorporated within both electrodes of commercial anode-supported SOFCs using a single salt solution step after a coating of pNE within the porous microstructure. The optimization of catalyst loading was performed by varying the cerium nitrate solution concentrations between 0.4 and 2.0 M. The ceria nanoparticles are distributed at the near-electrolyte region in both electrodes, but with microstructural variance due to the precursor molarity and solid loading. The time-dependent polarization resistance (Rp) variation was categorized into three zones by the nano-catalyst loading. Zone I referred to the baseline performance for the low-catalyst loading and fluctuating Rp. However, the cells in Zone II and III showed a continuous time-dependent activation as low as 0.275 Ω cm2 at 750 °C. The results suggest that the nano-CeO2 film reduces coarsening and related degradation of the backbone. In addition, the pNE-assisted dip infiltration enhanced infiltrant deposition efficiency by reducing the number of infiltration steps.

High Performance Commercial SOFC Cathodes Achieved with YSZ Nanoparticles

The electrochemical performance of solid oxide fuel cell (SOFC) cathodes was improved via integration of ultra-high surface area ceramic nanoparticles, up to 115 m2·g-1, generated with a novel processing method herein introduced. The processing method generates the high surface area nanoparticles at traditional SOFC sintering temperatures in two steps. In the first step, a hybrid inorganic-organic material comprising the ceramic precursors is sintered in an inert atmosphere at any temperature between 850°C-1350°C. During this step, an amorphous carbon template is generated in situ, preventing coarsening of the ceramic nanoparticles. The carbon template is then removed during the second step by a mild calcination in air at 700°C. Yttria-stabilized zirconia (YSZ), lanthanum strontium cobalt ferrite (LSCF), gadolinium-doped ceria (GDC), and strontium titanate (STO) have all been successfully prepared by this method. YSZ nanoparticles (nYSZ) were incorporated into a lanthanum strontium manganite-YSZ (LSM-YSZ) cathode of a commercial cell, resulting in a 90% increase in maximum power density. Impedance spectroscopy indicates the large improvement in power density was attributed to a combination of significant improvement in polarization resistance, a 45% decrease, and ohmic resistance, a 35% decrease. Remarkably, the performance of the cell modified with nYSZ was higher than cells modified with two mixed ionic electronic conductors (MIEC): PrxBa1-xCo3-δ (PBC) and LaxSr1-xCoyFe1-yO3-δ (LSCF). Both MIECs enhanced the density of active sites, but, unlike nYSZ, did not significantly improve ohmic resistance. The results demonstrate a novel pathway to achieve high performance in commercial SOFCs.

Effect of Gas Leakage on the Performance of Planar Solid Oxide Fuel Cells

Solid oxide fuel cell (SOFC) is a promising power source with its strong advantage being the use of solid oxide electrolyte. This allows long time operation of the cell without electrolyte depletion. Due to the solid nature of SOFCs, sealing of the cell to the peripheral attachments becomes an issue, especially in planar SOFC type. This defect in gas sealing causes gas-leakage to the outside, as well as, gas-crossover through the peripheral areas of the cell. These leakages lead to a reduction in the open-circuit voltage (OCV) and the overall cell performance. Most previous reports made on gas crossover were only based on H2 crossover through the thin electrolyte membrane. In this work, the performance of a gas-leaked cell was compared with one with a gas-tight sealing. Both cells were 100 cm2 planar SOFCs operated at 750 and supplied with H2 and air gases at the anode and cathode respectively. The cells were supplied by a commercial SOFC producer in South Korea. Electrochemical Impedance Spectroscopy (EIS) and steady-state polarization (SSP) techniques were used in comparing the performance of the cells. An inert gas step addition (ISA) method [1] was also employed in determining quantitatively the partial pressure of water formed at the anode and its resulting internal short current. The ISA was first used to investigate the flow and partial pressure effect on the performance of a molten carbonate fuel cell (MCFC). The method adds nitrogen gas to the anode gas flow and the addition simultaneously increases the reactant gas flow until the added nitrogen arrives at the cell. The nitrogen addition port is placed ca. 5 m ahead of the anode electrode and is supplied through a 1/4-inch stainless tube, thus several seconds are required by the N2 gas to reach the cell. The SSP behavior showed that the OCV and the polarization voltages recorded were higher in the gas-tight cell than in the gas-leaked cell. The impedance spectra, on the other hand, showed a remarkable decrease in the gas-leaked cell and was attributed to the decrease in the water-induced mass transfer resistance of the cell. Through the ISA method, the partial pressure of water formed at the anode as a result of the gas leak was quantitatively determined and was observed to be significantly higher in the case of the gas-leaked cell. Similarly, the computed internal short current was greater in the case of the gas-leaked cell.[1] C.-G. Lee, B.-S. Kang, H.-K. Seo, H.-C. Lim, J. Electroanal. Chem., 540, 169–188 (2003).

Impacts of Hydrogen-Natural Gas Mixtures on a Commercial Solid Oxide Fuel Cell System

In this study, the emissions and performance of a commercial Solid Oxide Fuel Cell system with micro-combined heat and power (SOFC mCHP) capabilities are analyzed at various power output levels and with various hydrogen (H2) – natural gas (NG) fuel mixture concentrations. The SOFC mCHP system, although designed to be fueled by pure NG, is intentionally fueled with mixtures between 0 and 30% vol of H2 mixed with NG (balance) and is operated between 0.5 and 1.5 kW. Since these units are used in residential and commercial applications, it is important to ensure that if H2 becomes widely injected into the NG system that the corresponding H2-NG mixtures would not negatively impact the emissions or performance of the system. The performance of the system is characterized by measurement of major exhaust species concentrations (carbon dioxide, carbon monoxide, methane, water, nitric oxide, nitrogen dioxide, etc.). These measurements confirm that NOx emissions are extremely low and that adding hydrogen to the NG system does not increase NOx emissions. In addition, the system’s efficiency at part load experienced a small reduction with increasing H2 concentrations in the mixture, compared to pure NG operation.

Enhancing Activity, Charge Transport, Power Production, and Stability of Commercial Solid Oxide Fuel Cells with Yttria-Stabilized Zirconia Nanoparticles

Interconnected networks of 10–30 nm yttria-stabilized zirconia (YSZ) nanoparticles dramatically enhance both the electrocatalytic activity and bulk charge transport of commercial lanthanum strontium manganite (LSM)-YSZ solid oxide fuel cell (SOFC) cathodes. The improvement in both electrode functions increases the maximum power density of the commercial SOFC by 90%. In comparison, modifying cathodes with lanthanum strontium cobalt ferrite (LSCF) and praseodymium barium cobaltite (PBC) nanoparticles, highly active catalysts with mixed ionic-electronic conductivity (MIEC), only enhances electrocatalytic activity. The combination of dual enhanced electrode functions with nanoYSZ results in a maximum power density that is 50% and 11% higher than LSCF and PBC, respectively. Finally, the performance stability over time is highest for nanoYSZ modified cells.

(Invited) Sputtered Thin Films for Very High Power, Efficient, and Low-Cost Commercial SOFCs

Sputtering of thin electrolyte layers has been demonstrated to increase solid oxide fuel cell (SOFC) performance in very small-scale, e.g., button cells. The few cases where thin film techniques were brought in to early stages of commercialization (e.g., Lilliputian and SiEnergy) showed remarkable low temperature SOFC performance, but required sophisticated cell designs processed with Si and MEMs type technologies. This work takes advantage of low cost, conventional ceramic processing to build large format (10 cm x 10 cm) half-cells upon which the sputtered layers above are added to dramatically increase SOFC performance. In this work, an electron-blocking layer which increases the open circuit cell voltage of the GDC electrolyte based cell and a Gd doped ceria (GDC) buffer layer which mitigates reactions between the cathode and electron blocking layer are deposited by sputtering. This presentation will present progress towards developing increased SOFC performance using this sputtering technology at the commercial-scale. Challenges encountered or expected with thin film development for SOFC commercialization will be discussed.

A comparative performance analysis of a solid oxide fuel cell and gas turbine combined cycles with carbon capture technologies

This study presents a performance prediction of triple combined cycles that use a solid oxide fuel cell (SOFC) and a gas turbine combined cycle (GTCC) with carbon capture technologies. Post- and oxy-combustion capture technologies were comparatively analyzed. The component design parameters of a commercial F-class gas turbine and SOFC were used. Minimizing the turbine inlet temperature (i.e., no extra fuel supplied to the combustor) resulted in higher net cycle efficiency. With post-combustion capture, the net cycle efficiency reached approximately 70 % when no fuel was supplied to the combustor, but the maximum CO2 capture rate was limited to 80 %. When a dual combined cycle was adopted, the CO2 capture rate increased to 91 %, while the net efficiency was approximately 69 %. With oxy-combustion capture, the optimum pressure ratio was higher than in the normal triple combined cycle, and the net cycle efficiency was lower than that of the post-combustion cycle. However, there was a critical advantage of a larger power output with nearly complete carbon capture. The impact of the location of the oxygen supply was examined in the oxy-combustion cycle with extra fuel supplied to the combustor, and supplying all the fuel to the SOFC improved the cycle performance.

Fast RTO Applied to a Commercial SOFC System

The experimental implementation of real-time optimization (RTO) to a commercial solid-oxide fuel-cell (SOFC) system is reported in this paper. The goal of RTO is to maximize the system efficiency at steady state subject to several operating constraints. The proposed RTO strategy is a constraint-adaptation approach, which consists in adding bias correction terms to the constraints in the optimization problem. These bias terms are estimated during operation using transient measurements in combination with a dynamic model. The scheme enforces plant optimality by continuously detecting and tracking the set of active constraints. This approach drives the fuel-cell system quickly to the desired power demand, while maximizing the efficiency and paying attention to constraint satisfaction. As such, this RTO scheme has the ability to both control and optimize fuel-cell systems. This experimental system reached about 65% efficiency. In addition, it was possible to deal with slow drifts such as degradation without compromising on optimality.

Correlation between structural and electrochemical properties of potassium doped strontium silicates for electrolyte application in intermediate temperature solid oxide fuel cells

Electrolyte is the heart of the solid oxide fuel cell (SOFC), which can determine the working temperature. Currently, Yttria stabilized zirconia is used as electrolyte in commercial SOFCs, due to its high conductivity. The high working temperature (1073 K–1273 K) causes severe problems during SOFC design and operation. To reduce the working temperature of SOFCs to intermediate temperature (873 K–1073 K), here Sr1−XKXSiO3−δ (X = 0.00–0.20) solid solutions are synthesized by solid state reactions, characterized by different techniques. XRD patterns of Sr1−XKXSiO3−δ solid solutions can be indexed to monoclinic c2/c space group (15) structure. 29Si solid state NMR spectra of SrSiO3 and Sr0.95K0.05O3−δ shows a sharp single peak at −83.5 ppm. In 10–20 mol% K-doped samples, the additional broad peak at −89.0 ppm, is due to the presence of amorphous K2Si2O5 phase. FE-SEM and WDS mapping of SrSiO3−δ and Sr0.80K0.20SiO3−δ shows the segregation of amorphous K2Si2O5 along the grain boundaries. High temperature impedance study of Sr0.80K0.20SiO3−δ exhibits the conductivity, which is comparable to other solid electrolytes in the literature, which makes it as promising solid electrolyte for intermediate temperature SOFCs.

Analysis of Long-Term and Thermal Cycling Tests for a Commercial Solid Oxide Fuel Cell

The effects of isothermally long-term and thermal cycling tests on the performance of an ASC type commercial solid oxide fuel cell (SOFC) have been investigated. For the long-term test, the cells were tested over 5000 h in two stages, the first 3000 h and the followed 2000 h, under the different flow rates of hydrogen and air. Regarding the thermal cycling test, 60 cycles in total were also divided into two sections, the temperature ranges of 700 °C to 250 °C and 700 °C to 50 °C were applied for the every single cycle of first 30 cycles and the later 30 cycles, respectively. The results of long-term test show that the average degradation rates for the cell in the first 3000 h and the followed 2000 h under different flow rates of fuel and air are 1.16 and 2.64%/kh, respectively. However, there is only a degradation of 6.6% in voltage for the cell after 60 thermal cycling tests. In addition, it is found that many pores formed in the anode of the cell which caused by the agglomeration of Ni after long-term test. In contrast, the vertical cracks penetrating through the cathode of the cell and the in-plane cracks between the cathode and barrier layer of the cell formed due to the coefficient of thermal expansion (CTE) mismatch after 60 thermal cycling tests.