Solid Oxide Fuel Cell Generator Research Articles

An innovative integration of torrefaction, gasification, and solid oxide fuel cell for carbon–neutral utilization of biomass waste: Process development, economic, exergy, advanced exergy, and exergoeconomics analysis

An integrated novel process based on torrefaction, gasification, and solid oxide fuel cell (SOFC) has been developed for biomass waste valorization. Process sustainability analysis has been done through economic, exergy, advanced exergy, and exergoeconomics indicators. According to economic analysis, the internal rate of return (IRR) of this process dropped to 7% at 100–90% of the process efficiency and this process is not economically feasible below 90% operational efficiency. While the subsidized process IRR dropped from 20 to 13% at 100–80% of the process efficiency. Subsidized process is also not economically feasible below 80% process efficiency. The overall process electric power generation potential from SOFC and steam turbine generator is around 1331 kW. Gasifier and HeatXC have the highest exergy destructions (1110.7 and 1220.9 kW) with exergy efficiencies of around 82% and 79%, respectively. Gasifier, HeatXC, and SOFC have significant potential of exergy improvement due to higher avoidable exergy destruction. Therefore, process exergy and economic performance can be improved by targeting these components.

Optimization of solid oxide fuel cell power generation voltage prediction based on improved neural network

Abstract This paper proposes a method for predicting the generation voltage of a solid oxide fuel cell based on the data results of a stand-alone solid oxide fuel single cell simulation model under ideal conditions, with the aim of improving the generation efficiency and extending the service life of the solid oxide fuel cell. In this paper, a modified back propagation (BP) neural network algorithm is used to improve the prediction accuracy of the solid oxide fuel cell generation voltage by using the whale algorithm to optimize the BP neural network model to improve its convergence and achieve the effect of improving the prediction accuracy. First, the characteristics of the independent solid oxide fuel cell are introduced and simulated. Second, the long short-term memory network model, linear regression network model and BP neural network are simulated and compared, and the results show that the BP neural network prediction model is more accurate and can be optimized and improved. Finally, the BP neural network is optimized and simulated using the whale algorithm, and the simulation results show that the method has better convergence and higher prediction accuracy than the traditional BP neural network prediction model.

Development of Large-Scale Proton-Conducting Fuel Cells for Next Generation SOFC

Solid oxide fuel cells (SOFCs) are known to exhibit an exceptional energy conversion efficiency over 80 % of the various fuel cell types and have environmentally friendly systems with fuel flexibility. Unfortunately, the SOFC based on yttria-stabilized zirconia (YSZ) electrolytes has a major obstacle to commercialization due to its high cost and low durability at high operating temperature range (800~1000 oC). To overcome this issue, many researchers have made efforts in studying materials with performance comparable to conventional SOFCs at intermediate temperature range (500~700 oC). Among these efforts, to use a proton conductive material with a perovskite structure (ABO3) is regarded as an attractive solution. A lot of previous literatures have already proved the potential of proton-conducting oxide fuel cells (PCFCs) as a next generation of SOFCs. However, most of the results are based on laboratory-scale, so the reliability and feasibility have not been confirmed yet. In the attempt of entering the market with the PCFCs, several issues that must be faced are related to large-scale production. Firstly, when it comes to large-scale cell, the difference in the thermal expansion coefficient (TEC) between the electrode and the electrolyte dominantly affects the overall mechanical property of cells. So, the shrinkage rate after sintering should be elaborately controlled to inhibit several problems such as cracking, lifting and warping. Secondly, the low sinterability of BaCeO3 based proton conductors requires a high sintering temperature, which is more serious problem particularly in large-scale cells. That is, the possibility of Ba evaporation during the heat treatment increase, involving in formation of a secondary phase, which eventually causes performance deterioration. To our knowledge, few literatures are reported on this topic, large-scale PCFCs fabrication. In this work, we attempt to establish large-scale anode-supported PCFCs with BaCe0.6Zr0.2Y0.1Yb0.1 produced by citric-nitrate synthesis method. The electrostatic slurry spray deposition (ESSD) technology was used for each layer fabrication of large-scale cells. An anode functional layer (AFL) was adopted to adjust the TEC and shrinkage rate between the anode and the electrolyte. The quantitative shrinkage rates depending on temperature were analyzed by Dilatometer (Linseis Co.). A scanning electron microscope (SEM, JEOL Co.) was used for microstructural analysis. To examine Ba evaporation and interlayer diffusion, energy dispersive X-Ray spectroscopy (EDX) was used, and the phase development of the synthesized BCZYYb was analyzed by X-ray diffractometer (XRD, Rigaku Co.). The I-V curves and impedance spectra of the single cell were measured in the range of 500 ℃~700 ℃ with humidified hydrogen (~3 % water vapor). Finally, a short-term stability test (100 hours) was performed to confirm the electrochemical durability.

A computational fluid dynamics and finite element analysis design of a microtubular solid oxide fuel cell stack for fixed wing mini unmanned aerial vehicles

Computational fluid dynamics (CFD) and finite element analysis (FEA) are important modelling and simulation techniques to design and develop fuel cell stacks and their balance of plant (BoP) systems.The aim of this work is to design a microtubular solid oxide fuel cell (SOFC) stack by coupling CFD and FEA models to capture the multiphysics nature of the system. The focus is to study the distribution of fluids inside the fuel cell stack, the dissipation of heat from the fuel cell bundle, and any deformation of the fuel cells and the stack canister due to thermal stresses, which is important to address during the design process. The stack is part of an innovative all-in-one SOFC generator with an integrated BoP system to power a fixed wing mini unmanned aerial vehicle. Including the computational optimisation at an early stage of the development process is hence a prerequisite in developing a reliable and robust all-in-one SOFC generator system. The presented computational model considers the bundle of fuel cells as the heat source. This could be improved in the future by replacing the heat source with electrochemical reactions to accurately predict the influence of heat on the stack design.

Enhanced Performance of Gadolinia-Doped Ceria Diffusion Barrier Layers Fabricated by Pulsed Laser Deposition for Large-Area Solid Oxide Fuel Cells

Diffusion barrier layers are typically introduced in solid oxide fuel cells (SOFCs) to avoid reaction between state-of-the-art cathode and electrolyte materials, La1–xSrxCo1–yFeyO3-δ and yttria-stabilized zirconia (YSZ), respectively. However, commonly used layers of gadolinia-doped ceria (CGO) introduce overpotentials that significantly reduce the cell performance. This performance decrease is mainly due to the low density achievable with traditional deposition techniques, such as screen printing, at acceptable fabrication temperatures. In this work, perfectly dense and reproducible barrier layers for state-of-the-art cells (∼80 cm2) were implemented, for the first time, using large-area pulsed laser deposition (LA-PLD). In order to minimize cation interdiffusion, the low-temperature deposited barrier layers were thermally stabilized in the range between 1100 and 1400 °C. Significant enhanced performance is reported for cells stabilized at 1150 °C showing excellent power densities of 1.25 W·cm–2 at 0.7 V and at a operation temperature of 750 °C. Improved cells were finally included in a stack and operated in realistic conditions for 4500 h revealing low degradation rates (0.5%/1000 h) comparable to reference cells. This approach opens new perspectives in manufacturing highly reproducible and stable barrier layers for a new generation of SOFCs.

From Powdered Oxide to Shaped Metal: an Easy Way to Prepare a Porous Metallic Alloy for SOFC

AbstractThis work reports a proof of concept to obtain a shaped porous metallic alloy by the reduction at low temperature of an oxide precursor shaped at high temperature. A mixed cations oxide selected for potential applications in solid oxide fuel cells (SOFCs), is prepared using Pechini's polymer route and consolidated using the spark plasma sintering (SPS) technique at temperature in the 900 °C – 1,100 °C range. A pellet of pure AB2O4 spinel‐like structure with 10% of open porosity is obtained. The reduction of this pellet under H2 flow at low temperature (800 °C) allows obtaining a highly porous (48%) metallic pellet which meets all necessary characteristics to be used as mechanical support for the third generation of SOFC (3G‐SOFC). The use of oxide precursors widen the accessible temperature range allowing the possibility to stack in one step an oxide precursor of the 3G‐SOFC with full densification of the electrolyte. This proof of concept opens the way to the easy and cheap “one step” building of an oxide precursor of 3G‐SOFC which will be in situ activated during the warming up of the cell.

Modelling and control of solid oxide fuel cell generation system in microgrid

Abstract Compared with other kinds of fuel cells, solid oxide fuel cell (SOFC) has been widely used in microgrids because of its higher efficiency and longer operation life. The weakness of SOFC lies in its slow response speed when grid disturbance occurs. This paper presents a control strategy that can promote the response speed and limit the fault current impulse for SOFC systems integrated into microgrids. First, the hysteretic control of the bidirectional DC-DC converter, which joins the SOFC and DC bus together, is explored. In addition, an improved droop control with limited current protection is applied in the DC-AC inverter, and the active synchronization control is applied to ensure a smooth transition of the microgrid between the grid-connected mode and the islanded mode. To validate the effectiveness of this control strategy, the control model was built and simulated in PSCAD/EMTDC.

Development of Ammonia-Fueled SOFC

Ammonia has been studied as an energy carrier because of carbon-free and high hydrogen capacity. We have investigated performance of ammonia-fueled SOFC (Solid Oxide Fuel Cell) to study the possibility of ammonia as an energy carrier. In SOFC generation system, stack, which is made by cells, sealing glass and other materials, are main parts. These parts need ammonia resistance at 700-800 degree. So we developed sealing glass which has an ammonia resistance at 700-800 degree and fabricated 200W class stack. Ammonia was directly supplied to the anode chamber. The performance of ammonia-fueled SOFC was same as well as that of hydrogen-fueled SOFC.

Tailoring the microstructure of La0.6Sr0.4Co0.2Fe0.8O3−α cathode material: the role of dispersing agent

A lower operating temperature below 600 °C of the solid oxide fuel cells (SOFCs) is a key determinant of device performance. With this in mind, the roles of dispersing agents were investigated for synthesizing a cathode material made of La0.6Sr0.4Co0.2Fe0.8O3−α (LSCF) for application in intermediate temperature solid oxide fuel cells (IT-SOFCs). In the present study, LSCF was synthesized following a sol–gel method with the aid of an activated carbon and ethylene glycol as dispersing agents. X-ray diffractometer measurements indicate that a single perovskite phase of LSCF started to develop at the temperature of 500 °C and completely formed at 700 °C. Scanning electron microscope analysis confirmed that a well dispersed LSCF powders were successfully synthesized achieving a surface area of 12.05 m2 g−1 as corroborated by the BET surface area analysis. This finding shows significant improvements of modifying the structural properties of cathode material and could be used to fabricate the next generation of SOFCs.

A Thermo Fluid and Thermo Mechanical Modelling of a Microtubular Solid Oxide Fuel Cell Stack for Unmanned Aerial Vehicles

This work presents a three-dimensional thermo fluid and thermo mechanical computational analysis of a microtubular solid oxide fuel cell (SOFC) stack as part of a microtubular SOFC generator. The latter powers a lithium-ion battery as a microtubular SOFC hybrid power system to extend the flight endurance of a mini unmanned aerial vehicle. The microtubular SOFC stack and balance of plant components, comprising microtubular SOFC generator, were designed based on computational fluid dynamics (CFD) assumptions. The stack design process has been further upgraded with thermo mechanical finite element analysis (FEA) simulation to capture deformations and stresses in the stack due to thermal expansion of microtubular SOFCs and manifolds. The developed microtubular SOFC stack will be built based on CFD and FEA predictions and tested to determine the suitability of the microtubular SOFC hybrid power system for this application.

Beyond the 3rd Generation of Planar SOFC: Development of Metal Foam Supported Cells with Thin Film Electrolyte

The manufacturing of thin and gas tight electrolyte in solid oxide fuel cells (SOFCs) remains challenging especially when alloys are used for the substrate. In this work, we present a porosity graded multi-layer structure supporting thin film electrolyte, as a further evolution of the metal supported planar cell architecture. The substrate is made of NiCrAl metal foam impregnated with La0.1Sr0.9TiO3-α (LST) ceramic. Furthermore, a 20 µm thick composite anode functional layer with LST and Gd0.1Ce0.9O2-α (GDC) was deposited onto the substrate. The surface of the anode functional layer is later engineered with a suspension of nano-particles with 40 nm average particle size of yttria-stabilized zirconia (YSZ). This results in a mesoporous layer with a smooth surface. Finally, a gas-tight GDC electrolyte was deposited by EB-PVD method. The thickness of the thin-film YSZ layer and the gas-tight CGO layer was approximately 1 µm and 2 µm, respectively. Button half cells with size up to 25cm² were successfully produced showing an air leakage rate down to 0.7 Pa·m·s-1 satisfying the gas-tightness quality control threshold of the state of the art metal supported SOFCs at DLR. Full cells with La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathodes showed an OCV of 0.97 V at 750°C and power density of about 80mW/cm² was obtained at 0.7 V.

A Thermo Fluid and Thermo Mechanical Modelling of a Microtubular Solid Oxide Fuel Cell Stack for Unmanned Aerial Vehicles

This work presents a three-dimensional thermo fluid and thermo mechanical computational analysis of a microtubular solid oxide fuel cell (SOFC) stack as part of a microtubular SOFC generator. The latter powers a lithium-ion battery as a microtubular SOFC hybrid power system to extend the flight endurance of a mini unmanned aerial vehicle.The microtubular SOFC stack and balance of plant components, comprising microtubular SOFC generator, were designed based on computational fluid dynamics (CFD) assumptions. The stack design process has been further upgraded with thermo mechanical finite element analysis (FEA) simulation to capture deformations and stresses in the stack due to thermal expansion of microtubular SOFCs and manifolds. The developed microtubular SOFC stack will be built based on CFD and FEA predictions and tested to determine the suitability of the microtubular SOFC hybrid power system for this application.

Various Types of Applications with Double Perovskite Structure

Perovskite oxides with variable oxygen non-stoichiometry play a prominent role in many fields, including fuel cells, catalysis and gas storage. One interesting class of materials for solid oxide fuel cells (SOFCs) are cation ordered layered perovskite oxides due to their mixed ionic and electronic conductivity and fast oxygen kinetics. Even though progress has been made in cathode materials to lower the cathodic polarization, still it is also important for fuel cell technology to achieve highly efficient anode that realize long term stability with enhanced tolerance to carbon buildup (coking) and sulfur contamination (poisoning) from hydrocarbon fuels. Here, we report identification of redox-stable cation layered perovskite anode, with superior electrochemical performance in both hydrogen and hydrocarbons. Further, double perovskite materials will have immediate and profound implications for a new generation of SOFCs, proton conducting SOFC, oxygen separation membranes, electrolyzers, as well as other processes involving oxygen/electron transport.

Electrochemical Performance of Cu-GDC Cermet Anode for Solid Oxide Fuel Cells Using Octane Fuel

Introduction For many potential mobile robot applications, current power supply technology (such as the lithium ion battery technology) is in fact a key limiting factor due to its low energy density. Solid oxide fuel cells (SOFCs) are a promising alternative and can overcome limitations of current battery technology. This is because SOFCs can use not only hydrogen but also hydrocarbon fuels which have high energy density such as gasoline and so on. However, hydrocarbon is broken down into hydrogen and carbon at a high temperature and carbon precipitate on anodes.The rate of carbon deposition for the nikkel-gadolinia doped ceria (Ni-GDC) was slower than that for the nikkel-yttria stabilized zirconi (Ni-YSZ). Ceria can be reduced from Ce4+ to Ce3+, which causes the suppression of carbon deposition on the carbon deposition on the Ni-GDC anode1). Moreover, cupper based cermets anode is stable in hydrocarbon environments2). Therefore, we paid attention to Cu-GDC cermet anode. The objective of this research is to demonstrate octane direct introduction generation of SOFCs using Cu-GDC anode. Experimental Surface-polished YSZ pellets of 2 mm in thickness were used for the electrolyte. Pt cathode electrode and Pt reference electrode were prepared on the surface and side of the pellets, respectively, by firing Pt paste at 1300 oC for 1 h. Then, a commercially available CuO powder and GDC powder (CuO/GDC=55/45 (wt)) were thoroughly mixed in a vacuum using the planetary ball mill (LP-1, Ito Seisakusho Co., Ltd., 200 rpm, 24 h), and made into CuO-GDC pastes using ethyl-cellulose and organic solvent. The CuO-GDC paste was screen-printed in diameter of 8mm on the YSZ pellets and sintered at 900 oC for 1 h.Octane and steam were supplied to the SOFC cell by bubbling carrier gas (He) at a constant rate. Octane bubbler temperature was 30 oC, and Steam/Carbon ratio (S/C) were controlled by changing the temperature of the water bubbler from 30 to 70 oC. Electrochemical property was measured over a temperature range of 800-700 oC. During the constant current generation, exhaust gas was analyzed by gas chromatography. Results Figure 1 shows current-voltage (I - V) and current-power (I - P) characteristics for the cells at 750 oC. Octane-direct introduction generation is possible in SOFCs by using the Cu-GDC anode. A power generation characteristic improves gradually with the rise of S/C. For the lower S/C, the I - V curves are highly nonlinear, while the I - V curve for S/C=8.86 is essentially linear. Figure 2 shows impedance spectra for the cells with the Cu-GDC anode at 750 oC under open circuit conditions. The ohmic resistances that we associate with the electrolyte are obtained from the high-frequency intercept of the arc with the real axis, are the same and small values, while the total impedance from the low-frequency intercept in the arc with the real axis is increased with the S/C. The difference between the total impedance and electrolyte impedance is the anode electrode impedance. Therefore, the dominant factor of a power generation characteristic is anode electrode resistance. References 1) Hirofumi Sumi, Toshiaki Yamaguchi, Koichi Hamamoto et al., “Impact of direct butane microtubular solid oxide fuel cells” J. Power Sources, 220 (2012) 74-782) R.J. Gorte, H. Kim, J.M. Vohs, “Novel SOFC anodes for the direct electrochemical oxidation of hydrocarbon” J. Power Sources, 106 (2002) 10-15.

Mathematical model for the analysis of structure and optimal operational parameters of a solid oxide fuel cell generator

Solid oxide fuel cells are globally recognized as a very promising technology in the area of highly efficient electricity generation with a low environmental impact. This technology can be advantageously implemented in many situations in Brazil and it is well suited to the use of ethanol as a primary energy source, an important feature given the highly developed Brazilian ethanol industry. In this perspective, a simplified mathematical model is developed for a fuel cell and its balance of plant, in order to identify the optimal system structure and the most convenient values for the operational parameters, with the aim of maximizing the global electric efficiency. In this way it is discovered the best operational configuration for the desired application, which is the distributed generation in the concession area of the electricity distribution company Elektro. The data regarding this configuration are required for the continuation of the research project, i.e. the development of a prototype, a cost analysis of the developed system and a detailed perspective of the market opportunities in Brazil.

Modeling and Control of Solid Oxide Fuel Cell Generation System Integrated in Microgrid

This paper presents a control strategy of solid oxide fuel cell (SOFC) generation system integrated into microgrid. To enhance the dynamic response of SOFC, storage battery is paralleled via a DC bus, and the hysteretic control of bi-directional DC-DC converter is adopted. The common DC-AC inverter adopts an improved droop control. The active synchronization control is applied to ensure the smooth mode transition of microgrid. The simulation results show the dynamic performance of SOFC generation system in different operation modes.

A Predictive Model of SOFC Thermal Management Based on LS-SVM

The thermal management is crucial to the safety and lifespan of Solid Oxide Fuel Cell (SOFC) generation system. For the model-predictive control design, a model of SOFC thermal management system is proposed on the least squares support vector machine (LS-SVM). The model is composed of some thermal modules including SOFC stack, combustor, heat-exchanger and thermal equilibrium apparatus. It predicts the temperature distribution in SOFC generation system by computing the electrochemical reaction in the stack, the gas flow and the heat exchange through the modules. Checked by the experimental data, the model can be used for system temperature fast prediction with high precision and strong generalization ability, which meets the requirement of the research on the online predictive control design of SOFC generation system.

Experimental Modeling of Transients in Large SOFC Systems

This work investigates the dynamic operation of a large solid oxide fuel cell (SOFC) system using the system identification modeling approach. Transient modeling can be of particular interest in order to describe and optimize start-up and shut-down procedures in SOFC systems; moreover, mathematical description of transients is helpful in the diagnostic of hazardous conditions during dynamic operation (i.e., load following). Physical based models—described by differential equations—are usually complex and need significant computing time. To achieve real-time capability, the focus is on empirical models. In this study, the transient operation of a large SOFC generator is reproduced by using the system identification approach that is based on the definition of a black-box model and on the identification of main model coefficients based on real experimental data. In particular, the start-up of the system and its dynamics under fuel sensitivity experiments are investigated. First, the work valuably shows some experimental results of a large SOFC generator under dynamic operation. In particular, modeling results show that the system identification approach is an effective tool for the description of the transient behavior of SOFC large systems. The simulation of the start-up of a 100 kWe (electric) SOFC system shows the possibility to save ∼20% of start-up time using an electric air heater rated a 30% in power than the nominal one. The increase of natural gas flow during the start-up operation is instead not beneficial in term of yielding a faster procedure; rather, it leads to an excessive cooling of the stack due to internal reforming of natural gas (the higher amount of fuel burnt in the combustion zone does not lead to a more efficient way to preheat the cathode air). The results of this work are fully supported by experimental data available from a real generator running in Italy through years 2006–2009 and thus believed to be a valuable contribution for the scientific and engineering community.

ChemInform Abstract: From Ni‐YSZ to Sulfur‐Tolerant Anode Materials for SOFCs: Electrochemical Behavior, in situ Characterization, Modeling, and Future Perspectives

AbstractReview: 217 refs.

Operation of a solid oxide fuel cell under direct internal reforming of liquid fuels

This paper investigates the feasibility of state-of-the-art solid oxide fuel cells (SOFC) operating under direct internal reforming (DIR) of liquid fuels. A thermodynamic model of the combined heat and power solid oxide fuel cell generator (μCHP-SOFC) running on methanol and ethanol, respectively, has been developed. System performances achieved with these two fuels are compared to the baseline plant operated with methane, and are evaluated considering either internal or external vaporization plus pre-heating of the liquid fuel. The achieved lower heating value (LHV) efficiencies for the conversion into electricity of methane, methanol and ethanol are found comparable, ranging from 51 to 56%. The efficiency penalty observed when switching from methane to the liquid fuels is modest, or even nil (ethanol case), provided that the fuel is vaporized and pre-heated within the SOFC ‘hot-box’.Experimental sessions on planar Ni-based anode supported SOFCs running on methanol and ethanol, respectively, are also presented. The fuel cell operation under direct internal steam-reforming of these two fuels is assessed at 800 and 1000°C, while varying the steam-to-fuel (S/F) ratio and the fuel utilization (FU) factor. Methanol is easily converted at both 800°C and 1000°C when directly fed to the Ni anode; whereas, direct reforming of ethanol requires an operating temperature as high as 1000°C.