Symmetric solid oxide fuel cells (SSOFCs) based on the Co-free La0·5Sr0·5Fe0·9Nb0·1O3-δ (LSFNb) perovskite oxide are prepared by the sol-gel method. The structural stability and catalytic activity of ...LSFNb as an electrode for both the hydrogen oxidation reaction and oxygen reduction reaction are studied. We show that Nb substitution in La0·5Sr0·5FeO3-δ greatly improves its chemical and phase stability under reducing atmosphere. At 800 °C, the area specific polarization resistances (ASRp) of La0·5Sr0·5Fe0·9Nb0·1O3-δ symmetric cells are as low as 0.06 and 0.24 Ω cm2 in air and wet H2 (3% H2O), respectively. LSFNb based electrolyte-supported SSOFCs deliver peak power densities of 1000 mW cm-2 at 850 °C in wet H2/air. In addition to high performance, the symmetric cell shows stable power output under load (measured for 140 h at a current density of 520 mA cm−2, 800 °C) under air/humidified H2 operation, indicating that LSFNb may be a particularly promising new symmetric electrode material for solid oxide fuel cells.
•Nb improve the stability of La0·5Sr0·5FeO3-δ in reducing atmosphere.•The ORR and HOR are investigated using distribution of relaxation times (DRT).•At 800 °C, The ASR of SSOFCs are as low as 0.06 and 0.24 Ω cm2 in air and wet H2.
Schematic of solid oxide fuel cell – homogenous charge compression ignition engine hybrid system.
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•Engine operation in the hybrid system is experimentally analysed for the first ...time.•HCCI engine is experimented while varying the operating conditions of the system.•HCCI engine yields a significant amount of power while emitting very low NOx emission.•It has been found how each system control parameter affects HCCI engine operation.•System operating conditions enabling successful HCCI engine operation are identified.
A solid oxide fuel cell (SOFC) hybrid system is a system that combines an SOFC with an additional power generation device to increase the efficiency of the system. The SOFC–gas turbine hybrid system has been primarily investigated for SOFC hybrid systems. However, the current power generation capacity of an SOFC is less than several MWs; for this generation capacity, an internal combustion engine is generally more efficient and economical than a gas turbine. Focusing on this point, recently, the concept of an SOFC–internal combustion engine hybrid system was proposed. However, the operation of this system has not been experimentally studied yet. In this paper, as the first step in an experimental investigation of the hybrid system, an experimental study on the operation of an internal combustion engine fuelled by SOFC anode off-gas was conducted. To successfully combust the SOFC anode off-gas, which includes a large amount of diluents (H2O and CO2), the homogeneous charge compression ignition (HCCI) method was selected instead of spark ignition as the combustion strategy of the internal combustion engine in the hybrid system. For the HCCI engine experiments, a single-cylinder HCCI engine and experimental equipment for emulating SOFC anode off-gas were constructed. Various HCCI engine experiments were performed while varying several system control parameters, e.g., the fuel utilization factor of an SOFC, which primarily affects the composition and flow rate of the engine intake gas. The experiments indicated that, in general system operating condition, HCCI engine operation yields a significant amount of power (w/25–30% gross indicated efficiency) and produces significantly low NOx emissions (<5 ppm @ O2 15%) under stable HCCI combustion (<5% COV IMEPg, which is the coefficient of variance of the gross indicated mean effective pressure). Considering that the experiment was performed using a small single-cylinder engine, these experimental results reveal that the use of an HCCI engine as the bottoming cycle in an SOFC hybrid system is promising. In addition, it has been found how each system control parameter affects HCCI engine operation. It was confirmed that HCCI engine operation was not always stable in all system operating conditions. System operating conditions that induce an exceedingly low engine load (<1.8 bar IMEPg, which is the gross indicated mean effective pressure) should be avoided as it decreases the stability of engine operation. Additionally, system operating conditions that make an engine intake gas with excessive dilution (fuel molar fraction < 0.125) should be avoided to decrease the amount of unburned CO emission and maintain a CO combustion efficiency higher than 90%.
Sr segregation on a perovskite oxide surface immensely affects the oxygen reduction activity and the durability of solid oxide fuel cells cathode. Herein, a facile strategy is proposed, which employs ...a high-entropy perovskite oxide as a cathode to suppress the Sr segregation during the long-term operation. The as-prepared high-entropy La0·8Sr0·2MnO3-δ (LSM) incorporates five components into A-site of LSM perovskite, including La, Pr, Nd, Sm and Sr (La0.2Pr0.2Nd0.2Sm0.2Sr0·2MnO3-δ, HE-LSM). The homogeneously dispersive multiple rare-earth metal species in A-site of perovskite are thermodynamically stable at high temperature. Besides, the lattice distortion of HE-LSM caused by the high dispersity of A-site cations will lead to the formation of disordered stress field around Sr, which can limit the transport rate of Sr. Further long-term stability test indicates that HE-LSM is rather stable under the operation condition, demonstrating that high-entropy perovskite oxide is a potential cathode material which can suppress the cation segregation for solid oxide fuel cell.
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•High-entropy perovskite oxides are potential cathode materials.•LSM incorporates five components into A-site forming high-entropy oxide.•The disordered stress field around Sr can limit the transport rate of Sr.•High-entropy perovskite cathodes can suppress the Sr segregation.
Low temperature solid oxide fuel cell (LT-SOFC) can be a source of power for vehicles, online grid, and at the same time reduce system cost, offer high reliability, and fast start-up. A huge amount ...of research work, as evident from the literature has been conducted for the enhancement of the ionic conductivity of LT electrolytes in the last few years. The basic conduction mechanisms, advantages and disadvantages of different LT oxide ion conducting electrolytes {BIMEVOX systems, bilayer systems including doped cerium oxide/stabilised bismuth oxide and YSZ/DCO}, mixed ion conducting electrolytes {doped cerium oxides/alkali metal carbonate composites}, and proton conducting electrolytes {doped and undoped BaCeO3, BaZrO3, etc.} are discussed here based on the recent research articles. Effect of various material aspects (composition, doping, layer thickness, etc.), fabrication methods (to achieve different microstructures and particle size), design related strategies (interlayer, sintering aid etc.), characterization temperature & environment on the conductivity of the electrolytes and performance of the fuel cells made from these electrolytes are shown in tabular form and discussed. The conductivity of the electrolytes and performance of the corresponding fuel cells are compared. Other applications of the electrolytes are mentioned. A few considerations regarding the future prospects are pointed.
•Basic theories, advantages and disadvantages of different classes LT-SOEs covered.•Effects of composition, fabrication methods, and other strategies discussed.•Conductivity of different classes LT-SOEs is presented and compared.•Performance of the fuel cells fabricated from the electrolytes have been discussed.•Applications of the LT-SOEs in different fields are covered.
•Review of hybrid solid oxide fuel cell- gas turbine dynamic operation and control.•Different types of hybrid system stall/surge control strategies are discussed.•Optimization, CO2 capture, hybrid ...system integration with other cycles is reviewed.•Many control strategies for SOFC-GT dynamic operation are available & demonstrated.•Studies suggest high efficiency and good controllability for SOFC-GT systems.
This paper presents a review of system design and analysis, and transient control and optimization of solid oxide fuel cell-gas turbine (SOFC-GT) hybrid systems for different system configurations. The main feature of SOFC power systems is production of less harmful chemical and acoustic emissions at a higher efficiency compared to conventional power production technologies. Microturbines have been shown amenable to integration with a high temperature fuel cell due to the well-matched temperature and pressure characteristics of an SOFC and microturbine in a hybrid system. Different configurations of hybrid SOFC-GT systems are briefly discussed. The main focus of this paper is investigation of different control strategies and transient performance characteristics of hybrid SOFC-GT systems in the literature. Different control strategies including variable and fixed speed operation of shaft using PI control methods are discussed. Different types of bypass valves for hybrid system control such as recuperator bypass are used to control the inlet temperature of the air entering the stack. In addition, SOFC bypass valves are used to control the mass flow through the SOFC stack. Different control methods are described to avoid stall/surge in the compressor. The main components of a hybrid system and their effects on the system performance are thoroughly discussed. Impacts of heat exchangers on a hybrid system are also determined and pressure losses between the recuperator and combustor for three different conditions are evaluated. Effects of different system parameters such as Steam-to-Carbon ratio (S/C), fuel utilization and operating pressures on system performance are determined. Net efficiencies of different hybrid system configurations are compared. Other applications of a hybrid system such as those that include CO2 capture and sequestration are investigated. Finally, system optimization and investigation of alternative fuels are discussed.
Solid oxide fuel cells (SOFCs) have potential to be the cleanest and most efficient electrochemical energy conversion devices with excellent fuel flexibility. To make SOFC systems more durable and ...economically competitive, however, the operation temperature must be significantly reduced, which depends sensitively on the development of highly active electrocatalysts for oxygen reduction reaction (ORR) at low temperatures. Here we report a novel silver nanoparticle-decorated perovskite oxide, prepared via a facile exsolution process from a Sr0.95Ag0.05Nb0.1Co0.9O3‑δ (SANC) perovskite precursor, as a highly active and robust ORR electrocatalyst for low-temperature SOFCs. The exsolved Sr0.95Ag0.05Nb0.1Co0.9O3‑δ (denoted as e-SANC) electrode is very active for ORR, achieving a very low area specific resistance (∼0.214 Ω cm2 at 500 °C). An anode-supported cell with the new heterostructured cathode demonstrates very high peak power density (1116 mW cm–2 at 500 °C) and stable operation for 140 h at a current density of 625 mA cm–2. The superior ORR activity and stability are attributed to the fast oxygen surface exchange kinetics and the firm adhesion of the Ag nanoparticles to the Sr0.95Nb0.1Co0.9O3−δ (SNC0.95) support. Moreover, the e-SANC cathode displays improved tolerance to CO2. These unique features make the new heterostructured material a highly promising cathode for low-temperature SOFCs.
In part A of this review, we have introduced the progress of the research and the application status of unitized regenerative proton exchange membrane fuel cells. In addition to this Proton Exchange ...Membrane (PEM)-based Unitized Regenerative Fuel Cell (URFC), other URFC technologies with different electrolytes have also been reported in the literature, which form the basis for emphasis in this part of the review. Unitized Regenerative Alkaline Fuel Cells (UR-AFC) have long been utilized for aerospace applications, while the recent development of Anion Exchange Membrane (AEM) has stimulated their further development, especially on the AEM-based UR-AFCs. Vast research works have been reported on the bifunctional oxygen catalyst development, while the latest UR-AFC prototypes are also being briefly introduced. Despite their potential cost-efficiency and better reactivity, cell performance and round-trip efficiency of the current UR-AFCs are still lower than their PEM-based counterparts. Unitized regenerative solid oxide fuel cell, which is more commonly cited as Reversible Solid Oxide Fuel Cell (RSOFC), is a high-temperature URFC technology with superior performance and reversibility. Review works conducted on this type of URFC are separated into two categories, that is, RSOFC with oxygen ion conducting electrolyte and RSOFC with proton ion conducting electrolyte. Despite the highest efficiency among various URFC technologies, the application of RSOFCs, however, is restricted by their limited long-term stability and poor cycle ability. Unitized regenerative microfluidic fuel cell, also referred to as the reversible microfluidic fuel cell, is a newly-emerging URFC research trend which benefits a lot from its membraneless configuration. However, limited research works have been conducted on this new technology.
Reversible solid oxide fuel cell (rSOC) is an efficient means of converting chemical energy into electrical energy, offering a promising solution to the imbalance between energy production and ...consumption. The performance of rSOC in dual-mode operation, utilizing syngas as fuel, is significantly influenced by variations in fuel composition. This study aims to develop an rSOC model using Aspen Plus and the extreme learning machine (ELM) algorithm to evaluate the impact of different fuel compositions on stack performance in both solid oxide fuel cell (SOFC) and solid oxide electrolytic cell (SOEC) modes. Results indicate that the concentrations of H2 and H2O are critical for optimal performance in dual-mode operation. Additionally, the water gas shift (WGS) reaction is employed to modify syngas composition for improved performance. When the molar fraction of H2/H2O is maintained between 50 % and 60 %, the rSOC achieves a maximum round-trip efficiency of 67.5 %. The optimal syngas composition, with H2/H2O/CO2/CO ratios of 50/5/35/10, can reach a maximum round-trip efficiency of 68.5 %. This study provides theoretical insights into the selection of syngas composition for rSOC in dual-mode operation.
•Aspen Plus software is employed to develop an rSOC model for dual modes.•ELM is integrated to predict rSOC performance under varying syngas compositions.•Effect of gas compositions on carbon deposition and fully oxidized are considered.•An optimal gas composition of H2/H2O/CO2/CO for dual-mode operation is identified.
Micro-tubular flame-assisted fuel cell stacks Milcarek, Ryan J.; Garrett, Michael J.; Ahn, Jeongmin
International journal of hydrogen energy,
12/2016, Volume:
41, Issue:
46
Journal Article
Peer reviewed
Open access
Similar to the original direct flame fuel cell the flame-assisted fuel cell, which has a solid oxide fuel cell (SOFC) operating in combustion exhaust, can potentially simplify the fuel cell system ...and has applications in micro-Combined Heat and Power. Development and testing of a 9 micro-tubular flame-assisted fuel cell stack is demonstrated in this work. Two different systems are investigated having 1) fixed fuel flow rate and varying air flow rate and 2) fixed total flow rate of air and fuel for the micro-Combined Heat and Power burners. The micro-tubular flame-assisted fuel cell stack achieves a significant performance of 237 mW cm−2 in model methane combustion exhaust at 0.5 V and 790 °C with a lanthanum strontium manganite based cathode. Electrochemical impedance spectroscopy reveals that the fuel cell ohmic losses are unaltered by variations in the exhaust species concentrations while the polarization losses increase with decreasing first-stage combustion fuel-air equivalence ratio. Variations in the combustion exhaust temperature effects both the ohmic and polarization losses.
•A 9 micro-tubular flame-assisted fuel cell stack (15.03 cm2) is tested.•Peak power density of 246 mW cm−2 in model methane combustion exhaust.•Electrochemical impedance spectroscopy conducted on flame-assisted fuel cells.•Polarization losses are dependent upon the exhaust equivalence ratio.
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