Conventional Solid Oxide Fuel Cell Research Articles

Characterization of Ca-doped YCoO3 Perovskite-type oxide as cathode for solid oxide fuel cells

Solid oxide fuel cell (SOFC) uses solid oxide as an electrolyte and has a high-power generation efficiency. One of the major problems in the development of SOFC is the side reaction that occurs at the interface between the electrode and the electrolyte. (Y, Ca)CoO[Formula: see text] materials were evaluated as a new air electrode material to replace the conventional (La, Sr)CoO3 materials. Y[Formula: see text]Ca[Formula: see text]CoO[Formula: see text] has good compatibility with Y-stabilized ZrO2 (YSZ) electrolyte. In addition, the power generation performance was equal to or better than the conventional SOFC cells.

Presentation and Performance of a Planar Solid Oxide Fuel Cell with Chaotic Gas Channels

Flow condition in gas channels determines the distribution and diffusion of reactants, governing electrochemical reactions in the solid oxide fuel cell (SOFC). It is found that the magnitude and direction of fluid velocity change with the geometric position in the channel, which leads to larger secondary flow velocity components and enhances mass transfer between fluids. Laser Doppler velocimetry experiment is conducted to verify the accuracy of numerical results of fluid flow in chaotic flow channels. Herein, a 3D numerical model with coupled multiphysics fields is built to evaluate fluid flow in channels and SOFC performance. The distribution characteristics of reactants in chaotic flow channel and the characteristics of temperature distribution, current density and power density in SOFCs caused by structures of straight and chaotic flow channels are analyzed and discussed. Compared with conventional straight flow channel SOFCs, the average current density of SOFC with chaotic flow channel is improved and the power density is increased by 9.7%. The reactant homogeneity in the electrode is also improved, which reduces the concentration polarization loss of SOFC.

Design and sensitivity analysis of a multistage solid oxide fuel cell hybrid system with an inter-cooled-recuperated gas turbine and organic Rankine cycle

A solid oxide fuel cell (SOFC) hybrid system with an inter-cooled-recuperated gas turbine(ICRGT) and organic Rankine cycle (ORC) was designed to address exergy destruction in the burner of a conventional SOFC and gas turbine (GT) system. In unfired mode of this system, SOFC acts as the GT heater and reheater instead of burners; burners are used only to aid load regulation in fired mode. In unfired mode, the system electrical efficiency is 69.86 % and the overall efficiency is 82.22 %. The total exergy destruction of the system is 21.93 % lower than that in fired mode by exergy analysis, which indicates the effectiveness of reducing afterburner exergy destruction, and the superior energy efficiency of this mode. For the design analysis, we analyzed the influence of different factors on the system, including the number of SOFC modules, turbine outlet temperature, burner exhaust into the turbine, oxidant utilization of SOFC cathode(OUC), and fuel utilization of SOFC anode(FUA) on the system. For the sensitivity analysis, we determined the variation rules of the components and system parameters for fuel proportions of 70–105 %. This work provides a reference for optimizing the design and operation of SOFC-GT and other SOFC hybrid systems.

Comparison of Carbon Deposition and Removal from Ni-YSZ and Ni-BCZY Composites Using Operando Optical Methods

Solid oxide fuel cells (SOFCs) are attractive devices for power generation because they can operate with a variety of fuels, including H2, hydrocarbon fuels, biogas, and syngas. Conventional SOFC anode composites comprised of Ni-YSZ (YSZ = yttria-stabilized zirconia), however, suffer from performance degradation due to surface accumulation of carbon from hydrocarbon cracking. Alternative electrolyte materials such as yttria-doped barium cerate/zirconate mixtures (BCZY) offer the promise of reduced carbon formation over the Ni-BCZY electrode and lower operating temperatures by the conduction of protons instead of oxide ions. In this study, 50%-50% Ni-8YSZ and 50%-50% Ni-BCZY27 composites were exposed to CH4 in the absence and presence of either CO2 or H2O. The degree of carbon deposition and mechanism of carbon removal in the absence of fuel was estimated in the presence of steam using operando Fourier transform infrared emission spectroscopy (FTIRES) and near-infrared thermal imaging (NIRTI) at 750 °C. Upon exposure to each fuel condition, carbon removal using steam results in more CO2 + CO product formation from Ni-8YSZ implying more carbon formation on Ni-8YSZ compared to Ni-BCZY27. Carbon removal of cells exposed to CH4 alone indicate limited formation and fast depletion of CO over Ni-BCZY27; depletion of CO2, however, happens more slowly. Depletion of CO and CO2 in the Ni-8YSZ system happens more gradually suggesting the deposition of carbon over Ni-BCZY27 occurs less readily and its removal is more facile through gasification. Interestingly, the cracking of CH4 over Ni-8YSZ is accompanied by a larger degree of cooling compared to Ni-BCZY27 whereas both dry and wet reforming result in similar cooling over Ni-8YSZ and Ni-BCZY27. The results will be discussed in the context of recent work using operando spectroscopies to characterize CH4 fuel utilization in Ni-8YSZ based SOFCs in the absence and presence of various reformers.

Fast ion-conductive electrolyte based on a doped LaAlO3 with an amorphous surface layer for low-temperature solid oxide fuel cells

Ion transport in solid oxide electrolytes is a key process involved in advanced green energy conversion devices such as solid oxide fuel cells (SOFCs). Conventional SOFC electrolytes require a high operational temperature (over 700 °C) to maintain considerable bulk and grain boundary diffusion of the ions to enable sufficient ionic conductivity for efficient fuel cell operation. The present study explores a novel ion conduction expressway in an amorphous/crystalline heterostructure, La0·8Sr0·2Al0·8Zn0·2O3-δ (LSAZ), which can boost the mobility of ions at a relatively low temperature (450–550 °C) for SOFCs. The LSAZ heterostructure includes an insulating perovskite core and a superionic-conducting amorphous surface layer. This electrolyte exhibits a superior conductivity of 0.319 S cm−1 at 550 °C, and it is employed in a SOFC which demonstrates a remarkable performance of 1296 mW cm−2 at 550 °C, which is 300 times higher than a SOFC with the LSAZ being densified at 1400 °C for 10 h. A superionic conducting amorphous surface layer enriched by high oxygen vacancy defects facilitates ionic conduction along the grain boundary and interfaces between the nanoparticles of LSAZ. Our finding provides an efficient way to design advanced highly conductive electrolytes for solid oxide fuel cells to be operated at reduced temperatures.

Robust Direct Hydrocarbon Solid Oxide Fuel Cells with Exsolved Anode Nanocatalysts

Perovskite anodes with in situ exsolved nanocatalysts have been proven to overcome carbon deposition and increase anode catalytic activity as an alternative to conventional Ni/YSZ anodes for direct hydrocarbon solid oxide fuel cells (SOFCs). This study, for the first time, demonstrates the state-of-the-art exsolution over cathode-supported SOFCs, which achieve the highest cell performance compared to conventional electrolyte-supported SOFCs with perovskite anodes using CH4 as a fuel. The dendritic channel structure of cathode supports retains a high active surface during high-temperature electrolyte sintering. Sr2Ti0.8Co0.2FeO6-δ perovskite ceramic is employed as anodes, and Co-Fe alloy nanoparticles are exsolved after reduction, which increases the cell power output by about 40%. The peak power densities of the cells are 0.82, 0.59, 0.43, and 0.33 W cm-2 at 800 °C using hydrogen, methane, methanol, and ethanol, respectively. The SOFCs with the exsolved nanocatalysts demonstrate stable power generation up to 110 h using methane, methanol, and ethanol fuels. Interestingly, the perovskite anodes show high methane fuel utilization by the complete oxidation of methane, which is in contrast to the partial oxidation over Ni catalysts. Robust hydrocarbon SOFCs have been developed by coupling anode catalyst exsolution with dendritically channeled cathode supports.

Effect of radial flows in fuel channels on thermal performance of counterflow tubular solid oxide fuel cells

Increasing the volumetric power density of solid oxide fuel cell (SOFC) stacks could enable their wider adoption in powering vehicles. The radial flows generated by inserts in gas channels of the tubular SOFC could enhance electrochemical reactions in porous electrodes and improve the power density. In this study, numerical simulations are performed to examine the influence of the enhanced exothermic electrochemical reactions on the temperature distributions in a counterflow tubular SOFC with inserts. We show that the radial flow in the fuel channel could improve the SOFC power density by 30% but lead to an increase in the maximum cell temperature gradient from 12 ℃/cm to 23 ℃/cm. The effects of radial flows under different inlet mass flow rates of hydrogen and methane are also examined. Compared with the conventional tubular SOFC, the percentage of power density improvements and the maximum cell temperature gradients of the tubular SOFC with inserts both increase with increasing inlet hydrogen mass flow rates. The maximum cell temperature gradient is increased from 12.8 ℃/cm to 47.5 ℃/cm as the percentage of net power density improvement is increased from 20% to 45%. We also demonstrate that increasing the inlet methane flow rate could adversely affect the SOFC performance, since the strong radial flow can remove the steam in porous anode, which impedes the methane steam reforming reaction and consequently reduces the output power density. The present work helps improve our understanding of heat and mass transfer characteristics of the radial flows in the tubular SOFC and helps build a foundation for SOFC channel designs.

(Invited) High-Temperature Electrosynthesis of Hydrogen and Syngas - Technology Status and Development Needs

High-temperature solid oxide electrolysis cell (SOEC) technology has been considered and developed for production of hydrogen (from steam) and syngas (from mixtures of steam and carbon dioxide). The SOEC, a solid oxide fuel cell (SOFC) in reverse or electrolysis operating mode, is traditionally derived from the more technologically advanced SOFC. The SOEC uses the same materials and operates in the same temperature range (600˚-800˚C) as the conventional SOFC. The SOEC therefore has the advantages shown by the SOFC such as flexibility in cell and stack designs, multiple options in cell fabrication processes, and choice in operating temperatures. In addition, at the high operating temperature of the SOEC, the electrical energy required for the electrolysis is reduced and the unavoidable Joule heat is used in the splitting process. SOEC technology has made significant progress toward practical applications in the last several years. To date, SOEC single cells, multi-cell stacks and systems have been fabricated/built and operated. However, further improvements are needed for the SOEC in several areas relating to the key drivers (efficiency, reliability and cost) to enable commercialization. This paper provides an overview on the status of SOEC technology, especially zirconia based technology, and discusses R&D needs to move the technology toward practical applications and widespread uses.

(Invited) Gradient Ni-SDC Anode By Reactive Co-Sputtering for Low Temperature Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are attracting attention as next-generation energy conversion devices due to their high efficiency, eco-friendliness, and scalability. However, the high operation temperature of conventional SOFCs (> 800°C) has posed several practical issues such as thermal degradation and limited material choice. To overcome this limitation, low-temperature SOFC (LT-SOFC, operation temperature <600°C) is actively being researched these days. Ni-YSZ (nickel-yttria stabilized zirconia) is commonly used as anode material in SOFCs. Ni-YSZ anodes are reasonably conductive at high operating temperatures and stable under harsh reducing conditions. However, at lower operating temperatures, the low conductivity of Ni-YSZ becomes an issue for use as an anode. Using doped ceria instead of YSZ is considered an alternative because the doped ceria has higher conductivity compared to YSZ due to the co-existence of multivalent states, i.e., Ce3+ and Ce4+, which can be further improved by doping. Moreover, if one adopts a carefully designed anode structure, e.g., gradient structure, the electrochemical performance of Ni-doped ceria anode can be further improved. Employing nanoscale components, e.g., thin films, are also one of the strategies to improve the electrode kinetics at the low operating temperature of LT-SOFCs. Thin film electrodes with short electronic and ionic paths as well as high surface area contribute to low ohmic and activation resistances. While high uniformity, reproducibility and throughout are practical concerns in thin film fabrication, reactive sputtering, which can produce uniform ceramic thin films from metal target in reactive gas environment in high reproducibility ad deposition rate, is a suitable candidate for thin film components for SOFCs. In this study, we fabricate a Ni-Samaria doped ceria(SDC) gradient anode by reactive co-sputtering. We prepare and characterize the cells with homogeneous and gradient-structured Ni-SDC thin film anodes. The gradient Ni-SDC thin film anode is composed of three layers, whose compositions are graded in a way that the Ni content increases from bottom (near electrolyte-anode interface) to top (anode top-surface). Possibly due to the combination of facilitated ionic conduction near electrolyte-anode interface and higher catalytic activity at anode surface, we observe the improved anode kinetics with lower activation resistance in the cell with gradient-structured Ni-SDC anode compared to the one with homogeneous anode.

Reactive Sputtered NiO-YSZ Anode Functional Layer for Thin Film Low-Temperature Solid Oxide Fuel Cell

Solid oxide fuel cell (SOFC) is one of the most promising next-generation electrochemical energy conversion devices because of its wide choice of fuels, cleanliness and, high efficiency of up to 70-85%( with heat utilization). Recently, low-temperature SOFC (< 600 ℃) has been studied to overcome the limitations of conventional SOFC, e.g., thermal stability, cost, and limited application. However, lowering operated temperature is challenging due to slow charge transfer and ion transport rates. Therefore, SOFC design with thin-film stacks, namely thin-film SOFC (TF-SOFC) fabricated on porous anode support, have been usually adopted for sufficient power density even at this temperature regime.A ceramic-metal composite (cermet) of Ni and YSZ (yttria-stabilized zirconia) is the most common anode or anode functional layer (AFL) material of TF-SOFC, because Ni-YSZ cermet has reasonable cost, chemical stability in a reducing atmosphere at high temperature, and similar thermal expansion coefficient to that of YSZ electrolyte. Various thin-film techniques have been reported for AFL fabrication, e.g., pulsed laser deposition (PLD), RF sputtering, etc. Among those, reactive sputtering method, which uses metal target in controlled gas conditions (e.g., oxygen condition for oxide deposition), is a versatile method to deposit various types of thin films with fast deposition speed (up to > 1um/hr), which is beneficial in manufacturability regarding the usual thickness range of AFL (a few microns).In this study, therefore, we studied physical and chemical properties of nanocomposite Ni-YSZ films fabricated by using the reactive sputtering deposition technique, focusing on the effect of sputter parameters. In particular, Oxygen partial pressure significantly affects deposition speed, surface morphology, composition, electrochemical performance, and thermal durability at 450 ℃. It is shown that excessive O2/Ar partial pressure ratio (> 0.2) significantly reduces the deposition speed by approximately one order of magnitude compared to the lower ratio case. In morphological analysis, O2/Ar partial pressure ratio affect nano-structured of anode, after annealing process at 1200℃ with air. Also, the Ni-YSZ anode sputtered at the environment of O2/Ar partial pressure ratio of 0.1 sample shows the lowest activation resistance when applied to LT-SOFC’s anode. The O2/Ar 0.5 sample shows surface Ni agglomeration due to high NiO-to-metallic Ni ratio.

A comprehensive investigation of direct ammonia-fueled thin-film solid-oxide fuel cells: Performance, limitation, and prospects

SummaryAmmonia is a promising carbon-free hydrogen carrier. Owing to their nickel-rich anodes and high operating temperatures, solid oxide fuel cells (SOFCs) can directly utilize NH3 fuel—direct-ammonia SOFCs (DA-SOFCs). Lowering the operating temperature can diversify application areas of DA-SOFCs. We tested direct-ammonia operation using two types of thin-film SOFCs (TF-SOFCs) under 500 to 650°C and compared these with a conventional SOFC. The TF-SOFC with a nickel oxide gadolinium-doped ceria anode achieved a peak power density of 1330 mW cm−2 (NH3 fuel under 650°C), which is the best performance reported to date. However, the performance difference between the NH3 and H2 operations was significant. Electrochemical impedance analyses, ammonia conversion quantification, and two-dimensional multi-physics modeling suggested that reduced ammonia conversion at low temperatures is the main cause of the performance gap. A comparative study with previously reported DA-SOFCs clarified that incorporating a more active ammonia decomposition catalyst will further improve low-temperature DA-SOFCs.

Direct ethanol solid oxide fuel cells integrated with internal reforming for renewable power generation

Solid oxide fuel cells (SOFCs) can directly convert bio-ethanol (a product of biomass process) into renewable power with high energy efficiency and low environmental impact, while it is still a challenge to achieve stable power generation because ethanol fuel readily causes carbon deposition over the state-of-the-art Ni-based anodes. This study has developed the anode supports integrated with internal reformers to convert ethanol into syngas, and the internal reformers were constructed by packing Ru-GDC nanofibrous catalysts within microchannels embedded in anode supports. The internal reforming increased the maximum power density (MPD) from 388.4 to 944.5 mW cm−2 at 800 °C and a low ethanol concentration of 6.5%, which is the highest-recorded MPD of oxygen ion-conducting SOFCs using ethanol fuel. The MPD increased with operation temperature and ethanol concentration while high ethanol concentration reduced ethanol conversion and potentially promoted carbon deposition. Adding steam with ethanol like conventional ethanol-fueled SOFCs greatly decreased MPD due to fuel dilution and the reduced open circuit voltage. The direct ethanol SFOCs with internal reformers demonstrated stable power generation at a current density of 1.0 A cm−2 for 236 h.

Recent Progress in the Design, Characterisation and Application of LaAlO3- and LaGaO3-Based Solid Oxide Fuel Cell Electrolytes.

Solid oxide fuel cells (SOFCs) are efficient electrochemical devices that allow for the direct conversion of fuels (their chemical energy) into electricity. Although conventional SOFCs based on YSZ electrolytes are widely used from laboratory to commercial scales, the development of alternative ion-conducting electrolytes is of great importance for improving SOFC performance at reduced operation temperatures. The review summarizes the basic information on two representative families of oxygen-conducting electrolytes: doped lanthanum aluminates (LaAlO3) and lanthanum gallates (LaGaO3). Their preparation features, chemical stability, thermal behaviour and transport properties are thoroughly analyzed in terms of their connection with the target functional parameters of related SOFCs. The data presented here will serve as a starting point for further studies of La-based perovskites, including in the fields of solid state ionics, electrochemistry and applied energy.

Production of a monolithic fuel cell stack with high power density

The transportation sector is undergoing a technology shift from internal combustion engines to electric motors powered by secondary Li-based batteries. However, the limited range and long charging times of Li-ion batteries still hinder widespread adoption. This aspect is particularly true in the case of heavy freight and long-range transportation, where solid oxide fuel cells (SOFCs) offer an attractive alternative as they can provide high-efficiency and flexible fuel choices. However, the SOFC technology is mainly used for stationary applications owing to the high operating temperature, low volumetric power density and specific power, and poor robustness towards thermal cycling and mechanical vibrations of conventional ceramic-based cells. Here, we present a metal-based monolithic fuel cell design to overcome these issues. Cost-effective and scalable manufacturing processes are employed for fabrication, and only a single heat treatment is required, as opposed to multiple thermal treatments in conventional SOFC production. The design is optimised through three-dimensional multiphysics modelling, nanoparticle infiltration, and corrosion-mitigating treatments. The monolithic fuel cell stack shows a power density of 5.6 kW/L, thus, demonstrating the potential of SOFC technology for transport applications.

Design and energy analysis of solid oxide fuel cell and gas turbine hybrid systems with membrane reactor

ABSTRACT The methanol-reforming solid oxide fuel cell (SOFC) emits high concentration of CO2 from the anode outlet. To achieve the goal of clean and low-carbon power generation, a CO2 capture unit is integrated with SOFC. In this work, the CO2 capture unit were set at different places in the conventional SOFC and gas turbine (GT) hybrid system. One was to place the water-gas-shift membrane reactor (WGSMR) at the anode inlet (SOFC-MRpre) and the other at the anode outlet (SOFC-MRpost). The key parameters, including the anode off-gas recycling ratio (RR), steam-to-carbon ratio (S/C), and operating pressure, have been investigated. Besides, the effects of the parameters on the power production, electrical efficiency, system efficiency, and CO2 capture capacity of the two processes were analyzed. It was found that the electrical and system efficiencies reached 53.3% and 41.8% for the SOFC-MRpre process, while 62.0% and 60.4% for the SOFC-MRpost process, respectively. The results show that placing the membrane reactor at the anode outlet can significantly reduce the energy consumption of the vacuum and blower, thus increasing the system efficiency. Besides, near-zero carbon emissions with only a 7.3% energy penalty can be achieved by the SOFC-MRpost process. These results reveal that the SOFC-MRpost process has more advantages than the SOFC-MRpre process.

Insights on the electrochemical performance of indirect internal reforming of biogas into a solid oxide fuel cell

The use of biogas in solid oxide fuel cells (SOFCs) is a viable approach for generating power from renewables. However, the direct use of dry biogas in SOFCs causes many issues concerning the durability of cells. Currently, the conventional approach consists of the use of an external reformer. Nevertheless, other approaches are possible to reduce the complexity of SOFCs. In this paper, we have investigated an indirect internal dry reforming occurring in the anodic chamber of a SOFC as a viable method to minimise the balance of the plant and simplify the feed management. This approach consisted of coupling a foam coated with NiCo/SDC powder in contact with the anode of a conventional SOFC cell. The electrochemical experiments demonstrated promising performances at 800 °C by feeding dry biogas with a maximum power density above 500 mW cm−2 @ 625 mV. The endurance test revealed a stable behaviour over 500 h. We analysed these results according to the physico-chemical properties of both catalyst and cell. The combined electrochemical and physico-chemical analyses corroborated the occurrence of multistep reactions in the anodic chamber.

Semiconductor ionic based Sm0.2Ce0.8O2−δ-La0.6Sr0.4Fe0.8Cu0.2O3-δ heterostructure for low temperature ceramic fuel cells

Structural design/doping strategy is an efficient method to prepare electrolytes with high oxygen ionic conductivity, but there is still hindrance for solid oxide fuel cell (SOFC) commercialization. Recent advances in semiconductor ionic materials have developed a novel strategy in designing low-temperature electrolyte materials. Here, a heterostructure composite of LSFC (La 0.6 Sr 0.4 Fe 0.8 Cu 0.2 O 3-δ ) and SDC (Sm 0.2 Ce 0.8 O 2−δ ) is developed. The LSFC-SDC composite exhibits a high ionic conductivity, >0.1S/cm at 550 °C. With symmetrical NCAL (Ni 0.8 Co 0.15 Al 0.05 LiO 2-δ )-coated electrode, cells with SDC-LSFC electrolyte exhibit high open-circuit voltage (OCV), and achieve a significant power improvement (>1000 mW/cm 2 ) compared with pure SDC electrolyte at 550 °C. The short-term stability result has proven the operating ability of SDC-LSFC electrolyte under fuel cell environment (H 2 /air). This work demonstrates a new developing route of low-temperature solid oxide fuel cell (LTSOFC), which is different from the conventional SOFC.

Effect of Oxygen Partial Pressure on Reactive-Sputtered Ni-YSZ Anode Properties for Low-Temperature Solid Oxide Fuel Cell

Solid oxide fuel cell (SOFC) is a promising next-generation energy conversion device because of its high efficiency, cleanliness, and fuel flexibility. Recently, SOFC operating at low- to intermediate-temperature (LT to IT) range (< 600 ℃) has been studied to overcome the limitations of conventional SOFC, e.g., thermal stability, cost, and limited application. In lowered temperature range, however, charge transfer and transport rates slow down; therefore, SOFCs design with thin film stacks, namely thin film SOFC (TF-SOFC) fabricated on porous anode support have been usually adopted for sufficient power density even at this temperature regime.TF-SOFC usually uses Ni-YSZ (nickel-yttria-stabilized zirconia) cermet for anode functional layer (AFL) to accommodate the deposition of dense electrolyte layers on anode support with relatively large pores because of its reasonable cost, catalytic activity, and electrical conductivity. While various thin film techniques have been reported for AFL fabrication, e.g., pulsed layer deposition (PLD), RF sputtering, etc. Among such techniques, reactive sputtering method, which uses metal target in controlled gas environment (e.g., oxygen environment for oxide deposition), is a versatile method to deposit various types of thin films with fast speed (up to > 1um/hr), which is beneficial in manufacturabilily regarding the usual thickness range of AFL (a few microns). Furthermore, the reactive co-sputtering method can control anode properties such as composition ratio, deposition speed, and morphology in wide ranges.In this study, we fabricate reactive sputtered Ni-YSZ cermet anodes, as prototypes for AFLs of TF-SOFCs, by using a single metal target with various oxygen partial pressure conditions, and characterize their physical and chemical properties. Oxygen partial pressure significantly affects deposition speed, surface morphology, composition, electrochemical performance and its thermal durability at 450 ℃. The Ni-YSZ anode sputtered at the environment of O2/Ar partial pressure ratio of 0.1 sample shows the lowest activation resistance when applied to LT-SOFC’s anode. It is also shown that excessive O2/Ar partial pressure ratio (> 0.2) significantly reduces the deposition speed by approximately one order of magnitude compare to the lower ratio case.

Thermodynamic analysis of 100% system fuel utilization solid oxide fuel cell (SOFC) system fueled with ammonia

The system efficiency of solid oxide fuel cells (SOFCs) fueled with ammonia or pure hydrogen always underperforms compared to the SOFCs fueled with carbon-based fuels. Hence, improving the efficiency of SOFCs fueled with pure hydrogen or hydrogen carriers such as ammonia is required to promote hydrogen economy. This study deals with the thermodynamic analyses of SOFC with 100% system fuel utilization configuration achieved by a dead-end anode (DEA) loop. The results are compared with the conventional SOFC configuration with the afterburner setup. It is shown that the energy efficiency and exergy efficiency of ammonia-fueled recirculation system are 12.17% points and 11.39% points higher than the conventional system. Energy balance comparison shows that the reduction in heat loss through exhaust gas is one of the significant factors for improving the system efficiency. The improvement in the exergy efficiency of the recirculation system is attributed to the reduction in exergy destructions in air preheaters and the elimination of exergy destruction at the afterburner. In addition, a parametric analysis and artificial neural network– genetic algorithm (ANN-GA) based optimization are performed to understand the effects of stack fuel utilization, current density, stack operating temperature, radiation loss, the pressure ratio across the membrane, and species removal rate in anode off-gas on system efficiency. The system efficiency as high as 75% lower heating value (LHV) can be achieved by the DEA loop configuration with operating the system at lower stack fuel utilizations.

Development of high performance and low‐cost solid oxide fuel cell stacks: Numerical optimization of flow channel geometry

Solid oxide fuel cell (SOFC) stacks with small volume and weight are essential to obtain higher specific and volumetric power densities as an alternative to conventional SOFC stacks with interconnectors having machined flow channels. This can be achieved by employing thin sheet interconnectors with flow channels formed by stamping methods rather than conventional machining of thick bulk materials. Besides the determination of process parameters providing defect free manufacturing of the desired channel design, the channel geometry is also significant for the cell performance. This study, therefore, focuses on the performance based parametric optimization of those flow channels in SOFCs by numerical simulations. In this respect, the effects of rib width, channel depth and rib angle on the cell performance are numerically investigated after the model validation with experimental results. The optimum rib width, channel depth and rib angle are determined to be 0.5 mm, 0.5 mm and 90°, respectively, within the parameter ranges considered in this study. In addition, the rib width is turned out to be the most effective parameter on the cell performance, while the cell performance almost remains unchanged for different channel depths.