Single-chamber Solid Oxide Fuel Cell Research Articles

Investigation of Single-step Fabrication of a Cathode-supported Planar Single-chamber Solid Oxide Fuel Cell and Its Performance

This study presents a cathode-supported planar solid oxide fuel cell (SOFC) fabrication made via a single step co-sintering method and investigation of its performance. The materials used are NiO-CGO, CGO and CGO-LSCF for anode, cathode, electrolyte, respectively. Our study shows that increasing the cell size has a detrimental effect on cell single step co-sinterability. Increasing cathode thickness and reducing electrolyte thickness led to curvature decrease at the edges, however these adjustments were not enough to achieve a curvature-free cathode-supported cell. Thus, three porous alumina cover plates (total mass of 49.35 g) placed on the top of the cell during sintering were utilized to suppress curvature formation, and as a result, a nearly curvature- free cathode-supported cell was obtained. Performance of the cells were investigated. The results showed that increasing cathode thickness and decreasing electrolyte thickness had negative effects on cell performance despite enhanced single step co-sinterability of the cell. The maximum power density and OCV of the final planar cell (thickness 60-40-800 µm, anode-electrolyte-cathode) were found to be 1.71 mW cm-2 and 0.2 V, respectively, in a fuel rich condition (R:1.6). Additionally, the maximum OCV and power density among the all cells were measured from the cell (thickness 60-40-400 µm, anode-electrolyte-cathode) as 0.56 V and 24.79 mW cm-2, respectively, in a fuel rich condition (R:2.4).

A Study of the Electrochemical Characteristics of Single-Chamber Solid Oxide Fuel Cells Based on Platinum and Strontium-Doped Lanthanum Manganite Electrodes and Fed with a Methane–Air Mixture

A Study of the Electrochemical Characteristics of Single-Chamber Solid Oxide Fuel Cells Based on Platinum and Strontium-Doped Lanthanum Manganite Electrodes and Fed with a Methane–Air Mixture

Performance of Single-Chamber Solid Oxide Fuel Cells Based on Ni and Ni–Cu Alloy Anodes and Fed with a Methane–Air Mixture

Performance of Single-Chamber Solid Oxide Fuel Cells Based on Ni and Ni–Cu Alloy Anodes and Fed with a Methane–Air Mixture

Comparison of different infiltration amounts of CeO2 inside Ni-YSZ anodes to improve stability and efficiency of Single-Chamber SOFCs operating in methane

Electrochemically active oxide-based anodes capable of working in Single-Chamber Solid Oxide Fuel Cells (SC-SOFCs) were developed. Their performance is related to the selectivity of the electrodes. Tests are carried out on lab-scale devices with YSZ pellets as solid electrolytes in electrolyte supported cells. Selecting methane as a fuel, a gas mixture in the ratio CH4/O2 = 2 was chosen. The Ni-YSZ (NiO:YSZ=60:40) anode was optimized through CeO2 nanocatalysts infiltration to enhance the anode catalytic activity and make its reduction easier. Several infiltration amounts were compared, from null to 15% of the electrode weight. Both symmetric and complete cells (with LSCF-based cathodes) were tested in H2 and CH4/O2. For increasing amounts of infiltrated CeO2, symmetric cells tests describe an area specific resistance (ASR) reduction from 40 Ω cm2 to 1.7 Ω cm2 in hydrogen and from 11 Ω cm2 to 3.9 Ω cm2 in the methane/oxygen mixture. While complete cells tests displayed an ASR drop from 30 Ω cm2 to 2.9 Ω cm2 in H2, and from 8.7 Ω cm2 to 4.3 Ω cm2 in the methane/oxygen mixture, while OCP and power grew from 478 mV and 3.7 mW cm-2 to 766 mV and 13 mW cm-2.

Single chamber Solid Oxide Fuel Cells selective electrodes: A real chance with brownmillerite-based nanocomposites

In this contribution brownmillerite-based nanocomposite cathode for Single-Chamber Solid Oxide Fuel Cells is developed. These cells can be very attractive especially for small and cheap devices because of the absence of seals. The efficiency of SC-SOFCs is strictly connected to the selectivity of anode and cathode, the bottleneck for this technology. The development of a cathode inert in fuel oxidation is particularly challenging. Our strategy is to start from a catalytically un-active support (CFA = Ca2FeAl0.95Mg0.05O5) and induce the formation of iron oxide based nanoparticles, expected to activate oxygen. Symmetric (CFA + FeOx/CGO/CFA + FeOx) and complete cells (CFA + FeOx/CGO/Ni-CGO) are studied in air and methane/oxygen 2:1 mixture. The Area Specific Resistance of CFA + FeOx is less than 1/3 that of CFA. The high selectivity allows to reach an efficiency of 25%; power still needs to be increased but we demonstrated the possibility to develop selective low cost electrodes. The effect of air, methane/oxygen exposure and the heat treatments were carefully investigated.

Solid oxide fuel cells based on ceramic membranes with mixed conductivity: improving efficiency

Modern approaches to increasing the efficiency of solid-oxide fuel cells (SOFCs) based on electrolytic membranes with mixed conductivity are considered. These approaches are based on material-science concepts (expansion of the electrolytic domain boundary due to the doping of basic oxides and development of various composite materials) and various technological solutions (application of electron-blocking layers on the anode and cathode sides, rational selection of the electrolyte thickness, and optimization of the electrolyte and electrode structures by synthesizing heterostructures). The methods of mathematical modelling of devices with an electrolytic membrane having mixed conductivity are analyzed in order to determine the most efficient design and optimal operation conditions for SOFCs. The application of nanocomposite electrolytes with a core – shell structure and salt composites is considered. Data on new design solutions — single-layer and single-chamber SOFCs — are presented. The prospects of the proposed approaches are evaluated.The bibliography includes 384 references.

The numerical investigation of a planar single chamber solid oxide fuel cell performance with a focus on the support types

Single chamber solid oxide fuel cells (SC-SOFCs) could be an alternative to the conventional dual chamber types since they do not need any sealant and electrolyte crack growth does not lead to failure in performance. However, the reduced reactant activity due to spectator species present at anode and cathode results in a significantly decreased performance. The focus of this paper is to present a comparative study on the performance of single-chamber anode-, cathode, and electrolyte-supported cells. Our results show that anode-supported cells offer significantly better performance compared to electrolyte-supported cells. The cathode-supported cells show a similar performance to anode-supported cell close to open circuit voltages, i.e. voltages above 0.92 V, after which the cell current density decreases due to lack of oxygen at the cathode catalyst layer. Finally, a time-dependent performance study of the cathode-supported cell concept is presented and discussed.

Modeling and Optimization of the BSCF-Based Single-Chamber Solid Oxide Fuel Cell by Artificial Neural Network and Genetic Algorithm

Fuel cells could be a highly effective and eco-friendly technology to transform chemical energy stored in fuel to useful electricity and thus are presently appraised as a standout among the most encouraging advancements for future energy demand. Solid oxide fuel cells (SOFCs) have several advantages over other types of fuel cells, such as the flexibility of fuel used, high energy conversion, and relatively inexpensive catalysts due to high-temperature operation. The single chambers, wherein the anode and cathode are exposed to the same mixture of fuel, are promising for the portable power application due to the simplified, compact, sealing-free cell structure. The empirical regression models, such as artificial neural networks (ANNs), can be used as a black-box tool to simulate systems without solving the complicated physical equations merely by utilizing available experimental data. In this study, the performance of the newly proposed BSCF/GDC-based cathode SOFC was modeled using ANNs. The cell voltage was estimated with cathode preparation temperature, cell operating temperature, and cell current as input parameters by the one-layer feed-forward neural network. In order to acquire the appropriate model, several network structures were tested, and the network was trained by backpropagation algorithms. The data used during the training, validation, and test are the actual experimental results from our previous study. The optimum conditions to achieve maximum power of the cell were then determined by the genetic algorithm and the developed ANN.

Effect of the angle between gas flow direction and electrode on single-chamber SOFC stacks

Single-chamber solid oxide fuel cell (SC-SOFC) stacks with different angles between the gas flow direction and the electrode were fabricated and tested in a diluted methane-oxygen mixture. The gas tubes with separated gas vents were used for transmission of the reactant gasses. Experimental results showed that the performance of the two-cell stack at a gas flow angle (θ) of 45° was greatly enhanced compared with that at 0 and 90°. At a furnace temperature of 700 °C and a CH4/O2 ratio of 2, the maximum output power of the anode-first configuration was 154 mW at θ = 45°, which was 51% higher than that obtained at θ = 90°. Additionally, the maximum power of the anode-first stack was higher than that of the cathode-first one at θ = 45°, which was contrary to the results obtained at θ = 90°. The stack with an angled configuration of θ = 45° will generate a more attractive power for portable power applications.

Spatially Resolved Photoemission and Electrochemical Characterization of a Single-Chamber Solid Oxide Fuel Cell

The present paper pinpoints the feasibility of in operando near-ambient pressure characterization of an operating single chamber solid oxide fuel cell (SC-SOFC) by means of spatially resolved X-ray photoelectron spectroscopy. The results are based on an innovative and unique setup expanding the capabilities of the scanning photoelectron microscopes. In particular, the impact of getting access to the low mbar range on the very observability of chemical-state changes in an LSM cathode have been highlighted. Ex situ and in situ electrochemical measurements at OCP and close circuit cell conditions complemented the photoemission mapping and spectroscopy. The latter has evidenced the evolution of the chemical state of Sr upon the exposure of the typical SC-SOFC CH4–O2 gas feed.

Single‐step fabrication of an anode supported planar single‐chamber solid oxide fuel cell

AbstractWe present single‐step‐co‐sintering manufacture of a planar single‐chamber solid oxide fuel cell (SC‐SOFC) with porous multilayer structures consisting of NiO/CGO, CGO and CGO‐LSCF as anode, electrolyte, and cathode, respectively. Their green tapes were casted with 20 μm thickness and stacked into layers of anode, electrolyte, and cathode (10:2:2), then hot‐pressed at 2 MPa and 60°C for 5 minutes (deemed optimal). Subsequently, hot laminated layers were cut into 40 × 40 mm cells and co‐sintered up to 1200°C via different sintering profiles. Shrinkage behavior and curvature developments of cells were characterized, determining the best sintering profile. Hence, anode‐supported SC‐SOFCs were fabricated via a single‐step co‐sintering process, albeit with curvature formation at edges. Subsequently, anode thickness was increased to 800 μm and electrolyte reduced to 20 μm to obtain SOFCs with drastically reduced curvature with the help of a porous alumina cover plate.

Significantly Improving the Durability of Single-Chamber Solid Oxide Fuel Cells: A Highly Active CO2-Resistant Perovskite Cathode

The single-chamber solid oxide fuel cell (SC-SOFC) represents an attractive alternative to batteries for micropower applications given its simplified stack design, easy gas management, lower operation temperature, and quicker start-up. Its stable operation over long duration relies on the availability of CO2-resistant cathode materials with high oxygen reduction reaction (ORR) activity. Here, we reported a novel perovskite oxide cathode SrSc0.075Ta0.025Fe0.9O3−δ (SSTF75), which provides CO2 resistance and high ORR activity. A peak power density of 1430 mW cm–2 was achieved with the SSTF75/Sm0.2Ce0.8O1.9 cathode at 650 °C with a methane and oxygen gas mixture (1:1 v/v ratio). It retained stable voltage performance at 600 °C for an over 90 h duration when discharged at a current density of 1000 mA cm–2. This work not only represents an advancing step in the SC-SOFC field but also authenticates an effective codoping strategy for the design of a CO2-resistant cathode for low-temperature applications.

Selective Electrodes for Mixed Reactant Fuel Cells

Objectives We examine the option to operate fuel cells, in particular solid oxide fuel cells (SOFCs), on a mixture of fuel with air and apply the same mixture to both the anode and cathode. This kind of cell is referred to as a mixed-reactant fuel-cell (MR-FC or MR-SOFC). Operating a fuel cell on a uniform mixture of the reactants allows significant changes in the cell design having, potentially, higher power density and higher fuel utilization as well as enabling the use of porous electrolyte thin layers and lowering production costs. To achieve this the symmetry has to be broken by using different materials as catalysts for the anode and cathode. The primary challenge is selectivity, allowing the anode only fuel oxidation by oxygen ions emerging from the solid electrolyte and the cathode only oxygen reduction while all materials in the cell should not catalyze the direct chemical reaction within the mixture. The aim is to discuss potential ways to achieve that selectivity and test it. Selectivity is in particular a challenge in MR- SOFCs as they should operate at elevated temperature where many reactions are active and selectivity is difficult to be achieved. New results Selectivity can be controlled by materials properties, cell design in particular the electrode design and operation conditions.1 The following material properties affect selectivity: the work function, electron energy levels and energy band banding at the surface, point defects, in particular in the surface layer, generation of local electrical fields by surface additives and tendency towards reduction of the oxides in the cell which serve as the electrolyte, electrodes and possibly also as the interconnects and current collectors. Proper electrode design can enhance selectivity taking advantage of the different diffusion coefficients and concentration gradients in the gas components i.e. fuel, oxygen and reaction product. Working conditions that can contribute to selectivity are: temperature, flow rate hence residence time in the hot zone and electrical current drawn from the cell as it affects the concentration gradients in the gas phase at the electrodes. These factors apply to all mixed reactant fuel cells and allow to enhance selectivity in them. They are crucial for the high temperature MR-SOFCs. Test design is discussed suggesting that first each material is tested separately to screen those that enhance the forbidden chemical reaction within the gas mixture. Preliminary experimental results are reported. The procedure suggested to test selectivity and cell performance is discussed. Moderately diluted hydrogen can be used as the fuel in the mixture, as found experimentally contrary to common believe, despite the high temperatures used (600°C) as long as no catalyst is present. It is emphasized that single chamber SOFC reported so far are not true MR-SOFCs as one of the electrode is not selective. Significance Determining the catalytic properties of materials, in the present case those relevant to solid oxide fuel cells, is of general interest and importance. Achieving selectivity will provide the basic necessary condition for the construction of mixed reactant solid oxide fuel cells. Once this is achieved accelerating reaction rates will be the next challenge. Acknowledgement This research was supported by Israel Science Foundation ISF under grant No. 699/11. References I. Riess, Funct. Mater. Lett. 8 1540010 (2015).

Fabrication and evaluation of a novel wavy Single Chamber Solid Oxide Fuel Cell via in-situ monitoring of curvature evolution

Wavy type Single Chamber Solid Oxide Fuel Cells (SC-SOFCs) are beneficial for improved triple phase boundary conditions contributing to higher performance, compared with planar type SC-SOFCs of the same diameter. This study presents a fabrication process for wavy-type, cathode-supported SC-SOFCs with a single fabrication step via co-sintering of a triple-layer structure consisting of NiO/CGO-CGO-LSCF, with a thickness ratio of 1:3:9 respectively. Curvature evolution occurs due to different sintering behaviour of each layer during the co-sintering process. In-situ observation of each layer during the co-sintering process allows for minimisation of mismatched stresses to avoid unnecessary warping and cracking. Bilayers, consisting of NiO/CGO-CGO and CGO-LSCF, are co-sintered at 1200°C. In-situ observation, to monitor the shrinkage of each material and the curvature evolution of the structures, is performed using a long focus microscope (Infinity K-2). Monitoring curvature behaviour in real time minimised the development of undesired curvature in the triple-layer structure. Performance testing of wavy cell is carried out in a methane-air mixture (CH4:O2=1:1). The wavy SC-SOFC generated 0.39V and 9.7mWcm−2 at 600°C, which produced 260% and 540% increments in OCV and in maximum power density, respectively, over the planar SC-SOFC under the same operational conditions.

Synthesis and characteristics of La0.6Sr0.4Co0.2Fe0.8O3-δ perovskite cathode material by microwave assisted sol – gel method

In this study, LSCF 6428 was synthesized by microwave assisted sol – gel method. XRD and SEM analyses were used to determine the single-phase and nanocrystalline structure. Properties of this perovskite material including specific area, thermal expansion coefficient (TEC) and resistance of cathode were studied. The results showed that well-crystalline perovskite was obtained at microwaved of 500 W in 10 minutes, stirred at 90 oC in 2 hours and calcined at 900 oC in 1 hours. The surface area of the material was 13.384 m2/g. The properties of materials were also improved by mixing with Gadolinium doped ceria (GDC) at the ratio 7:3 (w/w). At this ratio, TEC of composite matched with electrolyte. The resistance of cathode was 0.17 – 0.2 Ω in the range of temperature from 580 – 700 oC. Microwave assisted sol – gel was an easy, economical and time – saving method to synthesis LSCF 6428 for Single Chamber - Solid oxide fuel cell (SC-SOFC) cathode application.

Effect of catalyst layer configuration on single chamber solid oxide fuel cell performance

The purpose of the current study is to numerically evaluate the effect of coplanar and perpendicular catalyst layer configurations on the performance of a single chamber solid oxide fuel cell (SC-SOFC). Three different catalyst layer configurations, coplanar, single-cell perpendicular and two-cell stack are used. Fuel is a mixture of hydrogen and air (50% hydrogen and 50% air by volume). An in-house computational fluid dynamics code is utilized to solve the nonlinear governing equations of mass, momentum, energy, charge balance and gas-phase species coupled with kinetics equations. Results show that the perpendicular catalyst layer configuration is more suitable for SC-SOFC than the coplanar configuration. This is due to shorter path of the oxygen ion transportation from cathode to anode in perpendicular compared to coplanar configuration. In addition, results indicate that adding another anode and cathode electrode on the other face of the electrolyte and providing a simple two-cell stack improve the cell performance. Finally, in order to present a suitable configuration of a SCSOFC two-cell stack, a parametric study is performed.

Laser induced densification of cerium gadolinium oxide: Application to single-chamber solid oxide fuel cells

In single-chamber solid oxide fuel cells (SC-SOFC), anode and cathode are placed in a gas chamber where they are exposed to a fuel/air mixture. Similarly to conventional dual-chamber SOFC, the anode and the cathode are separated by an electrolyte. However, as in the SC-SOFC configuration the electrolyte does not play tightness role between compartments, this one can be a porous layer. Nevertheless, it is necessary to have a diffusion barrier to prevent the transportation of hydrogen produced locally at the anode to the cathode that reduces fuel cell performances. This study aims to obtain directly a diffusion barrier through the surface densification of the electrolyte Ce0.9Gd0.1O1.95 (CGO) by a laser treatment. KrF excimer laser and Yb fiber laser irradiations were used at different fluences and number of pulses to modify the density of the electrolyte coating. Microstructural characterizations confirmed the modifications on the surface of the electrolyte for appropriate experimental conditions showing either grain growth or densified but cracked surfaces. Gas permeation and electrical conductivities of the modified electrolyte were evaluated. Finally SC-SOFC performances were improved for the cells presenting grain growth at the electrolyte surface.

Study on Direct Flame Solid Oxide Fuel Cell Using Flat Burner and Ethylene Flame

Solid-oxide fuel cells (SOFCs) have received significant attention due to their high efficiency, flexible fuel selection, low emissions in exhaust gases and relatively low cost. The SOFCs are also an alternative energy sources which operate at high temperature fuel cell technology [1-2]. Unlike lower temperature fuel cells, any carbon monoxide (CO) formed is transformed to carbon dioxide (CO2) at the high operating temperature, and so hydrocarbon fuels can be used directly through internal reforming or even direct oxidation. Conventional SOFCs are also excellent devices for efficient power generation. However, they are facing various challenges to overcome high cost, durability problems related to materials degradation and particularly the interconnecting and sealing materials. Single chamber SOFCs and direct flame solid oxide fuel cells (DFFCs) [3-4] are also alternative SOFC concepts that do not face the sealing problem. But the potential explosion in a single chamber SOFCs could be dangerous as a fuel oxidant mixture is fed to the high temperature fuel cell, especially if operating conditions are not well-defined. This problem can be avoided if DFFC is used where the fuel and oxidant are mixed at the point of use in a flame removing the dangerous dead of explosive mix. Besides, the DFFC provides simple cell configuration, rapid start-up and no external heater required, and it is suitable for portable applications. But the performance of the DFFC is still relatively poor, which hinders its practical applications. Therefore, the studies of DFFCs are important for designing the DFFCs for practical applications and investigating the appropriate operating conditions as well as improving the cell performance. In this study, a direct flame SOFC setup is designed and implemented based on fuel rich ethylene/air premixed flames to investigate the Ni-GDC (gadolinium-doped ceria) electrolyte supported fuel cell’s performance. The diameter of Ni-doped ceria anode and LSCF (lanthanum strontium cobalt ferrite)-GDC cathode layer is 10 mm and GDC-electrolyte is 20 mm. A flat flame burner (64 mm outer diameter) along with stainless steel stabilisation plate was used for the investigations. The stabilisation plate was placed above the burner surface and is used to stabilise the flame. The fuel cell was attached to the stabilisation plate in such a way that the anode facing to flame front and the cathode exposed to ambient air. Silver paste and wires were applied as current collectors to both sides of the fuel cells. Fig. 1 shows the schematic of the DFFC experimental setup. I-V (current-voltage), open circuit voltage (OCV), cell temperature and electrochemical impedance of the fuel cell were investigated under different operating conditions. The cell temperature was measured using a fine-wire R-type thermocouple against different ERs and distances between the burner surface and the fuel cell. The thermocouple was located 2 mm below the anode layer. The temperature was found are in the range of 628 -700 °C for the distance separations at 15 to 30 mm. It was observed that the temperature was decreased with increasing the distances. It can be explained by the fact that flame shape is largely distorted by the distance and more soot was formed in the inner flame. Relationship between OCV and cell temperature at various distances is shown in Fig. 2. Highest cell temperature and flame stability were observed for the ER of 1.52 at the distance separation 15mm. The fuel cell also exhibits an OCV of 0.84 V with the same condition. It was also found that the position of the fuel cell with respect to the flame have a significant effect on the cell temperature and the performance. The fuel cell achieved a peak power density of 41 mW/cm2 and a peak current density of 121 mA/cm2with ER at 1.52 and temperature at 700 °C. In near future different hydrocarbon fuels (e.g., methane and propane) and fuel cells can be used for the further investigations over a range of operating conditions.

Anode-supported single-chamber solid oxide fuel cell based on cobalt-free composite cathode of Nd0.5Sr0.5Fe0.8Cu0.2O3−δ–Sm0.2Ce0.8O1.9 at intermediate temperatures

As a candidate of cathode material of single-chamber solid oxide fuel cell (SC-SOFC), cobalt-free mixed ionic electronic conductor (MIEC) Nd0.5Sr0.5Fe0.8Cu0.2O3−δ (NSFCu) is synthesized by sol–gel method with ethylene diamine tetraacetic acid and citric acid as co-complexing agents. The XRD shows NSFCu is stable after CO2 treatment and chemical compatible with SDC at high temperatures. CO2-TPD (CO2-temperature programmed desorption) demonstrates both CO2 adsorption and desorption phenomenon on NSFCu surface. However, the polarization resistances (Rp) of NSFCu and SDC (10:4 in weight) composite electrodes showed no decay in 5% CO2. Single cell using N2–O2–CH4 mixed gas (CH4 to O2 ratio = 1.5) as fuel shows maximum power density of 635 mW cm−2 at 700 °C. These results suggest that NSFCu-SDC is a promising composite cathode material for application in single-chamber solid oxide fuel cell.

Flame-assisted fuel cells running methane

In this study, the flame-assisted fuel cell (FFC1) was investigated by using methane/air flames. The confrontation between FFC temperature and fuel concentration at various conditions was investigated which uncovered the complex behavior of FFCs performance. Variations in fuel/air equivalence ratio, fuel flow rate and distance between FFC and burner outlet were studied. A critical distance for FFC placement above the burner outlet was uncovered, which has a significant impact on FFC performance. A high power density of 791 mW cm−2 was achieved which is comparable to the dual chamber solid oxide fuel cell (SOFC) and single chamber SOFC. The short-term test exhibited good stability of the FFCs under operation despite the presence of carbon formation on the anode surface.