Solid Oxide Fuel Cell Anode Research Articles

Phase Field Modeling of Cubic to Tetragonal Transformation in YSZ and its Effect on Ionic Conductivity Degradation and Mechanical Damages

During the high-temperature operation of solid oxide fuel cells (SOFCs), the degradations of electrolyte material yttria-stabilized zirconia (YSZ) in both ionic conductivity and mechanical strength can be caused by the cubic to tetragonal phase transformation. In this work, microelasticity phase field model is built to simulate the YSZ phase transformation considering the effects of grain boundary and solid morphology. The YSZ skeleton in real SOFC anode is reconstructed using focused ion beam-scanning electron microscopy (FIB-SEM) dual-beam technique. The ionic conductivity degradation and the mechanical damages under external mechanical loads of brittle YSZ phase in anode are investigated based on the phase field simulation results. The simulation results may provide theoretical guidelines for improving the SOFC anode during fabrication.

Internal Conversion in the Membrane-Supported SOFC

Steam reforming is a highly endothermic process of hydrogen or synthesis gas production from methane or other hydrocarbon fuels. Metals from group VIII of the Periodic table are catalysts for steam reforming; nickel is the most commonly used among them. Platinoid catalysts: rhodium, ruthenium and palladium are more active, but less frequently used due to their high cost. Nickel catalysts have proven their effectiveness due to the simplicity of their production, stability and chemical activity [1]. It is known that the heat required for the endothermic process of steam reforming can be provided by an electrochemical reaction in a stack of high-temperature solid oxide fuel cells [2,3]. In the case of internal reforming, the process of steam reforming of methane proceeds directly at the anode of a solid oxide fuel cell (SOFC) due to the high operating temperature and the presence of nickel in the composition [4,5]. The advantage of internal reforming is not only thermal, but also chemical integration of reforming agent and generator – the water vapor produced during the SOFC anodic electrochemical reaction can be used for reforming without the need for anode recycling organization. Also, the endothermic effect of steam reforming can be used to control the temperature of the stack. As it was shown in work [6] feeding of the mixture containing 30% of methane into the electrolyte-supported SOFC stack to the input leads to 22% of methane observed at the output. Thus, based on the literature data, we cannot expect a high conversion rate in the process of internal methane reforming. Therefore, studies of the internal methane conversion process were carried out on an experimental short stack of two 100x100 mm electrolyte-supported SOFCs. A whole series of experiments were carried out on H2+CH4+H2O mixtures with different sets of conditions – an increase in the ratio and consumption of methane, and then a decrease in temperature. The ranges of methane consumption and other key parameters of the experiment were based on the results of the analysis of available literature data on the experimental study of the kinetics of methane steam conversion on cermet SOFC anodes. Prior to the experiments, discussions were mainly caused by the probable carbon deposition at the anodes and the associated rapid performance degradation, the capabilities of the anodes for internal conversion were upper estimated according to the fuel consumption of SOFCs, so it was assumed that, at worst case, the conversion provides only its internal consumption needs. The results of experiments at an operating temperature of 850°C showed that the kinetics of internal conversion was largely underestimated. The assembly of two SOFCs converts methane up to concentrations not exceeding the calculated equilibrium ones, up to the maximum available flow rate on the equipment used – 187 ml/min – even without current passing. This fuel flow rate is capable of providing a current of up to 53 A, while the rated operating current of these SOFCs is about 20 A, up to 30 A on methane-rich fuel. This means, that the conversion capabilities of SOFC even in the absence of current are at least twice higher than their own needs. The current further stimulates the conversion by generating additional steam. In order to discover the limits of conversion capabilities, the temperature was lowered to 750°C. The result of the conversion at maximum flow rate proceeding up to equilibrium values was repeated. Thus, in the course of the experiments, it was not possible to obtain methane concentrations in the exhaust gas that significantly exceed the equilibrium ones. This result turned out to be extremely unexpected and undoubtedly positive, since it demonstrates an extremely high potential of internal conversion and opens the way to a sharp decrease in the requirements for the degree of conversion of fuel supplied to SOFC, abandonment of a bulky fuel processor, reduction of costs for SOFC cooling and, thereby, an increase in efficiency and reducing the mass and dimensions of SOFC power plants. This work was carried out with financial support from the Russian Scientific Foundation, grant no. 17-79-30071.

Thermo-Mechanically Coupled Peridynamic Modelling of Fracture Formation in Solid Oxide Fuel Cell Anode

Fracture formation can be observed in brittle yttria-stabilized zirconia (YSZ) in Ni-YSZ composite anode during high-temperature operation of solid oxide fuel cells (SOFCs). It is quite difficult to predict the fracture formation in solid materials accurately based on the classical continuum mechanics theory, because of the singularity problems in partial differential equations. In this work, an ordinary state-based-peridynamic (OSB-PD) model is proposed to predict the fracture formation in SOFC anode based on real microstructures reconstructed using focused ion beam-scanning electron microscopy (FIB-SEM) dual-beam technique. The key factors determining anode microstructure strength is analyzed based on the simulation results upon the comparison among different anode microstructures. The thermo-mechanical coupling effect is investigated by considering the influence of both external mechanical loads and temperature distribution.

The 3D Reconstruction and Simulation of Solid Oxide Fuel Cell Anode

The 3D Focused Ion Beam - Scanning Electron Microscopy (FIB-SEM) technique has been used to study the ceramic microstructures with the accuracy of tens of nanometers. There are several reports about the 3D reconstruction about the Ni-YSZ electrode in SOFC or SOEC mode (1-3). In this work, samples taken from full size, 10×10 cm2, solid oxide fuel cell (SOFC) single cells were reconstructed with the FIB-SEM tomography. Three samples were chosen from the same production batch, including a cell without reduction, a cell with 5 hours reduction and a cell with 100 hours test with humidified hydrogen, respectively. Figure 1 shows the SEM micrograph and reconstructed anode for the cell after 100 hours test. Different from the button cells, the full size anode-supported SOFC need a strong support layer and a smaller porosity is also acceptable. The lattice Boltzmann method (LBM) was used to simulate the physical processed in the reconstructed porous electrode. The 3D microstructure was remeshed to cubic voxels for numerical analysis. The triple-phase-boundary length was automatically identified and the parameters in the exchange current density equation were fitted to the polarization curves. Detailed results will be submitted in the full length draft.

Jet Fuel Desulfurization for Portable Solid Oxide Fuel Cell Applications

Solid oxide fuel cells (SOFCs) are capable of utilizing energy-dense hydrocarbon fuels such as jet fuels for highly efficient power generation. Currently, a major challenge for using the jet fuel (e.g. JP8) in SOFC power systems is its sulfur content, which poisons the SOFC catalyst and anode. Sulfur contents in jet fuels could be as high as 3000 ppm although typical sulfur contents could be in the range from 550 and 750 ppm. The reduction of sulfur to <1 ppm is generally desired and required to ensure reliable SOFC operation. Various technologies have been developed to remove sulfur from jet fuel. However, most of these technologies are designed for large-scale desulfurization at industrial facilities or for stationary applications. Due to their complexity and substantial weight and size, these systems are not suitable for onboard integration with portable fuel cells. Therefore, our research aimed at developing a lightweight, compact desulfurization reactor for onboard applications. After several versions of improvements, including the use of selective laser sintering (SLS) 3D printing method, we have developed a miniature one-piece stainless-steel reactor which is capable of removing >99.5% sulfur in the jet fuel with the final sulfur concentrations close to a sub-ppm level. The reactor could be adapted to the desulfurization of other liquid hydrocarbon fuels such as gasoline and diesel. The reactor designs, desulfurizing materials, operation conditions and effectiveness of the technology will be discussed in this paper.

Comparative Study of the Performance of Syngas-Fueled Carbon-Air Solid Oxide Fuel Cells Using Anodes Based on M-Doped CeO2 (M: Mo or Mo-Cu)

The use of syngas to feed solid oxide fuel cells (SOFCs) appears as an attractive alternative due to the possibility of being obtained from renewable sources such as biomass or from other solids of carbonaceous composition such as solid wastes through reforming reactions. The use of syngas in SOFCs has been studied in several previous works, directing the efforts to obtain an anode material with the appropriate electrocatalytic activity for the electrooxidation of syngas, able to tolerate carbon deposition and avoid sulfur poisoning [1]. The Ni-YSZ anode has been studied in the electrooxidation of syngas, being one of its advantages the catalysis of the water gas shift (WGS) reaction, generating more H2 with respect to CO and therefore improving the reaction kinetics [2]. One of the disadvantages presented by Ni-YSZ is the decrease of its performance in long term tests, due to the catalytic activity of Ni towards the reverse Boudouard reaction, so that carbon deposits block the triple phase boundaries (TPBs) of the anode [3]. CeO2-based materials are suitable for use as anodes in fuel cells fed with carbonaceous fuels due to their resistance to carbon deposition and sulfur poisoning [4, 5]. Recently it has been reported that the addition of molybdenum to CeO2 (Mo-doped CeO2 or CMO) confers catalytic activity to the carbon gasification reaction and an increase in the electrical conductivity of CeO2 [6]. Furthermore, it has been reported that the addition of copper nanoparticles to Mo-doped CeO2 increases about 10 times its electrical conductivity [7].Two nanomaterials for SOFC anodes were synthesized: Mo-doped CeO2 (CMO) and Cu,Mo-doped CeO2 (CMCuO). Both nanomaterials were synthesized by the combustion method with 10 wt.% total metal loading following the experimental procedures detailed in [6] and [7] correspondingly. The SOFCs were fabricated using a CMO-YSZ or CMCuO-YSZ composite as anode, a dense YSZ electrolyte and a LSM-YSZ cathode. Both SOFCs were fed with air at the cathode and humidified syngas at the anode (syngas + 3 vol.% H2O). The morphology of the SOFCs was studied by SEM, while the crystal structure and chemical stability of the materials were studied by XRD and EDS. The cells were characterized by EIS at OCV condition at different temperatures and syngas concentrations, while the cell performance was studied by linear sweep voltammetry.An ADIS analysis obtained from the EIS data for both fuel cells in Figure 1 clearly shows the presence of two phenomena at high frequencies related to the electrooxidation reactions of H2 and CO, these phenomena are sensitive to temperature changes, the differences in their charge transfer resistance values suggest that both reactions are carried out with different kinetics. The processes shown at low frequencies are related to diffusional limitations of each gas towards triple phase boundaries (TPBs), processes sensitive to changes in syngas concentration. Cell tests, operating at 800°C, showed a maximum electrical power density of 114 mW cm-2 at a current density of 208 mA cm-2 and a cell voltage of 549 mV for SOFC with CMO-YSZ anode and a maximum electrical power density of 120 mW cm-2 at a current density of 200 mA cm-2 and a cell voltage of 600 mV for SOFC with CMCuO-YSZ. The addition of copper to the CMO produces a slight improvement in the electrocatalytic activity of the material and reduced ohmic resistance by almost 50% (see Figure 2), however the ASR of the cell with CMCuO anodes does not show a substantial improvement with respect to the cell with CMO anodes. In addition, the ohmic resistance is the most important component in the ASR of both cells. SEM images of the cells after tests show that the CMCuO anode surface exhibits fractures and delamination of the material, which is not observed on the CMO anode surface. The X-ray diffraction spectra do not show the presence of new phases in any of the two anode materials so the delamination of the CMCuO anode is related to the differences in thermal expansion coefficients (TECs) of the materials whose value must be measured to prove this hypothesis.[1] T.M. Gür (2013) Chem. Rev., 113(8), 6179-6206.[2] O. Costa Nunez et al. (2005) J. Power Sources, 141(2), 241-249.[3] T.M. Gür et al. (2010) J. Power Sources, 195(4), 1085-1090.[4] I. Sreedhar et al. (2019), J. Electroanal. Chem., 848, 113315.[5] N. Mahato et al. (2015) Prog. Mater. Sci., 72, 141-337.[6] I. Díaz‐Aburto et al. (2019) Fuel Cells, 19(2), 147-159.[7] I. Díaz-Aburto et al. (2021), J. Electrochem. Sci. Technol., [epub ahead of print: https://doi.org/10.33961/jecst.2020.01571]. Figure 1

Optimization of Methane Reforming for High Efficiency and Stable Operation of SOFC Stacks

: Solid Oxide Fuel Cells (SOFCs) is an efficient and clean pathway to generate electricity. In addition to hydrogen, SOFCs also provide the possibility for the utilization of a variety of carbon containing fuels. However, the application of carbon-based fuels in SOFC remains to be further studied. In this study, an external reformer was used to create appropriate reforming syngas from methanol and avoid carbon deposition. The performance and the efficiency of SOFC were researched with methanol-reformed syngas as fuel. The thermodynamic calculation and experimental work of water vapor reforming reaction of methanol fuel were carried out to study the composition of reforming gas under different temperature and steam-carbon ratio conditions, where the experimental results and the computational results matched well. The mole fraction of hydrogen in reformed syngas was about 55% within the temperature of 700~800 ℃, nevertheless, this value reached 70% if the moisture was removed. Therefore, the reformed syngas should be applied to SOFCs before being condensed and dried. Based on the comparison between the experimental results and the calculated ones, the appropriate components were selected to prepare the reforming syngas, feeding into the anode of SOFC to test the performance and the efficiency. Optimal temperature and steam-carbon ratio conditions for methanol vapor reforming were obtained. Under these conditions, the power density of SOFC exceeded 0.4 W/cm2 and the efficiency reached 50% (LHV). The main conclusions confirmed the high efficiency and feasibility of the methanol-fueled SOFC power generation system.

Catalyst-Exsolving Anode-Supported Solid Oxide Fuel Cell

Exsolution is the process in which cations that make up the lattice of a mixed ionic/electronic conductor (MIEC) are reduced to metals and migrate to the surface of the host ceramic. These materials have become quite attractive for solid oxide fuel cells (SOFCs) because they can facilitate oxygen and electron transport through their bulk and act as electrocatalysts on the surface of SOFC anodes. Also, because of the nature of the exsolution process, the highly dispersed nano-catalysts have strong particle-host interactions which have shown resistance to common SOFC failure mechanisms such as agglomeration and coking. However, the practical application of such materials has not been well studied since most research focuses on the electrolyte-supported cells, which offer a quick method for screening electrochemical activity but the large ohmic resistance makes this cell unrealistic for real energy conversion devices, especially at lower temperatures.Here, we use a scalable ceramic processing technique to fabricate a ceramic-anode-supported SOFC that exsolves nano-catalysts for low temperature operation (600°C). SrFe0.2Ni0.4Mo0.4O3- δ (SFNM) is used as the anode material due to its high conductivity and exsolution ability. By shifting the mechanically supporting layer from the electrolyte to this anode, we are able to drastically reduce the overall ohmic resistance of the cell. Additionally, we avoid extra processing steps for conventional catalyst deposition by taking advantage of the in-situ catalyst exsolution. During the exsolution process, we show that our cell performance increases over time, up to a peak power density of 300 mW/cm2 at 600°C with H2 fuel. Further, we discuss two major challenges facing exsolution-anode-supported SOFCs along the way and we show our efforts to identify and address the root causes of these problems.

Electrochemical Characteristics of SOFC Anodes Operated at High Fuel Utilization

High energy conversion efficiency in solid oxide fuel cell (SOFC) systems can be achieved by improving the fuel utilization. However, when the SOFCs are operated under high fuel utilization, the downstream part of the anode is exposed to high steam concentration and hence high P(O2) atmospheres, and this has a negative impact on the stability of Ni-based cermet anodes. At this stage, no reports dealt with the degradation phenomena of the anode under such severe conditions. In this study, we aimed to clarify degradation phenomena at the downstream part of practical cells operated at high fuel utilizations by using bottom cells. Fuel gases that simulated severe conditions were supplied to single cells. The change in electrochemical properties was monitored during discharge operation, and the microstructural evolution of the anode was quantitatively analyzed by the FIB–SEM technique.

Simulation of a Flat-Tube Solid Oxide Fuel Cell with Symmetric Double-Sided Cathode Considering Different Fuel Compositions

Due to its high operating temperature, solid oxide fuel cells (SOFCs) can use a variant of hydrocarbon fuels. Then the methane steam reforming (MSR) and water gas shift (WGS) reactions are active within the anode during the energy conversion process. On one hand, the air velocity controls the heat within a SOFC, e.g., through control of heat convection, on the other hand, the internal endothermal reactions also have an impact on the heat balance through different fuel composition. It should be noted that the carbon deposition greatly reduces the catalytic property of the anode material.The reforming process can be synthetized by the following electrochemical reactions:2CO ↔ C(s)+ CO2 (1)CO+H2 ↔ C(s)+H2O (2)C n H2n+2 ↔ nC(s)+(n+1)H2 (3)Thus, it is important to investigate the effect of internal reforming reactions of different fuel composition on cell performance.Numerical simulations can reduce the cost of experimental design and achieve desirable accuracy. A flat-tube SOFC with a symmetric double-sided cathode is built using the commercial software COMSOL Multiphysics®. Our model includes the simulation of the ion, electron, momentum, heat, and mass transport phenomena. Also, MSR and WGS reactions are considered in the model. The geometric representation of the flat-tube SOFC anode is shown in Figure 1. Figure 1

Highly Active and Stable a-Site Deficient La0.4Sr0.4Ti0.94Ni0.06O3-δ SOFC Anode Material with in-Situ Exsolved of Ni Nanoparticles

La-doped strontium titanates with a perovskite structure are promising candidates of the anode materials for solid oxide fuel cells (SOFCs) owing to their good chemical compatibility with other components and superior redox-stability. Among these La-doped SrTiO3 (LST), A-site deficient LST materials have attracted much interest due to their improved electrochemical characteristics. Recently, exsolution in A-site deficient LST has been intensively studied, because catalytic active and durable metal nanoparticles can be exsolved on the LST surface. In this study, we developed the A-site deficient Ni-doped La0.4Sr0.4TiO3 (LSTN)-Ce0.9Gd0.1O1.95 (GDC) composite anodes, and investigate their electrochemical performance and redox stability on La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte-based SOFCs. The maximum power density(MPD) of LSTN44-GDC anode based cell was 0.698 mW cm-2 at 900℃ in wet H2 fuel (3% H2O). Also, during redox cyclic tests combined with long-term stability test, The LSTN44-GDC cell maintained its performance without any degradation. All these results demonstrate that the A-site deficient LSTN-GDC is a promising material for an efficient and stable SOFC anode.

Application of High-Temperature Raman Spectroscopy (RS) for Studies of Electrochemical Processes in Solid Oxide Fuel Cells (SOFCs) and Functional Properties of their Components

SOFC efficiency is directly determined by the electrodes, optimization of which is related to the study of the mechanisms of electrochemical current-generating reactions taking place. Such studies are tricky due to the high operating temperature of SOFCs, high current loads, and corrosive gas media. A promising research method is Raman spectroscopy (RS) under operating conditions of SOFC. At ISSP RAS, a combined experimental technique and setup have been created that combines the capabilities of traditional electrochemical methods, as well as high-temperature Raman spectroscopy [1]. In order to study the processes in the electrochemically active zone, a special geometry of samples was developed on basis of optically transparent single crystal membranes of an anionic conductor with a counter-electrode of a toroidal shape. With the use of this combined technique and special geometry of samples in previous works, studies of the kinetics of reduction and morphological changes of nickel in composite SOFC anodes were carried out. It was shown that the first reduction cycle differs significantly from the subsequent ones both in the initial delay and in the total time of the process. SEM studies have shown that these changes are associated with a morphological rearrangement that occurs during the first reduction cycle: the grain size of NiO is significantly reduced compared to the initial one. For model SOFCs investigated in the OCV mode [2] after the initial microstructural rearrangement in the redox cycle, the behavior of standard cermet anodes in a H2–N2 flowing atmosphere can be described using Avrami model. The influence of the composition of fuel on Raman spectra obtained from the internal interface in the current load mode was also investigated [3], and the correlations of obtained data with the cell voltage were studied. It was shown that the corresponding mechanisms that determine the reaction kinetics can be associated with the transfer of ions through the GDC|YSZ. Subsequent rate limiting steps such as electrochemical oxidation of hydrogen in the Ni-GDC layer are undetectable for the geometry under test due to the limited penetration depth of the laser beam. Comparative studies of model SOFCs with a supporting anode substrate (ASC) and a supporting solid electrolyte (ESC) were carried out using the in-situ RS technique [4]. It was shown that the addition of the GDC indicator layer makes it possible to carry out an in-situ study of the chemical potential of oxygen at the internal interface of the anode|electrolyte depending on current load or fuel mixture, but the GDC/YSZ two-layer thin-film electrolyte exhibits electronic or gas leakage due to poor stability in a reducing atmosphere. Despite the significantly lower internal resistance compared to the ESC, the quality of the ASC thin film membrane severely limits research depending on the operating temperature, current load and fuel composition. In this case, the use of thin-film membranes significantly reduces the effect of 8YSZ on the Raman spectra of the internal interface. After post-processing and normalization, the obtained Raman spectra show a similar effect of the current load or the hydrogen content in the fuel gas mixture on the GDC peak area (460 cm-1). The linear dependence of the OCV on the peak area of ~460 cm-1 makes it possible to assess the relationship between changes in the peak area and the evolution of the chemical potential of oxygen at the anode under a current load. Comparative analysis of the anodic impedance for different fuel mixtures suggests that spectroscopic measurements of the internal interfaces provide direct information on the contribution of the fuel oxidation reaction to the total losses in SOFC. In addition to studies of complete fuel cells, high-temperature Raman spectroscopy is used to study the structure of single-crystal samples of anionic conductors [5], including at the operating temperature of SOFCs. High-temperature RS allows one to obtain additional information on the microstructure of samples both at room temperature and at working temperature, where most other research methods do not allow research. New combined technique was used to study other components of high-temperature electrochemical devices: sealing glasses [6] for SOFCs and optical glasses [7]. This work was supported by Russian Scientific Foundation, grant no. 17-79-30071.[1] D.A.Agarkov et al. ECS Trans., vol.68, iss.1, pp.2093-2103 (2015).[2] D.A.Agarkov et al. Solid State Ionics, vol.302, pp.133-137 (2017).[3] D.A.Agarkov et al. Solid State Ionics, vol.319C, pp.125-129 (2018).[4] D.A.Agarkov et al. Solid State Ionics, vol.344, p.115091 (2020).[5] D.A.Agarkov et al. Solid State Ionics, vol.346, p.115218 (2020).[6] A.Allu et al. ACS Omega, vol.2, pp.6233-6243 (2017).[7] M.K.Kokila et al. Solid State Sciences, vol.107, p.106360 (2020). Figure 1

Exsolution of Ni Nanoparticles from A-Site-Deficient Layered Double Perovskites for Dry Reforming of Methane and as an Anode Material for a Solid Oxide Fuel Cell.

Exsolution is a promising technique to design metal nanoparticles for electrocatalysis and renewable energy. In this work, Ni-doped perovskites, (Pr0.5Ba0.5)1-x/2Mn1-x/2Nix/2O3-δ with x = 0, 0.05, 0.1, and 0.2 (S-PBMNx), were prepared to design exsolution systems as solid oxide fuel cell anodes and for catalysis applications. X-ray diffraction and transmission electron microscopy (TEM) analyses demonstrated that correlating A-site deficiency with Ni content can effectively induce exsolution of all Ni under H2 atmosphere at T ∼ 875 °C, yielding the reduced (exsolved) R-PBMNx materials. On heating the exsolution systems in air, metal incorporation in the oxide lattice did not occur; instead, the Ni nanoparticles oxidized to NiO on the layered perovskite surface. The lowest area-specific resistance (ASR) under wet 5% H2/N2 in symmetrical cells was observed for R-PBMN0.2 anode (ASR ∼ 0.64 Ω cm2 at 850 °C) due to the highest Ni particle density in the R-PBMNx series. The best performance for dry reforming of methane (DRM) was also obtained for R-PBMN0.2, with CH4 and CO2 conversion rates at 11 and 32%, respectively, and the highest production of H2 (37%). The DRM activity of R-PBMN0.2 starts at 800 °C and is sustained for up to at least 5 h operation with little carbon deposition (0.017 g·gcat-1·h-1). These results clearly demonstrate that varying Ni-doping in layered double perovskite oxides is an effective strategy to manipulate the electrochemical performance and catalytic activity for energy conversion purposes.

Exploring the Role of Humidity, Temperature, and Mixed Ionic and Electronic Conductivity on SOFC Anode Electrocatalysis

Infiltration of nanoscale electrocatalysts into Ni/yttria-stabilized zirconia (Ni-YSZ) cermets has been shown to improve the electrochemical performance of solid oxide fuel cell (SOFC) anodes. While infiltrated electrodes in SOFCs result in improved cell performance, long-term operation leads to coarsening of the infiltrated nanoparticles and negates the short-term performance improvements. This study explores the roles of humidity, temperature, and number of cycles of nanocatalyst infiltration in improving mixed conduction within the Ni-YSZ electrode. Two mixed conduction phases were studied: Gd0.1Ce0.9O2-δ (GDC) as an infiltrant into Ni-YSZ electrodes, and Ni/transition metal doped-YSZ electrodes infiltrated with Ni. Analysis of impedance data from these cells shows improved electrochemical performance in infiltrated cells with mixed conduction compared with infiltrated cells containing purely ionic and electronic conducting phases. Improved anode performance is attributed to the availability of electronic pathways through predominantly ionic-conducting phases to connect distant Ni nanoparticles and/or Ni grains.

Artificial intelligence technique based performance estimation of solid oxide fuel cells

In General, a larger number of experimental data would be required for optimizing the performance efficiency of the electrodes in solid oxide fuel cells (SOFC), as it was likely to involve many complex chemical and physical reactions. Therefore, in this study, we have attempted the artificial intelligence (AI) technique for analyzing the performance of the anode and cathode electrodes of SOFC under various key parameters that normally influences the efficiency of the electrodes. Since the cost of SOFC elements is expensive, computational trials with the aid of AI would not only be curtailing the preparation cost but also ensures less time consumption. Among the variety of AI methods available in the literature, the Support Vector Machine (SVM) appears to be one of the excellent and effective machine learning techniques. Hence, we have developed a SVM model and predicted the maximum current density and power density of Nickel oxide-samarium-doped ceria (NiO-SDC) composite anode and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode electrodes of SOFC. The input parameters such as stack temperature, supply voltage were supplied to the SVM model and obtained maximum current density and power density as output and it decides the working performance of the electrodes. We have also predicted that the maximum current density and power density of 1160 mA cm2 and 225 mW cm2 respectively at 800 °C. To validate the results as predicted from SVM, we have experimented using Yttrium stabilized zirconia electrolyte-supported single cell with our prepared NiO-SDC anode and LSCF cathode which exhibited a maximum current and power density of 1170 mA cm2 and 227 mW cm2 at 800 °C using H2 as fuel. It has been found that that the theoretical predicted data current and power densities of the electrodes from the SVM approach reasonably agrees well with the experimental results.

A-Asterisk Algorithm as an Alternative to Evaluate the Geometric Tortuosity in Digitally Created SOFC Anodes

A solid oxide fuel cell (SOFC) contains complex materials that facilitate the energy conversion process. The diffusion media play an important role in facilitating the reactant gases to reach the electrochemical active regions. Porosity and tortuosity are crucial parameters describing the diffusion to be analyzed in a SOFC anode. This paper aims to evaluate the feasibility of using the A-asterisk algorithm to compute the geometric tortuosity within SOFC anodes. A three-dimensional structure, which is digitally created, represents the SOFC anode, in which the possible paths that follow the fluid flow are analyzed. A-asterisk algorithm is used to generate possible paths, and therefore the geometric tortuosity can be computed considering an averaged distance. A tortuosity-porosity correlation is proposed, and the results are compared with previous studies. Results show that the A-asterisk algorithm is a capable algorithm to evaluate the geometric tortuosity values in SOFC anodes with different particle size distribution and porosities.

Thermo-Mechanically Coupled Peridynamic Modelling of Fracture Formation in Solid Oxide Fuel Cell Anode

Fracture formation can be observed in brittle yttria-stabilized zirconia in Ni-YSZ composite anode during high-temperature operation of solid oxide fuel cells. It is difficult to predict the fracture formation in brittle solid materials accurately based on the classical continuum mechanics theory because of the singularity problems in partial differential equations. An ordinary state-based-peridynamic model is proposed to predict the fracture formation under external loads in SOFC anode in micro-scale using focused ion beam-scanning electron microscopy dual-beam technique in this work. The thermo-mechanical coupling effect is also investigated by simulating the formation and propagation of macro-scale crack in single cell under thermal shock.

The 3D Reconstruction and Simulation of Solid Oxide Fuel Cell Anode

The 3D Focused Ion Beam - Scanning Electron Microscopy (FIB-SEM) technique has been used to study the ceramic microstructures with the accuracy of tens of nanometers. Samples taken from commercial size, 10×10 cm2, solid oxide fuel cell (SOFC) single cells were reconstructed with the FIB-SEM tomography. Three samples were chosen from the same production batch, including a cell without reduction, a cell with 5 hours reduction, and a cell with 80 hours high temperature test with humidified hydrogen, respectively. The triple-phase-boundary length and volume fractions were identified for the samples. The lattice Boltzmann method (LBM) was used to simulate the physical processed in the reconstructed porous electrode. The parameters in the exchange current density equation were fitted to the polarization curves.

Electrochemical Characteristics of SOFC Anodes Operated at High Fuel Utilization

High energy conversion efficiency in solid oxide fuel cell (SOFC) systems can be achieved by improving the fuel utilization. However, when the SOFCs are operated under high fuel utilization, the downstream part of the anode is exposed to high steam concentration and hence high P(O2) atmosphere. This has a negative impact on the stability of Ni-based cermet anodes. At this stage, no reports dealt with the degradation phenomena of the anode under such severe conditions. In this study, we aimed to clarify degradation phenomena at the downstream part of practical cells operated at high fuel utilizations by using bottom cells. The change in electrochemical properties of single cells was monitored during discharge operation with supplying fuel gases that simulated severe conditions.

Jet Fuel Desulfurization for Portable Solid Oxide Fuel Cell Applications

Solid oxide fuel cells (SOFCs) are capable of utilizing energy-dense hydrocarbon fuels such as jet fuels for highly efficient power generation. Currently, a major challenge for using the jet fuel (e.g. JP-8) in SOFC power systems is its sulfur content, which poisons the SOFC anode and fuel reforming catalysts. The reduction of sulfur to <1 ppmw is generally desired and required to ensure reliable SOFC operation. Our research aimed at developing a lightweight, compact desulfurization reactor for onboard application in portable fuel cell systems. After several versions of improvements, including the use of a selective laser sintering (SLS) 3D printing method, we have developed a miniature one-piece stainless-steel reactor which can remove >99.5% sulfur in the jet fuel with the final sulfur concentrations close to a sub-ppm level. The reactor could be adapted to the desulfurization of other liquid hydrocarbon fuels such as gasoline and diesel.