Feasibility of palm‐biodiesel fuel for a direct internal reforming solid oxide fuel cell

The feasibility of a direct internal reforming (DIR) solid oxide fuel cell (SOFC) running on wet palm‐biodiesel fuel (BDF) was demonstrated. Simultaneous production of H₂‐rich syngas and electricity from BDF could be achieved. A power density of 0.32 W cm^?2 was obtained at 0.4 A cm^?2 and 800 °C under steam to carbon ratio of 3.5. Subsequent durability testing revealed that a DIR‐SOFC running on wet palm‐BDF exhibited a stable voltage of around 0.8 V at 0.2 A cm^?2 for more than 1 month with a degradation rate of approximately 15 % / 1000 h. The main cause of the degradation was an increase in the ohmic resistance. Copyright © 2012 John Wiley & Sons, Ltd.     

Two-dimensional dynamic simulation of a direct internal reforming solid oxide fuel cell

This study presents a two-dimensional mathematical model of a direct internal reforming solid oxide fuel cell (DIR-SOFC) stack which is based on the reforming reaction kinetics, electrochemical model and principles of mass and heat transfer. To stimulate the model and investigate the steady and dynamic performances of the DIR-SOFC stack, we employ a computational approach and several cases are used including standard conditions, and step changes in fuel flow rate, air flow rate and stack voltage. The temperature distribution, current density distribution, gas species molar fraction distributions and dynamic simulation for a cross-flow DIR-SOFC are presented and discussed. The results show that the dynamic responses are different at each point in the stack. The temperature gradients as well as the current density gradients are large in the stack, which should be considered when designing a stack. Further, a moderate increase in the fuel flow rate improves the performances of the stack. A decrease in the air flow rate can raise the stack temperature and increase fuel and oxygen utilizations. An increased output voltage reduces the current density and gas utilizations, resulting in a decrease in the temperature.     

Development of paper-structured catalyst for application to direct internal reforming solid oxide fuel cell fueled by biogas

A flexible paper-structured catalyst (PSC) that can be applied to the anode of a solid oxide fuel cell (SOFC) was examined for its potential to enable direct internal reforming (DIR) operation. The catalytic activity of three types of Ni-loaded PSCs: (a) without the dispersion of support oxide particles in the fiber network (PSC-A), (b) with the dispersion of (Mg,Al)O derived from hydrotalcite (PSCB), and (c) with the dispersion of (Ce,Zr)O_2-δ (PSCC), for dry reforming of CH₄ was evaluated at operating temperatures of 650–800 °C. Among the PSCs, PSC-C exhibited the highest CH₄ conversion with the lowest degradation rate. The electrochemical performance of an electrolyte-supported cell (ESC) was evaluated under the flow of simulated biogas at 750 °C for cases without and with the PSCs on the anode. The application of the PSCs improved the cell performance. In particular, PSC-C had a remarkably positive effect on stabilizing DIRSOFC operation fueled by biogas.     

Performance analysis of a solid oxide fuel cell with reformed natural gas fuel

In the present study a two‐dimensional model of a tubular solid oxide fuel cell operating in a stack is presented. The model analyzes electrochemistry, momentum, heat and mass transfers inside the cell. Internal steam reforming of the reformed natural gas is considered for hydrogen production and Gibbs energy minimization method is used to calculate the fuel equilibrium species concentrations. The conservation equations for energy, mass, momentum and voltage are solved simultaneously using appropriate numerical techniques. The heat radiation between the preheater and cathode surface is incorporated into the model and local heat transfer coefficients are determined throughout the anode and cathode channels. The developed model has been compared with the experimental and numerical data available in literature. The model is used to study the effect of various operating parameters such as excess air, operating pressure and air inlet temperature and the results are discussed in detail. The results show that a more uniform temperature distribution can be achieved along the cell at higher air‐flow rates and operating pressures and the cell output voltage is enhanced. It is expected that the proposed model can be used as a design tool for SOFC stack in practical applications. Copyright © 2009 John Wiley & Sons, Ltd.     

CeO2 coated NaFeO2 proton-conducting electrolyte for solid oxide fuel cell

Nowadays, the low-temperature operation has become an inevitable trend for the development of SOFCs. Transition metal layered oxides are considered as promising electrolyte materials for low-temperature solid oxide fuel cells (LT-SOFCs). In this work, we report the CeO₂ coated NaFeO₂ as an electrolyte material for LT-SOFC. The study results revealed that the piling of CeO₂ significantly influenced the open-circuit voltage (OCV) as well as the power output of the fuel cells. In comparison with pure NaFeO₂, the denser structure of CeO₂ coated NaFeO₂ leads to higher OCV (1.06 V, 550 °C). The electrochemical impedance spectrum (EIS) fitted results showed that NaFeO₂–CeO₂ composites possessed higher ionic boundary conductivity. This is because that the hetero-interfaces between NaFeO₂ and CeO₂ provide fast ion conducting path. The high ionic conductivity of CeO₂ coated NaFeO₂ lead to admirable fuel cell power output of 727 mW cm^?2 at 550 °C.     

Numerical modeling and parametric analysis of solid oxide fuel cell button cell testing process

In laboratory studies of solid oxide fuel cell (SOFC), performance testing is commonly conducted upon button cells because of easy implementation and low cost. However, the comparison of SOFC performance testing results from different labs is difficult because of the different testing procedures and configurations used. In this paper, the SOFC button cell testing process is simulated. A 2‐D numerical model considering the electron/ion/gas transport and electrochemical reactions inside the porous electrodes is established, based on which the effects of different structural parameters and configurations on SOFC performance testing results are analyzed. Results show that the vertical distance (H) between the anode surface and the inlet of the anode gas channel is the most affecting structure parameter of the testing device, which can lead to up to 18% performance deviation and thus needs to be carefully controlled in SOFC button cell testing process. In addition, the current collection method and the configuration of gas tubes should be guaranteed to be the same for a reasonable and accurate comparison between different testing results. This work would be helpful for the standardization of SOFC button cell testing.     

A non-sealed solid oxide fuel cell micro-stack with two gas channels

Non-sealed solid oxide fuel cell (NS-SOFC) micro-stacks with two gas channels were fabricated and operated successfully under various CH₄/O₂ gas mixtures in a box-like stainless-steel chamber. The cells with an anode-facing-cathode configuration were connected in serial by zigzag sliver sheets. Each cell consisted of the Ni/yttria-stabilized zirconia (YSZ) anode, the YSZ electrolyte, and the Sm_0.2Ce_0.8O_1.9-impregnated (La_0.75Sr_0.25)_0.95MnO₃ cathode. In this configuration, to ensure the identical gas distribution over the electrode surfaces, two gas channels with small vents flanking the stacks were used as gas channels of methane and oxygen for anodes and cathodes, respectively. The selectivity requirement of both the anode and cathode for the oxidation and reduction of CH₄ and O₂ was lowered and the sheets could extend the residence time of gas flow over the electrode surface. By the direct flame heat with a liquefied petroleum gas burner, the stacks presented a rapid start-up and full utilization of the exhaust gas. Eventually, an open-circuit voltage (OCV) of 1.8 V and maximum power output of 276 mW was produced by a two-cell stack. For a four-cell stack, a maximum power output of 373 mW was obtained.     

NiMo-calcium-doped ceria catalysts for inert-substrate-supported tubular solid oxide fuel cells running on isooctane

A calcium-doped ceria (Ce_1-xCa_xO_2−δ, 0 ≤ x ≤ 0.3) has been applied as a ceramic support in NiMo-based catalysts for an internal reforming tubular solid oxide fuel cell running on isooctane. Introducing calcium into the CeO₂-based ceramic was found to improve conductivity of Ce_1-xCa_xO_2−δ. The Ce_0.9Ca_0.1O_2−δ (x = 0.10) sample exhibited an optimum conductivity of 0.045 S cm⁻¹ at 750 °C. The transport of oxygen ions in Ce_1-xCa_xO_2−δ promoted the catalytic partial oxidation of isooctane in the NiMo–Ce_1-xCa_xO_2−δ catalyst, which increased the fuel conversion as well as H₂ and CO yields. As a result, the NiMo–Ce_0.9Ca_0.1O_2−δ (x = 0.10) catalyst exhibited a high isooctane conversion of 98%, and the H₂ and CO yields achieved 74% and 83%, respectively, for reforming of isooctane and air at the O/C ratio of 1.0 at 750 °C. Furthermore, the NiMo–Ce_0.9Ca_0.1O_2−δ catalyst has been applied as an internal reforming layer for an inert-substrate-supported tubular solid oxide fuel cell running on isooctane/air. Due to its high reforming activity, the single cell presented an initial maximum power density of 355 mW cm⁻² in isooctane/air at 750 °C and displayed stable electrochemical performance during ~30 h operation. These results demonstrated the application feasibility of the NiMo–Ce_0.9Ca_0.1O_2−δ catalyst for direct internal reforming solid oxide fuel cells running on isooctane/air.     

Improvement of solid oxide fuel cell performance by a core-shell structured catalyst using low concentration coal bed methane fuel

A core-shell structured catalyst Ni-BaO-CeO₂@SiO₂ (@NBC; 7.87% Ni content) with high catalytic activity and thermal stability is prepared and utilized for partial oxidation of methane. The catalyst is introduced into the Ni-8 mol% Y-stabilized ZrO₂ anode of a conventional solid oxide fuel cell (CC) by direct spraying (denoted as P-@NBC//CC) and indirect loading as an independent catalyst layer (denoted as Y-@NBC//CC) to improve the coking resistance and cell stability when low concentration coal bed methane is used. At 800°C, the maximum power density of P-@NBC//CC and Y-@NBC//CC increases by ~26.8% and 32.8%, respectively, over that of CC (0.63 W cm⁻²). At a discharge current of 0.16 A at 800°C, the voltage of CC drops to 0 V after 16 hours. In contrast, the voltage of P-@NBC//CC decreases from 0.8 to 0.6 V within 30 hours, and that of Y-@NBC//CC decreases from 0.8 to 0.7 V over 180 hours. The manner of loading of the catalyst layer has a significant effect on the cell stability. The indirect loading mode as an independent catalyst layer has an advantage over the direct spraying method. The postmortem microstructure of the cell reveals that direct spray loading on the anode surface allows the catalyst particles to penetrate into the anode layer and blocks the anode pores, resulting in a lower porosity and higher diffusion resistance.     

Durability of direct internal reforming of methanol as fuel for solid oxide fuel cell with double-sided cathodes

Direct internal reforming of methanol is applied as fuel for a Ni-YSZ anode-supported solid oxide fuel cell with a flat tube based on double-sided cathodes. It achieves a power density (PD) of 0.25 W/cm² at 0.8 V, reaching about 90% of that is fueled by H₂. And the cell has been operated for more than 120 h by the direct internal reforming of methanol. The durability and apparent advantage for using humidified methanol may lead to widespread applications by direct internal reforming method for this new designed SOFC in the future.     

Fabrication of hydrogen electrode supported cell for utilized regenerative solid oxide fuel cell application

A utilized regenerative solid oxide fuel cell (URSOFC) provides the dual function of performing energy storage and power generation, all in one unit. When functioning as an energy storage device, the URSOFC acts like a solid oxide electrolyzer cell (SOEC) in water electrolysis mode; whereby the electric energy is stored as (electrolyzied) hydrogen and oxygen gases. While hydrogen is useful as a transportation fuel and in other industrial applications, the URSOFC also acts as a solid oxide fuel cell (SOFC) in power generation mode to produce electricity when needed. The URSOFC would be a competitive technology in the upcoming hydrogen economy on the basis of its low cost, simple structure, and high efficiency. This paper reports on the design and manufacturing of its anode support cell using commercially available materials. Also reported are the resulting performance, both in electrolysis and fuel cell modes, as a function of its operating parameters such as temperature and current density. We found that the URSOFC performance improved with increasing temperature and its fuel cell mode had a better performance than its electrolysis mode due to a limited humidity inlet causing concentration polarization. In addition, there were great improvements in performance for both the SOFC and SOEC modes after the first test and could be attributed to an increase in porosity within the oxygen electrode, which was beneficial for the oxygen reaction.     

Performance analysis of a tubular solid oxide fuel cell with an indirect internal reformer

A 2‐D steady‐state mathematical model of a tubular solid oxide fuel cell with indirect internal reforming (IIR‐SOFC) has been developed to examine the chemical and electrochemical processes and the effect of different operating parameters on the cell performance. The conservation equations for energy, mass, momentum as well as the electrochemical equations are solved simultaneously employing numerical techniques. A co‐flow configuration is considered for gas streams in the air and fuel channels. The heat radiation between the preheater and reformer surface is incorporated into the model and local heat transfer coefficients are determined throughout the channels. The model predictions have been compared with the data available in the literature. The model was used to study the effect of various operating conditions on the cell performance. Numerical results indicate that as the cell operating pressure increases, the reforming reaction extends to a larger portion of the cell and the maximum temperature move away from the cell inlet. As a result, a more uniform temperature prevails in the solid structure which reduces thermal stresses. Also, at higher excess air, the rate of heat transfer to the air stream is augmented and the average cell temperature is decreased. Copyright © 2010 John Wiley & Sons, Ltd.     

Basic properties of a liquid tin anode solid oxide fuel cell

An unconventional high temperature fuel cell system, the liquid tin anode solid oxide fuel cell (LTA-SOFC), is discussed. A thermodynamic analysis of a solid oxide fuel cell with a liquid metal anode is developed. Pertinent thermochemical and thermophysical properties of liquid tin in particular are detailed. An experimental setup for analysis of LTA-SOFC anode kinetics is described, and data for a planar cell under hydrogen indicated an effective oxygen diffusion coefficient of 5.3 × 10⁻⁵ cm² s⁻¹ at 800 °C and 8.9 × 10⁻⁵ cm² s⁻¹ at 900 °C. This value is similar to previously reported literature values for liquid tin. The oxygen conductivity through the tin, calculated from measured diffusion coefficients and theoretical oxygen solubility limits, is found to be on the same order of that of yttria-stabilized zirconia (YSZ), a traditional SOFC electrolyte material. As such, the ohmic loss due to oxygen transport through the tin layer must be considered in practical system cell design since the tin layer will usually be at least as thick as the electrolyte.     

Two strategies for multi-objective optimisation of solid oxide fuel cell stacks

This paper focuses on multi-objective optimisation (MOO) to optimise the planar solid oxide fuel cell (SOFC) stacks performance using a genetic algorithm. MOO problem does not have a single solution, but a complete Pareto curve, which involves the optional representation of possible compromise solutions. Here, two pairs of different objectives are considered as distinguished strategies. Optimisation of the first strategy predicts a maximum power output of 108.33 kW at a breakeven per-unit energy cost of 0.51 $/kWh and minimum breakeven per-unit energy cost of 0.30 $/kWh at a power of 42.18 kW. In the second strategy, maximum efficiency of 63.93%at a breakeven per-unit energy cost of 0.42 $/kWh is predicted, while minimum breakeven per-unit energy cost of 0.25 $/kWh at efficiency of 48.3% is obtained. The present study creates the basis for selecting optimal operating conditions of SOFC under the face of multiple conflicting objectives.     

Perovskite materials for highly efficient catalytic CH4 fuel reforming in solid oxide fuel cell

SOFC (solid oxide fuel cell, SOFC) is recognized to be efficient green energy technology in the 21st century. However, when hydrocarbons are directly used as fuel, carbon deposition is easy to occur in Ni-based anode, thus losing electrochemical catalytic activity. Fuel pre-reforming is also called on-cell reforming of hydrocarbons, which has been a promising solution for alleviating the carbon deposition problem in cermet anodes to varying degrees. And the key factor is to find an efficient and stable fuel reforming catalyst. Perovskite oxides have stable structure, highly catalytic activity and adjustable thermal expansion coefficient for using on the cells, showing great potentials of application for fuel reforming. In this paper, we summarize the application of perovskite catalyst in CH₄ fuel reforming based on the research of our group and other scholars, and puts forward the corresponding views and perspective, especially in perovskite catalyst with Ni exsolution.     

Use of ash-free “Hyper-coal” as a fuel for a direct carbon fuel cell with solid oxide electrolyte

“Hyper-coal”, produced by the Kobe Steel Company, was investigated by analytical and physico-chemical methods to consider its potential usability as a fuel for a direct carbon fuel cell with solid oxide electrolyte (DC-SOFC). The performed tests showed that DC-SOFCs fed with this processed fossil coal were characterized by stable operation with reasonable current and power densities. The performance of the fuel cells can be improved by using iron as a catalyst for the anodic reaction and by the choice of appropriate working conditions.     

Performance comparison of three solid oxide fuel cell power systems

An energy analysis of three typical solid oxide fuel cell (SOFC) power systems fed by methane is carried out with detailed thermodynamic model. Simple SOFC system, hybrid SOFC‐gas turbine (GT) power system, and SOFC‐GT‐steam turbine (ST) power system are compared. The influences of air ratio and operative pressure on the performance of SOFC power systems are investigated. The net system electric efficiency and cogeneration efficiency of these power systems are given by the calculation model. The results show that internal reforming SOFC power system can achieve an electrical efficiency of more than 49% and a system cogeneration efficiency including waste heat recovery of 77%. For SOFC‐GT system, the electrical efficiency and cogeneration efficiency are 61% and 80%, respectively. Although SOFC‐GT‐ST system is more complicated and has high investment costs, the electrical efficiency of it is close to that of SOFC‐GT system. Copyright © 2013 John Wiley & Sons, Ltd.     

Numerical simulation of intermediate-temperature direct-internal-reforming planar solid oxide fuel cell

A numerical model for an anode-supported intermediate-temperature direct-internal-reforming planar solid oxide fuel cell (SOFC) was developed. In this model, the volume-averaging method is applied to the flow passages in the SOFC by assuming that a porous material is inserted in the passages as a current collector. This treatment reduces the computational time and cost by avoiding a full three-dimensional simulation while maintaining the ability to solve the flow and pressure fields in the streamwise and spanwise directions. In this model, quasi-three-dimensional multicomponent gas flow fields, the temperature field, and the electric potential/current fields were simultaneously solved. The steam-reforming reaction using methane, the water-gas shift reaction, and the electrochemical reactions of hydrogen and carbon monoxide were taken into account. It was found that the endothermic steam-reforming reaction led to a reduction in the local temperature near the inlet and limited the electrochemical reaction rates therein. Computational results indicated that the local temperature and current density distributions can be controlled by tuning the pre-reforming rate. It was also found that a small amount of heat loss from the sidewall can cause significant nonuniformity in the flow and thermal fields in the spanwise direction.     

High-temperature mechanical properties of a glass sealant for solid oxide fuel cell

The high-temperature mechanical properties of a newly developed silicate-based glass sealant, designated as GC-9, have been studied for use in planar solid oxide fuel cell (pSOFC). Four-point bending tests were conducted at room temperature, 550 °C, 600 °C, 650 °C, 700 °C and 750 °C to investigate the variation of flexural strength, elastic modulus, and stress relaxation with temperature for the given glass sealant. Weibull statistic analysis was applied to describe the fracture strength data. The results indicated that the flexural strength was increased with temperature when the testing temperature was below the glass transition temperature (T_g, 668 °C). This was presumably caused by a crack healing effect taking place at high temperatures for glasses. However, with a further increase of temperature to a level higher than T_g, significant stress relaxation was observed to cause extremely large deformation without breaking the specimen. When the controlled displacement rate was increased by an order of magnitude, the stress relaxation effect at 750 °C became less effective. However, the mechanical stiffness of the given glass was significantly reduced at a temperature higher than T_g.     

A right-angular configuration for the single-chamber solid oxide fuel cell

A right-angular configuration for the single-chamber solid oxide fuel cell (SC-SOFC) has been proposed and operated successfully in a methane-oxygen mixture (CH₄:O₂ = 2:1) with a total flow rate of 300 mL min⁻¹. It was fabricated by attaching the Ni/yttria-stabilized zirconia (YSZ) anode and the Sm_0.2Ce_0.8O_1.9-impregnated La_0.7Sr_0.3MnO₃ (LSM) cathode on two mutually perpendicular planes of a YSZ electrolyte substrate. Effect of the relative position of the electrodes on the ohmic resistance has been investigated. It is shown that the cell exhibits the smallest ohmic resistance when the two electrodes are symmetrically located on the two planes. Compared with the conventional coplanar SC-SOFC, this configuration can make full use of the edge area of the electrolyte substrate and shorten the conductive channel of oxygen ion, leading to a remarkable reduction in ohmic resistance, an elevation of the open-circuit voltage, and, ultimately, an improved performance. The simple stack, consisting of two right-angular cells connected in series on an electrolyte, generated an open-circuit voltage 1.4 V at 700 °C and a maximum power 14.9 mW at 800 °C.