Improvement of the internal reforming of metal-supported SOFC at low temperatures

Automotive Solid oxide fuel cells (SOFCs) require improvements in mechanical robustness, power generation at low temperatures, and system compactness. To address these issues, we attempt to improve the internal reformation of metal-supported SOFCs (MS-SOFCs) via catalyst infiltration. After introducing nickel/gadolinium-doped ceria (Ni/GDC) nanoparticles, power densities of 1.16 Wcm⁻² with hydrogen (3%H₂O) and 0.85 Wcm⁻² with methane (Steam-to-Carbon ratio, S/C = 1.0) are obtained at 600 °C, 0.7 V. This is the highest performance achieved in previous studies on MS-SOFCs. Internal reforming with various hydrocarbon is also demonstrated. In particular 0.64 Wcm⁻² at 600 °C, 0.7 V is obtained when the fuel is iso-octane. We develop a numerical model to separately analyze reforming and electrochemical reaction. Catalyst infiltration dramatically increases the number of active sites for steam reforming. In addition, ruthenium/gadolinium-doped ceria (Ru/GDC) should be suitable as a catalyst metal at low temperatures because of the lower activation energy of steam reforming.     

Internal reforming SOFC running on biogas

Direct feeding of biogas to SOFC, which is derived from municipal organic wastes, has been investigated as a carbon-neutral renewable energy system. CH₄/CO₂ ratio in the actual biogas fluctuated between 1.4 and 1.9 indicating biogas composition is strongly affected by the kinds of organic wastes and the operational conditions of methane fermentation. Using anode-supported button cells, stable operation of biogas-fueled SOFC was achieved with the internal reforming mode at 800 °C. Cell voltage above 0.8 V was recorded over 800 h at 200 mA cm⁻². It has been revealed that air addition to actual biogas reduced the risk of carbon formation and led to more stable operation without compromising cell voltage due to the lowering of anodic overvoltage.     

Structured catalyst supports and catalysts for the methane indirect internal steam reforming in the intermediate temperature SOFC

Open cell metal foams made from Ni, Fe–Cr steel and Ni–Al intermetallic were studied as candidate catalyst supports for the internal indirect methane steam reforming. All the samples exhibited good corrosive resistance during 500–1000 h testing in H₂–H₂O–Ar environment at 600 °C. NiO/8YSZ composite based catalysts doped with fluorite-like (Pr_0.3Ce_0.35Zr_0.35O₂) or perovskite-like (La_0.8Pr_0.2Mn_0.2Cr_0.8O₃) complex oxides with high lattice oxygen mobility and promoted with Pt or Ru were prepared and deposited on the foam-structure supports. Both good catalyst adhesion and stable catalyst performance were achieved in the case of the Ni–Al foam supported catalysts. The Fe–Cr support reacted with the catalytic active components resulting in fast catalyst deactivation. The foam supported catalyst performance was compared with the same catalyst prepared in a form of 0.25 mm fraction. Porous supports with different porosities were prepared by the metal foam deformation and the catalyst performance depending on the support porosity (75–95%) was studied.     

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.     

Study on paper-structured catalyst for direct internal reforming SOFC fueled by the mixture of CH4 and CO2

Inorganic fiber network including YSZ fiber which acts as catalyst support was created by the simple paper-making process, and novel Ni-loaded paper-structured catalysts (PSCs) with excellent catalytic activity for the dry reforming of methane were designed and developed. The PSCs exhibited high fuel conversion comparable to the conventional powdered catalysts with less than one-tenth catalyst weights. The significant advantages of the PSCs are their high mechanical flexibility and material workability. So far, a functionally-graded catalytic reaction field which leads to uniform temperature distribution during biogas reforming resulting in stable operation of planar SOFC was successfully developed by the PSC array based on the kinetic simulation model built in this research.     

The effect of electrolyte type on performance of solid oxide fuel cells running on hydrocarbon fuels

A two-dimensional model is developed to simulate the performance of methane fueled solid oxide fuel cells (SOFCs), focusing on the effect of electrolyte type on SOFC performance. The model considers the heat and mass transfer, direct internal reforming (DIR) reaction, water gas shift reaction (WGSR), and electrochemical reactions in SOFCs. The electrochemical oxidation of CO in oxygen ion-conducting SOFC (O-SOFC) is considered. The present study reveals that the performance of H-SOFC is lower than that of O-SOFC at a high temperature or at a low operating potential, as electrochemical oxidation of CO in O-SOFC contributes to power generation. This finding is contrary to our common understanding that proton conducting SOFC (H-SOFC) always performs better than O-SOFC. However, at a high operating potential of 0.8 V or at a lower temperature, H-SOFC does exhibit better performance than O-SOFC due to its higher Nernst potential and higher ionic conductivity of the electrolyte. This indicates that the proton conductors can be good choices for SOFCs at intermediate temperature, even with hydrocarbons fuels. The results provide better understanding on how the electrolyte type influences the performance of SOFCs running on hydrocarbon fuels.     

Internal reforming of hydrocarbon fuels in tubular solid oxide fuel cells

The application of heterogeneous catalysis has an important role to play in the successful commercial development of solid oxide fuel cell (SOFC) technology. In this paper, we present an SOFC that combines a catalyst layer with a conventional anode, allowing internal reforming via partial oxidation (POX) of fuels such as methane, propane, butane, biomass gas, etc., without coking and yielding stable power output. The catalyst layer is fabricated on the anode simply by catalyst support coating and reforming catalyst impregnation. The composition and microstructure of catalyst support layer as well as the catalyst composition was easily tailored to meet the demand of in situ reforming. The usage of catalyst layer as an integrated part of the traditional SOFC will provide a simple low-cost power-generating system at substantially higher fuel efficiency and faster start-ups, and may accelerate the application of SOFCs through the direct use of hydrocarbon fuels.     

Paper-structured catalyst for the steam reforming of biodiesel fuel

Architectonics of the paper-structured catalyst for the application to the biofuel reformer or direct internal reforming SOFC (DIRSOFC) was studied. Inorganic fiber network, “paper”, composed of yttria-stabilized zirconia (YSZ) fiber (Zf), alumina fiber (Af) and inorganic binder (Al₂O₃ sol (As) or ZrO₂ sol (Zs) or CeO₂ sol (Cs)) was prepared by a simple paper-making process. Then, the catalytic activities of the Ni and Ni–MgO loaded papers called “paper-structured catalysts (PSCs)” for the steam reforming of biodiesel fuels (BDFs) were evaluated. Ni–MgO loaded PSC using Cs as an inorganic binder, Ni–MgO/ZfAfCs, exhibited excellent performance over Ru/γAl₂O₃ catalyst beads. Formation of light hydrocarbons, especially C₂H₄, was eliminated and water–gas shift reaction was more promoted compared to the catalyst beads.     

Advanced tubular solid oxide fuel cells with high efficiency for internal reforming of hydrocarbon fuels

Solid oxide fuel cells (SOFCs) constitute an attractive power-generation technology that converts chemical energy directly into electricity while causing little pollution. NanoDynamics Energy (NDE) Inc. has developed micro-tubular SOFC-based portable power generation systems that run on both gaseous and liquid fuels. In this paper, we present our next generation solid oxide fuel cells that exhibit total efficiencies in excess of 60% running on hydrogen fuel and 40+% running on readily available gaseous hydrocarbon fuels such as propane, butane etc. The advanced fuel cell design enables power generation at very high power densities and efficiencies (lower heating value-based) while reforming different hydrocarbon fuels directly inside the tubular SOFC without the aid of fuel pre-processing/reforming. The integrated catalytic layered SOFC demonstrated stable performance for >1000 h at high efficiency while running on propane fuel at sub-stoichiometric oxygen-to-fuel ratios. This technology will facilitate the introduction of highly efficient, reliable, fuel flexible, and lightweight portable power generation systems.     

An additional layer in an anode support for internal reforming of methane for solid oxide fuel cells

Anode supported solid oxide fuel cells (SOFCs) have been extensively investigated for their ease of fabrication, robustness, and high electrochemical performance. SOFCs offer a greater flexibility in fuel choice, such as methane, ethanol or hydrocarbon fuels, which may be supplied directly on the anode. In this study, SOFCs with an additional Ni–Fe layer on a Ni–YSZ support are fabricated with process variables and characterized for a methane fuel application. The addition of Ni–Fe onto the anode supports exhibits an increase in performance when methane fuel is supplied. SOFC with a Ni–Fe layer, sintered at 1000 °C and fabricated using a 20 wt% pore former, exhibits the highest value of 0.94 A cm⁻² and 0.85 A cm⁻² at 0.8 V with hydrogen and methane fuel, respectively. An impedance analysis reveals that SOFCs with an additional Ni–Fe layer has a lower charge transfer resistance than SOFCs without Ni–Fe layer. To obtain the higher fuel cell performance with methane fuel, the porosity and sintering temperature of an additional Ni–Fe layer need to be optimized.     

Optimization of a 30 kW SOFC combined heat and power system with different cycles and hydrocarbon fuels

Solid oxide fuel cells (SOFCs) could generate power cleanly and efficiently by using a wide range of fuels. Through the recovery and utilization of the energy in the SOFC tail gas, SOFC combined heat and power (CHP) systems achieve efficient cascade utilization of fuels. In this article, an efficient 30 kW SOFC CHP system with multiple cycles is designed based on a commercial kw-level SOFC device. The energy and substances could be recycled at multiple levels in this system, which makes the system do not need external water supply anymore during working. Meanwhile, the performance, fuel applicability, flexibility and reliability of the system are investigated. Finally, an optimized operating condition is confirmed, in which the electrical efficiency is 54.0%, and the thermoelectric efficiency could reach 88.8% by using methanol as fuel.     

Steam reforming of ethanol on Rh/SiCeO2 washcoated monolith catalyst: Stable catalyst performance

The performance of a new Rh/CeSiO₂ catalyst supported on a ceramic monolith for steam reforming (SR) of ethanol for hydrogen generation was investigated. It provides several advantages over a traditional pellet based catalyst in that it will reduce weight, size and pressure drop in the reactor. The effect of steam to ethanol molar ratio and temperature were first investigated on a powdered catalyst in order to establish the preferred reaction conditions to be used for tests on the monolith. The optimum temperature for coke free, high selectivity and stable catalyst operation was 1073 K at a steam to ethanol molar ratio of 3.5. The monolith supported catalyst was evaluated for aging stability, on/off performance and coke regeneration using steam gasification. After 96 h of SR of ethanol at 1028 K and water/ethanol molar ratio of 3.5 the monolith supported catalyst retained stable performance throughout the entire time on stream with the only products being H₂, CO, CO₂. Some coke formation was observed using Raman spectra, however, it did not cause any permanent deactivation. Regeneration via steam gasification at 973 K with 20% steam in N₂ was successful for coke removal and complete catalyst regeneration.     

Effects of crystal Structure of yttria- and scandia-stabilized zirconia in nickel-based SOFC anodes on carbon deposition and oxidation behavior

The effect of crystal structure of yttria- (YSZ) and scandia-stabilized zirconia (ScSZ) in nickel-based SOFC anodes was investigated in relation with carbon deposition and oxidation behavior in methane fuel. The lattice parameter of the zirconia decreased by the dissolution of 1-2 mol%Ni to YSZ and ScSZ. For Ni-doped ScSZ, the lattice parameter of the zirconia increased by the Ni dissolution, and the crystal structure of the zirconia was modified after reduction treatment. New finer Ni particles were formed around original Ni grains accompanied by the decrease in Ni solubility to ScSZ after reduction treatment. Carbon deposition was initiated near the boundary between Ni particles and YSZ (or ScSZ) substrate in dry methane atmosphere. Furthermore, the rod-shaped carbon was observed to grow from the new finer Ni particles on the ScSZ substrate. On the other hand, a large amount of amorphous carbon was promoted to be deposited on Ni-YSZ cermet at a high temperature of 1273 K. The amorphous carbon, however, was oxidized at lower temperatures than graphite. The carbon deposition and oxidation behavior was strongly affected by the morphology and crystallinity of deposited carbon.     

天然气水蒸气重整与SOFC耦合应用

固体氧化物燃料电池（SOFC）系统具有高能源效率和使用可再生燃料的可能性,将在未来的可持续能源系统中发挥重要作用。过去几年燃料电池的发展很快,但在成本、稳定性和市场份额方面,该技术仍处于早期发展阶段。在以天然气为燃料的SOFC系统中,燃料的重整过程和燃料利用水平都可能影响系统运行的稳定性、热量和能量平衡,从而影响系统的使用寿命、输出功率和效率。因此,对燃料重整过程的设计与控制对有效的SOFC电池运行具有重要意义。对天然气在SOFC系统中的重整器配置方式（包括外重整和内重整）、重整参数和重整燃料利用方式进行了详细的综述分析,并对未来天然气SOFC系统的发展进行了展望。     

Operational behavior and reforming kinetics over Ni/YSZ of a planar type pre-reformer for SOFC systems

At Forschungszentrum Jülich GmbH, a multi-component SOFC design based on planar stacks has been developed, in which all hot system components are scaled to a nominal SOFC stack power of 5 kW. To optimize the SOFC system it is necessary to investigate the effects of design and operating parameters on the system components like pre-reformer and afterburner. A special designed 5-layer planar type steam pre-reformer on basis of Ni/YSZ has been built and tested for operational behavior and kinetics of steam reforming with methane. This paper summarizes and discusses the experimental results on the global reaction kinetics of a Jülich planar pre-reformer in the temperature range between 350 °C and 620 °C at ambient pressure (1 bar). The species compositions of product gas at different feed compositions, flow rates and temperatures are determined by using gas-chromatographic methods and dew-point measurements. The reproducibility of experiments in the low temperature range (especially less than 430 °C) was only assured, when the catalyst has been reduced before every kinetic experiment. The proposed kinetic expression of Arrhenius type (second order with respect to mole fraction of methane and first order with respect to mole fraction of water) gives a good agreement with the experimental results of the methane steam reforming. It is general effective for different steam to carbon ratios. The temperature distribution in the pre-reformer and the loss of heat are also discussed.     

Influence of current densities in SOFC and PEFC stacks on a SOFC–PEFC combined system

A solid oxide fuel cell (SOFC)–polymer electrolyte fuel cell (PEFC) combined system was investigated by numerical simulation. Here, the effect of the current densities in the SOFC and the PEFC stacks on the system's performance is evaluated under a constant fuel utilization condition. It is shown that the SOFC–PEFC system has an optimal combination of current densities, for which the electrical efficiency is highest. The optimal combination exists because the cell voltage in one stack increases and that of the other stack decreases when the current densities are changed. It is clarified that there is an optimal size of the PEFC stack in the parallel-fuel-feeding-type SOFC–PEFC system from the viewpoint of efficiency, although a larger PEFC stack always leads to higher electrical efficiency in the series-fuel-feeding-type SOFC–PEFC system. The 40 kW-class PEFC stack is suitable for the 110 kW-class SOFC stack in the parallel-fuel-feeding type SOFC–PEFC system.     

Modeling of SOFC with indirect internal reforming operation: Comparison of conventional packed-bed and catalytic coated-wall internal reformer

In the present work, mathematical models of indirect internal reforming solid oxide fuel cells (IIR-SOFC) fueled by methane were developed to analyze the thermal coupling of an internal endothermic reforming with exothermic electrochemical reactions and determine the system performance. The models are based on steady-state, heterogeneous, two-dimensional reformer and annular design SOFC models. Two types of internal reformer i.e. conventional packed-bed and catalytic coated-wall reformers were considered here. The simulations indicated that IIR-SOFC with packed-bed internal reformer leads to the rapid methane consumption and undesirable local cooling at the entrance of internal reformer due to the mismatch between thermal load associated with rapid reforming rate and local amount of heat available from electrochemical reactions. The simulation then revealed that IIR-SOFC with coated-wall internal reformer provides smoother methane conversion with significant lower local cooling at the entrance of internal reformer.     

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.     

An overview of the methanol reforming process: Comparison of fuels,catalysts, reformers,and systems

One of the main challenges facing power generation by fuel cells involves the difficulties related to hydrogen storage. Several methods have been suggested and studied by researchers to overcome this problem. Among these methods, using fuel reformers as a component of the fuel cell system is a practical and promising alternative to hydrogen storage. Among many hydrogen carrier fuels used in reformers, methanol is one of the most attractive ones because of its distinctive properties. To design and improve of the methanol reformate gas fuel cell systems, different aspects such as promising market applications for reformate gas–fueled fuel cell systems, and catalysts for methanol reforming should be considered. Therefore, our goal in this paper is to provide a comprehensive overview on the past and recent studies regarding methanol reforming technologies, while considering different aspects of this topic. Firstly, different fuel reforming processes are briefly explained in the first section of the paper. Then properties of various fuels and reforming of these fuels are compared, and the characteristics of commercial reformate gas–fueled systems are presented. The main objective of the first section of the paper is to give information about studies and market applications related to reformation of various fuels to understand advantages and disadvantages of using various fuels for different practical applications. In the next sections of the paper, advancements in the methanol reforming technology are explained. The methanol reforming catalysts and reaction kinetics studies by various researchers are reviewed, and the advantages and disadvantages of each catalyst are discussed, followed by presenting the studies accomplished on different types of reformers. The effects of operating parameters on methanol reforming are also discussed. In the last section of this paper, methanol reformate gas–fueled fuel cell systems are reviewed. Overall, this review paper provides insight to researchers on what has been accomplished so far in the field of methanol reforming for fuel cell power generation applications to better plan the next stage of studies in this field.     

Enhanced coking resistance of Ni cermet anodes for solid oxide fuel cells based on methane on‐cell reforming by a redox‐stable double‐perovskite Sr2MoFeO6‐δ

Carbon deposition on a Ni‐based anode is troublesome for the direct power generation from methane‐based fuels using solid oxide fuel cell. In this paper, a redox‐stable double‐perovskite Sr₂MoFeO_6‐δ (SMFO) is applied as an independent on‐cell reforming catalyst over a Ni‐YSZ anode to improve coking resistance. The morphology, catalytic activity and electrochemical performance for wet methane/coal‐bed gas (CBG) are investigated. A Ni‐YSZ anode supported cell with SMFO generates a high power output of 1.77 W·cm^?2 and exhibits favorable stability operated on wet CH₄ at 800°C. Post‐mortem micro‐structural analyses of cells indicate the cell operated on CBG shows coking probably due to the heavy carbon compounds in CBG.