Direct Internal Reforming Molten Carbonate Fuel Cell Research Articles

A new alkali-resistant Ni/Al2O3-MSU-1 core–shell catalyst for methane steam reforming in a direct internal reforming molten carbonate fuel cell

An alkali-resistant catalyst for direct internal reforming molten carbonate fuel cell (DIR-MCFC) is prepared by growing a thin shell of mesoporous MSU-1 membrane on Ni/Al2O3 catalyst beads. The MSU-1 shell is obtained by first depositing a monolayer of colloidal silicalite-1 (Sil-1) on the catalyst bead as linkers and then using NaF stored in the beads to catalyze the growth of the MSU-1 layer. The resulting core–shell catalysts display excellent alkali-resistance and deliver stable methane conversion and hydrogen yield in an out-of-cell test simulating the operating conditions of an operating DIR-MCFC. Higher conversion and yield (i.e., up to over 70%) are obtained from the new core–shell catalyst with MSU-1 shell compared to the catalyst with microporous Sil-1 shell. A mathematical model of the reaction and poisoning of the core–shell catalyst is used to predict the optimum shell thickness for its reliable use in a DIR-MCFC.

Thermodynamic analysis of application of organic Rankine cycle for heat recovery from an integrated DIR-MCFC with pre-reformer

This work deals with waste heat recovery from a proposed direct internal reforming molten carbonate fuel cell (DIR-MCFC), including an integrated pre-reformer. In this regard, some advantages are attainable over exhaust gas recycling. For instance, due to low temperature in the pre-reformer, carbon deposition and coke formation resulting from higher hydrocarbons can be eliminated. In this study, the cathode outlet provides the heat requirement for the pre-reforming process. After partial heat recovery from the cathode outlet, the stream still has a considerable energy and exergy (352.55°C and 83.687kW respectively). This study investigates waste heat recovery from the proposed DIR-MCFC, using an organic Rankine cycle (ORC) with two different configurations. In the first case, the cathode outlet provides the heat requirement for the pre-reforming process; then, it enters the heat recovery vapor generator of the organic Rankine cycle. In the second case, the cathode outlet is split into two streams for using in an ORC and supplying the pre-reforming process required heat. Several substances are selected as working fluids in order to compare their performance in the waste heat recovery system. The overall results at optimum conditions indicate that the energy and exergy efficiencies of the compound system are increased and its exergy loss is decreased with cathode splitting for all substances (1.1% average over all fluids). It is concluded that cathode splitting has a significant impact on the substances which have better performance in the first case. In both cases, toluene is the most efficient working fluid. In the second case, global energy and exergy efficiencies are found to be 60.45% and 57.75%, respectively, which are almost 2.67% higher compared to the first case for toluene.

Control of a direct internal reforming molten carbonate fuel cell system using wavelet network-based Hammerstein models

Inspired by a direct internal reforming molten carbonate fuel cell (DIR-MCFC) coupled with complicated nonlinear dynamics, the identification and control design of the Hammerstein model is presented. Through the sequential identification procedure, the static nonlinearity block is considered as the wavelet network which is trained and validated by the on-line learning algorithm, and the linear dynamic block is described by the state-space model in which parameters are estimated by the recursive least square algorithm. Using the numerical interpolation technique to approximate the implicit nonlinear function, we present a composite control framework consists of a nonlinear inversion and linear control. Through the closed-loop simulation tests, the nonlinear inversion design for the nonlinearity cancellation of a class of nonlinear systems is validated.

Identification and Control of a fuel cell system using wavelet network-based Hammerstein models

Inspired by a direct internal reforming molten carbonate fuel cell (DIR-MCFC) coupled with complicated nonlinear dynamics, the identification and control design of the Hammerstein model is presented. Through the sequential identification procedure, the static nonlinearity block is considered as the wavelet network which is trained and validated by the on-line learning algorithm, and the linear dynamic block is described by the state-space model in which parameters are estimated by the recursive least square algorithm. When a nonlinear inversion via the numerical interpolation technique is established, a composite control framework is used to ensure the good output regulation.

Direct internal reforming molten carbonate fuel cell with core–shell catalyst

A sort of core–shell catalyst as a novel anti-alkali-poisoning concept was prepared, tested and applied in the direct internal reforming molten carbonate fuel cell (DIR-MCFC). Results showed that the core–shell catalyst possessed good alkali-poisoning resistance capacity, which was explained well by the micropore model of the catalyst. And the cell performance could keep above 0.75V during 100 h test. When the steam carbon ratio was 2 (S/C = 2) and the current density was 150 mA cm −2, the cell potential varied from 0.826 to 0.751 V and the voltage fluctuant phenomenon was explained specifically. Furthermore, the short stack (three cells) was also assembled, and the maximum output power density of the short stack was 338.4 mW cm −2. The above results indicated that the core–shell catalyst could be applied into the DIR-MCFC successfully.

Preparation of core (Ni base)–shell (Silicalite-1) catalysts and their application for alkali resistance in direct internal reforming molten carbonate fuel cell

Alkali-resistant Ni/SiO 2–Sil-1 and Ni/Al 2O 3–Sil-1 core–shell catalysts were prepared for use in direct internal reforming molten carbonate fuel cell (DIR-MCFC). A thin zeolite shell was grown on the surface of catalyst beads to create a diffusion barrier against alkali poisons in the vapors generated from the electrolyte during DIR-MCFC operation. The synthesis of low defect zeolite shell was investigated and the effects of shell thickness on catalyst activity were examined. A mathematical model of the reaction and alkali-poisoning was developed and the optimum zeolite shell thickness was determined. The experimental and modeling results demonstrated that the core–shell catalyst is more resistant to alkali poisoning and a zeolite shell thickness of 3.5 μm can protect the catalyst for at least 100 h following a failure of the anode barrier in DIR-MCFC to give sufficient time for repair.

Electrolyte effect on the catalytic performance of Ni-based catalysts for direct internal reforming molten carbonate fuel cell

An active and tolerant Ni-based catalyst for methane steam reforming in direct internal reforming molten carbonate fuel cells (DIR-MCFCs) was developed. Deactivation of reforming catalysts by alkali metals from the electrolyte composed of Li 2CO 3 and K 2CO 3 is one of the major obstacles to be overcome in commercialization of DIR-MCFCs. Newly developed Ni/MgSiO 3 and Ni/Mg 2SiO 4 reforming catalysts show activities of ca. 80% methane conversion. Subsequent to electrolyte addition to the catalyst, however, the activity of Ni/Mg 2SiO 4 decreases to ca. 50% of its initial value, whereas Ni/MgSiO 3 catalyst retains its initial activity. Results obtained from temperature-programmed reduction and X-ray photoelectron spectroscopy identify unreduced Ni 3+ as a decisive factor in keeping catalytic activity from the electrolyte.

Optimum start-up strategies for direct internal reforming molten carbonate fuel cell systems

The study of start-up performance for a direct internal reforming molten carbonate fuel cell (DIR-MCFC) system is presented. Since a kW-class stack is assembled with an additional preheating design, the improvement of start-up behavior is conducted to find the proper operating strategy. For a cold start-up fuel cell system, both start-up delay and inverse response are strictly detected. When the optimum operating strategy is determined by solving the steady-state optimization algorithm subject to stack temperature constraint, the rapid system start-up as well as the maximum power output can be achieved simultaneously.

The catalytic performance of Ni/MgSiO 3 catalyst for methane steam reforming in operation of direct internal reforming MCFC

Active and tolerant Ni-based catalyst for methane steam reforming in direct internal reforming molten carbonate fuel cell (DIR-MCFC) was developed. Deactivation of reforming catalysts by alkali metals from electrolyte composed of Li 2CO 3 and K 2CO 3 is one of the major obstacles to be overcome in commercialization of DIR-MCFC. Newly developed Ni/MgSiO 3 reforming catalyst showed activities of ca. 82% methane conversion for 240 min in out-of-cell test. In duration test, the unit cell containing Ni foam impregnated with Ni/MgSiO 3 in anode gas channel did not give performance degradation for more than 2000 h, while the unit cell assembled with Ni/MgSiO 3-coated anode showed a significant performance loss after an operation of 1200 h. Results obtained from X-ray diffraction and Brunauer–Emmett–Teller technique revealed that Ni sintering and support deterioration were decisive factors in decreasing the catalytic activity.

Preparation of alkali-resistant, Sil-1 encapsulated nickel catalysts for direct internal reforming-molten carbonate fuel cell

Abstract A thin layer of silicalite-1 zeolite membrane was grown on the surface of Ni/SiO 2 and Ni/Al 2 O 3 catalyst beads after seeding and secondary regrowth to create core–shell catalysts that are resistant to alkali poisoning from direct internal reforming-molten carbonate fuel cell (DIR-MCFC). The zeolite shell thickness was optimized to prevent poisoning and minimize diffusion resistance. An out-of-cell test was designed to simulate the fuel cell operating conditions, which showed that the new core–shell catalysts maintained a high activity similar to the original fresh catalyst in spite of the exposure to alkali vapor at high temperature. The conventional Ni/SiO 2 and Ni/Al 2 O 3 catalysts suffered higher than 80% decrease in activity for steam reforming of methane reaction (SRM).

Structural Characteristics of (NiMgAl)Ox Prepared from a Layered Double Hydroxide Precursor and its Application in Direct Internal Reforming Molten Carbonate Fuel Cells

Abstract(NiMgAl)Ox materials prepared from layered double hydroxide (LDH) precursors show a typical mesoporous structure with an average pore size of about 6 nm, excellent activity for the methane steam reforming (MSR) reaction at 650 °C, and a strong resistance against Li poisoning, suggesting the possibility for future application in direct internal reforming molten carbonate fuel cells (DIR‐MCFC). X‐ray diffraction (XRD) experiments indicate that the molar ratio of Al/Mg exerts a strong effect on the properties of both the LDH precursors and final catalysts. Temperature‐programmed reduction (TPR) analysis reveals that the Al/Mg molar ratio influences the properties of Ni in the final catalyst. The catalytic performance of the catalysts prepared is greatly influenced by the molar ratio of Al/Mg for MSR. The activity gradually increases with an increase in the Al/Mg ratio (0.14–1.5). However, with further increases in the amount of Al added (Al/Mg = 2), the activity decreases. The activity is strongly related to the BET surface area and Ni dispersion. The Li‐poisoning test proves that Mg‐rich catalysts lose their activity quickly upon exposure to Li, while Al‐rich catalysts maintain virtually all of their original activity. NiMgAl (Al/Mg = 1.5) is found to be an excellent catalyst for the DIR‐MCFC, having both the highest activity and strongest resistance against Li poisoning.

Visualization of electrolyte volatile phenomenon in DIR-MCFC

Volatilization of molten salt is one of the factors that control the performance of molten carbonate fuel cells (MCFC). Volatilization of molten salt promotes cross-leakage and the corrosion of metallic components. Moreover, piping blockage is caused by the solidification of volatile matter. Because reforming catalysts filling the anode channel are polluted by molten salt volatile matter in direct internal reforming molten carbonate fuel cells (DIR-MCFC), the volatilization of molten salt is an especially serious subject. However, neither the behaviour nor the volatilization volume of molten salt volatile matter has heretofore been elucidated on. Because molten salt volatile matter that has strong alkalinity cannot be supplied directly to an analyzer, its volatilization volume is small, and analytical accuracy is poor. Therefore, an attempt has been made to elucidate about the electrolyte volatile phenomenon in an MCFC by using a non-contact image measurement technique. A 16 cm 2 MCFC single cell frame has an observation window and an irradiation window. The image of the volatile phenomenon is shown by irradiating a YAG laser light sheet 2 mm thick from an irradiation window into the anode channel, and taking measurements from an observation window with a high spatial resolution video camera (12 bit). As a result, though the volatile matter is not observed in an anode channel at OCV, the volatile matter flows in a belt-like manner from the inlet side near the electrode toward the outlet at a current density of 150 mA cm −2. In addition, volatile matter is difficult to observe with the conventional thickness of an anode electrode. Because the composition of these volatile matters is 15Li 2CO 3/85K 2CO 3 (the result of conversion into molten salt) by ion chromatography analysis, it is not an electrolyte (62Li 2CO 3/38K 2CO 3) but rather the volatile matter of potassium, such as KOH. Therefore, it is understood that the volatile matter K 2CO 3 is generated as KOH, comprising the water generated by the cellular reaction with an electrolyte, in a reaction with CO 2. Conversely, the volatile matter flows to the surface of the cathode electrode without regard to changes in current density. In addition, the volatile matter exists on the electrode surface, although it decreases more or less with the conventional thickness of the cathode electrode. Therefore, it is understood that the volatile matter, in order for it not to be related to the cellular reaction, does not comprise the dispersion of molten salt.

B214 MCFCの電解質揮発現象の可視化

Volatilizing of molten carbonate as electrolyte in Molten Carbonate Fuel Cell (MCFC) is one of degradation factors. The Volatilization of the molten carbonate brings the cross-leak and the corrosion of the metallic materials. Moreover, the piping blockage caused by solidification of the volatile chemical species in piping will be happened at lowering temperature. Especially, since the reforming catalysts filled to the anode channel in Direct Internal Reforming Molten Carbonate Fuel Cells (DIR-MCFC) are polluted by volatile species from the molten carbonate, volatilizing of the molten carbonate is an important issue. However, the behavior of molten carbonate volatile issue has been not elucidated, since the volatilization volume is too small amount to analyze them. Last symposium, we informed that at anode side, amount of volatilized particle was increasing with increasing current density. Although volatilization phenomenon was observed at cathode side, there was no relationship between amount of volatilized particle and current density. The volatile chemical species from anode and cathode were potassium rich composition.

Simulation of the performance for the direct internal reforming molten carbonate fuel cell. Part I: distributions of temperature, energy transfer and current density

This study examined the temperature distributions of the anode and cathode gases of the cell body as well as the current density distributions at each point of the direct internal reforming molten carbonate fuel cell (DIR-MCFC) using numerical modelling. The model was based on assumptions and experimental data from a 5 cm × 5 cm sized unit cell operation. The results showed there was an approximately 13°C temperature difference between the initial point (0, 0) and end point (1, 1) of the cell body and the temperature increased steadily along with the direction of the anode gas flow. The temperature distribution of the anode gases showed a similar trend to those of the cell body. The temperature of the anode gases was an average 11°C lower than that of the cell body. The temperature distributions of cathode gases were relatively higher than those of the anode gases and the cell body. The temperature distributions at each point of the cell body, including the anode and cathode gases, could be explained by the different rates of the electrochemical, methane steam reforming and water–gas shift reactions at each point in the cell body. The current density distribution at the entrance of the cell was the highest at 290 mA cm−2, and decreased steadily to 150 mA cm−2 at the exit. These results were also confirmed by the amount of hydrogen reacted in the electrochemical reaction (referred to Part II). Finally, modelling simulations showed a non-uniform distribution of the temperature and current density throughout the DIR-MCFC were observed. In addition, it was confirmed that the distributions of the reaction rates and gas compositions at each point of the cell also showed a great deal of difference throughout the DIR-MCFC. The non-uniformity of these temperature distributions can lead to deterioration in the cell performance. These might provide the necessary information for solving these problems. Copyright © 2005 John Wiley & Sons, Ltd.

Evaluation of volatile behaviour and the volatilization volume of molten salt in DIR-MCFC by using the image measurement technique

The volatilization of molten salt is one of the factors that control the performance of molten carbonate fuel cells (MCFC). Volatilization of molten salt promotes the cross-leakage and corrosion of metallic components. Moreover, pipe blockage is caused by the solidification of volatile matter. Especially, because reforming catalysts filling the anode channel are polluted by molten salt volatile matter in direct internal reforming molten carbonate fuel cells (DIR-MCFC), volatilizing of the molten salt is a weighty subject. However, neither the behaviour nor the volatilization volume of molten salt volatile matter has been elucidated, because molten salt volatile matter that has strong alkalinity cannot be supplied directly to an analyzer, its volatilization volume is small, and the analytical accuracy is poor. Therefore, an attempt was made to elucidate the behaviour of vaporized alkali hydroxide by using a non-contact image measurement technique. The DIR-MCFC electrolyte is generally 62Li 2CO 3/38K 2CO 3. Consideration was given to the DIR-MCFC catalyst pollution mechanism as follows. Molten salt volatile matter is KOH generated as water generated in the cell reacts with the electrolyte. The generated KOH returns to K 2CO 3 again in high CO 2 concentration regions, and catalyst pollution is caused by the adherence of the K 2CO 3 to the catalyst. Moreover, the K 2CO 3 particles mutually cohere when the generated water assists bonding and blocks the piping. The present report experimentally evaluates the volatilization volume of KOH, the change from KOH to K 2CO 3, and the particulate growth of K 2CO 3, using the image measurement technique. In measuring the KOH volatilization volume, K 2CO 3 is generated as KOH volatilized by heating it in a crucible in an electric furnace reacts with CO 2, and is then injected into a reaction tube. The amount of K 2CO 3 is measured by measuring the image of the K 2CO 3 particle with a YAG laser and a CCD camera, thereby obtaining the KOH volatilization volume from the calculation of the stoichiometry of the amount of K 2CO 3. In order to study the change from KOH to K 2CO 3, the particulate growth of K 2CO 3 can be monitored by taking a picture of a K 2CO 3 particle generated with KOH and CO 2 for an extended period. As a result, a conglomerate is generated by the mutual adhesion small particles, causing piping blockage.

Effect of lithium carbonate on nickel catalysts for direct internal reforming MCFC

Despite many advantages of the direct internal reforming molten carbonate fuel cell (DIR-MCFC) in producing electricity, there are many problems to solve before practical use. The deactivation of reforming catalyst by alkali like lithium is one of the major obstacles to overcome. A promising method is addition of TiO 2 into the Ni/MgO reforming catalyst, which resulted in the increased resistance to lithium poisoning as we previously reported. To understand how added titania worked, it is necessary to elucidate the deactivation mechanism of the catalysts supported on metal oxides such as MgO and MgO–TiO 2 composite oxide. Several supported nickel catalysts deactivated by lithium carbonate were prepared, characterized and evaluated. The Ni/MgO catalyst turned out to be most vulnerable to lithium deactivation among the employed catalysts. The activity of the Ni/MgO gradually decreased to zero with increasing amount of lithium addition. Deactivation by lithium addition resulted from the decrease of active site due to sintering of nickel particles as well as the formation of the Li y Ni x Mg 1− x− y O ternary solid solution. These were evidenced by H 2 chemisorption, temperature programmed reduction, and XRD analyses. As an effort to minimize Li-poisoning, titanium was introduced to MgO support. This resulted in the formation of Ni/Mg 2TiO 4, which seemed to increase resistance against Li-poisoning.

Development of nickel catalyst supported on MgO–TiO 2 composite oxide for DIR-MCFC

As an effort to synthesize supported Ni reforming catalysts resistant to Li poisoning, which is essential in commercializing the direct internal reforming molten carbonate fuel cells (DIR-MCFC), a series of Ni catalysts supported on MgO–TiO 2 composite oxides with varying ratio of Mg to Ti were prepared. Under the Li-free condition, the supported Ni reforming catalysts were active regardless of the ratio of Mg to Ti; however, when Li was introduced to the catalysts, the catalysts lost their activities with different degrees. Temperature-programmed reduction (TPR) and X-ray diffraction (XRD) results indicated that the addition of relatively small fraction of TiO 2 into the NiO/MgO catalyst system was effective in obstructing the formation of Ni x Mg 1− x O solid solution and in increasing resistance to Li poisoning. The Ni catalysts supported on the composite oxides with Mg/Ti ratios of 2–7 turned out to be far more resistant to Li poisoning, showing approximately 60% of their original activities even under severe lithium carbonate condition, than the ones with other Mg/Ti ratios.

Feasibility study of the co-generation system with direct internal reforming-molten carbonate fuel cell (DIR-MCFC) for residential use : Sugiura, K. and Naruse, I. Journal of Power Sources, 2002, 106, (1–2), 51–59

Feasibility study of the co-generation system with direct internal reforming-molten carbonate fuel cell (DIR-MCFC) for residential use : Sugiura, K. and Naruse, I. Journal of Power Sources, 2002, 106, (1–2), 51–59

Optimum operating conditions of DIR-MCFC without vapor-phase carbonate pollution

In direct internal reforming-molten carbonate fuel cells (DIR-MCFC), deterioration of catalytic activity takes place in the anode channel due to both liquid-phase pollution and vapor-phase pollution. Although the liquid-phase pollution can be solved by installing protective barrier, an effective defense method and a reactivation method of vapor-phase polluted catalyst have not established yet. In order to study the reactivation method, the adhesion form of potassium compounds in the polluted catalyst under the various gas conditions was evaluated by using a thermogravimetric analyzer in which water vapor can feed. Additionally, the activity of the treated catalyst was also tested by a differential reactor. As a result, KOH changes to K 2CO 3 under a CO 2 concentration of 25% or more. KOH becomes a solid-phase from the liquid-phase when it is changed into K 2CO 3. Therefore, the catalyst can not be reactive because K 2CO 3 chokes pores of the catalyst. However, the activity of the polluted catalyst is revived to 80% of the initial activity by controlling the gas species concentration, especially CO 2. Moreover, the catalytic activity can be revived under a steam–carbon ratio of 2.0 or more. Based on the results obtained by these fundamental experiments, the reactivation methods of catalyst polluted are proposed as follows: (i) catalyst should be loaded more upstream in the anode; (ii) in order to reactivate the polluted catalyst, the DIR-MCFC should maintain a steam–carbon ratio of 2.0 or more; (iii) gas conditions to activate the catalyst should be applied regularly.

Feasibility study of the co-generation system with direct internal reforming-molten carbonate fuel cell (DIR-MCFC) for residential use

The possibility of introducing a co-generation system with a direct internal reforming-molten carbonate fuel cell (DIR-MCFC) for residential use is examined by a feasibility study. First, the structure of a system, which can maintain the cell temperature (650 °C) without the heat supply, is constructed by calculating heat and material balances among the system components. Secondly, a model family, which might use the co-generation system with a DIR-MCFC, is constructed from the results of a questionnaire on room layout, number of family members, and the number of electric appliances and consumption of electric power in Osaka. Thirdly, calculating the electric power and hot-water demand supply balance optimizes the scale of the co-generation system with a DIR-MCFC for residential use. Finally, the running costs of this optimum system using city gas or propane gas are considered. As a result, the optimum scale of a co-generation system a with DIR-MCFC and using city gas is 3 kW, while it is 6 kW for the case using propane gas. The co-generation system using city gas is suitable for a house. On the other hand, the system using propane gas is suitable for an apartment.