Performance and effective kinetic models of methane steam reforming over Ni/YSZ anode of planar SOFC

Under mass/heat transfer and species diffusion limitations, the detailed thermodynamic investigations and experimental measurements were carried out to study and evaluate the performance of methane steam reforming and to develop its effective kinetic models over Ni/YSZ anode of the planar solid oxide fuel cell developed by Central Research Institute of Electric Power Industry (CRIEPI) of Japan. Based on the kinetic models of methane steam reforming developed by Xu and Froment, the effective kinetic models were developed. Combining the experiment data with the iteration calculation, the effective factor (C_e) is found to be 5.0 × 10^?4. Using these effective kinetic models, the detailed distributions of temperature, species, methane conversion, and carbon formation and gasification activity are presented under wide range of operating conditions. The results show that the local temperature in the reactor and the methane conversion are sensitive to the operating parameters. The region of the lowest local temperature and the most possible region of carbon formation are at the front of the porous anode sample. Due to the limitation of contact time, heat transfer and species diffusion, the methane conversion appreciably decreases with an increase of S/C ratio.     

Thermodynamic evaluation of methanol steam reforming for hydrogen production

Thermodynamic equilibrium of methanol steam reforming (MeOH SR) was studied by Gibbs free minimization for hydrogen production as a function of steam-to-carbon ratio (S/C = 0–10), reforming temperature (25–1000 °C), pressure (0.5–3 atm), and product species. The chemical species considered were methanol, water, hydrogen, carbon dioxide, carbon monoxide, carbon (graphite), methane, ethane, propane, i-butane, n-butane, ethanol, propanol, i-butanol, n-butanol, and dimethyl ether (DME). Coke-formed and coke-free regions were also determined as a function of S/C ratio.Based upon a compound basis set MeOH, CO₂, CO, H₂ and H₂O, complete conversion of MeOH was attained at S/C = 1 when the temperature was higher than 200 °C at atmospheric pressure. The concentration and yield of hydrogen could be achieved at almost 75% on a dry basis and 100%, respectively. From the reforming efficiency, the operating condition was optimized for the temperature range of 100–225 °C, S/C range of 1.5–3, and pressure at 1 atm. The calculation indicated that the reforming condition required from sufficient CO concentration (<10 ppm) for polymer electrolyte fuel cell application is too severe for the existing catalysts (T_r = 50 °C and S/C = 4–5). Only methane and coke thermodynamically coexist with H₂O, H₂, CO, and CO₂, while C₂H₆, C₃H₈, i-C₄H₁₀, n-C₄H₁₀, CH₃OH, C₂H₅OH, C₃H₇OH, i-C₄H₉OH, n-C₄H₉OH, and C₂H₆O were suppressed at essentially zero. The temperatures for coke-free region decreased with increase in S/C ratios. The impact of pressure was negligible upon the complete conversion of MeOH.     

Steam reforming of methane over unsupported nickel catalysts

This paper describes a study of steam reforming of methane using unsupported nickel powder catalysts. The reaction yields were measured and the unsupported nickel powder surface was studied to explore its potential as a catalyst in internal or external reforming solid oxide fuel cells. The unsupported nickel catalyst used and presented in this paper is a pure micrometric nickel powder with an open filamentary structure, irregular ‘fractal-like’ surface and high external/internal surface ratio. CH₄ conversion increases and coke deposition decreases significantly with the decrease of CH₄:H₂O ratio. At a CH₄:H₂O ratio of 1:2 thermodynamic equilibrium is achieved, even with methane residence times of only ∼0.5 s. The CH₄ conversion is 98 ± 2% at 700 °C and no coke is generated during steam reforming which compares favorably with supported Ni catalyst systems. This ratio was used in further investigations to measure the hydrogen production, the CH₄ conversion, the H₂ yield and the selectivity of the CO, and CO₂ formation. Methane-rich fuel ratios cause significant deviations of the experimental results from the theoretical model, which has been partially correlated to the adsorption of carbon on the surface according to TEM, XPS and elemental analysis. At the fuel: water ratio of 1:2, the unsupported Ni catalyst exhibited high catalytic activity and stability during the steam reforming of methane at low-medium temperature range.     

Construction of fuel reformer using proton conducting oxides electrolyte and hydrogen-permeable metal membrane cathode

We constructed a reformer of methane based on an electrochemical principle. This apparatus consists of the proton conducting ceramics electrolyte and the hydrogen-permeable metal membrane cathode. For methane reforming, a mixture of methane and oxygen gas is supplied to the porous Ag cathode. The hydrogen ions, which formed by the anode reaction: CH₄ + O₂ → CO₂ + 4H⁺ + 4e⁻, are transported through the proton conducting ceramics to the cathode. Then, the hydrogen is formed at the cathode by the reaction: 4H⁺ + 4e⁻ → 2H₂. The hydrogen, which permeates through the metal membrane cathode, is 100% purity.The hydrogen separation ability of the reformer was investigated at 400–650 °C by measuring the electric current through the proton conducting oxide electrolyte. Since the ionic transport number of the proton conducting oxide is nearly unity, the current through the electrolyte corresponds to the proton flux through the electrolyte.The current measurements showed that the extracted proton flux through the electrolyte increased with increasing the applied voltage as well as temperature as we expected. However, the current measurements under the low voltage revealed that the extracted current was lesser than the expected value from Ohm's law. The decrease of the current is possibly caused for the reduction of the effective voltage by the anode polarization. In order to separate the hydrogen with higher efficiency, the applied voltage must be as low as possible using the thinner electrolyte and the improved anode.     

Improving the stability of direct-methane solid oxide fuel cells using anode barrier layers

Solid oxide fuel cells (SOFCs) were characterized with methane as the fuel, both with and without an inert porous layer placed between the anode and the fuel stream. For a given set of operating conditions, SOFCs were stable without coking above a critical current density. The barrier layer decreased the critical current density, e.g. from 1.8 to <0.6 A cm⁻² at 800 °C. This much-increased stable operating range is discussed in terms of mass transport through the barrier layer.     

Fuel effects on start-up energy and efficiency for automotive PEM fuel cell systems

This paper investigates the effects of various fuels on hydrogen production for automotive PEM fuel cell systems. Gasoline, methanol, ethanol, dimethyl ether and methane are compared for their effects on fuel processor size, start-up energy and overall efficiencies for 50 kW_e fuel processors. The start-up energy is the energy required to raise the temperature of the fuel processor from ambient temperature (20 °C) to that of the steady-state operating temperatures. The fuel processor modeled consisted of an equilibrium-ATR (autothermal), high-temperature water gas shift (HTS), low-temperature water gas shift (LTS) and preferential oxidation (PrOx) reactors. The individual reactor volumes with methane, dimethyl ether, methanol and ethanol were scaled relative to a gasoline-fueled fuel processor meeting the 2010 DOE technical targets. The modeled fuel processor volumes were, 25.9 L for methane, 30.8 L for dimethyl ether, 42.5 L for gasoline, 43.7 L for ethanol and 45.8 L for methane. The calculated fuel processor start-up energies for the modeled fuels were, 2712 kJ for methanol, 3423 kJ for dimethyl ether, 6632 kJ for ethanol, 7068 kJ for gasoline and 7592 kJ for methane. The modeled overall efficiencies, correcting for the fuel processor start-up energy using a drive cycle of 33 miles driven per day, were, 38.5% for dimethyl ether, 38.3% for methanol, 37% for gasoline, 34.5% for ethanol and 33.2% for methane assuming a steady-state efficiency of 44% for each fuel.     

Hydrogen production for fuel cells through methane reforming at low temperatures

Hydrogen production for fuel cells through methane (CH₄) reforming at low temperatures has been investigated both thermodynamically and experimentally. From the thermodynamic equilibrium analysis, it is concluded that steam reforming of CH₄ (SRM) at low pressure and a high steam-to-CH₄ ratio can be achieved without significant loss of hydrogen yield at a low temperature such as 550 °C. A scheme for the production of hydrogen for fuel cells at low temperatures by burning the unconverted CH₄ to supply the heat for SRM is proposed and the calculated value of the heat-balanced temperature is 548 °C. SRM with and/or without the presence of oxygen at low temperatures is experimentally investigated over a Ni/Ce–ZrO₂/θ-Al₂O₃ catalyst. The catalyst shows high activity and stability towards SRM at temperatures from 400 to 650 °C. The effects of O₂:CH₄ and H₂O:CH₄ ratios on the conversion of CH₄, the hydrogen yield, the selectivity for carbon monoxide, and the H₂:CO ratio are investigated at 650 °C with a constant CH₄ space velocity. Results indicate that CH₄ conversion increases significantly with increasing O₂:CH₄ or H₂O:CH₄ ratio, and the hydrogen content in dry tail gas increases with the H₂O:CH₄ ratio.     

Hydrogen production from steam and autothermal reforming of LPG over high surface area ceria

Steam and autothermal reforming reactions of LPG (propane/butane) over high surface area CeO₂ (CeO₂ (HSA)) synthesized by a surfactant-assisted approach were studied under solid oxide fuel cell (SOFC) operating conditions. The catalyst provides significantly higher reforming reactivity and excellent resistance toward carbon deposition compared to the conventional Ni/Al₂O₃. These benefits of CeO₂ are due to the redox property of this material. During the reforming process, the gas–solid reactions between the hydrocarbons present in the system (i.e. C₄H₁₀, C₃H₈, C₂H₆, C₂H₄, and CH₄) and the lattice oxygen (O_O^x) take place on the ceria surface. The reactions of these adsorbed surface hydrocarbons with the lattice oxygen (C_nH_m + O_O^x → nCO + m/2(H₂) + V_O + 2e′) can produce synthesis gas (CO and H₂) and also prevent the formation of carbon species from hydrocarbons decomposition reactions (C_nH_m ⇔ nC + 2mH₂). Afterwards, the lattice oxygen (O_O^x) can be regenerated by reaction with the steam present in the system (H₂O + V_O + 2e′ ⇔ O_O^x + H₂). It should be noted that V_O denotes as an oxygen vacancy with an effective charge 2⁺.At 900 °C, the main products from steam reforming over CeO₂ (HSA) were H₂, CO, CO₂, and CH₄ with a small amount of C₂H₄. The addition of oxygen in autothermal reforming was found to reduce the degree of carbon deposition and improve product selectivities by completely eliminating C₂H₄ formation. The major consideration in the autothermal reforming operation is the O₂/LPG (O/C molar ratio) ratio, as the presence of a too high oxygen concentration could oxidize the hydrogen and carbon monoxide produced from the steam reforming. A suitable O/C molar ratio for autothermal reforming of CeO₂ (HSA) was 0.6.     

Hydrogen production for fuel cells by autothermal reforming of methane over sulfide nickel catalyst on a gamma alumina support

Experimental and modelling studies have been conducted on catalytic autothermal reforming (ATR) of methane for hydrogen production over a sulfide nickel catalyst on a gamma alumina support. The experiments are performed with different feedstock under thermally neutral conditions. The results show that the performance of the reformer is dependent on the molar air-to-fuel ratio (A/F), the molar water-to-fuel ratio (W/F) and the flowrate of the feedstock mixture. The optimum conditions for high methane conversion and high hydrogen yield are A/F = 3–3.5, W/F = 2–2.5 and a fuel flowrate below 120–250 l h⁻¹. Under these conditions, a methane conversion of 95–99% and a hydrogen yield of 39–41% on a dry basis can be achieved and 1 mole of methane can produce 1.8 moles of hydrogen at an equilibrium reactor temperature of not exceeding 850 °C.A two-dimensional reactor model is developed to simulate the conversion behaviour of the reactor for further study of the reforming process. The model includes all aspects of the major chemical kinetics and the heat and mass transfer phenomena in the reactor. The predicted results are successfully validated with experimental data.     

The effect of a ceria coating on the H2S tolerance of a molten carbonate fuel cell

To enhance the performance of anodes in molten carbonate fuel cells (MCFCs), in terms of their sulfur tolerance, we modified the surface characteristics of a conventional Ni–10 wt% Cr anode through dip coating using a ceria sol. The performance of the ceria-coated anode was 0.4 V higher than that of the uncoated anode when H₂S (80 ppm) was introduced under a current density of 150 mA cm⁻² for 180 h. H₂S acted as a poison of the non-modified Ni electrode, regardless of its operating conditions, to form Ni₃S₂, which caused the voltage drop. The ceria-coated anode had the ability to suppress such a voltage drop because ceria can react with H₂S to form Ce₂O₂S. Our results suggest that the presence of a CeO₂ coating layer can reduce the degree of sulfur poisoning of the anode under the operating conditions – e.g., a reducing atmosphere and a high temperature – experienced by MCFCs.     

Autothermal reforming study of diesel for fuel cell application

Diesel is one of the best hydrogen storage systems, because of its very high hydrogen volumetric density (100 kg H₂ m⁻²) and gravimetric density (15% H₂). In this study, several catalysts were selected for diesel reforming. Three experimental catalysts (Pt on gadolinium-doped ceria, Rh and Ru on the same support) and two commercial catalysts (FCR-HC14 and FCR-HC35, Süd-Chemie, Inc.) were used to reform diesel. The effects of operating conditions, such as temperature, O₂/C16 and H₂O/C16 on autothermal reforming (ATR) were investigated. In addition, by analyzing the concentrations of products and the temperature profiles along the catalyst bed, we studied the reaction characteristics for a better understanding of the ATR reaction. The fuel delivery and heat transfer between the front exothermic part and the rear endothermic part of the catalyst bed were found to be significant. In this study, the characteristic differences between a surrogate fuel (C₁₆H₃₄) and commercial grade diesel for the ATR were also examined.     

Hydrogen production with integrated microchannel fuel processor for portable fuel cell systems

An integrated microchannel methanol processor was developed by assembling unit reactors, which were fabricated by stacking and bonding microchannel patterned stainless steel plates, including fuel vaporizer, heat exchanger, catalytic combustor and steam reformer. Commercially available Cu/ZnO/Al₂O₃ catalyst was coated inside the microchannel of the unit reactor for steam reforming. Pt/Al₂O₃ pellets prepared by ‘incipient wetness’ were filled in the cavity reactor for catalytic combustion. Those unit reactors were integrated to develop the fuel processor and operated at different reaction conditions to optimize the reactor performance, including methanol steam reformer and methanol catalytic combustor. The optimized fuel processor has the dimensions of 60 mm × 40 mm × 30 mm, and produced 450sccm reformed gas containing 73.3% H₂, 24.5% CO₂ and 2.2% CO at 230–260 °C which can produce power output of 59 Wt.     

Solid oxide fuel cells operated by internal partial oxidation reforming of iso-octane

Two types of solid oxide fuel cells (SOFCs), with thin Ce_0.85Sm_0.15O_1.925 (SDC) or 8 mol% Y₂O₃-stabilized ZrO₂ (YSZ) electrolytes, were fabricated and tested with iso-octane/air fuel mixtures. An additional Ru–CeO₂ catalyst layer, placed between the fuel stream and the anode, was needed to obtain a stable output power density without anode coking. Thermodynamic analysis and catalysis experiments showed that H₂ and CO were primary reaction products at ≈750 °C, but that these decreased and H₂O and CO₂ increased as the operating temperature dropped below ≈600 °C. Power densities for YSZ cells were 0.7 W cm⁻² at 0.7 V and 790 °C, and for SDC cells were 0.6 W cm⁻² at 0.6 V and 590 °C. Limiting current behavior was observed due to the relatively low (≈20%) H₂ content in the reformed fuel.     

A 75-kW methanol reforming fuel cell system

A 75-kW methanol reforming fuel cell system, which consists of a fuel cell system and a methanol auto-thermal reforming fuel processor has been developed at Dalian Institute of Chemical Physics, Chinese Academy of Sciences (CAS). The core of the fuel cell system is a group of CO tolerant PEMFC stacks with a double layer composite structured anode. The fuel cell stacks show good CO tolerance even though 140 ppm CO was present in the reformate stream during transients. The auto-thermal reforming (ATR) fuel cell processor could adiabatically produce a suitable reformate without external energy consumption. The output of hydrogen-rich reformate was approximately 120 N m³ h⁻¹ with a H₂ content near 53% and the CO concentrations generally were under 30 ppm. The fuel cell system was integrated with the methanol reforming fuel processor and the peak power output of the fuel cell system exceeded 75 kW in testing. The hydrogen utilization approached 70% in the fuel cell system.     

High power-density single-chamber fuel cells operated on methane

Single-chamber solid oxide fuel cells (SC-SOFCs) incorporating thin-film Sm_0.15Ce_0.85O_1.925 (SDC) as the electrolyte, thick Ni + SDC as the (supporting) anode and SDC + BSCF (Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ) as the cathode were operated in a mixture of methane, oxygen and helium at furnace temperatures of 500–650 °C. Because of the exothermic nature of the oxidation reactions that occur at the anode, the cell temperature was as much as 150 °C greater than the furnace temperature. Overall, the open circuit voltage was only slightly sensitive to temperature and gas composition, varying from ∼0.70 to ∼0.78 V over the range of conditions explored. In contrast, the power density strongly increased with temperature and broadly peaked at a methane to oxygen ratio of ∼1:1. At a furnace temperature of 650 °C (cell temperature ∼790 °C), a peak power density of 760 mW cm⁻² was attained using a mixed gas with methane, oxygen and helium flow rates of 87, 80 and 320 mL min⁻¹ [STP], respectively. This level of power output is the highest reported in the literature for single chamber fuel cells and reflects the exceptionally high activity of the BSCF cathode for oxygen electro-reduction and its low activity for methane oxidation.     

Performance of Ni/ScSZ cermet anode modified by coating with Gd0.2Ce0.8O2 for an SOFC running on methane fuel

A Ni/scandia-stabilized zirconia (ScSZ) cermet anode was modified by coating with nano-sized gadolinium-doped ceria (GDC, Gd_0.2Ce_0.8O₂) prepared using a simple combustion process within the pores of the anode for a solid oxide fuel cell (SOFC) running on methane fuel. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed in the anode characterizations. Then, the short-term stability for the cells with the Ni/ScSZ and 2.0 wt.%GDC-coated Ni/ScSZ anodes in 97%CH₄/3%H₂O at 700 °C was checked over a relative long period of operation. Open circuit voltages (OCVs) increased from 1.098 to 1.179 V, and power densities increased from 224 to 848 mW cm⁻², as the operating temperature of an SOFC with 2.0 wt.%GDC-coated Ni/ScSZ anode was increased from 700 to 850 °C in humidified methane. The coating of nano-sized Gd_0.2Ce_0.8O₂ particle within the pores of the porous Ni/ScSZ anode significantly improved the performance of anode supported cells. Electrochemical impedance spectra (EIS) illustrated that the cell with Ni/ScSZ anode exhibited far greater impedances than the cell with 2.0 wt.%GDC-coated Ni/ScSZ anode. Introduction of nano-sized GDC particles into the pores of porous Ni/ScSZ anode will result in a substantial increase in the ionic conductivity of the anode and increase the triple phase boundary region expanding the number of sites available for electrochemical activity. No significant degradation in performance has been observed after 84 h of cell testing when 2.0 wt.%GDC-coated Ni/ScSZ anode was exposed to 97%CH₄/3%H₂O at 700 °C. Very little carbon was detected on the anodes, suggesting that carbon deposition was limited during cell operation. Consequently, the GDC coating on the pores of anode made it possible to have good stability for long-term operation due to low carbon deposition.     

Determination of the boundary of carbon formation for dry reforming of methane in a solid oxide fuel cell

The boundary of carbon formation for the dry reforming of methane in direct internal reforming solid oxide fuel cells (DIR-SOFCs) with different types of electrolyte (i.e., an oxygen ion-conducting electrolyte (SOFC-O²⁻) and a proton-conducting electrolyte (SOFC-H⁺)) was determined by employing detailed thermodynamic analysis. It was found that the required CO₂/CH₄ ratio decreased with increasing temperature. The type of electrolyte influenced the boundary of carbon formation because it determined the location of water formed by the electrochemical reaction. The extent of the electrochemical reaction also played an important role in the boundary of carbon formation. For SOFC-O²⁻, the required CO₂/CH₄ ratio decreased with the increasing extent of the electrochemical reaction due to the presence of electrochemical water in the anode chamber. Although for SOFC-H⁺ the required CO₂/CH₄ ratio increased with the increasing extent of the electrochemical reaction at high operating temperature (T > 1000 K) following the trend previously reported for the case of steam reforming of methane with addition of water as a carbon suppresser, an unusual opposite trend was observed at lower operating temperature. The study also considered the use of water or air as an alternative carbon suppresser for the system. The required H₂O/CH₄ ratio and air/CH₄ ratio were determined for various inlet CO₂/CH₄ ratios. Even air is a less attractive choice compared to water due to the higher required air/CH₄ ratio than the H₂O/CH₄ ratio; however, the integration of exothermic oxidation and the endothermic reforming reactions may make the use of air attractive. Water was found to be more effective than carbon dioxide in suppressing the carbon formation at low temperatures but their effect was comparable at high temperatures. Although the results from the study were based on calculations of the SOFCs with different electrolytes, they are also useful for selecting suitable feed compositions for other reactors; including conventional reformers and membrane reactors with hydrogen removal.     

Thermodynamic equilibrium calculations of hydrogen production from the combined processes of dimethyl ether steam reforming and partial oxidation

Thermodynamic analyses of producing a hydrogen-rich fuel-cell feed from the combined processes of dimethyl ether (DME) partial oxidation and steam reforming were investigated as a function of oxygen-to-carbon ratio (0.00–2.80), steam-to-carbon ratio (0.00–4.00), temperature (100 °C–600 °C), pressure (1–5 atm) and product species.Thermodynamically, dimethyl ether processed with air and steam generates hydrogen-rich fuel-cell feeds; however, the hydrogen concentration is less than that for pure DME steam reforming. Results of the thermodynamic processing of dimethyl ether indicate the complete conversion of dimethyl ether to hydrogen, carbon monoxide and carbon dioxide for temperatures greater than 200 °C, oxygen-to-carbon ratios greater than 0.00 and steam-to-carbon ratios greater than 1.25 at atmospheric pressure (P = 1 atm). Increasing the operating pressure has negligible effects on the hydrogen content. Thermodynamically, dimethyl ether can produce concentrations of hydrogen and carbon monoxide of 52% and 2.2%, respectively, at a temperature of 300 °C, and oxygen-to-carbon ratio of 0.40, a pressure of 1 atm and a steam-to-carbon ratio of 1.50. The order of thermodynamically stable products (excluding H₂, CO, CO₂, DME, NH₃ and H₂O) in decreasing mole fraction is methane, ethane, isopropyl alcohol, acetone, n-propanol, ethylene, ethanol and methyl-ethyl ether; trace amounts of formaldehyde, formic acid and methanol are observed.Ammonia and hydrogen cyanide are also thermodynamically favored products. Ammonia is favored at low temperatures in the range of oxygen-to-carbon ratios of 0.40–2.50 regardless of the steam-to-carbon ratio employed. The maximum ammonia content (i.e., 40%) occurs at an oxygen-to-carbon ratio of 0.40, a steam-to-carbon ratio of 1.00 and a temperature of 100 °C. Hydrogen cyanide is favored at high temperatures and low oxygen-to-carbon ratios with a maximum of 3.18% occurring at an oxygen-to-carbon ratio of 0.40 and a steam-to-carbon ratio of 0.00 in the temperature range of 400 °C–500 °C. Increasing the system pressure shifts the equilibrium toward ammonia and hydrogen cyanide.     

A study of Ni + 8YSZ/8YSZ/La0.6Sr0.4CoO3−δ ITSOFC fabricated by atmospheric plasma spraying

An intermediate temperature solid oxide fuel cell (ITSOFC) based on 8YSZ electrolyte, La_0.6Sr_0.4CoO_3−δ (LSCo) cathode, and Ni − 8YSZ anode coatings were consecutively deposited onto a porous Ni-plate substrate by atmospheric plasma spraying (APS). The spray parameters including current, argon and hydrogen flow rate, and powder feed rate were investigated by an orthogonal experiment to fabricate a thin gas-tight 8YSZ electrolyte coating (80 μm). By proper selection of the spray parameters to decrease the particles velocity and temperature, the sprayed NiO + 8YSZ coating after reducing with hydrogen shows a good electrocatalytic activity for H₂ oxidation. With the same treatment, 100–170 μm dimensions LSCo particle could keep phase structure after spraying. And the deposited LSCo cathode shows a good cathode performance and chemical compatibility with 8YSZ electrolyte after operating at 800 °C for 50 h. Output power density of the sprayed cell achieved 410 mW cm⁻² at 850 °C and 260 mW cm⁻² at 800 °C. Electrochemical characterization indicated that IR drop of 8YSZ electrolyte, cathodic polarization, and the contact resistance at LSCo/8YSZ interface were the main factors restricting the cell performance. The results suggested that the use of APS cell allowed the reduction of the operating temperature of the SOFC to below 850 °C with lower production costs.     

High-rate electrochemical partial oxidation of methane in solid oxide fuel cells

This paper describes results on direct-methane solid oxide fuel cell (air, LSM-YSZ|YSZ|Ni-YSZ, CH₄) operation for combined electricity and syngas production. Thermodynamic equilibrium predictions showed that efficient methane conversion to syngas is expected for SOFC operating temperature >700 °C and O²⁻/CH₄ ratios of ≈1. A simple thermal analysis was used to determine conditions where the cell produces enough heat to self-sustain its operating temperature; relatively low cell voltage and O²⁻/CH₄ ratios > 1 were found to be useful. Fuel cells operated at T ≈ 750 °C, V ≈ 0.4 V, and O²⁻/CH₄ ≈ 1.2 yielded electrical power output of ∼0.7 W cm⁻² and syngas production rates of ∼20 sccm cm⁻². Stable cell operation without coking for >300 h was achieved.