Internal reforming development for solid oxide fuel cells

Lee, Anthony L.; Zabransky, R.F.; Huber, Wolfgang

doi:10.1021/ie00101a009

Cited by 145 publications

(66 citation statements)

References 2 publications

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“…The first-order dependence on methane pressure in this rate expression is consistent with much of the literature data for testing pressures up to 41 atm, as noted by Lee et al (1990). It is also consistent with the earlier rate expression derived from testing at PNNL by King and coworkers (2005).…”

Section: Pressurization and Methane Reformingsupporting

confidence: 91%

Modeling of Pressurized Electrochemistry and Steam-Methane Reforming in Solid Oxide Fuel Cells and the Effects on Thermal and Electrical Stack Performance

Recknagle¹,

Khaleel²

2009

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Executive SummaryThis report summarizes work done to extend the electrochemical performance and methane reforming submodels to include the effects of pressurization and to demonstrate this new modeling capability by simulating large stacks operating on methane-rich fuel under pressurized and nonpressurized conditions. Pressurized operation boosts electrochemical performance, alters the kinetics of methane reforming, and affects the equilibrium composition of methane fuels. This work developed constitutive submodels that couple the electrochemistry, reforming, and pressurization to yield an increased capability of the modeling tool for prediction of solid oxide fuel cell (SOFC) stack performance.The electrochemistry model was advanced to characterize the increased SOFC performance due to diminished activation polarization. The activation polarization depends upon the exchange current density between the electrodes and electrolyte. The exchange current density is increased by elevated pressure resulting in decreased polarization loss. The Nernst potential is also increased with pressure, and, when augmented by the decreased polarization, provides increased cell voltage and stack power.The operating pressure has competing effects on reformation; it increases the methane conversion rate while also increasing the equilibrium methane concentration. The methane conversion rate expression developed by this work accounted for these effects. The rate expression used equilibrium gas compositions for temperatures ranging from 650° to 850°C and pressures of 1 to 10 atmospheres, and incorporated the steam-methane reaction equation. The gas compositions were used to calculate the equilibrium constant, and the reforming reaction equation established the form of the forward and backward terms. The combination of these elements resulted in an expression of the overall conversion rate that correctly accounts for the pressurization effect on the kinetics and the reverse reaction.The models accounting for the pressure effects on the electrochemistry and methane reforming were applied in stack simulations to examine how they can potentially change the distributions of fuel, air, current density, temperature, and reforming rates within large area stacks. An ordinary 20x20-cm cross-flow stack model geometry was used as a generic example of a "large" planar stack to demonstrate how the modeling tool can be applied to any proposed stack design for a similar analysis. We expect differences in the scalar distributions depending upon the size and configuration of the stack. We also expect the trends of pressurization effects on the reforming rates, temperatures, current density, gas concentrations, and pressure drops would be the same for any other planar stack under pressurized operation. Cases of operating pressures ranging from 1 to 10 atmospheres and 2 reformation rates differing by a factor of 10 were simulated. The predictions showed consistently increased electrical performance for both reforming rate cases with increased operating p...

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Section: Pressurization and Methane Reformingsupporting

confidence: 91%

Modeling of Pressurized Electrochemistry and Steam-Methane Reforming in Solid Oxide Fuel Cells and the Effects on Thermal and Electrical Stack Performance

Recknagle¹,

Khaleel²

2009

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“…The presence of temperature gradients and coking are the main limitations for DIR-SOFC. Research on direct internal reforming SOFC with Ni/YSZ anode is limited almost exclusively to methane [17][18][19][20][21][22][23], with few examples of IIR-SOFC using model fuels [24][25][26].…”

Section: Sofc Operating Modes With Hydrocarbon Fuelsmentioning

confidence: 99%

Direct Utilization of Liquid Fuels in SOFC for Portable Applications: Challenges for the Selection of Alternative Anodes

2009

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Solid oxide fuel cells (SOFC) have the advantage of being able to operate with fuels other than hydrogen. In particular, liquid fuels are especially attractive for powering portable applications such as small power generators or auxiliary power units, in which case the direct utilization of the fuel would be convenient. Although liquid fuels are easier to handle and transport than hydrogen, their direct use in SOFC can lead to anode deactivation due to carbon formation, especially on traditional nickel/yttria stabilized zirconia (Ni/YSZ) anodes. Significant advances have been made in anodic materials that are resistant to carbon formation but often these materials are less electrochemically active than Ni/YSZ. In this review the challenges of using liquid fuels directly in SOFC, in terms of gas-phase and catalytic reactions within the anode chamber, will be discussed and the alternative anode materials so far investigated will be compared.

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“…The kinetics of the steam reforming reaction have been extensively studied on Ni surfaces due to the indastrial importance of this reaction [1,2,3]. On the contrary much less information is available regarding the kinetics of the steam reforming reaction on Ni-YSZ cermets [4][5][6][7] and unfortunately, in some cases published data do not reflect true kinetics but the approach to thermodynamic equilibrium [7].…”

Section: Introductionmentioning

confidence: 99%

Catalysis, electrocatalysis and electrochemical promotion of the steam reforming of methane over Ni film and Ni-YSZ cermet anodes

Yentekakis

Jiang

Neophytides

et al. 1995

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Abstract. The kinetics of the steam reforming reaction of CH 4 were investigated at temperatures 750 to 950~ under both open-circuit and closed-circuit conditions on Ni-YSZ (Yttria Stabilized Zirconia) solid oxide fuel cell (SOFC) anodes and polycrystalline Ni film SOFC anodes of measured Ni surface area. It was found that the rate of methane reforming on the Ni surface exhibits a Langmuir-Hinshelwood type dependence on PCH4 and PH20 which results from competitive adsorption of carbonaceous species and oxygen or OH. Consequently the rate is maximized for intermediate PCH4 to PH:,O ratios. The reaction kinetics are affected significantly by cell current and potential under closed-circuit conditions. Over a rather wide range of operating conditions the observed rate changes are Faradaic, which implies negligible variation in the catalytic properties of the Ni surface with potential. At lower temperatures, however, and particularly under conditions of carbon deposition, the rates of CO, H2, CO2 and, more importantly, carbon formation exhibit pronounced non-Faradaic (NEMCA), or electrochemical promotion, behaviour. Some non-Faradaic hehaviour is also observed for higher H20 to CI-I4 ratios but in this ease the effect of applied potential is reproducible but not readily reversible.

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Internal reforming development for solid oxide fuel cells

Cited by 145 publications

References 2 publications

Modeling of Pressurized Electrochemistry and Steam-Methane Reforming in Solid Oxide Fuel Cells and the Effects on Thermal and Electrical Stack Performance

Modeling of Pressurized Electrochemistry and Steam-Methane Reforming in Solid Oxide Fuel Cells and the Effects on Thermal and Electrical Stack Performance

Direct Utilization of Liquid Fuels in SOFC for Portable Applications: Challenges for the Selection of Alternative Anodes

Catalysis, electrocatalysis and electrochemical promotion of the steam reforming of methane over Ni film and Ni-YSZ cermet anodes

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