Detailed H<sub>2</sub> and CO Electrochemistry for a MEA Model Fueled by Syngas

Lee, Won Yong; Ong, Katherine M.; Ghoniem, Ahmed F.

doi:10.1149/06801.3059ecst

Cited by 7 publications

(4 citation statements)

References 31 publications

(59 reference statements)

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“…Conversely, assuming that WGS and SMR are fast reactions, some authors estimate the OCV by substituting the equilibrium partial pressures in Eq. 4 (Stoots et al, 2009;Lee et al, 2015;Jin et al, 2018;Vágner et al, 2019), calculated assuming that both WGS and SMR go to equilibrium at local temperature and pressure, starting from the bulk gas composition. Therefore, using the equilibrium partial pressures allows to indirectly include species like CO and CH 4 in the estimation of the OCV.…”

Section: Introductionmentioning

confidence: 99%

Theoretical analysis of mixed open-circuit potential for high temperature electrochemical cells electrodes

Cammarata

Mastropasqua

2023

Front. Energy Res.

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The Nernst equilibrium potential calculates the theoretical OCV, which estimates the best performance achievable by an electrochemical cell. When multiple semi-reactions (or multiple ionic species) are active in one of the electrodes, the calculation of the theoretical OCV is not straightforward, since different Nernst potentials are associated to each semi-reaction. In this paper, analytical equations for calculation of the theoretical OCV are developed, using the mixed potential theory. The case of H2 and CO co-oxidation (or H2O and CO2 co-reduction) in solid oxide cells is used as a reference case, but similar conclusions can be drawn for other equivalent cases. OCV data from literature are used to calibrate and validate the model. The relative reaction rate of H2 and CO semi-reactions is estimated within the calibration process, and the result is in line with assumptions and suggestions given by other authors. The validation procedure shows predicted OCV values in line with experimental literature data, except for mixtures with relatively large CH4 concentration (e.g., 8%), for which the OCV is significantly underestimated. This is expected when thermochemical reactions, in parallel to electrochemical reactions occur, since the additional H2 produced by internal steam methane reforming is not accounted within the local mixed potential model. A fuel cell polarization model is developed based on the results from the calibration procedure, and it is used to predict the polarization behavior of an SOFC fed with a H2-H2O-CO-CO2 fuel mixture. It is found that either H2 or CO may be reduced rather than oxidized via an equivalent electrochemical water-gas-shift reaction.

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Section: Introductionmentioning

confidence: 99%

Theoretical analysis of mixed open-circuit potential for high temperature electrochemical cells electrodes

Cammarata

Mastropasqua

2023

Front. Energy Res.

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“…Specifically, the diffusion could be simplified to a single dimension, typically in the flow direction [24][25][26][27] or anode-thickness direction. [28][29][30][31] This captures some of the physics due to 1D gas diffusion and heterogeneous reactions at the solid/gas interfaces, while significantly reducing the computational effort required. Another more widely used approach to reducing the model order is by projection-based mathematical reduction, in which a set of data is mapped into sub-set with certain accuracy.…”

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confidence: 99%

The Performance of Syngas-Fueled SOFCs Predicted by a Reduced Order Model (ROM): Temperature and Fuel Composition Effects

Jin

Ku²,

Verma³

et al. 2018

J. Electrochem. Soc.

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An electrochemical reduced order model (ROM) has been developed in this study to simulate the performance of syngas-fueled anode-supported SOFCs with coupled bulk chemical reactions and multi-species gas diffusion in the electrodes. Experimental V-I curves with syngas fuel were used to validate the model to ensure its high fidelity. The model was used to investigate the effects of fuel composition and temperature on the electrochemical performance of the cell, chemical reaction rate and concentration distributions of gaseous species across the anode. The results show that H 2 electro-oxidation dominates the overall cell performance, and that CO contributes to the performance indirectly via water gas shift (WGS) reaction, especially at low CO:H 2 ratio and low current densities. Increasing the temperature enhances the performance of syngas-fueled SOFCs by increasing the rates of total electrochemical oxidation and the WGS reaction. The present work provides fundamental knowledge and framework for future performance simulations of large-scale and more complex syngas-fueled SOFC systems.

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“…20,22,23 Researchers have found that O spillover to CO on nickel is a more likely pathway than CO spillover to YSZ because CO molecules have a strong affinity to nickel sites. [24][25][26] However, most MEA models represent CO electrooxidation as a global reaction rather than implementing the detailed * Electrochemical Society Student Member.…”

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confidence: 99%

“…[18][19][20][21] However, understanding the mechanism for CO electro-oxidation is critical to accurately represent syngas mixtures, where CO is present in large enough quantities to contribute to cell current. 20,22,23 Researchers have found that O spillover to CO on nickel is a more likely pathway than CO spillover to YSZ because CO molecules have a strong affinity to nickel sites. [24][25][26] However, most MEA models represent CO electrooxidation as a global reaction rather than implementing the detailed O spillover pathway.…”

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confidence: 99%

Investigation of a Combined Hydrogen and Oxygen Spillover Mechanism for Syngas Electro-Oxidation on Ni/YSZ

Ong

Hanna

Ghoniem

2016

J. Electrochem. Soc.

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An accurate, comprehensive model for the individual and simultaneous electro-oxidation of H 2 and CO on Ni-YSZ is necessary to predict SOFC performance for a range of gaseous fuels. A mechanism that combines hydrogen (H) spillover to YSZ with oxygen (O) spillover to nickel is implemented in a previously-validated 1D-MEA model with detailed gas-phase transport and surface reforming kinetics in the anode. This model is then successfully fitted to a wide range of experimental polarization data for fuel mixtures. The H and O spillover pathways are then investigated in depth for two anode fuel mixtures: 20% H 2 + 80% N 2 and 20% H 2 + 80% CO. Although these studies confirm that H spillover is typically the dominant source of current, they also show that the current produced by O spillover is non-negligible at higher currents. Furthermore, it is observed that H 2 adsorption to nickel becomes the rate-limiting step at high currents in the hydrogen pathways, while the current produced by O spillover to C O(Ni) is never limited by the rate of CO adsorption. The model is then successfully compared to two independent lower temperature data sets. Together these results demonstrate that it is important to model both spillover pathways on Ni/YSZ and to account for rate-limiting H 2 adsorption at high currents. The thermochemical and electrochemical reaction mechanisms within a SOFC anode are complex, particularly when hydrocarbon species are involved.1-3 Elementary reaction steps are needed to accurately depict gas-phase chemistry, heterogeneous surface reforming, and heterogeneous charge-transfer reactions. Understanding the governing mechanisms for internal reforming and electrochemistry is paramount to optimize anode structure and operating conditions. More specifically, it is critical to identify the correct rate-limiting steps in these elementary mechanisms because those steps control the rate at which the cell can produce current. The elementary electro-oxidation reaction mechanisms for H 2 and CO require special attention because both of these fuels are dominant in practical SOFC fuel streams like reformed natural gas, coal syngas and biogas. 4 A couple of reaction mechanism types have been proposed to represent H 2 electrochemical oxidation at the triple-phase boundary (TPB) of Ni-YSZ: (1) hydrogen spillover and (2) oxygen spillover. Hydrogen (H) spillover mechanisms involve a charge-transfer step where hydrogen spills over from nickel to YSZ to react with oxygen. Oxygen (O) spillover mechanisms, on the other hand, involve a charge-transfer step where oxygen spills over from YSZ to nickel to react with hydrogen. Hydrogen electro-oxidation models typically select only one spillover pathway rather than implementing both the H and O spillover pathways simultaneously. Although a few researchers have used O spillover mechanisms to describe H 2 electro-oxidation, 5,6 the majority have implemented H spillover mechanisms.7-14 A few researchers have compared these two pathways and concluded that H spillover mechanisms are bett...

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Detailed H₂ and CO Electrochemistry for a MEA Model Fueled by Syngas

Cited by 7 publications

References 31 publications

Theoretical analysis of mixed open-circuit potential for high temperature electrochemical cells electrodes

Theoretical analysis of mixed open-circuit potential for high temperature electrochemical cells electrodes

The Performance of Syngas-Fueled SOFCs Predicted by a Reduced Order Model (ROM): Temperature and Fuel Composition Effects

Investigation of a Combined Hydrogen and Oxygen Spillover Mechanism for Syngas Electro-Oxidation on Ni/YSZ

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Detailed H2 and CO Electrochemistry for a MEA Model Fueled by Syngas

Cited by 7 publications

References 31 publications

Theoretical analysis of mixed open-circuit potential for high temperature electrochemical cells electrodes

Theoretical analysis of mixed open-circuit potential for high temperature electrochemical cells electrodes

The Performance of Syngas-Fueled SOFCs Predicted by a Reduced Order Model (ROM): Temperature and Fuel Composition Effects

Investigation of a Combined Hydrogen and Oxygen Spillover Mechanism for Syngas Electro-Oxidation on Ni/YSZ

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Detailed H₂ and CO Electrochemistry for a MEA Model Fueled by Syngas