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Journal of Applied Electrochemistry

, Volume 40, Issue 5, pp 943–954 | Cite as

SOFC fuelled by methane without coking: optimization of electrochemical performance

  • J. M. Klein
  • S. Georges
  • Y. BultelEmail author
Original Paper

Abstract

In recent years, fuel cell technology has attracted considerable attention from several fields of scientific research as fuel cells produce electric energy with high efficiency, emit little noise, and are non-polluting. Solid oxide fuel cells (SOFCs) are particularly important for stationary applications due to their high operating temperature (1,073–1,273 K). Methane appears to be a fuel of great interest for SOFC systems because it can be directly converted into hydrogen by direct internal reforming (DIR) within the SOFC anode. Unfortunately, internal steam reforming in SOFC leads to inhomogeneous temperature distributions which can result in mechanical failure of the cermet anode. Moreover this concept requires a large amount of steam in the fed gas. To avoid these problems, gradual internal reforming (GIR) can be used. GIR is based on local coupling between steam reforming and hydrogen oxidation. The steam required for the reforming reaction is obtained by the hydrogen oxidation. However, with GIR, Boudouard and cracking reactions can involve a risk of carbon formation. To cope with carbon formation a new cell configuration of SOFC electrolyte support was studied. This configuration combined a catalyst layer (0.1%Ir–CeO2) with a classical anode, allowing GIR without coking. In order to optimise the process a SOFC model has been developed, using the CFD-Ace+ software package, and including a thin electrolyte. The impact of a thin electrolyte on previous conclusions has been assessed. As predicted, electrochemical performances are higher and carbon formation is always avoided. However a sharp decrease in the electrochemical performances appears at high current densities due to steam clogging.

Keywords

SOFC Gradual internal reforming Simulation CFD-Ace+ 

List of symbols

Di

Diffusion coefficient of the i-th species (m2 s−1)

Di,eff

Effective diffusion coefficient of the i-th species (m2 s−1)

E0

Voltage between the electrolyte and the nickel at equilibrium (V)

F

Faraday constant (96500) (C mol−1)

Ji

Diffusion flux of the i-th species (mol m−2 s−1)

KE1

Equilibrium constant of steam methane reforming reaction (Pa2)

KE2

Equilibrium constant of water gas shift reaction (–)

KB

Equilibrium constant of Boudouard reaction (Pa−1)

KC

Equilibrium constant of Cracking reaction (Pa)

M

Molecular weight of the mixture of gases (kg kmol−1)

Pi

Partial pressure of the i-th species (Pa)

R

Universal gas constant (8.314) (J mol−1 K−1)

(S/V)eff

Effective surface-to-volume ratio (m2 m−3)

T

Temperature (K)

ac

Carbon activity (–)

dpore

Pore diameter (M)

H

Gas mixture enthalpy (J kg−1)

hB

Solid-phase enthalpy (J kg−1)

i

Current density (A m−2)

[i]

Molar concentration of the i-th species (kmol m−3)

[i]0

Reference concentration of the i-th species (kmol m−3)

ja0

Exchange current density of the anode (A m−2)

jat

Faradaic current due to anodic reaction (A m−2)

jct

Faradaic current due to cathodic reaction (A m−2)

P

Total pressure (Pa)

Q

Heat flux (W m−2)

rk

Reaction rate of the k-th reaction (Kmol m−3 s−1)

Ucell

Cell potential (V)

v

Fluid velocity (m s−1)

wi

Mass fraction of the i-th species (–)

xi

Molar fraction of the i-th species (–)

Greeks

α

Boudouard coefficient (–)

αa

Anodic Tafel constant (–)

αc

Cathodic Tafel constant (–)

β

Cracking coefficient (–)

δ

Shear stress tensor (–)

ε

Porosity (–)

ϕas

Ionic phase potential at anode (V)

ϕaM

Electronic phase potential at anode (V)

ϕes

Ionic phase potential of the electrolyte (V)

γ

Boudouard + Cracking coefficient (–)

λB

Thermal conductivity of the solid phase (W m−1 K−1)

ηa

Anode overpotential (V)

κ

Permeability (m2)

μ

Dynamic viscosity of the gas mixture (Pa s)

μi

Dynamic viscosity of the i-th species (Pa s)

ρ

Mass density of the gas mixture (kg m−3)

σas

Ionic phase conductivity at anode (Ω−1 m−1)

σaM

Electronic phase conductivity at anode (Ω−1 m−1)

σes

Ionic phase conductivity of the electrolyte (Ω−1 m−1)

τ

Tortuosity of pores (m m−1)

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Copyright information

© Springer Science+Business Media B.V. 2010

Authors and Affiliations

  1. 1.Laboratoire d’Electrochimie et de Physico-Chimie des Matériaux et des Interfaces (LEPMI)UMR 5631 CNRS-GINP-UJFSaint Martin d’HèresFrance

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