Elementary kinetic modeling and experimental validation of electrochemical CO oxidation on Ni/YSZ pattern anodes

Abstract

Carbon monoxide (CO) is a major component in typical feed gases for solid oxide fuel cells (SOFC). This paper presents a combined modeling and experimental analysis of electrochemical CO oxidation on Ni/YSZ patterned model anodes. A computational model representing the coupled behavior of heterogeneous chemistry and electrochemistry in terms of elementary reactions is developed, which allows for a quantitative description of electrochemical impedance spectra and current-voltage behavior. Excellent agreement between model and experiment was achieved for the complete experimental data set, which covers a wide range of CO/CO 2 /N 2 gas compositions (4.0 × 10 2 Pa ≤ pCO ≤ 5.1 × 10 4 Pa and 9.5 × 10 2 Pa ≤ pCO 2 ≤ 9.2 × 10 4 Pa) and operating temperatures (973 K ≤ T ≤ 1073 K). In the framework of the presented model a direct mechanistic interpretation of the experimentally observed electrochemical characteristics is obtained.

Sulfur Poisoning of Anode‐Supported SOFCs under Reformate Operation

“…Conventional Ni/YSZ cermet anodes act as a catalyst converting hydrocarbon fuels and steam into hydrogen and carbon monoxide [1] and as an electrocatalyst preferentially electro-oxidizing the hydrogen in the reformate. Even though carbon monoxide can be electro-oxidized as well and a stable operation in appropriate CO/CO 2 -mixtures is possible [2][3][4], in reformate-fuelled anode supported cells only H 2 is electro-oxidized at the triple phase boundaries. This is related to the fast catalytic watergas shift reaction on the Ni-surface in the substrate and the anode functional layer of an anode supported cell (ASC) [5].…”

Kinetics of CO/CO2 and H2/H2O reactions at Ni-based and ceria-based solid-oxide-cell electrodes

“…15,16 Acceptor-doped ceria is a well-known MIEC solid when exposed to a reducing environment and it exhibits high activity for the H 2 /H 2 O reaction when applied as an electrode. [17][18][19][20] Considerable effort has gone into understanding and modelling the reaction kinetics and mechanisms for the H 2 /H 2 O and CO/CO 2 reactions, especially for Ni-SZ electrodes, [21][22][23][24][25] but also more recently for ceria-based electrodes. 16,[26][27][28] However, relative activities for the CO/CO 2 and H 2 /H 2 O reactions are not well studied, even for conventional Ni-SZ electrodes.…”

Oxidation of H2, CO and syngas mixtures on ceria and nickel pattern anodes

“…This indicates that catalysis on ceria is probably better as well. If CO oxidation on nickel proceeds via a Langmuir Hinshelwood type reaction [34] then the site occupancy may be the limiting factor in case of nickel. Also the reaction is supposed Fig.…”

“…[20] and [24] observed considerable scatter or instability while operating with CO-CO 2 gas atmospheres. Yurkiv et al [34] propose an oxygen spillover kind of mechanism where oxidation happens in a Langmuir-Hinshelwood type reaction on the nickel surface involving adsorbed CO and oxygen. The oxygen from the electrolyte gives up an electron and spills over to the nickel surface.…”