A detailed look into hydrogen electrochemical oxidation on ceria anodes

Abstract

Using the Nernst-Planck-Poisson model and a detailed reaction mechanism, we studied the hydrogen electrochemical oxidation on a ceria anode. Resistances caused by surface kinetics, and bulk transport of oxide-ion vacancies and electrons are computed individually to identify the dominant resistive process. The effect of operating conditions like temperature and gas-phase composition on the polarization resistance is evaluated and compared with the experimental data obtained by Electrochemical Impedance Spectroscopy (EIS). The ratedetermining step is found to be the charge-transfer reaction in which hydrogen adsorbs at the surface oxide ions and forms hydroxyls along with the chargetransfer to adjacent cerium ions. Based on the rate-determining step, the exchange-current density is also calculated and validated with the experimental data.

Effect of H2S and HCl contaminants on nickel and ceria pattern anode solid oxide fuel cells

“…Correspondingly, OH • o and S x o are hydroxyl, and sulfur ions residing at anionic sites, respectively. In line with the previous findings [36,37], reaction (2) is the rate-determining step. The above scheme exhibits a global interaction of sulfur with ceria with an assumption that OH • o and S x o do not diffuse into the bulk.…”

“…We find that a rise in polarization resistance occurs primarily at low frequencies, even for pattern electrode cells, which is consistent with our previous findings. In our previous studies [36,37], where the model was developed for hydrogen oxidation on ceria, the low-frequency process was attributed to the electrochemical process, including adsorption, charge transfer, and desorption. Even if sulfur does not participate in the charge transfer process, it is possible to link an increase in polarization resistance to the adsorption of sulfur species on ceria even if sulfur does not participate in charge transfer.…”

“…In this section, we undertake elementary kinetic modeling of H 2 S poisoning of ceria pattern electrode cells to develop an approach to quantify the effect of contaminants from microscopic experiments like these and use them in macroscopic simulations. The base model with pure hydrogen oxidation is based on the reaction scheme published previously [37]. Due to limited knowledge about sulfur interaction with ceria-based SOFC anodes, we assume that (i) sulfur does not electrochemically oxidize under reducing conditions, and (ii) sulfur does not chemically react with ceria to form cerium sulfides.…”

“…In previous works, we have used nickel and ceria pattern electrode cells to analyze the oxidation of hydrogen and carbon monoxide and mixtures thereof and highlighted the possible use of (un)doped ceria as an anode material in its reduced state [34,35]. Combined with modeling, this has proved to be a useful exercise in understanding the differences in the oxidation mechanism between nickel and ceria and, indeed, proposed possible reaction schemes [5,36,37]. Further, we derived TPB-based kinetics from the pattern electrode cell experimental data and proposed a procedure for implementing such kinetic information in the computational fluid dynamic model [38,39].…”

Modeling the impedance response and steady state behaviour of porous CGO-based MIEC anodes

“…Nevertheless, the aim is to formulate a simplified surface reaction overpotential accounting for the rate limiting step. Tabish et al 56 summarized the different rate-determining steps for ceria electrodes reported in the literature and concluded that the majority of the studies depict a charge transfer step to be the rate-determining step, though there are differences in the understanding of how and where this rate limiting charge transfer process takes place. We therefore use the following formulation for the surface reaction overpotential Z SR , which implies that the charge transfer is the ratedetermining step and that all other intermediate steps are very close to the equilibrium.…”