Hydrogen Oxidation and Water Dissociation over an
Oxygen-Enriched Ni/YSZ Electrode
in the Presence of an Electric Field: A First-Principles-Based Microkinetic
Model
Elucidating
the sulfur poisoning or coking for electrochemical
cells (e.g., a solid oxide fuel cell (SOFC) and a solid oxide electrolysis
cell (SOEC)) is highly dependent on studying such mechanisms by which
said catalysts deactivate under experimentally relevant conditions.
For a SOFC (or a SOEC) system, this requires the inclusion of the
effect of a negative (or a positive) electric field when modeling
the elementary catalytic reactions. In this contribution, the field
effects on hydrogen oxidation and water decomposition over the triple
phase boundary (TPB) region of the Ni/YSZ electrode are investigated
using a field-dependent microkinetic model. Our results first show
that the field effects on the Ni surface of the Ni/(YSZ+O) model are
different as compared to a pure Ni(111) surface due to a difference
in the charge distribution on the said surfaces. Between 400 to 1200
K, the negative fields assist in hydrogen oxidation over the TPB region
of the Ni/(YSZ+O) cermet, which can potentially result in a larger
probability for the said model to have oxygen vacancies at the TPB.
Consequently, deactivation from sulfur poisoning or coking can increase
since such vacancies are active for sulfur adsorption or coke formation.
On the other hand, a high positive electric field can decrease the
water decomposition rate to form hydrogen as compared to when the
field is absent. Overall, this study provides insights for considering
the electric field effects on the hydrogen oxidation and water dissociation
over Ni/(YSZ+O) electrodes
