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

Abstract

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.

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