Effect of Varying RuO2 (100) Thin-Film Stoichiometry on the Activity-Stability Compromise in the Oxygen Evolution Reaction: Pathway to RuO2 Degradation

Abstract This study investigates the electrochemical properties of ruthenium dioxide RuO2 (100) thin films to understand the effect of varying oxygen deposition ambience on the activity-stability compromise and the degradation pathways consisting of the Lattice Oxygen Mechanism (LOM) and Adsorption Evolution Mechanism (AEM). Electrochemical evaluation of the RuO2 films in the oxygen evolution reaction (OER) in both alkaline and acidic media shows a lower overpotential for less oxygenated films than for more oxygenated films. Stability analysis reveals that, under alkaline conditions, the less oxygenated RuO2 thin-film samples experience a ∼16.5% reduction in current density, while the more oxygenated films experience a ∼9% reduction after 3 h. In acidic conditions, a higher current reduction of ∼21% was observed for the less oxygenated samples, whereas an improved current output of up to 17% was observed for the more oxygenated samples. The Ru dissolution trend for less oxygenated and more oxygenated films showed more than an order of magnitude variation under alkaline conditions and less than 1 order of magnitude under acidic conditions. Additionally, Ru metal dissolution increased by an average of 2 orders of magnitude under acidic conditions compared to alkaline conditions. Faradaic efficiency (FE) was considerably low for the more oxygenated films under both acidic and alkaline conditions. Based on the observed high current density, low overpotential, and high FE, we hypothesize that while LOM is operative in less oxygenated samples, AEM is operative in more oxygenated samples.