Identification of the molecular pathways of RuO2 electroreduction by in-situ electrochemical surface-enhanced Raman spectroscopy.

[Display omitted] • Au@RuO x core–shell nanostructures are fabricated to amplify the Raman signals. • Electroreduction of RuO x is in-situ studied using the borrowing SERS strategy. • Direct evidences of OH intermediate are obtained during RuO x electroreduction. • A two-step molecular pathway is proposed for RuO 2 electroreduction. RuO 2 is one of the most promising catalysts for oxygen evolution reaction (OER), a key reaction in water electrolysis. However, the fundamental insights about the structural evolution of RuO 2 under different electrochemical environments remain unclear. Herein, the molecular reaction pathways of the electroreduction of RuO x in alkaline and neutral conditions are identified using in-situ electrochemical surface-enhanced Raman spectroscopy. Au@RuO 2 core–shell nanostructures are fabricated to amplify the Raman signals of species adsorbed on RuO x surfaces. Using such core–shell nanostructures, direct spectroscopic evidences of OH intermediate during the RuO 2 electroreduction process are obtained, which is further confirmed by D 2 O isotopic substitution experiments. A molecular pathway that RuO 2 is reduced to Ru through a two-step reduction process has been proposed. This work provides insightful information on the structural evolution of RuO x with electrochemical environments. [ABSTRACT FROM AUTHOR]