Effect of the annealing atmosphere on the electrochemical properties of RuO2 nano-oxides synthesized by the Instant Method

Ruthenium oxide materials have been synthesized by an "Instant method" assisted by microwave irradiation. The "as-synthesized" material has been annealed at different temperatures from 200 degrees C to 450 degrees C, under different atmospheres, air and nitrogen. The different samples were characterized by X-ray diffraction, transmission electron microscopy and cyclic voltammetry (capacitance, charges involved, etc.). The physicochemical and electrochemical characterizations have evidenced that the main effect of the annealing atmosphere is the modification of the transition temperature from an amorphous hydrated phase to a crystalline phase of ruthenium oxide (ca. 300 degrees C under air and ca. 350 degrees C under inert atmosphere according to XRD measurement). The activity of the different catalysts towards the oxygen evolution reaction was evaluated by linear scan voltammetry. In the high overpotential region (E> 1.6V vs. RHE), higher catalytic activities were obtained after annealing at high temperatures, i.e. 400-450 degrees C, independently on the annealing atmosphere. In the low overpotential region (E < 1.5 V vs. RHE), higher activity in terms of exchange current density j(0) was obtained for hydrated ruthenium oxide compounds, which was explained by the ability of materials to oxidize water molecules trapped in the ruthenium oxide lattice. (C) 2017 Elsevier B.V. All rights reserved.