Investigation of Oxygen Evolution Reaction at LaRuO 3 , La 3.5 Ru 4 O 13 , and La 2 RuO 5

Abstract Development of electrocatalysts is important for reducing the voltage loss due to the oxygen evolution reaction (OER) in metal-air batteries and water electrolyzers. In the present work, the electrocatalytic activity towards oxygen evolution for a series of lanthanum-ruthenium compounds has been investigated by steady-state current-potential measurements in alkaline media to understand the effect of structure, valence state of the transition metal ion, and the role of surface adsorbed hydroxyl species. Compounds of the perovskite family, LaRuO 3 , La 3.5 Ru 4 O 13 , and La 2 RuO 5, were prepared by the Pechini process and calcined at different temperatures to obtain the desired phases. X-ray photoelectron spectroscopy of LaRuO 3 and La 2 RuO 5 showed shifts of the Ru-3d peaks towards higher binding energies indicative of a highly oxidized surface with possibly high surface hydroxylation. The electrochemical activity of the compounds at 0.8  V vs. NHE was in the order of 10 −6  A/cm 2 and the mass specific activity was about 80  mA/g . Tafel slopes were in the vicinity of 60  mV/decade for LaRuO 3 (orthorhombic) and La 3.5 Ru 4 O 13 (orthorhombic), and about 80  mV/decade for La 2 RuO 5 (monoclinic). In addition FT-IR results indicate high surface coverage by hydroxide species. The reaction order with respect to OH − ions was found to be lower than unity. It is possible that strong interaction of hydroxide groups with ruthenium at the surface of the electrode makes it difficult to dissociate the Ru-OH bond and prevent further interaction with dissolved OH − even at high overpotentials.