Hexavalent Ru Catalyst with Both Lattice Oxygen and Metal Ion Mechanisms Coactive for Water Oxidation

Green hydrogen from water requires the development of efficient and low-cost catalysts for anodic oxygen evolution reaction (OER), which is the main obstacle for electrochemical water splitting. Herein, we focus on an OER catalyst (Pb₂CoRuO₇) featuring Ru⁶⁺, which exhibits an ultralow overpotential of 176 mV at 10 mA cm^-2 and a Tafel slope of 30.52 mV dec^-1 vs 340 mV at 10 mA cm^-2 and a Tafel slope of 111.54 mV dec^-1 for RuO₂ in 1.0 M KOH solution. In situ X-ray absorption experiments demonstrated the gradual conversion of Ru⁵⁺ ions into high-valence Ru⁶⁺, while a portion of Co³⁺ ions transformed into Co⁴⁺ during the OER process. Density functional theory calculations revealed that the ultrahigh OER activity of Pb₂CoRuO₇ was contributed by both metal-site adsorbate evolution (MAE) at the Co site and the lattice-oxygen-vacancy-site (LOV) mechanism involving lattice oxygen located between Ru⁶⁺ and Co. Our work presents a new and unusual OER catalyst where both the MAE and LOV mechanisms cooperatively facilitate catalytic activity.