Comparative Study of Ru-Transition Metal Alloys and Oxides as Oxygen Evolution Reaction Electrocatalysts in Alkaline Media

The oxygen evolution reaction (OER), as the anodic reaction in water electrolyzers, generally exhibits much higher overpotentials than the hydrogen evolution reaction (HER) and thus requires the development of more active, robust, and stable electrocatalysts. In this work, a series of carbon-supported Ru–M alloy nanoparticles (M = Ir, Co, Ni, and Fe), transition metal (TM)-doped RuO2 nanoparticles such as Ru1–xMnxO2, Ru1–xCoxO2, Ru1–x–yMnxCoyO2, Ru1–xFexO2, Ru1–xNixO2, and Ru1–xVxO2/C, as well as RuO2, MnO2, Co3O4, and Co3–xMnxO4 nanoparticles have been synthesized with comparable nanoparticle sizes and compared for their OER intrinsic activities in alkaline media. All studied Ru–M alloy nanoparticles exhibited higher OER activity than pure Ru nanoparticles, and among them, Ru1–xIrx/C (x = 0.3–1) catalysts were found to be the most active. All studied Ru–TM oxide nanoparticles exhibited higher OER activity than the corresponding Ru–TM alloy nanoparticles with 30–50 atom % Co-doped RuO2/C catalysts being the most active. The OER enhancement on Ru–TM oxides is ascribed to the weaker O adsorption to their surfaces relative to the respective Ru–TM alloys. Small amounts of Mn (≤0.15 atom %)-doped RuO2 nanoparticles also slightly enhanced the OER kinetics. In contrast to Co and Mn, Ni-, Fe-, and V-doped RuO2 nanoparticles inhibited the OER. Among Ru–TM oxide nanoparticles, Ru0.7Co0.3O2/C and Ru0.85Mn0.15O2/C represent promising bifunctional catalysts for both the OER and oxygen reduction reaction (ORR).